WO2021178601A1

WO2021178601A1 - Crosslinked hydrogel compositions, methods of making same, and uses thereof

Info

Publication number: WO2021178601A1
Application number: PCT/US2021/020760
Authority: WO
Inventors: Shenqiang REN; Pratahdeep GOGOI
Original assignee: The Research Foundation For The State University Of New York
Priority date: 2020-03-03
Filing date: 2021-03-03
Publication date: 2021-09-10

Abstract

Provided are composite materials, hydrogels, and methods of making and using the composite materials and hydrogels. The composite materials have a hydrogel layer that may be sandwiched between hydrophobic materials, such as, for example, polydimethylsiloxane. The hydrogels have a polymer network and water, where the polymer network is a plurality crosslinked polymers. The composite materials may be used in various cooling applications.

Description

CROSSLINKED HYDROGEL COMPOSITIONS, METHODS OF MAKING SAME,

AND USES THEREOF

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No.

62/984,599, filed March 3, 2020, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

[0002] Personal cooling solutions are primitive in nature. Such solutions are typically heavy, and each comes with their respective set of challenges. For example, gel packs are heavy, warm quickly, and become slouched and bulky. In another example, ice packs are inflexible, heavy, and result in excessive condensation. In yet another example, phase change coolants become “activated” at a high cooling point, resulting in a very brief cooling experience. In yet another example, evaporative cooling products are dependent on low humidity and circulating air, and cannot become cool enough to affect body temperature. [0003] Sports athletes are required to maintain consistent performance over long durations, which is in reference to both the training and competitive phases. A considerable amount of body heat generation takes place and is reflected by their discomfort, and may result, though highly unlikely, in a lethal phenomenon known as hyperthermia which can affect the whole body or can be localized or regional. Carrying out strenuous activities in environments with prevailing high temperatures causes further irritation of such conditions. This can also be said regarding the uniforms of military personnel, firefighters, and other law- enforcement officers, as it forms an essential part in improving their safety during work. This has given rise to an immense interest to develop methods enabling faster recovery between the aforementioned periods. The performance level is inversely proportional to the rising environmental heat. One method attracting immense focus is the application of cooling prior to the training regimen, also known as precooling. Precooling is beneficial for enhancing the performance, as it significantly reduces the impact of heat and increases the training performance and the overall well-being of the athlete. However, the benefits of precooling start wearing off after the first 20-25 minutes of training. Therefore, it is suggested that the use of cooling apparatus during training may prolong the benefits of cooling in allowing for recuperation. Also, the rate of thermal strain is relatively higher during training as opposed to resting conditions and hence allows in maintaining a consistent performance. This led to an increase of methods like the application of rigid ice, cooling packs and vests, and cryogenic rooms.

[0004] Phase change materials (PCMs) have a low-temperature range and high energy density in the melting solidification. Amongst the various kinds of PCMs of interest, water- based hydrogel has gained popularity owing to its desirable characteristics such as non toxicity, affordability, stability, and eco-friendliness. Often termed as smart networks, in response to minor changes in the environment, they display a remarkable change in their physiology and can retain an immense amount of water. As hydrophilic polymer networks infiltrated with water, these hydrogels simultaneously behave as solid due to a three- dimensional cross-linking network formed within the liquid. This interwoven structure carries the fluid and thus provides an elastic force that can be completed by hydrogel’s expansion and contraction, and thus is responsible for its solidity.

SUMMARY OF THE DISCLOSURE

[0005] The present disclosure provides compositions, composite materials, and uses thereof. Methods of making the composite materials are also provided.

[0006] In an aspect, the present disclosure provides composite materials. The composite materials comprise one or more composition(s) of the present disclosure. In various examples, one or more of the hydrogel(s) is made by a method of the present disclosure. Non-limiting examples of composite materials are provided herein. Without intending to be bound by any particular theory, it is considered that the hydrogel networks of the composite materials can constrain the dimension of the ice crystals, which induces homogenous and small ice crystals.

[0007] A composite material comprises various layers. The composite material comprises one or more hydrogel layers having a first surface and a second surface opposite the first surface. The composite material also comprises one or more layers comprising a hydrophobic materials. The layer comprising the hydrophobic material (e.g., a first layer) may be disposed on the first surface of the hydrogel layer. In various examples, the composite material further comprises a second layer comprising a hydrophobic material (that is the same or different than the hydrophobic material of the first layer) is disposed on the second surface of the hydrogel layer. For example, the composite material may comprise additional hydrogel layers and layers comprising a hydrophobic material, where the hydrogel layers and layers comprising a hydrophobic material alternate, such as shown in Figures 3a and 4a (e.g., each additional hydrogel layer is disposed between corresponding layers of the one or more additional layers comprising a hydrophobic material). The composite structure may have various combinations and orientations of these layers.

[0008] In an aspect, the present disclosure provides hydrogels (e.g., compositions). In various examples, a hydrogel is made by a method of the present disclosure. Non-limiting examples of hydrogel are provided herein. A hydrogel may be may be referred to as a crosslinked (e.g., covalently and ionically crosslinked) hydrogel or ductile ice.

[0009] In an aspect, the present disclosure provides methods of making hydrogels

(e.g., compositions) and composite materials comprising the hydrogels. Non-limiting examples of composites are provided herein.

[0010] In an aspect, provided are precursors for 3D printing (e.g., stereolithographic printing), methods of making the precursors for 3D printing, and 3D printed articles.

[0011] In an aspect, the present disclosure provides uses of the composite materials.

Also provided are uses of hydrogels of the present disclosure.

BRIEF DESCRIPTION OF THE FIGURES

[0012] For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying figures.

[0013] Figure 1 shows a) cold retention of a single layer of hydrogel-PDMS sample with 85% water content; b) comparison of the cold retention of the samples based on water content; c) comparison of the cold retention based on the number of hydrogel layers with 85% water content; d) comparison of the cold retention of the samples based on the number of hydrogel layers at a constant overall sample thickness with 85% water content; e) comparison of the cold retention of the samples based on the weight percent of fumed silica in a single hydrogel layer with 85% water.

[0014] Figure 2 shows a) stress-strain curve of a single layer of hydrogel-PDMS sample with 85% water content; b) comparison of the Young’s modulus of the samples based on water content; c) comparison of the Young’s modulus of the samples based on the number of hydrogel layers with 85% water content; d) comparison of the Young’s modulus of the samples based on the number of hydrogel layers at a constant overall sample thickness with 85% water content; e) comparison of the Young’s modulus of the samples based on the weight percent of fumed silica in a single thick hydrogel layer with 85% water.

[0015] Figure 3 shows (a) synthesis of the cooling composite material i. Schematic illustration of solution A comprising of Acrylamide, Sodium alginate, H2O, and Tetramethylethylenediamine. ii. Schematic illustration of solution B comprising of N,N’- Methylenebisacrylamide, Calcium Sulfate, Ammonium Persulfate solutions in water iii. Sol B mixed with Sol A to form the hydrogel precursor iv. Sol B mixed with fumed silica- infused Sol A to form the fumed silica-infused hydrogel precursor v. Process of putting the hydrogel precursor in molds followed by pressing for preparation of the hydrogel vi. Process of putting the fumed silica-infused hydrogel precursor in molds followed by pressing for preparation of the fumed silica-infused hydrogel vii. Preparation of sandwich structured hydrogel -PDMS composite viii. Preparation of sandwich structured fumed silica-infused hydrogel-PDMS composite (b) An image showing the fabricated hydrogel-PDMS structure without fumed silica (c) An image showing the fabricated hydrogel-PDMS structure infused with fumed silica (d) A hydrogel composite when retrieved from freezing environmental conditions (e) An image highlighting the flexible nature of the hydrogel composite when subjected to freezing conditions.

[0016] Figure 4 shows (a) a schematic illustration of the thermal test (b) A schematic illustration depicting the transformation process of nano-ice to water (c) The steady-state thermal simulation of PDMS/hydrogel sandwich structure (d) Temperature vs. time profiles depicting the time taken by the composite to reach 20 °C with varying amount of water content (inset depicting the time taken by the samples of hydrogel with increasing water content to reach 20 °C). (e) Temperature vs. time profiles of hydrogels with the increasing number of layers (inset depicting the time taken by samples with different number of hydrogel layers to reach 20 °C).

[0017] Figure 5 shows a mechanical property evaluation of composite hydrogel (a)

Compressive stress-strain curves of hydrogel with 80 wt.%, 90 wt.%, and 95 wt.% water content respectively (inset: Young’s modulus of hydrogels with 80 wt.%, 85 wt.%, 90 wt.%, 95 wt.% water content) (b) Compressive stress-strain curves of samples with a different number of hydrogel layers maintaining a constant overall sample thickness (inset: Young’s modulus of samples with a different number of hydrogel layers).

[0018] Figure 6 shows (a) temperature vs. time profiles depicting the time taken by the hydrogel infused with fumed silica to reach 20 °C for different concentrations (inset depicting the time taken by samples to reach a temperature of 20 °C with different percentages of fumed silica) (b) Compressive stress-strain curves of hydrogel with 1 wt.% fumed silica, hydrogel with 2 wt.% fumed silica, and hydrogel with 3 wt.% fumed silica, respectively (The inset: Young’s modulus of hydrogels with 1 wt.%, 2 wt.%, and 3 wt.% fumed silica). [0019] Figure 7 shows (a) a representation of printed hydrogel evaluation process at different times (0-20 min) (b-c) Simulation of printed hydrogel under varying amounts of pressure (d) Compressive stress-strain curves of hydrogel when subjected to different cycles (e) Temperature vs. time profiles of hydrogel with and without PDMS. [0020] Figure 8 shows a bar chart representation depicting the time for which the hydrogel composite can maintain its temperature below 0 °C and 20 °C for samples with different amount of water content.

[0021] Figure 9 shows temperature vs. time profiles representing different hydrogel composites with increasing number of layers and their effect on the overall cooling time. [0022] Figure 10 shows a bar chart depicting the time for which the hydrogel composite can maintain its temperature below 0 °C and 20 °C for samples with varying number of hydrogel layers (with the constant overall sample thickness fixed).

[0023] Figure 11 shows a bar chart representation of the time for which the hydrogel composite can maintain its temperature below 0 °C and 2 0°C for samples with different number of hydrogel layers (with unrestricted overall sample thickness).

[0024] Figure 12 shows a representation of the Young’s modulus of hydrogel composites with 80 wt.%, 85 wt.%, 90 wt.% and 95 wt.% water content as observed during the mechanical evaluation tests.

[0025] Figure 13 shows compressive stress-strain curves of samples with 5 and 7 layers of hydrogel (thickness per layer ~ 2 mm) respectively as observed during the mechanical evaluation tests.

[0026] Figure 14 shows a bar chart representation of Young’s modulus of samples with 5 and 7 hydrogel layers as observed during the mechanical evaluation tests.

[0027] Figure 15 shows Young’s modulus of samples with different number of hydrogel layers maintaining a constant overall sample thickness as observed during the mechanical evaluation tests.

[0028] Figure 16 shows a bar chart depicting the time taken by the hydrogel composites infused with fumed silica to reach a temperature of 20 °C (indicative of the cooling effect, starting from -20 °C) for different samples. [0029] Figure 17 shows Young’s modulus of the hydrogel composites with 1 wt.%,

2 wt.% and 3 wt% fumed silica as observed during the mechanical evaluation tests.

[0030] Figure 18 shows images depicting the printed hydrogel composite during the uniaxial compression test with varying amount of compression loading. [0031] Figure 19 shows a line chart representation indicative of the displacement at the numbered points on the hydrogel composite in proportion to increasing amount of strain (the Strain-displacement curve).

[0032] Figure 20 shows a schematic of the set up used to perform thermal analysis of the samples

DETAILED DESCRIPTION OF THE DISCLOSURE

[0033] Although claimed subject matter may be described in terms of certain examples, other examples, including examples that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, and process step changes may be made without departing from the scope of the disclosure.

[0034] Ranges of values are disclosed herein. The ranges set out a lower limit value and an upper limit value. Unless otherwise stated, the ranges include the lower limit value, the upper limit value, and all values between the lower limit value and the upper limit value, including, but not limited to, all values to the magnitude of the smallest value (either the lower limit value or the upper limit value).

[0035] As used herein, unless otherwise stated, the term “group” refers to a chemical entity that is monovalent (i.e., has one terminus that can be covalently bonded to other chemical species), divalent, or polyvalent (i.e., has two or more termini that can be covalently bonded to other chemical species). The term “group” also includes radicals (e.g., monovalent and multivalent, such as, for example, divalent radicals, trivalent radicals, and the like). Illustrative examples of groups include:

-¾-CH_{3 >} -tQ , -§-^ch ₂-§-, _and ^"KZH_.

[0036] The present disclosure provides compositions, composite materials, and uses thereof. Methods of making the composite materials are also provided.

[0037] In an aspect, the present disclosure provides composite materials. The composite materials comprise one or more composition(s) of the present disclosure. In various examples, one or more of the hydrogel(s) is made by a method of the present disclosure. Non-limiting examples of composite materials are provided herein. Without intending to be bound by any particular theory, it is considered that the hydrogel networks of the composite materials can constrain the dimension of the ice crystals, which induces homogenous and small ice crystals. [0038] A composite material comprises various layers. The composite material comprises one or more hydrogel layers having a first surface and a second surface opposite the first surface. The composite material also comprises one or more layers comprising a hydrophobic materials. The layer comprising the hydrophobic material (e.g., a first layer) may be disposed on the first surface of the hydrogel layer. In various examples, the composite material further comprises a second layer comprising a hydrophobic material (that is the same or different than the hydrophobic material of the first layer) is disposed on the second surface of the hydrogel layer. For example, the composite material may comprise additional hydrogel layers and layers comprising a hydrophobic material, where the hydrogel layers and layers comprising a hydrophobic material alternate, such as shown in Figures 3a and 4a (e.g., each additional hydrogel layer is disposed between corresponding layers of the one or more additional layers comprising a hydrophobic material). The composite structure may have various combinations and orientations of these layers.

[0039] The hydrogel layer comprises various components. The hydrogel layer comprises a polymer network and water. The polymer network may be an interpenetrating polymer network. In various examples, the polymer network does not form observable distinct domains. The polymer network may comprise a plurality of covalently-crosslinked polymer chains; a plurality of ionically-crosslinkable polymer chains; and an ionic component. The hydrogel layer may have a water content of 60-95 wt.%, including all 0.1 wt.% values and ranges therebetween, based on the total weight of the hydrogel layer (e.g., 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, or 95 wt.%). The covalently-crosslinked polymer chains and the ionically-crosslinkable polymer chains may be intertwined.

[0040] Various covalently-crosslinked polymer chains may be used. The covalently- crosslinked polymer chains may be hydrophilic. The covalently-crosslinked polymer chains may have one or more charged groups. Non-limiting examples of covalently-crosslinked polymer chains include polyacrylamides, polyvinyl alcohol, polyalkylene oxides (such as, for example, polyethyleoxides, polypropylene oxide, and the like), starches, celluloses (such as, for example, carboxymethyl celluloses (CMCs) and the like), polyacrylonitriles, and the like, and combinations thereof. The covalently-crosslinked polymer chains may have a molecular weight, which may be an Mw and/or an Mn, of 40,000 to 150,000 g/mol, including all 0.1 g/mol values and ranges therebetween. The crosslinks and/or polymers may be formed in situ or be pre-formed. The polymer chains of the covalently crosslinked polymer chains may be a combination of two or more structurally distinct polymer chains. The individual polymer chains of the covalently crosslinked polymer chains may be homopolymers, copolymers (such as, for example, graft copolymers, block copolymers, random copolymers, and the like), and the like, or a combination thereof. The individual polymer chains of the covalently crosslinked polymer chains may be naturally occurring materials.

[0041] Various crosslinking groups may crosslink the covalently-crosslinked polymer chains. For example, a covalently-crosslinked polymer may be crosslinked by one or more of the following groups:

groups, wherein R' and R" are independently chosen from H,

and the like, and combinations thereof (e.g.,

and the like).

[0042] Various ionically-crosslinkable polymer chains may be used. The ionically- crosslinkable polymer chains may comprise one or more (e.g., a plurality of) charged groups, such as, for example, cationic groups, anionic groups, and a combination thereof. In various examples, the ionically crosslinked polymer chains are ionic polymers. The ionically- crosslinkable polymer chains may be crosslinked by one or more ionic bonds, which may be interchain and/or intrachain. The ionic bonds may be formed in situ or be pre-formed. The ionic bonds may be formed from one or more ionic components and one or more individual polymer chains of the ionically-crosslinkable polymer chains. In various examples, ionically- crosslinkable polymer chains have a charge opposite of the ionic component. Thus, in various examples, individual ionic bonds are formed between one or more anionic group(s) of one or more ionically crosslinked polymer chain(s) and one or more cationic ionic component(s) of one or more ionic component(s), or the individual ionic bonds are formed between one or more cationic group(s) of one or more ionically crosslinked polymer chain(s) and one or more anionic component(s) of one or more ionic component(s). The individual polymer chains of the ionically crosslinked polymer chains may be a combination of two or more structurally distinct polymer chains. The individual polymer chains of the ionically crosslinked polymer chains may be naturally occurring materials. Non-limiting examples of cationic groups include alkylammonium groups, and the like, sulfonium groups, and the like, and combinations thereof. Non-limiting examples of anionic groups include carboxylates, nitrates, sulfonates, sulfates, phosphates, phosphonates, and the like, and combinations thereof. Non-limiting examples of ionically-crosslinkable polymers include alginates (e.g., sodium alginates and the like), polyglutamates, polynucleotides, polyethylene terephthalates, and the like, and combinations thereof. In various examples, the ionically crosslinked polymer chains are chosen from ionically crosslinked biopolymers, such as, for example, ionically crosslinked alginates (e.g., sodium alginate and the like), ionically crosslinked polynucleotides (e.g., RNAs, single-stranded DNAs, and the like), and the like, and combinations thereof. Non-limiting examples of ionically crosslinked polymer chains include polyglutamates (such as, for example, y-poly(glutamate)s, tetrahydrofolyl-poly(glutamate) polymers, 5,10-methenyltetrahydrofolate polyglutamates, 5,10-methylenetetrahydrofolate polyglutamate polymers, [Glu(-Cys)]n-Gly(l-), where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, and the like), alginates, DNA polyanions, heparans (such as, for example, heparan sulfate a-D-A- sulfoglucosamine polyanion, heparan sulfate a-D-glucosaminide 3 -sulfate poly anion, heparan sulfate a-D-glucosaminide 6-sulfate polyanion, heparan sulfate a-D-glucosaminide polyanion, heparan sulfate A -acetyl -a-D-gl ucosami ni de polyanion, and the like), poly(2,5- ethylene furandicarboxylate)(l-), polyethylene terephthalate)(l-), poly(nucleoside 5'- monophosphate) polyanion, poly(xylylviologen), poly[2-(methacryloxy)ethyl phosphorylcholine], RNA polyanions (such as, for example, RNA polyanion 2',3'-cyclic phosphates, RNA polyanion nucleotide 2'-phosphates, RNA_(n>-3 '-adenine ribonucleotide polyanions, RNA_(n>-3 '-uridine ribonucleotide polyanions, and the like), and the like, and combinations thereof. The ioncally-crosslinkable polymer chains may have a molecular weight, which may be an Mw and/or an Mn, of 100,000-200,000 g/mol g/mol, including all 0.1 g/mol values and ranges therebetween (e.g., 120,000-190,000 g/mol).

[0043] Various ionic components may be used. For example, the ionic components are a plurality of cations, a plurality of anions, or a combination thereof. In various examples, the ionic component is polyvalent (such as, for example, a divalent cation or divalent anion or a tri valent cation or tri valent anion).

[0044] Various amounts of the covalently-crosslinked polymer chains, ionically-crosslinkable polymer chains, and anionic components may be used. For example, the polymer (e.g., covalently crosslinked polymer(s), ionically crosslinked polymer(s), or both) to ionic component weight percent (based on the total weight of hydrophilic polymer and ionic component, which may or may not include the counterion of the ionic component) ratio is 3:1 to 6:1, including all 0.1 ratio values and ranges therebetween.

[0045] The hydrogel layers may comprise one or more additives. The additives may provide one or more desirable cooling and/or mechanical function(s), one or more desirable property(ies), or one or more desirable function(s) and one or more desirable property(ies). Non-limiting examples of additives include polar liquids (such as, for example, alcohols (e.g, ethanol and the like), ketones (e.g., acetone and the like), glycols, particles, which may be nanoparticles (such as, for example, silica aerogel particles). The nanoparticles may be thermally insulating. In the case of liquid additives, the liquid additive(s) may be present at 1-5 percent by weight (based on the total weight of the composition), including all 0.1 percent by weight values and ranges therebetween. In the case of solid (e.g., particulate) additives, the solid additive(s) may be present at 1-10 percent by weight (based on the total weight of the composition), including all 0.1 percent by weight values and ranges therebetween. In the case of silica aerogel particles, the silica aerogel particles may have an average size (e.g., average linear dimension, such as, for example, a linear dimension (e.g., a diameter) of 5-150 nm, including all 0.1 nm values and ranges there between. The silica aerogel particles may be nonporous and/or mesoporous. In the case of silica aerogel particles, the silica aerogel particles may phase separate and be thermal insulating, and may present as one or more discrete domain(s) (e.g., discrete layer(s)). In various examples, the additive is fumed silica and is present in the amount of 0.1-5 wt.% (based on the total weight of the hydrogel composition).

[0046] The hydrogel layers may further comprise a polyether. Non-limiting examples of polyethers include polyethylene glycol, polypropylene glycol, and the like, and combinations thereof. The molecular weight of the poly ether may be 10,000 to 100,000 g/mol, including all integer molecular weight values and ranges therebetween. The amount of polyether may be 0.1 to 1 percent by weight (based on the total weight of the composition), including all 0.01 values and ranges therebetween.

[0047] In various examples, the hydrogel layer is configured as a structure having one or more (e.g., a plurality) of pores and/or void spaces (e.g., voids). The structure may be a lattice. The layer comprising a hydrophobic material may be disposed within the one or more pores or void spaces. The voids may have a longest linear dimension (e.g., diameter) of 1-50, including all 0.1 nm values and ranges therebetween. [0048] Various hydrophobic materials may be used. Non-limiting examples of hydrophobic materials include poly dimethyl siloxanes, textiles, fabrics, silica aerogels, polymers, glasses, metals, metalloids, semiconductor materials (such as for example, inorganic semiconductor materials, organic semiconducting materials (e.g., polymers, small molecules, and the like), and the like), polymers (such as, for example, polyethylene and the like), and the like, and combinations thereof. Non-limiting examples of textiles and/or fabrics include Kevlar, Nomax, nylons, polyethylenes, polypropylenes, cotton, and the like, and combinations thereof. The textile or fabric may comprise naturally-occurring fibers (such as, for example, cotton and the like), synthetic fibers (such as for example, polyethylene and the like), or a combination thereof. The layers comprising a hydrophobic material may be referred to as thermally-insulating layer(s) or thermally-conducting layer(s) depending on the layer’s ability to transfer heat. A material may be selected for its ability to transfer heat depending on the desired use.

[0049] In various examples, one or more of the layers comprising a hydrophobic material may be surface treated. Examples of surface treatments include, but are not limited to, plasma treatment, chemical treatment, photochemical treatment, and the like, and combinations thereof. The treatment may be performed prior to the formation of the composite materials.

[0050] The layers of the composite materials may have various thicknesses. For example, a layer comprising a hydrophobic material has a thickness of 0.1 mm to 1 mm, including all 0.01 mm values and ranges therebetween. In various examples, the hydrogel layer has a thickness of 1 to 10 mm, including all 0.01 mm values and ranges therebetween. [0051] Composite materials of the present disclosure may have various desirable traits/features. For example, the composite material has a desirable Young’s modulus. The Young’s modulus of 50-2000 kPa, including all 0.1 kPa values and ranges therebetween (e.g., 50-500 kPa, 100-1800 kPa). In various other examples, the composite material exhibits a desirable retention time. The retention time is the time it takes 90% or greater, 95% or greater, 99% or greater, or 100% of water to undergo a solid to liquid phase transition. For example, the composite material exhibits a retention time of at least 3, 3.5, 4, 4.5, 5, 5.5, or 6 hours or 3 hours to 6 hours, including all 0.1 minute values and ranges therebetween.

[0052] In an aspect, the present disclosure provides hydrogels (e.g., compositions). In various examples, a hydrogel is made by a method of the present disclosure. Non-limiting examples of hydrogel are provided herein. A hydrogel may be may be referred to as a crosslinked (e.g., covalently and ionically crosslinked) hydrogel or ductile ice. [0053] The hydrogel comprises various components. The hydrogel comprises a polymer network and water. The polymer network may be an interpenetrating polymer network. In various examples, the polymer network does not form observable distinct domains. The polymer network may comprise a plurality of covalently-crosslinked polymer chains; a plurality of ionically-crosslinkable polymer chains; and an ionic component. The hydrogel may have a water content of 60-95 wt.%, including all 0.1 wt.% values and ranges therebetween, based on the total weight of the hydrogel (e.g., 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, or 95 wt.%). The covalently- crosslinked polymer chains and the ionically-crosslinkable polymer chains may be intertwined. The hydrogels or composites comprising one or more hydrogels may be ductile (e.g., mechanically flexible and/or stretchable without structural failure).

[0054] Various covalently-crosslinked polymer chains may be used. The covalently- crosslinked polymer chains may be hydrophilic. The covalently-crosslinked polymer chains may have one or more charged groups. Non-limiting examples of covalently-crosslinked polymer chains include polyacrylamides, polyvinyl alcohol, polyalkylene oxides (such as, for example, polyethyleoxides, polypropylene oxide, and the like), starches, celluloses (such as, for example, carboxymethyl celluloses (CMCs) and the like), polyacrylonitriles, and the like, and combinations thereof. The covalently-crosslinked polymer chains may have a molecular weight, which may be an Mw and/or an Mn, of 40,000 to 150,000 g/mol, including all 0.1 g/mol values and ranges therebetween. The crosslinks and/or polymers may be formed in situ or be pre-formed. The polymer chains of the covalently crosslinked polymer chains may be a combination of two or more structurally distinct polymer chains. The individual polymer chains of the covalently crosslinked polymer chains may be homopolymers, copolymers (such as, for example, graft copolymers, block copolymers, random copolymers, and the like), and the like, or a combination thereof. The individual polymer chains of the covalently crosslinked polymer chains may be naturally occurring materials.

[0055] Various crosslinking groups may crosslink the covalently-crosslinked polymer chains. For example, a covalently-crosslinked polymer may be crosslinked by one or more of the following groups:

groups, wherein R' and R" are independently chosen from H,

and the like, and combinations thereof (e.g.,

and the like).

[0056] Various ionically-crosslinkable polymer chains may be used. The ionically- crosslinkable polymer chains may comprise one or more (e.g., a plurality of) charged groups, such as, for example, cationic groups, anionic groups, and a combination thereof. In various examples, the ionically crosslinked polymer chains are ionic polymers. The ionically- crosslinkable polymer chains may be crosslinked by one or more ionic bonds, which may be interchain and/or intrachain. The ionic bonds may be formed in situ or be pre-formed. The ionic bonds may be formed from one or more ionic components and one or more individual polymer chains of the ionically-crosslinkable polymer chains. In various examples, ionically- crosslinkable polymer chains have a charge opposite of the ionic component. Thus, in various examples, individual ionic bonds are formed between one or more anionic group(s) of one or more ionically crosslinked polymer chain(s) and one or more cationic ionic component(s) of one or more ionic component(s), or the individual ionic bonds are formed between one or more cationic group(s) of one or more ionically crosslinked polymer chain(s) and one or more anionic component(s) of one or more ionic component(s). The individual polymer chains of the ionically crosslinked polymer chains may be a combination of two or more structurally distinct polymer chains. The individual polymer chains of the ionically crosslinked polymer chains may be naturally occurring materials. Non-limiting examples of cationic groups include alkylammonium groups, and the like, sulfonium groups, and the like, and combinations thereof. Non-limiting examples of anionic groups include carboxylates, nitrates, sulfonates, sulfates, phosphates, phosphonates, and the like, and combinations thereof. Non-limiting examples of ionically-crosslinkable polymers include alginates (e.g., sodium alginates and the like), polyglutamates, polynucleotides, polyethylene terephthalates, and the like, and combinations thereof. In various examples, the ionically crosslinked polymer chains are chosen from ionically crosslinked biopolymers, such as, for example, ionically crosslinked alginates (e.g., sodium alginate and the like), ionically crosslinked polynucleotides (e.g., RNAs, single-stranded DNAs, and the like), and the like, and combinations thereof. Non-limiting examples of ionically crosslinked polymer chains include polyglutamates (such as, for example, y-poly(glutamate)s, tetrahydrofolyl-poly(glutamate) polymers, 5,10-methenyltetrahydrofolate polyglutamates, 5,10-methylenetetrahydrofolate polyglutamate polymers, [Glu(-Cys)]n-Gly(l-), where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, and the like), alginates, DNA polyanions, heparans (such as, for example, heparan sulfate a-D-A- sulfoglucosamine polyanion, heparan sulfate a-D-glucosaminide 3 -sulfate poly anion, heparan sulfate a-D-glucosaminide 6-sulfate polyanion, heparan sulfate a-D-glucosaminide polyanion, heparan sulfate A -acetyl -a-D-gl ucosami ni de polyanion, and the like), poly(2,5- ethylene furandicarboxylate)(l-), polyethylene terephthalate)(l-), poly(nucleoside 5'- monophosphate) polyanion, poly(xylylviologen), poly[2-(methacryloxy)ethyl phosphorylcholine], RNA polyanions (such as, for example, RNA polyanion 2',3'-cyclic phosphates, RNA polyanion nucleotide 2'-phosphates, RNA_(n>-3 '-adenine ribonucleotide polyanions, RNA_(n>-3 '-uridine ribonucleotide polyanions, and the like), and the like, and combinations thereof. The ioncally-crosslinkable polymer chains may have a molecular weight, which may be an Mw and/or an Mn, of 100,000-200,000 g/mol g/mol, including all 0.1 g/mol values and ranges therebetween (e.g., 120,000-190,000 g/mol).

[0057] Various ionic components may be used. For example, the ionic components are a plurality of cations, a plurality of anions, or a combination thereof. In various examples, the ionic component is polyvalent (such as, for example, a divalent cation or divalent anion or a tri valent cation or tri valent anion).

[0058] Various amounts of the covalently-crosslinked polymer chains, ionically-crosslinkable polymer chains, and anionic components may be used. For example, the polymer (e.g., covalently crosslinked polymer(s), ionically crosslinked polymer(s), or both) to ionic component weight percent (based on the total weight of hydrophilic polymer and ionic component, which may or may not include the counterion of the ionic component) ratio is 3:1 to 6:1, including all 0.1 ratio values and ranges therebetween.

[0059] The hydrogels may comprise one or more additives. The additives may provide one or more desirable cooling and/or mechanical function(s), one or more desirable property(ies), or one or more desirable function(s) and one or more desirable property(ies). Non-limiting examples of additives include polar liquids (such as, for example, alcohols (e.g., ethanol and the like), ketones (e.g., acetone and the like), glycols, particles, which may be nanoparticles (such as, for example, silica aerogel particles). The nanoparticles may be thermally insulating. In the case of liquid additives, the liquid additive(s) may be present at 1-5 percent by weight (based on the total weight of the composition), including all 0.1 percent by weight values and ranges therebetween. In the case of solid (e.g., particulate) additives, the solid additive(s) may be present at 1-10 percent by weight (based on the total weight of the composition), including all 0.1 percent by weight values and ranges therebetween. In the case of silica aerogel particles, the silica aerogel particles may have an average size (e.g., average linear dimension, such as, for example, a linear dimension (e.g., a diameter) of 5-150 nm, including all 0.1 nm values and ranges there between. The silica aerogel particles may be nonporous and/or mesoporous. In the case of silica aerogel particles, the silica aerogel particles may phase separate and be thermal insulating, and may present as one or more discrete domain(s) (e.g., discrete layer(s)). In various examples, the additive is fumed silica and is present in the amount of 0.1-5 wt.% (based on the total weight of the hydrogel composition).

[0060] The hydrogels may further comprise a polyether. Non-limiting examples of polyethers include polyethylene glycol, polypropylene glycol, and the like, and combinations thereof. The molecular weight of the poly ether may be 10,000 to 100,000 g/mol, including all integer molecular weight values and ranges therebetween. The amount of polyether may be 0.1 to 1 percent by weight (based on the total weight of the composition), including all 0.01 values and ranges therebetween.

[0061] In various examples, the hydrogel is configured as a structure having one or more (e.g., a plurality) of pores and/or void spaces (e.g., voids). The structure may be a lattice. The voids may have a longest linear dimension (e.g., diameter) of 1-50, including all 0.1 nm values and ranges therebetween.

[0062] Hydrogels of the present disclosure may have various desirable traits/features.

For example, the hydrogel has a desirable Young’s modulus. The Young’s modulus of 50- 2000 kPa, including all 0.1 kPa values and ranges therebetween (e.g., 50-500 kPa, 100-1800 kPa).

[0063] In an aspect, the present disclosure provides methods of making hydrogels

[0064] A method may comprise mixing two or more discrete compositions (e.g., solutions A and solutions B in the Examples), where none of the individual compositions comprise all of the components required to form the covalent crosslinks and/or the ionic crosslinks. [0065] A method of making a hydrogel comprises various steps. A method of making the hydrogel may comprise contacting a first composition and a second composition to form a hydrogel precursor, the first composition comprising: one or more ionically-crosslinkable polymer(s); one or more monomer(s); water; and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof, and the second composition comprising: one or more crosslinking compound(s); water; and one or more ionic component s); and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof. After contacting the materials may be allowed so stand such that hydrogel precursor gelates (e.g., forms a hydrogel). The hydrogel precursor may be pressed prior to standing. The first composition may further comprise one or more additives as described herein (e.g., 0.1-5 wt.% fumed silica based on the total weight of the hydrogel composition). The hydrogel precursor resulting from the contacting may have any combination of these component amounts. The water (e.g., of the first composition or the second composition, or both) may make up the remainder of the composition(s). The percent by weight values are based on the total weight of the reaction mixture or portion thereof (e.g., first composition, second composition, and the like).

[0066] Various monomers and crosslinking compounds may be used to prepare the covalently-crosslinked polymer chains of the hydrogel. Non-limiting examples of monomers include acrylamides, vinyl alcohols, cyclic ethers (such as, for example, ethylene oxide, propylene oxide, and the like), acrylonitriles, and the like, and combinations thereof. The monomers may be present in the first composition in the amount of 4-21 wt.%, including all 0.01 wt.% values and ranges therebetween. Examples of crosslinking compounds include, but are not limited to, multiacrylamides (e.g., compounds comprising two or more acrylamide groups, such as, for example, diacrylamides (N,N’-methylenebisacrylamide (MBAA) and the like), and the like, and combinations thereof. Examples of crosslinking compounds include, but are not limited to,

O O

H H (N,N’-methylenebisacrylamide (MBAA))

The crosslinking compounds may be present in the second composition in the amount of 0.8- 3 wt%., including all 0.01 wt.% values and ranges therebetween.

[0067] Various ionically-crosslinkable polymers may be used to prepare the hydrogel.

Examples of ionically-crosslinkable polymers are provided herein. The ionically-crosslinkable polymers may be present in the first composition in the amount of 0.8-3 wt.%, including all 0.01 wt.% values and ranges therebetween.

[0068] Various ionic components may be used to prepare the hydrogel. Examples of ionic components are provided herein. In various examples, the ionic component is present in the second composition in the amount of 0.8-3 wt.%, including all 0.01 wt.% ranges and values therebetween.

[0069] Various catalysts and/or catalyst components may be used to prepare the hydrogel. Examples of more catalysts and/or catalyst components include, but are not limited to radical initiators, thermal initiators, photochemical initiators, and the like, combinations thereof. Non-limiting examples of radical initiators (which may be thermal initiators) include persulfates (such as, for example, ammonium persulfate, potassium persulfate, and the like, and combinations thereof). Non-limiting examples of photochemical initiators include lithium phenyl-2,4, 6-trimethylbenzoylphosphinate, and the like, and combinations thereof. In various examples, the amount of catalysts and/or catalyst components present in the first composition, second composition, or both is 0.2-1 wt.%, including all 0.01 wt.% values and ranges therebetween.

[0070] The contacting of the first composition and the second composition may be carried out at various temperatures. For example, the contacting is carried out at room temperature (e.g., 18-22 °C) in the ambient atmosphere. The contacting of the first composition and second composition may be performed with various ratios of the first composition to the second composition (v/v). In various examples, the ratio of the first composition to the second composition is 3:1 to 6:1 (v/v), including all 0.1 ratio values and ranges therebetween (e.g., 4:1 (v/v)).

[0071] The ionically crosslinked polymer chains or the covalently crosslinked polymer chains, or both, may be formed in a method of making a hydrogel or composite material (e.g., formed in situ ) or preformed.

[0072] A composite material may be prepared by a method described herein. A method may comprise a method of making a hydrogel of the present disclosure.

[0073] A method of preparing a composite material comprises contacting a hydrogel precursor with a hydrophobic material. Prior to contacting the hydrophobic material, the hydrogel precursor may be allowed to stand such that it forms a hydrogel. Prior to contacting the hydrophobic material with the hydrogel (formed from the hydrogel precursor), the hydrophobic material is coated with an adhering agent (e.g., a photoinitiator) or otherwise treated. Examples of adhering agents include, but are not limited to benzophenone and the like. Examples of treating include, but are not limited to, plasma treating, chemically treating, photochemically treating, and the like, and combinations thereof. Without intending to be bound by any particular theory, it is considered that treating and/or adhering agents may improve the ability for the hydrogel to adhere to the hydrophobic material. The contacted hydrogel (formed from the hydrogel precursor) and hydrophobic material may be UV-cured. Examples of hydrophobic materials are provided herein.

[0074] In an aspect, provided are precursors for 3D printing (e.g., stereolithographic printing), methods of making the precursors for 3D printing, and 3D printed articles.

[0075] Compositions for printing (e.g., printing precursor or ink) may comprise various components. For example, the printing precursor may comprise water, one or more monomers, one or more crosslinking compounds, optionally one or more rigidifying agents, optionally one or more photoinitiators, optionally one or more UV absorbers, and optionally one or more ionically-crosslinkable polymers.

[0076] Various monomers and crosslinking agents may be used. Examples of monomers and crosslinking compounds are provided herein. In various examples, the monomer is methylenebis acrylamide (MBAA) and the crosslinking compound is dimethyl acrylamide (DMAA). The monomers and crosslinking compounds can be mixed in various ratios. The volume ratios may be 2:1 to 6: 1, including all 0.1 ratio values and ranges therebetween. For example, the volume ratio of MBAA to DMAA is 4: 1.

[0077] Various rigidifying agents may be used. For example, the rigidifying agent may be a polyether, such as, for example, polyethylene glycol diacrylate (Mn = 700). The rigidifying agent may be present in the amount of 0.1-2 vol%. Without intending to be bound by any particular theory, it is considered that the rigidifying agent improves the strength of the hydrogel.

[0078] Various photoinitiators may be used. The photoinitiator may facilitate fast printing. Various photoinitiators are known in the art. For example, the photoinitiator is lithium phenyl-2, 4, 6-trimethylbenzoyl phosphinate (LAP). The photoinitiator may be present in the amount of 0.1-1 wt.%, including all 0.01 wt.% values and ranges therebetween.

[0079] Various UV absorbers may be used. The UV absorber may facilitate high resolution printing. UV absorbers are known in the art. For example, the UV absorber is Quinoline Yellow dye. The UV absorber may be present in the amount of 0.001-0.1 wt.%, including all 0.0001 wt.% values and ranges therebetween (e.g., 0.002 wt.%).

[0080] Various ionically-crosslinkable polymers may be used. Examples of ionically- crosslinkable polymers are provided herein. [0081] The printing precursor may be used in various printing technology. For example, the printing precursor may be used with a stereolithographic (SLA) printer. Various shapes may be produced via 3D printing, such as, for example, a lattice structure. Following printing, the printed structure may be contacted with (e.g., soaked in) aqueous solution comprising an ionic component. Various ionic components are described herein. For example, the ionic component is calcium sulfate. Following contacting with the aqueous solution comprising the ionic component, the printed structure may be contacted with a hydrophobic material. A lattice structure may be filled with a hydrophobic material, such as, for example, PDMS.

[0082] In an aspect, the present disclosure provides uses of the composite materials.

Also provided are uses of hydrogels of the present disclosure.

[0083] For example, the hydrogel precursor can be used in 3D printing (e.g., stereolithography). Following printing, the hydrogel precursor forms a hydrogel. The hydrogel may then be coated with a hydrophobic material (e.g., the hydrogel may have the hydrophobic material disposed thereon).

[0084] The composite materials may be used in wearable devices and other ductile cooling applications. For example, a composite material of the present disclosure may be used in cooling pads.

[0085] The steps of the methods described in the various examples disclosed herein are sufficient to carry out the methods of the present disclosure. Thus, in an example, a method consists essentially of a combination of the steps of the methods disclosed herein. In another example, a method consists of such steps.

[0086] The following Statements provide various embodiments and examples of the present disclosure.

Statement 1. A composition (which may be referred to as a hydrogel or ductile ice) comprising: a polymer network comprising a plurality of covalently crosslinked polymer chains (which may be hydrophilic); a plurality ionically crosslinked polymer chains (e.g., polymer chains with one or more (e.g., a plurality of) charged groups, such as, cationic groups, anionic groups, or a combination thereof) (which may be hydrophilic); an ionic component, wherein the ionically crosslinked polymer chains are crosslinked by a plurality of ionic bonds, which may be interchain and/or intrachain ionic bonds, formed by the ionic component and individual polymer chains, water; and a polyether. In various examples, the charged groups of the ionically crosslinked polymer chains and the ionic component have opposite charges. In various examples, the covalently crosslinked hydrophilic polymer chains have one or more charged groups covalently attached to the polymer backbone. Non-limiting examples of cationic charged groups include ammonium groups, such as for example, alkylammonium groups, and the like, sulfonium groups, and the like, and combinations thereof. Non-limiting examples of anionic charged groups include carboxylates, nitrates, sulfonates, sulfates, phosphates, phosphonates, and the like, and combinations thereof. The ionically crosslinked polymer chains and covalently crosslinked hydrophilic polymer chains may be intertwined. E.g., ionically crosslinked polymer chains and/or covalently crosslinked hydrophilic polymer chains do not form observable distinct domains. The polymer network may be an interpenetrating polymer network. The composition may be useful in additive manufacturing processes (e.g., as an ink in a 3-D printing process). The composition may be used without addition of any additional components to render the composition useful in additive manufacturing processes (e.g., as an ink in a 3-D printing process).

Statement 2. A composition according to Statement 1, wherein i) the individual ionic bonds are formed between one or more anionic group(s) of one or more ionically crosslinked polymer chain(s) and one or more cationic ionic component(s) of one or more ionic component s), or ii) the individual ionic bonds are formed between one or more cationic group(s) of one or more ionically crosslinked polymer chain(s) and one or more anionic component(s) of one or more ionic component(s).

Statement 3. A composition according to Statements 1 or 2, wherein individual polymer chains of the covalently crosslinked polymer chains are chosen from polyacrylamides, polyvinyl alcohol, polyalkylene oxides (such as, for example, polyethyleoxides, polypropylene oxide, and the like), starches, celluloses (such as, for example, carboxymethyl celluloses (CMCs) and the like), polyacrylonitriles, and the like, and combinations thereof. The individual polymer chains of the covalently crosslinked polymer chains may be preformed or formed in situ. The polymer chains of the covalently crosslinked polymer chains may be a combination of two or more structurally distinct polymer chains. The individual polymer chains of the covalently crosslinked polymer chains may be homopolymers, copolymers (such as, for example, graft copolymers, block copolymers, random copolymers, and the like), and the like, or a combination thereof. The individual polymer chains of the covalently crosslinked polymer chains may be naturally occurring materials. Statement 4. A composition according to any one of the preceding Statements, wherein the molecular weight (Mw and/or Mn) of the polymer chains of the covalently crosslinked polymer chains is 40,000 to 150,000 g/mol, including all integer g/mol values and ranges therebetween.

Statement 5. A composition according to any one of the preceding Statements, wherein the individual polymer chains of the covalently crosslinked polymer chains are crosslinked by groups chosen from

the like).

Statement 6. A composition according to any one of the preceding Statements, wherein individual polymer chains of the ionically crosslinked polymer chains are chosen from alginates (e.g., sodium alginates and the like), polyglutamates, polynucleotides, polyethylene terephthalates, and the like, and combinations thereof. The individual polymer chains of the ionically crosslinked polymer chains may be preformed or formed in situ. The individual polymer chains of the ionically crosslinked polymer chains may be a combination of two or more structurally distinct polymer chains. The individual polymer chains of the ionically crosslinked polymer chains may be naturally occurring materials. In various examples, the ionically crosslinked polymer chains are ionic polymers. In various examples, the ionically crosslinked polymer chains are chosen from ionically crosslinked biopolymers, such as, for example, ionically crosslinked alginates (e.g., sodium alginate and the like), ionically crosslinked polynucleotides (e.g., RNAs, single-stranded DNAs, and the like), and the like, and combinations thereof. Non-limiting examples of ionically crosslinked polymer chains include polyglutamates (such as, for example, y-poly(glutamate)s, tetrahydrofolyl- poly(glutamate) polymers, 5,10-methenyltetrahydrofolate polyglutamates, 5,10- methylenetetrahydrofolate polyglutamate polymers, [Glu(-Cys)]n-Gly(l-), where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, and the like), alginates, DNA polyanions, heparans (such as, for example, heparan sulfate a-D-A-sulfoglucosamine polyanion, heparan sulfate a-D- glucosaminide 3 -sulfate polyanion, heparan sulfate a-D-glucosaminide 6-sulfate polyanion, heparan sulfate a-D-glucosaminide polyanion, heparan sulfate A -acetyl -a-D-gl ucosam i ni de polyanion, and the like), poly(2, 5-ethylene furandicarboxylate)(l-), poly(ethylene terephthalate)(l-), poly(nucleoside 5'-monophosphate) polyanion, poly(xylylviologen), poly[2-(methacryloxy)ethyl phosphorylcholine], RNA polyanions (such as, for example,

RNA polyanion 2',3'-cyclic phosphates, RNA polyanion nucleotide 2'-phosphates, RNA_(n>-3'- adenine ribonucleotide polyanions, RNA_(n>-3 '-uridine ribonucleotide polyanions, and the like), and the like, and combinations thereof.

Statement 7. A composition according to any one of the preceding Statements, wherein the molecular weight (Mw and/or Mn) of the polymer chains of the ionically crosslinked polymer chains is 100,000-200,000 g/mol, including all integer g/mol values and ranges therebetween (e.g., 120,000-190,000 g/mol).

Statement 8. A composition according to any one of the preceding Statements, wherein the ionic component is a plurality of cations (e.g., cations chosen from Group I cations, Group II cations (such as, for example, beryllium cations, calcium cations, magnesium cations, barium cations, and the like, and combinations thereof), and transition metal cations, and the like, and combinations thereof), or the ionic component is a plurality of anions (e.g., anions chosen from sulfate anions, chloride anions, and the like, and combinations thereof), or a combination thereof. It may be desirable that the ionic component comprises a polyvalent ion (such as, for example, a divalent cation or a divalent anion), or two or more monovalent cations or two or more monovalent anions.

Statement 9. A composition according to any one of the preceding Statements, wherein the polymer (e.g., covalently crosslinked polymer(s), ionically crosslinked polymer(s), or both) to ionic component weight percent (based on the total weight of hydrophilic polymer and ionic component, which may or may not include the counterion of the ionic component) ratio is 3:1 to 6:1, including all 0.1 ratio values and ranges therebetween.

Statement 10. A composition according to any one of the preceding Statements, wherein the polyether is polyethylene glycol, polypropylene glycol, and the like, and combinations thereof. Statement 11. A composition according to any one of the preceding Statements, wherein the molecular weight of the poly ether is 10,000 to 100,000 g/mol, including all integer molecular weight values and ranges therebetween.

Statement 12. A composition according to any one of the preceding Statements, wherein the amount of polyether is 0.1 to 1 percent by weight (based on the total weight of the composition), including all 0.01 values and ranges therebetween.

Statement 13. A composition according to any one of the preceding Statements, wherein the amount of water is 70 to 95, including all 0.1 values and ranges therebetween, percent by weight (based on the total weight of the composition).

Statement 14. A composition according to any one of the preceding Statements, wherein the covalently crosslinked polymer chains or ionically crosslinked polymer chains, or both the covalently crosslinked polymer chains and the ionically crosslinked polymer chains are preformed or are formed in situ.

Statement 15. A composition according to any one of the preceding Statements, wherein the composition comprises one or more additives. The additives may provide one or more desirable cooling and/or mechanical function(s), one or more desirable property(ies), or one or more desirable function(s) and one or more desirable property(ies). Non-limiting examples of additives include polar liquids (such as, for example, alcohols (e.g, ethanol and the like), ketones (e.g., acetone and the like), glycols, particles, which may be nanoparticles (such as, for example, silica aerogel particles). The nanoparticles may be thermally insulating. In the case of liquid additives, the liquid additive(s) may be present at 1-5 percent by weight (based on the total weight of the composition), including all 0.1 percent by weight values and ranges therebetween. In the case of solid (e.g., particulate) additives, the solid additive(s) may be present at 1-10 percent by weight (based on the total weight of the composition), including all 0.1 percent by weight values and ranges therebetween. In the case of silica aerogel particles, the silica aerogel particles may have an average size (e.g., average linear dimension, such as, for example, a linear dimension (e.g., a diameter) of 5-150 nm, including all 0.1 nm values and ranges there between. The silica aerogel particles may be nonporous and/or mesoporous. In the case of silica aerogel particles, the silica aerogel particles may phase separate and be thermal insulating, and may present as one or more discrete domain(s) (e.g., discrete layer(s)). Statement 16. A composition according to any one of the preceding Statements, wherein the composition is in the form of layer, sheet, or the like.

Statement 17. A composition according to any one of the preceding Statements, wherein the composition defines a plurality of void spaces (air pockets) or comprises a plurality of voids.

The voids may have a longest linear dimension (e.g., a diameter) of 1-50 nm, including all 0.1 nm values and ranges therebetween.

Statement 18. A composite structure comprising: i) a layer of a composition of any one of Statements 1-17; and a layer of a hydrophobic and/or thermally-insulating material, or a layer of heat conducting (e.g., thermally-conducting) material, wherein the layer of the composition of any one of Statements 1-17 is disposed on at least a portion of (or all) of a surface of the layer of insulating material or at least a portion (or all) a surface of the layer of heat conducting (e.g., thermally-conducting) material, or ii) a layer of a composition of any one of Statements 1-17; a layer of a heat conducting (e.g., thermally-conducting) material; a layer of semiconductor material which needs thermal management; and optionally, a layer of a heat conducting (e.g., thermally-conducting) material; wherein the layer of heat conducting (e.g., thermally-conducting) material and the layer of a hydrophobic and/or thermally- insulating material are disposed on at least a portion (or all) of opposite sides (e.g., opposite exterior surfaces) of the layer of a composition of any one of Statements 1-17.

Statement 19. A composite structure according to Statement 18, comprising a layer of a heat conducting (e.g., thermally-conducting) material (e.g., a body-side or heat-side layer); a layer of a composition of any one of Statements 1-17; and a layer of a hydrophobic and/or thermally-insulating material (e.g., an exterior-side layer), wherein the layer of heat conducting (e.g., thermally-conducting) material and the layer of a hydrophobic and/or thermally-insulating material are disposed on at least a portion (or all) of opposite sides (e.g., opposite exterior surfaces) of the layer of a composition of any one of Statements 1-17.

Statement 20. A composite structure according to Statement 18, comprising a first layer of a hydrophobic and/or thermally-insulating material a first layer of a hydrophobic material; a first layer of a composition of any one of Statements 1-17; a second layer of a hydrophobic and/or thermally-insulating material, wherein the first layer of a hydrophobic and/or thermally-insulating material and the second layer of a hydrophobic and/or thermally- insulating material are disposed on at least a portion (or all) of opposite sides (e.g., opposite exterior surfaces) of the layer of a composition of any one of Statements 1-17. Statement 21. A composite structure according to Statement 20, further comprising a second layer of a composition of any one of Statements 1-17, wherein the second layer of a composition of any one of Statements 1-17 is disposed on at least a portion (or all) of a side (e.g., an exterior surface) of the second layer of the hydrophobic and/or thermally-insulating material.

Statement 22. A composite material according to any one of Statements 18-22, wherein the hydrophobic and/or thermally-insulating material is chosen from polydimethylsiloxanes, fumed silica, textiles, fabrics, silica aerogels, polymers, glasses, and the like, and combinations thereof, and/or the thermally-conducting material(s) is/are chosen from metals, metalloids, semiconductor materials (such as for example, inorganic semiconductor materials, organic semiconducting materials (e.g., polymers, small molecules, and the like), and the like), polymers (such as, for example, polyethylene and the like), and the like, and combinations thereof. Non-limiting examples of textiles and/or fabrics include Kevlar, Nomax, nylons, polyethylenes, polypropylenes, cotton, and the like, and combinations thereof. The textile or fabric may comprise naturally-occurring fibers (such as, for example, cotton and the like), synthetic fibers (such as for example, polyethylene and the like), or a combination thereof. The silica aerogel may be surface modified to provide a hydrophobic surface.

Statement 23. A composite material according to any one of Statements 18-22, wherein the thickness of the individual hydrophobic and/or thermally-insulating material layer(s) and/or the thermally-conducting layer(s) is 0.1 mm to 1 mm, including all 0.01 mm values and ranges therebetween.

Statement 24. A composite material according to any one of Statements 18-23, wherein the thickness of the individual composition of any one of claims 1-17 layer(s) is 2 mm to 10 mm, including all 0.1 mm values and ranges therebetween.

Statement 25. A composite material according to any one of Statements 18-24, wherein the at least a portion of (or all of) the surface or side (e.g., an exterior surface) of the individual hydrophobic and/or thermally-insulating material layer(s) that is disposed on an adjacent composition of any one of Statements 1-17 layers is surface treated (e.g., plasma treated, chemically treated, photochemically treated, and the like, and combinations thereof) prior to formation of the composite material. Statement 26. A composite material according to any one of Statements 18-25, wherein the composition of any one of Statements 1-17 layer(s) exhibits a retention time of at least 3, 3.5, 4, 4.5, 5, 5.5, or 6 hours or 3 hours to 6 hours, including all 0.1 hour values and ranges therebetween. The retention time is the time it takes 90% or greater, 95% or greater, 99% or greater, or 100% of the water to undergo a solid to liquid phase transition.

Statement 27. A composite material according to any one of Statements 18-26, wherein the composition of any one of claims 1-17 layer(s) exhibits a Young’s modulus of 50kPa to 500 kPa, including all 0.1 kPa values and ranges therebetween.

Statement 28. A method of making a composition of any one of Statements 1-17, comprising: contacting a first composition comprising: one or more ionically crosslinkable polymer(s) (which may be hydrophilic) and/or one or more ionically crosslinkable polymer monomer(s); one or more monomer(s) (which can react to form a covalently crosslinked polymer, which may be hydrophilic); water; and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof, and a second composition comprising: one or more crosslinking compound(s); one or more ionic component(s) (which may be referred to as an ionic crosslinker(s)); and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof, wherein the composition is formed. It may be desirable that necessary components (e.g., reactants) to form the covalently crosslinked polymer and/or the ionically crosslinked polymer (e.g., monomer(s), crosslinker(s), ionic component s), and, optionally, catalyst(s)) are not present in either the first composition or the second composition, or both the first and second compositions, or in a single composition.

Statement 29. A method according to Statement 28, wherein the one or more ionically crosslinkable polymer(s) is/are chosen from alginates (e.g., sodium alginate and the like), polyglutamate, poly(ethylene terephthalate), and the like, and combinations thereof.

Statement 30. A method according to Statements 28 or 29, wherein the one or more monomers(s) is/are chosen from acrylamides, vinyl alcohols, cyclic ethers (such as, for example, ethylene oxide, propylene oxide, and the like), acrylonitriles, and the like, and combinations thereof.

Statement 31. A method according to any one of Statements 28-30, wherein the one or more crosslinking compounds is/are chosen from multiacrylamides (e.g., compounds comprising two or more acrylamide groups, such as, for example, diacrylamides (N,N’- methylenebisacrylamide (MBAA) and the like), and the like, and combinations thereof. Statement 32. A method according to any one of Statements 28-31, wherein the one or more ionic component(s) is/are chosen from salts such as, for example, Group I cation salts, Group II cation salts, transition metal salts (such as, for example, sulfate salts (e.g., calcium sulfate), chloride salts (e.g., calcium chloride), and the like, and combinations thereof), and the like, and combinations thereof.

Statement 33. A method according to any one of Statements 28-32, wherein the one or more ionically crosslinkable polymer(s) is/are chosen from polyalginates, polyglutamates, polynucleotides, polyethylene terephthalates, and the like, and combinations thereof, or wherein the ionically crosslinkable polymer monomer(s) is/are chosen from carbohydrates (such as, for example, saccharides (e.g., mono-, di-, tri-saccharides, and the like), and the like), glutamates, terephthalates (such as, for example, ethylene terephthalate and the like), and the like, and combinations thereof. The individual polymer chains of the ionically crosslinked polymer may be a combination of two or more structurally distinct polymer chains. The individual polymer may be a naturally occurring material. In various example, the ionically crosslinked polymer chains are ionic polymers. In various example, the ionically crosslinkable polymer chains are chosen from ionically crosslinkable biopolymers, such as, for example, alginates (e.g., sodium alginate and the like), polynucleotides (e.g., RNAs, single-stranded DNAs, and the like), and the like, and combinations thereof. Non-limiting examples of ionically crosslinkable polymer chains include polyglutamates (such as, for example, y-poly(glutamate)s, tetrahydrofolyl-poly(glutamate) polymers, 5,10- methenyltetrahydrofolate polyglutamates, 5,10-methylenetetrahydrofolate polyglutamate polymers, [Glu(-Cys)]n-Gly(l-), where n is from 2 to 11, and the like), alginates, DNA polyanions, heparans (such as, for example, heparan sulfate a-D-ZV-sulfoglucosamine polyanion, heparan sulfate a-D-glucosaminide 3 -sulfate polyanion, heparan sulfate a-D- glucosaminide 6-sulfate polyanion, heparan sulfate a-D-glucosaminide polyanion, heparan sulfate L -acetyl -a-D-gl ucosam i ni de polyanion, and the like), poly(2, 5-ethylene furandicarboxylate)(l-), polyethylene terephthalate)(l-), poly(nucleoside 5'- monophosphate) polyanion, poly(xylylviologen), poly[2-(methacryloxy)ethyl phosphorylcholine], RNA polyanions (such as, for example, RNA polyanion 2',3'-cyclic phosphates, RNA polyanion nucleotide 2'-phosphates, RNA_(n>-3 '-adenine ribonucleotide polyanions, RNA_(n>-3 '-uridine ribonucleotide polyanions, and the like), and the like, and combinations thereof. Statement 34. A method according to any one of Statements 28-33, wherein the catalyst(s) is/are radical initiators, thermal initiators, photochemical initiators, and the like, and combinations thereof. Non-limiting examples of radical initiators (which may be thermal initiators) include persulfates (such as, for example, ammonium persulfate, potassium persulfate, and the like, and combinations thereof). Non-limiting examples of photochemical initiators include lithium phenyl-2,4, 6-trimethylbenzoylphosphinate, and the like, and combinations thereof.

Statement 35. A method according to any one of Statements 28-34, wherein the one or more ionically crosslinkable polymer(s) (which may be hydrophilic) is/are present at 0.8-3 wt.%, including all 0.01 wt.% values and ranges therebetween; and/or the one or more monomer(s) is/are present at 4-21 wt.%, including all 0.1 wt.% values and ranges therebetween; and/or the water is present at 75-95 wt.%, including all 0.1 wt.% values and ranges therebetween; and/or optionally, the one or more catalyst(s) and/or catalyst component(s) (e.g., of the first composition) is/are present at 0.2-1 wt.%, including all 0.01 wt.% values and ranges therebetween; and/or the one or more crosslinking compound(s) is/are present at 0.8-3 wt.%, including all 0.01 wt.% values and ranges therebetween; and/or the one or more ionic component(s) is/are present at 0.8-3 wt.%, including all 0.01 wt.% values and ranges therebetween; and/or the ionic component is present at 0.8-3 wt.%, including all 0.01 wt.% values and ranges therebetween; and/or optionally, the one or more catalyst(s) and/or catalyst component s) (e.g., of the second composition) is/are present at 0.2-1 wt.%, including all 0.01 wt.% values and ranges therebetween. The reaction mixture resulting from the contacting may have any combination of these component amounts. The water (e.g., of the first composition or the second composition, or both) may make up the remainder of the composition(s). The percent by weight values are based on the total weight of the reaction mixture or portion thereof (e.g., first composition, second composition, etc.)

Statement 36. A method according to any one of Statements 28-35, wherein the contacting (e.g., the reaction) is carried out at room temperature (e.g., 18-22 °C) in the ambient atmosphere.

Statement 37. A method according to any one of Statements 28-36, further comprising treating (e.g., plasma treating, chemically treating, photochemically treating, and the like, and combinations thereof) the thermal insulation layer to improve the adhesion between thermal insulation layer and the instant composition layer. Statement 38. A composite material comprising a hydrogel layer having a first surface and a second surface opposite the first surface; and a first layer comprising a first hydrophobic material, the first layer being disposed on the first surface of the hydrogel layer.

Statement 39. A composite material according to Statement 38, further comprising a second layer comprising a second hydrophobic material, the second layer being disposed on the second surface of the hydrogel layer.

Statement 40. A composite material according to Statements 38 or 39, wherein the first hydrophobic material is the same or different than the second hydrophobic material.

Statement 41. A composite material according to any one of Statements 38-40, wherein the hydrogel layer comprises a plurality of covalently-crosslinked polymer chains; a plurality of ionically-crosslinkable polymer chains; and an ionic component.

Statement 42. A composite material according to any one of Statements 38-41, wherein the hydrogel layer has a water content of 60-95 wt.% (based on the total weight of the hydrogel layer).

Statement 43. A composite material according to any one of Statements 38-42, wherein the first hydrophobic material and/or the second hydrophobic material are polydimethylsiloxane (PDMS).

Statement 44. A composite material according to any one of Statements 41-43, wherein the hydrogel layer further comprises one or more additives.

Statement 45. A composite material according to Statement 44, wherein the one or more additives are chosen from polar liquids, glycols, particles, nanoparticles, and combinations thereof.

Statement 46. A composite material according to Statement 45, wherein the particle or nanoparticle is fumed silica.

Statement 47. A composite material according to any one of Statements 41-46, wherein the hydrogel layer further comprises a polyether.

Statement 48. A composite material according to any one of Statements 41-47, wherein the individual polymer chains of the covalently-crosslinked polymer chains are chosen from polyacrylamides, polyvinyl alcohol, polyalkylene oxides, starches, celluloses, polyacrylonitriles, and combinations thereof. Statement 49. A composite material according to any one of Statements 41-48, wherein the individual polymer chains of the ionically-crosslinkable polymer chains are chosen from alginates, polyglutamates, polynucleotides, polyethylene terephthalates, and combinations thereof. Statement 50. A composite material according to any one of Statements 41-49, wherein the ionic component is chosen from beryllium cations, calcium cations, magnesium cations, barium cations, sulfate anions, chloride anions, and combinations thereof.

Statement 51. A composite material according to any one of Statements 39-50, further comprising one or more additional hydrogel layers and one or more additional layers comprising a hydrophobic material, wherein each additional hydrogel layer is disposed between corresponding layers of the one or more additional layers.

Statement 52. A composite material according to any one of Statements 38-51, wherein the hydrogel layer is configured as a structure having one or more pores; and the first layer is disposed within the one or more pores. Statement 53. A composite material according to Statement 52, wherein the structure having one or more pores is a lattice structure.

Statement 54. A hydrogel comprising a polymer network and water, wherein the polymer network comprises: a plurality of covalently-crosslinked polymer chains; a plurality of ionically-crosslinkable polymer chains; and an ionic component. Statement 55. A hydrogel according to Statement 54, further comprising one or more additives.

Statement 56. A hydrogel according to Statement 55, wherein the one or more additives are chosen from polar liquids, glycols, particles, nanoparticles, and combinations thereof.

Statement 57. A hydrogel according to Statement 56, wherein the particles or nanoparticles are fumed silica.

Statement 58. A hydrogel according to Statement 57, wherein the amount of fumed silica is 0.1-5 wt.% (based on the total weight of the hydrogel composition).

Statement 59. A hydrogel according to any one of Statements 54-58, further comprising a polyether. Statement 60. A hydrogel according to any one of Statements 54-59, wherein the polyether is chosen from polyethylene glycol, polypropylene glycol, and combinations thereof.

Statement 61. A hydrogel according to Statements 59 or 60, wherein the amount of poly ether is 0.1 to 1 wt.% (based on the total weight of the hydrogel composition).

Statement 62. A hydrogel according to any one of Statements 54-61, wherein the individual polymer chains of the covalently-crosslinked polymer chains are chosen from polyacrylamides, polyvinyl alcohol, polyalkylene oxides, starches, celluloses, polyacrylonitriles, and combinations thereof.

Statement 63. A hydrogel according to any one of Statements 54-62, wherein the molecular weight (Mw and/or Mn) of the polymer chains of the covalently-crosslinked polymer chains is 40,000 to 150,000 g/mol.

Statement 64. A hydrogel according to any one of Statements 54-63, wherein the covalently- crosslinked polymer chains are crosslinked by one or more of the following groups:

wherein R' and R" are independently chosen from H,

and combinations thereof.

Statement 65. A hydrogel according to any one of Statements 54-64, wherein the individual polymer chains of the ionically-crosslinkable polymer chains are chosen from alginates, polyglutamates, polynucleotides, polyethylene terephthalates, and combinations thereof.

Statement 66. A hydrogel according to any one of Statements 54-65, wherein the molecular weight (Mw and/or Mn) of the polymer chains of the ionically-crosslinkable polymer chains is 100,000-200,000 g/mol.

Statement 67. A hydrogel according to any one of Statements 54-66, wherein the ionic component is chosen from beryllium cations, calcium cations, magnesium cations, barium cations, sulfate anions, chloride anions, and combinations thereof. Statement 68. A hydrogel according to any one of Statements 54-67, wherein the hydrogel exhibits a Young’s modulus of 50-500 kPa.

Statement 69. A hydrogel according to any one of Statements 54-68, wherein the hydrogel has a water content of 60-95 wt.% (based on the total weight of the hydrogel layer).

Statement 70. A hydrogel according to any one of Statements 54-69, wherein the hydrogel layer is configured as a structure having one or more pores; and the first layer is disposed within the one or more pores.

Statement 71. A hydrogel according to any one of Statements 54-70, wherein the structure having one or more pores is a lattice structure.

Statement 72. A hydrogel according to any one of Statements 54-71, wherein the weight percent ratio of i) the plurality of covalently-crosslinked polymers chains, ii) the plurality of ionically-crosslinkable polymer chains, or iii) both, with respect to the ionic component is 3: 1 to 6:1.

Statement 73. A method of making a composite material according to any one of Statements 38-53, comprising: contacting a first composition and a second composition to form a hydrogel precursor, the first composition comprising: one or more ionically-crosslinkable polymer(s); one or more monomer(s); water; and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof, and the second composition comprising: one or more crosslinking compound(s); water; and one or more ionic component s); and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof, contacting the hydrogel precursor with a hydrophobic material, wherein the composite material according to any one of Statements 38-53 is formed.

Statement 74. A method according to Statement 73, wherein, prior to contacting the hydrogel precursor with the hydrophobic material, the hydrogel precursor is allowed to stand such that it forms a hydrogel.

Statement 75. A method according to Statements 73 or 74, wherein the hydrogel precursor is pressed prior to standing.

Statement 76. A method according to any one of Statements 73-75, wherein the hydrophobic material is coated with an adhering agent (e.g., a photoinitiator).

Statement 77. A method according to Statement 77, wherein the adhering agent (e.g., photoinitiator) is benzophenone. Statement 78. A method according to any one of Statements 73-77, wherein the hydrogel precursor in contact with the hydrophobic material is UV-cured.

Statement 79. A method according to any one of Statements 73-78, wherein the first composition further comprises one or more additives. Statement 80. A method according to Statement 79, wherein the one or more additives are chosen from polar liquids, glycols, particles, nanoparticles, and combinations thereof.

Statement 81. A method according to Statement 80, wherein the particles or nanoparticles are fumed silica.

Statement 82. A method according to Statement 81, wherein the amount of fumed silica is 0.1-5 wt.% (based on the total weight of the hydrogel composition).

Statement 83. A method according to any one of Statements 73-82, wherein the one or more monomers are chosen from acrylamides, vinyl alcohols, cyclic ethers, acrylonitriles, and the like, and combinations thereof.

Statement 84. A method according to any one of Statements 73-83, wherein one or more monomers are present in the amount of 4-21 wt.%.

Statement 85. A method according to any one of Statements 73-84, wherein the one or more crosslinking compounds are multiacrylamides.

Statement 86. A method according to any one of Statements 73-85, wherein the one or more crosslinking compounds are present in the amount of 0.8-3 wt.%. Statement 87. A method according to any one of Statements 73-86, wherein the ionically-crosslinkable polymers are chosen from alginates, polyglutamates, polynucleotides, polyethylene terephthalates, and combinations thereof.

Statement 88. A method according to any one of Statements 73-87, wherein the ionically-crosslinkable polymers are present in the amount of 0.8-3 wt.%. Statement 89. A method according to any one of Statements 73-88, wherein the ionic component is chosen from beryllium cations, calcium cations, magnesium cations, barium cations, sulfate anions, chloride anions, and combinations thereof.

Statement 90. A method according to any one of Statements 73-89, wherein the ionic component is present in the amount of 0.8-3 wt.%. Statement 91. A method according to any one of Statements 73-90, wherein the one or more catalysts and/or catalyst components are chosen from radical initiators, thermal initiators, photochemical initiators, and combinations thereof.

Statement 92. A method according to any one of Statements 73-91, wherein the one or more catalysts and/or catalyst components are present in the amount of 0.2-1 wt.%.

Statement 93. A method according to any one of Statements 73-92, wherein the ratio of the first composition to the second composition is 3 : 1 to 6: 1 (v/v).

[0087] The following examples are presented to illustrate the present disclosure. The examples are not intended to be limiting in any matter.

EXAMPLE 1

[0088] This example provides a description of compositions of the present disclosure and methods of making the compositions, and characterization of the compositions.

[0089] A goal was to prepare a composite material that can be cooled (e.g., down to subzero temperatures) and offer a desirable degree of cold retention (e.g., greater than ice) while retaining its flexibility at those temperatures.

[0090] Films of tough polyacrylamide (PAAm) hydrogel with both covalent and ionic crosslinking that are sandwiched between poly dimethyl siloxane (PDMS) layers to decrease the rate of heat conduction were formed. PDMS is hydrophobic and protects the hydrogel layers from dehydration in addition to its thermal contribution. Desirable thermally-insulating and mechanical properties of the material were observed when fumed silica was dispersed in the hydrogel matrix.

[0091] Experimental Method. Preparation of the Sample. The PDMS sandwich material was prepared by pouring it into molds with a thickness of 0.5-1 mm and baked in an oven at 60 °C for 2 hours.

[0092] The PAAm hydrogel precursor was prepared as a batch of two different solutions. The first solution (Sol A) comprised acrylamide (AAm, monomer), sodium alginate (ionically crosslinkable biopolymer), EbO and tetramethylethylenediamine (TEMED, catalyst). In the samples containing fumed silica, the additive was added to Sol A directly in the required quantity.

[0093] The second solution (Sol B) comprised N,N’-methylenebisacrylamide

(MBAA, crosslinker), calcium sulfate (ionic crosslinker), ammonium persulfate (APS, catalyst used along with TEMED). MBAA, APS and calcium sulfate solutions in water were prepared prior to making the second solution in concentrations of 0.109, 1.09 and 6.06 wt.% respectively. The concentrations of the different chemicals used in the two solutions are as given in Table 1.

[0094] Table 1. Concentrations of the chemicals used in the PAAm hydrogel precursor solutions.

[0095] The two PAAm hydrogel precursor solutions were thoroughly and quickly mixed in the ratio 4: 1 (Sol A : Sol B) in molds to enable gelation. The hydrogel was covered using glass plates and left to gel for 3 hours.

[0096] After the PDMS layers were cured, they were taken out of their molds and put into an Oxy-plasma chamber for 2 minutes to clean their surfaces and dipped into a benzophenone solution in Ethanol (10 wt.%, based on the total weight of the solution). The PDMS layers were coated with a layer of benzophenone and then completely dried. The benzophenone was used as a photosensitive adhesive to enable the adhesion of the PDMS layers onto the PAAm hydrogel layers.

[0097] The freshly treated PDMS layers were stacked onto the PAAm hydrogel layers in an alternating Hydrogel-PDMS sandwich structure to form the final sample. The final sample was then put into a UV oven for an hour to cure the adhesive and make the sample ready for testing.

[0098] The effect of various parameters on the properties of the samples was studied.

The parameters based on which the thermal and mechanical properties of the samples were tested are as follows: i) Based on the water content of the hydrogel. ii) Based on the number of hydrogel layers. iii) Based on the number of hydrogel layers given a constant overall sample thickness. iv) Based on the weight percentage of fumed silica in the hydrogel. [0099] Thermal testing. For thermal testing of a sample, a sample was first prepped by inserting a thermocouple into the middle layer of the sample and then the sample cooled to below freezing temperatures of water. The sample was then kept at room temperature and the temperature of the sample recorded over time until the sample reached room temperature. [0100] Mechanical Testing. For mechanical testing, the sample was cut into a cube or a cuboid depending on its thickness and subjected to compression testing at subzero temperatures.

[0101] Results. As seen in Figure 1, the samples tested for their cold retention according to the varying parameters showed the following trends: i) The cold retention of the samples exhibited a peak at 85% water content. ϋ) The cold retention of the samples increased with the increase in the number of hydrogel layers. It was seen that the cold retention of the sample increased by 60 minutes for every added layer of hydrogel. iii) For a constant overall sample thickness, the cold retention of the samples decreased with an increase in the number of hydrogel layers. iv) The maximum cold retention based on the weight percentage of fumed silica in the hydrogel was found at 2 wt.%. The cold retention for this sample was also considerably higher than the one without the addition of any fumed silica. [0102] The higher the Young’s Modulus of a material, the lower is its flexibility. As seen in Figure 2, the samples tested for their mechanical properties according to the varying parameters showed the following trends: i) The Young’s Modulus of the samples decreased with an increase in the water content. ii) The Young’s Modulus of the samples showed an increasing trend with the number of hydrogel layers. iii) For a constant overall sample thickness, the Young’s Modulus of the samples was found to decrease with the increase in number of hydrogel layers. iv) The Young’s modulus of the samples decreased with an increase in the weight percentage of fumed silica. The Young’s Modulus the samples with 2% or more fumed silica were found to be lower than the one without the addition of any fumed silica.

[0103] With the thermal and mechanical properties tested under the different varying parameters, it was seen that there is a trade-off between cold retention and flexibility in all the cases. A desirable balance between cold retention of the material and its flexibility was exhibited by the sample with 85% water content and 2 wt. % fumed silica. The constraint on the number of hydrogel layers will be dependent on the application of the material.

EXAMPLE 2

[0104] This example provides a description of compositions of the present disclosure and methods of making the compositions, and characterization of the compositions.

[0105] Owing to their cross-linked polymer networks, hydrogels exhibit the properties of elastic solids with deformability and softness. On the other hand, high-water content in hydrogels leads to liquid-like attributes of hydrogels, including permeability to a wide range of chemical and biological molecules, and transparency to optical and acoustic waves. Moreover, the unique properties of hydrogels, such as superior softness, wetness, responsiveness, biocompatibility, and bioactivity, indeed suggest the possibility of their crucial functions in cooling applications. The heat absorption due to water content in hydrogels makes it a cooling device, while water is abundant, non-corrosive, non-toxic, and non-flammable. Cooling represents a considerable fraction of energy consumption, while it is indispensable to develop eco-friendly, biocompatible, and ductile cooling materials for personal applications. Demonstrated herein is the ductile cooling ability with phase change of thermally passivated hydrogel composite materials with additive manufacturing ability. Thermal evaluation of such water-based composites indicates a superior cold retention capacity with a cooling comfort over 6 hours, while the composite displays a full recovery when strained up to 80% in uniaxial compression tests as a result of the intertwining between covalent and ionic bonds. A three-layered rectangular model was utilized to simulate the problem in a steady-state thermal analysis to study the cooling effect. These data indicate the potential of hydrogel as a cooling phase-change medium and its contribution towards ductile cooling applications.

[0106] Disclosed herein is a hydrogel-based PCM cooling material employing a layer-by-layer assembly of Ca-alginate/Polyacrylamide (PAAm) hydrogel and polydimethylsiloxane (PDMS), which shows chemical inertness, thermal stability, permeability to gases, and additive manufacturing capability in addition to its affordability. The PDMS layer prevents the dehydration of hydrogel layer, and serves as the thermal insulation barrier with thermal conductivity of 0.15 Wm flC ¹ as compared to the thermal conductivity of 0.60 Wm flC ¹ for pure water. Being hydrophobic, the outer layers of PDMS remain cold but dry. Also disclosed is the cooling relief through fabricating a Ca- alginate/PAAm hydrogel-PDMS composite, which possesses high flexibility and large cooling capacity. Owing to a great number of hydrophilic groups in three-dimensional chemical chains, the PAAm polymer can absorb as much as a hundred times of its mass in water. On one hand, the absorbed water is superior in heat control; and on the other, the mobility of water can be well managed in operation. The data show the desirable performance of the layer-by-layer fabricated hydrogel-PDMS composite in cooling and ductile mechanical properties, promising for wearable devices.

[0107] Figure 3a displays the schematic manufacturing illustration of the Ca- alginate/PAAm hydrogel based on the free radical polymerization method. As per Figure 3a, the hydrogel is composed of two solutions, solution A and solution B containing the hydrogel precursor, which are thoroughly mixed in the ratio 4: 1 (the detailed synthesis methods are described herein). The resulting mixture can be compress molded into different geometries. A similar process can be used to obtain the hydrogel infused with the fumed silica where the additive was added directly to solution A. The as-manufactured hydrogels have good elasticity and flexibility, as shown in Figures 3b and 3c. Furthermore, Figures 3d and 3e display its bending capability of hydrogels even under freezing conditions (-12 °C), which also show excellent softness and good flexibility bending up to 180 degrees.

[0108] Figure 4a shows the schematic diagram to perform thermal tests on the layer- by-layer hydrogel and PDMS sandwiched structure. The phase change process from the conversion of ice domain to water (Figure 4b), in which the ice domains separated by the polymer networks transform into an ice-water mixture, and subsequently to the liquid phase. To provide the understanding of such conversion of the composite structure, a steady-state thermal simulation is performed, as shown in Figure 4c. The geometry is simplified as a 2D three-layered rectangular block, indicative of the PDMS/Hydrogel/PDMS layers. Figure 4c shows the temperature contour of the hydrogel sandwich structure. The steady-state thermal transfer between the two surfaces induces a non-uniform temperature gradient across the sandwich structure, which is an effect caused by the hydrogel/PDMS sandwich layer structure with different thermal performance tendencies. Due to the presence of the polymer networks in the Ca-alginate/PAAm hydrogel, their thermal conductivity is lower than that of pure water. The polymer networks act as a restriction in thermal conduction pathways of pure water, while maintaining the shape of the hydrogel.

[0109] To analyze the cooling capacity of the composites, they were evaluated by comparing the incremental rate of the temperature of the samples within the same period. Figure 4d and 11a shows the temperature vs. time profiles of samples with different water content (Inset: Line chart of the time when the temperature reaches 20 °C for the different samples). The cold retention capacity of the samples exhibited a peak at 85 wt.% water content. The two methods of thermal conduction within the hydrogel are the conduction pathways of pure water and the conduction pathways of the polymer networks. With an increase in the water content, there is an increase in the pathways for conduction through pure water and a resultant decrease in the conduction pathways through the polymer network. The hydrogel with 85 wt.% water demonstrates its superiority in controlling the temperature increment rate by maintaining an optimum balance between the conduction pathways for pure water and the polymer networks. Also studied were the effect of thickness of the hydrogel layer on the cooling capacity of the material and Figure 4d indicates that there is a linear increase in the cold retention capacity of the composite material with the increase in hydrogel layer thickness. This can be attributed to the increase in the heat capacity of the material as the water content of the sample increases with increasing thickness of the hydrogel layer. Moreover, to elucidate the effect of the different number of layers on the cooling capacity of the sample, Figure 4e and 14 shows the temperature vs time profiles of the samples with a different number of hydrogel layers (individual hydrogel layer thickness of 1.9 mm). It is observed that the cooling capacity of the sample increases with an increasing number of hydrogel layers and the time for the temperature to reach 20 °C is highest for the seven layered hydrogel structure (450 min). It is observed that the cooling capacity of the sample increased by 60 minutes for every added layer of hydrogel.

[0110] The hydrogel composition influences its mechanical properties while its ductility and its toughness play an important role in its wearable applications. Figure 5a and 1 lb shows the stress-strain curves of the samples with hydrogel layers containing 80 wt.%,

85 wt.%, 90 wt.%, and 95 wt.% water content. The hydrogel containing 80 wt.% water exhibits the highest Young’s modulus (1,500 kPa), suggesting its lowest porosity amongst all the samples. When the water content is increased further, hydrogels containing 85 wt.% water show a decreased Young’s modulus (1,400 kPa), and the hydrogels containing 90 wt.% and 95 wt.% water content exhibit a much lower Young’s modulus of 600 kPa and 100 kPa respectively which indicates that the hydrogel with 95 wt.% water content exhibits the highest flexibility. However, there is also a decrease in the fracture energy of the material with increasing water constant which indicates a drop in its toughness. The increase in water content decreases the concentration of the polymer network in the hydrogel which further leads to a reduction in the energy absorption capacity of the material before fracture. As such, the hydrogel with 85 wt.% water content gives us a balance between flexibility and toughness. Figure 5b and Figure 16 inset shows Young’s modulus and fracture energy of the samples with varying hydrogel layer thickness. It is evident from the figure that there is a linear increase in Young’s modulus and fracture energy with the increase in hydrogel layer thickness. Figure 14 inset shows Young’s modulus and fracture energy of the samples with varying number of hydrogel layers. With an increase in the number of hydrogel layers, Young’s modulus and fracture energy of the samples exhibit a significant linear increase. The Young’s modulus of the samples with 5 and 7 layers of hydrogel (hydrogel layer thickness ~ 1.9 mm) is 285 kPa and 1,540 kPa respectively. However, when the total thickness of the sample is restricted to a constant overall thickness, an increment in the number of hydrogel layers (decrease in individual hydrogel layer thickness) results in a decreased overall Young’s modulus and fracture energy as shown in Figure 5b inset. Young’s modulus of samples with 1, 2, and 5 hydrogel layers is found to be 2,527 kPa, 1,310 kPa, and 285 kPa, respectively. This indicates that the thickness of the individual hydrogel layers has a higher impact on the mechanical properties of the material as compared to the number of hydrogel layers. The hydrogel with 85 wt.% water content exhibits the optimum overall performance (192 min cooling capacity and 1.4><10⁵ N/m² Young’s modulus). Moreover, the two-layered hydrogel sample with individual hydrogel layer thickness — 5 mm show good cooling capacity (340min) along with an acceptable Young’s modulus (1.3/ 10⁵ N/m²) and fracture energy (53.199 kJ m ²). However, with the dependence of the thermal and mechanical performance of the material on these varied parameters, there exists no definite configuration that provides the best results. The power of this material lies in its ability to be tailored to provide optimum thermal and mechanical performance according to the desired specifications.

[0111] Though organic materials offer convenient processing ability and high flexibility, it is well documented that inorganic materials offer a higher potential of mechanical and thermal stability. Consequently, the selection of an inorganic material was necessary for improving the properties of the PCMs further. Hollow silica micro- and nanospheres have recently gained popularity that can be attributed to their highly attractive features such as a lower density, high surface area, and remarkable thermal insulation performance. Fumed silica has been found to exhibit thermal conductivity as low as 0.02 Wm^K ¹ for specimens with thickness in the range of 25.5 to 25.8 mm. Moreover, these structures are capable of facilitating a high storage capacity along with thermal, chemical, and mechanical resistance, and are environmentally inert. Temperature vs. time profiles of the samples with different fumed silica content are shown in Figure 6a. It can be observed that the cooling capacity initially increases with an increase in fumed silica content but later decreases as the concentration of fumed silica is increased, reaching a max value of 100 min below 0 °C and 200 min to reach 20 °C for the sample with 2 wt.% fumed silica (Figure 17a). Subsequently, the stress-strain curves are plotted to assess the mechanical stiffness of the different samples. As seen in Figure 6b inset and Figure 17b, Young’s modulus for fumed silica added hydrogel was found to lie within the range of 2,250 kPa for 1 wt.% fumed silica to 250 kPa for 3 wt.% fumed silica. A gradual decrease in fracture energy with the increase in fumed silica content indicated the sample with 2 wt. % fumed silica provided a desirable balance between flexibility and toughness. The use of fumed silica in gel fabrication is considered to be important in this regard. In particular, fumed silica introduction indeed influences the cooling and mechanical properties of hydrogel via improving its cooling capacity as well as flexibility.

[0112] The hydrogel materials can be additively manufactured through a cross- linking process initiated by the UV light (Figure 7a). The pattern was printed continuously by exposing it to a dynamic mask generator and UV light. The printed sample was evaluated for its mechanical properties by a uniaxial compression test. The test with increasing maximum strains (60%, 80%, 90%, and 95%) was conducted on the printed hydrogel lattice and was indicative of the super-elastic performance. The maximum strain increased from 60%, 80%, to 90% for hydrogel lattice with a full recovery below 80% strain. When strain reached 90%, the residual strain was 5%. When the printed hydrogel was subjected to external stress, the ionic bonds broke initially to dissipate the external energy and thus protected the covalent bonds from breaking. As the part further deformed, Figures 7b and 57 show that the covalent network stretched primarily due to its elasticity. (Figure 19 depicts the printed hydrogel composite during the uniaxial compression test with an incrementing amount of compression loading. Figure 20 represents the displacement at the numbered points on the hydrogel composite in proportion to the increasing amount of strain). When the part is relieved of the stress, the covalent network tended to regain its original tangled state and thus the printed hydrogel recovered its original shape with the ionic bonds recombining together. The covalent network and the ionic network were in an intertwined state, granting the printed hydrogel the feature of highly recoverable compressibility. The lattice structure of the printed hydrogel was designed to cater to the cooling purpose. While the geometry is based on Schwarz Primitive surface, with periodically arranged small units, the entire structure has a high surface-to-volume ratio and porosity. The high porosity leads to a low thermal conductivity, which will benefit the cooling application. Compressive stress-strain curves of hydrogel with cycling are shown in Figure 7d. A steep increase in Young’s modulus was observed as soon as the strain rate exceeds 75% for all the samples. Figure 7e shows the temperature vs. time profiles of hydrogel with and without PDMS filled into the porous lattice structure. The results depicted the cooling capacity of hydrogel has a large improvement with PDMS.

[0113] The use of hydrogel composites as a phase change material for ductile cooling applications is described herein. The data display desirable cooling capacity and desirable mechanical properties. The optimum cooling and ductility performance suggest the water content of 85 wt.% and 7 layers of hydrogel composites. The introduction of fumed silica has greatly improved mechanical and thermal stability of cooling composites, in which 2 wt.% fumed silica provided a desirable balance of flexibility, toughness, and cooling ability. The printed composites reveal its super-elastic performance and cooling capacity.

[0114] Preparation of the Sample: Figure 9 shows the dependence of Young’s modulus of PDMS on the pre-polymer base and crosslinking agent mixing ratio and the curing temperature. As per this dependence, to obtain a PDMS which offers flexibility and toughness comparable to that of the hydrogel, the PDMS was prepared with a mixing ratio of 10:1 (Pre-polymer base: Crosslinking agent) at a curing temperature of 60 °C. PDMS sandwich materials with a thickness of 0.5-1 mm prepared in molds by curing in an oven at 60 °C for 4 to 5 hours. The Ca-alginate/PAAm hydrogel pre-cursor was prepared as a batch of two different solutions. The first solution (Sol A) comprised Acrylamide (AAm, monomer), Sodium alginate (Ionically cross-linkable biopolymer), and Tetramethylethylenediamine (TEMED, catalyst) and water. For the samples infused with fumed silica, the additive was added directly to Sol A in the required quantity. The second solution (Sol B) comprised N,N’-Methylenebisacrylamide (MBAA, covalent crosslinker), Calcium Sulfate (Ionic crosslinker) and Ammonium Persulfate (APS, photoinitiator) solutions in water. The solutions of MBAA, APS, and Calcium Sulfate in water were pre prepared before preparation of the Sol B in concentrations of 0.109 wt.%, 1.09 wt.%, and 6.06 wt.% respectively. The quantity of chemicals used in the preparation of Sol A and Sol B are as given in Table 2. To prepare the hydrogel precursor, Sol B is poured into Sol A in the volume ratio 4: 1 (Sol A : Sol B) and mixed thoroughly. The mixture is then quickly transferred into molds and pressed down upon by a glass plate and left to stand for 3 hours to complete gelation. The importance of the glass plate is to maintain a uniform surface on the hydrogel layers and to prevent any dehydration during gelation. After the PDMS layers are cured, they are removed from their molds and put into an Oxy -plasma chamber for 1 min to clean their surfaces followed by dipping into a Benzophenone solution in Ethanol (10 wt.%). Benzophenone has been found to counter the oxygen inhibition effect on the covalent crosslinking of hydrogel and PDMS and it also acts as a UV activated grafting agent for the same. The PDMS layers are allowed to get coated with a layer of Benzophenone and then dried off. The freshly treated PDMS layers are stacked onto the Ca-alginate/PAAm hydrogel layers in an alternating Hydrogel-PDMS sandwich structure, thus creating the final formed sample. The sample is then put into a UV oven for an hour to allow curing of the benzophenone and thus the sample is ready for testing (Figure 8). The effect of various parameters on the properties of the samples has been studied. The parameters based on which the thermal and mechanical properties of the samples were tested are as follows: 1) Based on the water content of the hydrogel. 2) Based on the thickness of the hydrogel layers. 3) Based on the number of hydrogel layers. 4) Based on the number of hydrogel layers while maintaining a constant overall sample thickness. 5) Based on the weight percentage of fumed silica in the hydrogel.

[0115] Precursor preparation for 3D printing: The precursor is prepared by mixing

Methylenebis acrylamide (MBAA) and Dimethyl acrylamide (DMAA) in a volume ratio of 4:1. Polyethylene glycol diacrylate (PEGDA, Mn=700) is added to the precursor in a concentration of 1.0 vol% to improve the strength of the cross-linked hydrogel. To facilitate fast printing, Lithium phenyl-2,4, 6-trimethylbenzoylphosphinate (LAP), a visible light photo initiator was added to the precursor in the amount of 0.2 wt%. To ensure the high-resolution printing, the UV absorber Quinoline Yellow dye (Sigma Aldrich) was added in an amount of 0.002 wt%. The precursor was then agitated utilizing an ultrasound sonicator.

[0116] Stereolithographic (SLA) printer setup: The custom-build SLA printer is composed of a digital micro-mirror device (DMD) based projector (PR04500 MV,

WinTech), a positioning stage (Velmex, Inc.), and a precursor vat. The DMD chip generates the dynamic masked images and they get focused on the projection plane of the vat to cure the precursor. The size of the projection envelop is 48 x 30 mm; its resolution is 1280 x 800 pixels, which results in a single-pixel size of 37.5 microns. The automation and the synchronization of the mask generation and the motion of the positioning stage is achieved by using a custom-programmed control software. The precursor vat is coated with a layer of Polydimethylsiloxane (PDMS, SYLGARD 184) at the base.

[0117] Stereolithographic (SLA) 3D printing process: The fast-paced SLA printing is based on a continuous printing configuration. The masked images are continuously generated and emitted; the positioning stage is elevating at a constant speed of 0.05 mm/sec. It takes 20 minutes for printing the object shown in Figure 7a; consuming 18 mL precursor in the process. After the printing, the crosslinked hydrogel is soaked in a Calcium sulfate (CaSCri) bath for 1 hour to enable the formation of the ionic bonding network.

[0118] Thermal testing: For thermal analysis of the sample, it is first prepped by inserting a thermocouple in the middlemost hydrogel layer of the sample and it is then cooled down to subzero temperatures using a refrigerator. The cooled down sample is then plugged into a thermometer which is attached to a computer set up. The sample is allowed to sit at room temperature and the software gives us the temperature vs time profile for the sample (Figure 10).

[0119] Mechanical Testing: Compression testing was performed on the samples under strain-controlled conditions to measure their mechanical strength. The samples were cut into cuboids and refrozen before testing. The stress-strain curves for the samples were plotted which were then used to calculate Young’s modulus and fracture energy of the samples to compare their mechanical properties. The dimensions of the samples used for mechanical testing are as shown in Table 3.

[0120] Figure 8 shows the bar chart representation depicting the time for which the hydrogel composite can maintain its temperature below 0 °C and 20 °C for samples with different amount of water content. From this figure, it is shown the hydrogel with 80 wt% water has the longest time maintaining under 0 °C and 20 °C. Figure 9 indicates the temperature vs. time profiles representing different hydrogel composites with increasing number of layers and their effect on the overall cooling time. Meanwhile, Figure 10 depicts the time for which the hydrogel composite can maintain its temperature below 0 °C and 20 °C for samples with varying number of hydrogel layers (with the constant overall sample thickness fixed). From the image, it can be seen that a one layer hydrogel not only had a better cooling time below 20 °C (370 mins) but also 0 °C (175 mins) and the time decreased with the increase of layer. When the hydrogel had 5 layers, the time to reach 0 °C and 20 °C separately was 135 and 290 min. However, the situation is different when the overall thickness of hydrogel was unrestricted. Figure 11 shows the temperature vs. time profiles of the samples with a varying number of hydrogel layers when the overall sample thickness is not constrained. The results indicate the performance increased with an increase in the number of hydrogel layers. Thus, the cooling capacity of the samples increased with an increasing number of hydrogel layers and the sample with 7 hydrogel layers demonstrates the best results (20 °C for 225 mins and 0 °C for 450 mins). It is observed that the cooling capacity of the sample increased by 60 minutes for every added layer of hydrogel. Figure 12 depicts the Young’s modulus of hydrogel composites with 80 wt.%, 85 wt.%, 90 wt.%, and 95 wt.% water content as observed during the mechanical evaluation tests. Figure 13 shows the compressive stress-strain curves for samples with 5 or 7 layers of hydrogel (thickness per layer ~ 2mm), respectively, as observed during the mechanical evaluation tests. Figure 14 shows a bar chart with the Young’s modulus of samples with 5 or 7 hydrogel layers. Young’s modulus of samples with different number of hydrogel layers maintain a constant overall sample thickness, as shown in Figure 15. Figure 16 depicts the time taken by the hydrogel composites infused with fumed silica to reach a temperature of 20 °C (indicative of the cooling effect, starting from -20°C) for different samples. Figure 17 reveals the Young’s modulus of the hydrogel composites with 1 wt.%, 2 wt.% and 3 wt% fumed silica. The sample with 2 wt% fumed silica have best cooling time (200 mins), however the sample with 1 wt% fumed silica has the best mechanical property (2250 kPa) via the two image. Figure 18 depicts the printed hydrogel composite during the uniaxial compression test with varying amount of compression loading (from 0% to 80%). Line chart of Figure 19 represents the displacement at the numbered points on the hydrogel composite in proportion to increasing amount of strain (the Strain-displacement curve).

[0121] Table 2: Quantity of chemicals used for Sol A and Sol B (85 wt.% water content).

[0122] Table 3: Dimensions of the samples used for mechanical testing.

Height Width Thickness

Criteria Value

(mm) (mm) (mm)

[0123] Although the present disclosure has been described with respect to one or more particular examples, it will be understood that other examples of the present disclosure may be made without departing from the scope of the present disclosure.

Claims

Claims:

1. A composite material comprising a hydrogel layer having a first surface and a second surface opposite the first surface; and a first layer comprising a first hydrophobic material, the first layer being disposed on the first surface of the hydrogel layer.

2. The composite material of claim 1, further comprising a second layer comprising a second hydrophobic material, the second layer being disposed on the second surface of the hydrogel layer.

3. The composite material of claim 2, wherein the first hydrophobic material is the same or different than the second hydrophobic material.

4. The composite material of claim 1, wherein the hydrogel layer comprises a plurality of covalently-crosslinked polymer chains; a plurality of ionically-crosslinkable polymer chains; an ionic component; and water.

5. The composite material of claim 4, wherein the hydrogel layer has a water content of 60- 95 wt.% (based on the total weight of the hydrogel layer).

6. The composite material of claim 2, wherein the first hydrophobic material and/or the second hydrophobic material are polydimethylsiloxane (PDMS).

7. The composite material of claim 4, wherein the hydrogel layer further comprises one or more additives.

8. The composite material of claim 7, wherein the one or more additives are chosen from polar liquids, glycols, particles, nanoparticles, and combinations thereof.

9. The composite material of claim 8, wherein the particle or nanoparticle is fumed silica.

10. The composite material of claim 4, wherein the hydrogel layer further comprises a polyether.

11. The composite material of claim 4, wherein the individual polymer chains of the covalently-crosslinked polymer chains are chosen from polyacrylamides, polyvinyl alcohol, polyalkylene oxides, starches, celluloses, polyacrylonitriles, and combinations thereof.

12. The composite material of claim 4, wherein the individual polymer chains of the ionically-crosslinkable polymer chains are chosen from alginates, polyglutamates, polynucleotides, polyethylene terephthalates, and combinations thereof.

13. The composite material of claim 4, wherein the ionic component is chosen from beryllium cations, calcium cations, magnesium cations, barium cations, sulfate anions, chloride anions, and combinations thereof.

14. The composite material of claim 2, further comprising one or more additional hydrogel layers and one or more additional layers comprising a hydrophobic material, wherein each additional hydrogel layer is disposed between corresponding layers of the one or more additional layers.

15. The composite material of claim 1, wherein the hydrogel layer is configured as a structure having one or more pores; and the first layer is disposed within the one or more pores.

16. The composite material of claim 15, wherein the structure having one or more pores is a lattice structure.

17. A hydrogel comprising a plurality of covalently-crosslinked polymer chains; a plurality of ionically-crosslinkable polymer chains; an ionic component; and water.

18. The hydrogel of claim 17, further comprising one or more additives.

19. The hydrogel of claim 18, wherein the one or more additives are chosen from polar liquids, glycols, particles, nanoparticles, and combinations thereof.

20. The hydrogel of claim 19, wherein the particles or nanoparticles are fumed silica.

21. The hydrogel of claim 20, wherein the amount of fumed silica is 0.1-5 wt.% (based on the total weight of the hydrogel composition).

22. The hydrogel of claim 18, further comprising a poly ether.

23. The hydrogel of claim 22, wherein the poly ether is chosen from polyethylene glycol, polypropylene glycol, and combinations thereof.

24. The hydrogel of claim 22, wherein the amount of polyether is 0.1 to 1 wt.% (based on the total weight of the hydrogel composition).

25. The hydrogel of claim 17, wherein the individual polymer chains of the covalently-crosslinked polymer chains are chosen from polyacrylamides, polyvinyl alcohol, polyalkylene oxides, starches, celluloses, polyacrylonitriles, and combinations thereof.

26. The hydrogel of claim 17, wherein the molecular weight (Mw and/or Mn) of the polymer chains of the covalently-crosslinked polymer chains is 40,000 to 150,000 g/mol.

27. The hydrogel of claim 17, wherein the covalently-crosslinked polymer chains are crosslinked by one or more of the following groups:

wherein R' and R" are independently chosen from H,

and combinations thereof.

28. The hydrogel of claim 17, wherein the individual polymer chains of the ionically-crosslinkable polymer chains are chosen from alginates, polyglutamates, polynucleotides, polyethylene terephthalates, and combinations thereof.

29. The hydrogel of claim 17, wherein the molecular weight (Mw and/or Mn) of the polymer chains of the ionically-crosslinkable polymer chains is 100,000-200,000 g/mol.

30. The hydrogel of claim 17, wherein the ionic component is chosen from beryllium cations, calcium cations, magnesium cations, barium cations, sulfate anions, chloride anions, and combinations thereof.

31. The hydrogel of claim 17, wherein the hydrogel exhibits a Young’s modulus of 50-500 kPa.

32. The hydrogel of claim 17, wherein the hydrogel has a water content of 60-95 wt.% (based on the total weight of the hydrogel layer).

33. The hydrogel of claim 17, wherein the hydrogel layer is configured as a structure having one or more pores; and the first layer is disposed within the one or more pores.

34. The hydrogel of claim 17, wherein the structure having one or more pores is a lattice structure.

35. The hydrogel of claim 17, wherein the weight percent ratio of i) the plurality of covalently-crosslinked polymers chains, ii) the plurality of ionically-crosslinkable polymer chains, or iii) both, with respect to the ionic component is 3 : 1 to 6: 1.

36. A method of making a composite material of claim 1, comprising: contacting a first composition and a second composition to form a hydrogel precursor, the first composition comprising: one or more ionically-crosslinkable polymer(s); one or more monomer(s); water; and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof, and the second composition comprising: one or more crosslinking compound(s); water; and one or more ionic component(s); and optionally, one or more catalyst(s), one or more catalyst component(s), or a combination thereof, contacting the hydrogel precursor with a hydrophobic material, wherein the composite material of claim 1 is formed.

37. The method of claim 36, wherein, prior to contacting the hydrogel precursor with the hydrophobic material, the hydrogel precursor is allowed to stand such that it forms a hydrogel.

38. The method of claim 37, wherein the hydrogel precursor is pressed prior to standing.

39. The method of claim 36, wherein the hydrophobic material is coated with an adhering agent.

40. The method of claim 39, wherein the adhering agent is benzophenone.

41. The method of claim 39, wherein the hydrogel precursor in contact with the hydrophobic material is UV-cured.

42. The method of claim 36, wherein the first composition further comprises one or more additives.

43. The method of claim 42, wherein the one or more additives are chosen from polar liquids, glycols, particles, nanoparticles, and combinations thereof.

44. The method of claim 43, wherein the particles or nanoparticles are fumed silica.

45. The method of claim 44, wherein the amount of fumed silica is 0.1-5 wt.% (based on the total weight of the hydrogel composition).

46. The method of claim 36, wherein the one or more monomers are chosen from acrylamides, vinyl alcohols, cyclic ethers, acrylonitriles, and combinations thereof.

47. The method of claim 46, wherein one or more monomers are present in the amount of 4- 21 wt.%.

48. The method of claim 36, wherein the one or more crosslinking compounds are multiacrylamides.

49. The method of claim 48, wherein the one or more crosslinking compounds are present in the amount of 0.8-3 wt.%.

50. The method of claim 36, wherein the ionically-crosslinkable polymers are chosen from alginates, polyglutamates, polynucleotides, polyethylene terephthalates, and combinations thereof.

51. The method of claim 50, wherein the ionically-crosslinkable polymers are present in the amount of 0.8-3 wt.%.

52. The method of claim 36, wherein the ionic component is chosen from beryllium cations, calcium cations, magnesium cations, barium cations, sulfate anions, chloride anions, and combinations thereof.

53. The method of claim 52, wherein the ionic component is present in the amount of 0.8-3 wt.%.

54. The method of claim 36, wherein the one or more catalysts and/or catalyst components are chosen from radical initiators, thermal initiators, photochemical initiators, and combinations thereof.

55. The method of claim 54, wherein the one or more catalysts and/or catalyst components are present in the amount of 0.2-1 wt.%.

56. The method of claim 36, wherein the ratio of the first composition to the second composition is 3:1 to 6:1 (v/v).