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Gels
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Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications
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Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Applications".

Deadline for manuscript submissions: closed (31 May 2024) | Viewed by 38006

Special Issue Editors

Dr. Valentina Nigro

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Guest Editor
Fusion and Technologies for Nuclear Safety and Security Department, ENEA Frascati Research Centre, 00044 Roma, Italy
Interests: materials science; soft matter; gels; scattering techniques; spectroscopy
Special Issues, Collections and Topics in MDPI journals
Dr. Francesca Limosani

E-Mail Website
Guest Editor
Fusion and Technologies for Nuclear Safety and Security Department, ENEA Casaccia Research Centre, 00123 Roma, Italy
Interests: chemical synthesis; electron transfer processes; hybrid materials for solar energy; electrochemical and biomedical applications; thin films; optical techniques
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In the preceding years, hydrogels have attracted great interest owing to their fascinating properties, attributes that have opened the possibilities of many applications in different fields.

Hydrogels are a highly versatile class of biomaterials, consisting of hydrophilic polymer networks that can be processed into bulk materials, as well as micro- or nanoparticles of both natural and synthetic origin.

Hydrogels are characterized by many fascinating properties, such as swelling, softness and sensitivity to external stimuli. Indeed, cross-linked hydrogel particles with size ranging from the nanometric to the micrometric, well known as microgels, can be tailored to achieve the desired degree of multi-functionality.

Their unique character result from their hybrid nature between polymers and colloids, leading to a rich phase behaviour that can be tuned through easily accessible control parameters. These features make microgels intriguing model colloids to explore phase transitions in complex systems, and highly attractive materials for several technological applications.

Owing to this wide variety of interesting properties, smart hydrogel-based materials have found many applications for innovative solutions in different fields, such as drug delivery, tissue engineering, agriculture, cultural heritage, sensing and biosensing.

This Special Issue focuses on experiments, simulation, synthesis methods and applications of smart hydrogels, microgels and nanogels. The topics may include synthesis methods, dynamics and structure, phase diagrams and interparticle interactions, besides their manifold applications in different fields.

Both original contributions and reviews are welcome.

Dr. Valentina Nigro
Dr. Francesca Limosani
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • hydrogels
  • microgels
  • polymers
  • colloids
  • synthesis
  • characterization
  • applications
  • swelling
  • phase behaviour
  • stimuli-responsive

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Related Special Issue

Published Papers (7 papers)

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Research

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15 pages, 5143 KiB  
Article
Antioxidant, Anti-Inflammatory Effects and Ability to Stimulate Wound Healing of a Common-Plantain Extract in Alginate Gel Formulations
by Ioana Bâldea, Ildiko Lung, Ocsana Opriş, Adina Stegarescu, Irina Kacso and Maria-Loredana Soran
Gels 2023, 9(11), 901; https://doi.org/10.3390/gels9110901 - 14 Nov 2023
Cited by 1 | Viewed by 1887
Abstract
Our study aimed to investigate the biological effects of a common-plantain (Plantago major L.) extract, encapsulated in alginate, on dermal human fibroblast cultures in vitro, in view of its potential use as a wound healing adjuvant therapy. Common-plantain extracts were obtained [...] Read more.
Our study aimed to investigate the biological effects of a common-plantain (Plantago major L.) extract, encapsulated in alginate, on dermal human fibroblast cultures in vitro, in view of its potential use as a wound healing adjuvant therapy. Common-plantain extracts were obtained by infusion and ultrasound extraction, and their total polyphenolic content and antioxidant capacity were determined by spectrophotometry. The best extract, which was obtained by infusion, was further encapsulated in sodium alginate in two different formulations. Fourier Transform Infrared Spectroscopy (FTIR) was used to demonstrate the existing interactions in the obtained common-plantain extract in the alginate formulations. The encapsulation efficiency was evaluated based on the total polyphenol content. These alginate gel formulations were further used in vitro to determine their biocompatibility and antioxidant and anti-inflammatory effects by spectrophotometry and ELISA, as well as their ability to stimulate fibroblast migration (scratch test assay) at different time points. In addition, the collagen 1 and 3 levels were determined by Western blot analysis. The data showed that the microencapsulated plantain extract formulations induced an antioxidant, anti-inflammatory effect, enhanced collagen production and increased wound closure in the first 8 h of their application. These results are encouraging for the use of this alginate plantain extract formulation as an adjuvant for skin wound healing. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications)
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Full article ">Figure 1
<p>Total polyphenol content (<b>a</b>) and antioxidant activity (<b>b</b>). Each data point is the mean ± the standard error of the mean of three independent experiments.</p> Full article ">Figure 2
<p>SEM micrographs of the microencapsulated PE sample.</p> Full article ">Figure 3
<p>The FTIR spectra of Na alginate, common-plantain extract and microencapsulated common-plantain extract: (<b>a</b>) 3750–2750 cm<sup>−1</sup>; (<b>b</b>) 1800–400 cm<sup>−1</sup> spectral domain.</p> Full article ">Figure 4
<p>Cell viability of fibroblasts treated with alginate and PE formulations after 48 h of exposure to dilutions of each sample extract (<b>left panel</b>) and the PE extract with different concentrations of polyphenols (µg mL<sup>−1</sup>, <b>right panel</b>); the results are expressed as % of the viability of untreated controls, with the toxicity limit at 70%. Lower panels show representative microscopical images of the living cells in culture after 24 h exposure to different alginate formulations (dilution 1:20) and the PE extract (5 µg mL<sup>−1</sup> of polyphenols), bar = 10 µm.</p> Full article ">Figure 5
<p>Collagen synthesis. Collagen 1 and 3 levels were determined by Western blot. Images (upper panel) were quantified by densitometry (lower panels), using GAPDH as a reference. Data are presented as the mean ± SD (<span class="html-italic">n</span> = 3); * = <span class="html-italic">p</span> &lt; 0.05, *** <span class="html-italic">p</span> &lt; 0.0001 compared to the control and between the treated groups.</p> Full article ">Figure 6
<p>Scratch wound assay. (<b>a</b>) Comparative microscopic images of dermal fibroblasts (objective 4×) following exposure to the alginate formulations containing the extract (dilution 1:20) and to PE (5 µg mL<sup>−1</sup> of polyphenols) at different time points, bar =10 µm; (<b>b</b>) quantification of the wound area closure was performed using the Image J software 1.8.0 and MiToBo plugging (2023). The results are presented as % of the initial wound area. The data are presented as mean ± SD (<span class="html-italic">n</span> = 3). * = <span class="html-italic">p</span> &lt; 0.05 vs. control.</p> Full article ">Figure 7
<p>Oxidative stress and inflammation. Malondialdehyde (MDA) was determined spectrophotometrically (TBA method); Il1α and Il1β were measured by ELISA after 48 h of exposure. Data are shown as mean ± SD (<span class="html-italic">n</span> = 3). * = <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.001, *** <span class="html-italic">p</span> &lt; 0.0001 compared to the control and between the treated groups.</p> Full article ">
12 pages, 3150 KiB  
Article
Colorimetric Sensors Based on Poly(acrylic Acid)/TiO2 Nanocomposite Hydrogels for Monitoring UV Radiation Exposure
by Sabina Botti, Francesca Bonfigli, Rosaria D’Amato, Jasmine Rodesi and Maria Gabriella Santonicola
Gels 2023, 9(10), 797; https://doi.org/10.3390/gels9100797 - 4 Oct 2023
Viewed by 1640
Abstract
In recent years, there has been an open debate on proper sun exposure to reduce the risk of developing skin cancer. The mainly encountered issue is that general guidelines for UV radiation exposure could not be effective for all skin types. The implementation [...] Read more.
In recent years, there has been an open debate on proper sun exposure to reduce the risk of developing skin cancer. The mainly encountered issue is that general guidelines for UV radiation exposure could not be effective for all skin types. The implementation of customized guidelines requires a method by which to measure the UV dose as a result of daily exposure to sunlight, ideally with an inexpensive, easy-to-read sensor. In this work, we present the characterization of nanocomposite hydrogel materials acting as colorimetric sensors upon exposure to UV light. The sensor was prepared using a poly(acrylic acid) (PAA) hydrogel matrix in which TiO2 nanoparticles and methylene blue (MB) were integrated. Raman mapping was used to determine the network structure of the hydrogel and its water distribution. The TiO2 nanoparticles dispersed in the PAA matrix maintain their photoactivity and catalyze a reaction by which methylene blue is converted into leuko-methylene. The conversion causes a discoloration effect that is visible to the naked eye and can therefore be used as an indicator of UV radiation exposure. Moreover, it was possible to tune the discoloration rate to the limit exposure of each skin type, simply by changing the ratio of titanium dioxide to dye. We obtained a response time ranging from 30 min to 1.5 h. Future work will be dedicated to the possibility of scaling up this range and to improve the sensor wearability; however, our study paves the way to the realisation of sensors suitable for public use, which could help us find a solution to the challenge of balancing sufficient UV exposure to prevent Vitamin D deficiency with excessive UV exposure that could ultimately cause skin cancer. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications)
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Full article ">Figure 1
<p>Raman spectra of PAA before hydration (a) and in gel state (b).</p> Full article ">Figure 2
<p>White light optical image of PAA (<b>a</b>) with the corresponding structural Raman maps (<b>b</b>).</p> Full article ">Figure 3
<p>White light optical image of PAA samples with 400 ppm (<b>a</b>), 600 ppm (<b>b</b>), and 800 ppm (<b>c</b>) of TiO<sub>2</sub> nanoparticles in transmission mode and the corresponding images in reflection mode (<b>d</b>–<b>f</b>). Objective 5×.</p> Full article ">Figure 4
<p>Raman spectrum of PAA hydrogel (<b>a</b>) compared with that of PAA/TiO<sub>2</sub>/BM composite hydrogel (<b>b</b>). TiO<sub>2</sub>/BM content is 400 and 80 ppm, respectively.</p> Full article ">Figure 5
<p>Folding parameter, R<span class="html-italic"><sub>Folding</sub></span>, as a function of TiO<sub>2</sub> content.</p> Full article ">Figure 6
<p>Luminescence spectra of PAA/TiO<sub>2</sub>/MB hydrogel composite: (<b>a</b>) before UV exposure; (<b>b</b>) after 1h of UV irradiation.</p> Full article ">Figure 7
<p>White light optical microscope image of transition region between non-irradiated and irradiated parts of PAA/TiO<sub>2</sub>/MB hydrogel with a TiO<sub>2</sub>/MB content of 800:80 ppm (<b>a</b>). Luminescence peak intensities measured along the red transition line (<b>b</b>).</p> Full article ">Figure 8
<p>I<sub>irradiated</sub>/I<sub>non- irradiated</sub> ratio as a function of irradiation time for the different gel formulations, with the corresponding best-fitted exponential decay curves.</p> Full article ">Figure 9
<p>Discoloration curves of PAA/TiO<sub>2</sub>/MB hydrogels with different TiO<sub>2</sub>/MB. The insets (<b>a</b>–<b>c</b>) show the photos of non-irradiated samples; the photos in the insets (<b>d</b>–<b>i</b>,<b>l</b>) correspond to irradiated hydrogels, partially covered during irradiation.</p> Full article ">
13 pages, 2779 KiB  
Article
Applying Gel-Supported Liquid Extraction to Tutankhamun’s Textiles for the Identification of Ancient Colorants: A Case Study
by Greta Peruzzi, Alessandro Ciccola, Adele Bosi, Ilaria Serafini, Martina Negozio, Nagmeldeen Morshed Hamza, Claudia Moricca, Laura Sadori, Gabriele Favero, Valentina Nigro, Paolo Postorino and Roberta Curini
Gels 2023, 9(7), 514; https://doi.org/10.3390/gels9070514 - 25 Jun 2023
Cited by 3 | Viewed by 1417
Abstract
The identification of the dyes present on a linen fragment from the tomb of Pharaoh Tutankhamun is the objective of the present study. Fiber optic reflectance spectroscopy (FORS) was applied to the archaeological sample for preliminary identification of the dyes and to better [...] Read more.
The identification of the dyes present on a linen fragment from the tomb of Pharaoh Tutankhamun is the objective of the present study. Fiber optic reflectance spectroscopy (FORS) was applied to the archaeological sample for preliminary identification of the dyes and to better choose the extraction methodology for different areas of the sample. The innovative gel-supported micro-extraction with agar gel and the Nanorestore Gel® High Water Retention (HWR) gel were applied to the archaeological sample after testing of the best concentration for the extraction of the agar gels substrates, performed on laboratory mock-ups by means of UV–Vis transmittance spectroscopy. Immediately after extraction, Ag colloidal pastes were applied on the gel surface and Surface Enhanced Raman Scattering (SERS) analysis was performed directly on them. The combination of information deriving from FORS and SERS spectra resulted in the successful identification of both indigo and madder and, in hypothesis, of their degradation products. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>UV–Vis transmittance spectra of agar gel at (<b>a</b>) C<sub>w</sub> = 2%, (<b>b</b>) C<sub>w</sub> = 3%, and (<b>c</b>) C<sub>w</sub> = 4% of the gel before extraction (green), after extraction from the madder paint mockup (orange), and after extraction from the madder textile mockup (red).</p> Full article ">Figure 2
<p>Optical microscope (4× magnification) images of Nanorestore Gel<sup>®</sup> soaked with the reducing extraction solution used for indigo extraction.</p> Full article ">Figure 3
<p>(<b>a</b>) Comparison between FORS spectra of indigo mockup (dark blue) and of the blue area of the archeological sample; (<b>b</b>) comparison between FORS spectra of madder mockup (red) and of the red area of the archaeological fragment (Bordeaux).</p> Full article ">Figure 4
<p>(<b>a</b>) Comparison between SERS spectra of 3% agar blank (gray) and 3% agar after extraction of the blue area (light blue); (<b>b</b>) comparison between SERS spectra of 3% agar after extraction of the indigo mockup (dark blue) and 3% agar after extraction of the blue area (light blue).</p> Full article ">Figure 5
<p>(<b>a</b>) Comparison between SERS spectra of 3% agar gel blank (gray), 3% agar gel after extraction from madder mockup (light red), and 3% agar gel after extraction from red area of archaeological sample (Bordeaux); (<b>b</b>) comparison between SERS spectra of Nanorestore Gel<sup>®</sup> blank (gray) and Nanorestore Gel<sup>®</sup> after extraction from red area of archaeological sample (Bordeaux).</p> Full article ">
15 pages, 3314 KiB  
Article
Carbonic Anhydrase Enhanced UV-Crosslinked PEG-DA/PEO Extruded Hydrogel Flexible Filaments and Durable Grids for CO2 Capture
by Jialong Shen, Sen Zhang, Xiaomeng Fang and Sonja Salmon
Gels 2023, 9(4), 341; https://doi.org/10.3390/gels9040341 - 16 Apr 2023
Cited by 7 | Viewed by 24219
Abstract
In this study, poly (ethylene glycol) diacrylate/poly (ethylene oxide) (PEG-DA/PEO) interpenetrating polymer network hydrogels (IPNH) were extruded into 1D filaments and 2D grids. The suitability of this system for enzyme immobilization and CO2 capture application was validated. IPNH chemical composition was verified [...] Read more.
In this study, poly (ethylene glycol) diacrylate/poly (ethylene oxide) (PEG-DA/PEO) interpenetrating polymer network hydrogels (IPNH) were extruded into 1D filaments and 2D grids. The suitability of this system for enzyme immobilization and CO2 capture application was validated. IPNH chemical composition was verified spectroscopically using FTIR. The extruded filament had an average tensile strength of 6.5 MPa and elongation at break of 80%. IPNH filament can be twisted and bent and therefore is suitable for further processing using conventional textile fabrication methods. Initial activity recovery of the entrapped carbonic anhydrase (CA) calculated from esterase activity, showed a decrease with an increase in enzyme dose, while activity retention of high enzyme dose samples was over 87% after 150 days of repeated washing and testing. IPNH 2D grids that were assembled into spiral roll structured packings exhibited increased CO2 capture efficiency with increasing enzyme dose. Long-term CO2 capture performance of the CA immobilized IPNH structured packing was tested in a continuous solvent recirculation experiment for 1032 h, where 52% of the initial CO2 capture performance and 34% of the enzyme contribution were retained. These results demonstrate the feasibility of using rapid UV-crosslinking to form enzyme-immobilized hydrogels by a geometrically-controllable extrusion process that uses analogous linear polymers for both viscosity enhancement and chain entanglement purposes, and achieves high activity retention and performance stability of the immobilized CA. Potential uses for this system extend to 3D printing inks and enzyme immobilization matrices for such diverse applications as biocatalytic reactors and biosensor fabrication. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications)
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Figure 1
<p>Hydrogel filament/grid fabrication system set-up.</p> Full article ">Figure 2
<p>Schematics of the formation of PEG-DA/PEO interpenetrating polymer network hydrogel (IPNH). (Orange stars represent free redicals at the growing chain ends; blue rectangles represent ethylene oxide repeating units).</p> Full article ">Figure 3
<p>FTIR spectra of PEG-DA, PEG-DA after UV-cured, PEO 900K powder, extruded PEG-DA/PEO IPNH, and extruded PEG-DA/PEO IPNH with entrapped NZCA (From top to bottom).</p> Full article ">Figure 4
<p>Properties of extruded PEG-DA/PEO IPNH filament: (<b>a</b>) Effect of curing on a surface or in air on the tensile strength and elongation of filaments extruded at 20 psi, (<b>b</b>) Effect of extrusion pressure on the diameter of filaments cured in air, and (<b>c</b>) Photos demonstrating the flexibility of a filament, which can be bent and twisted (Scale bars = 1 cm).</p> Full article ">Figure 5
<p>Extruded PEG-DA/PEO IPNH grids: (<b>a</b>) No-enzyme control (Scale bar = 1 cm), (<b>b</b>) NZCA-entrapped (Scale bar = 1 cm), (<b>c</b>) Assembled into 2 cm O.D. structured packing, and (<b>d</b>) Assembled packing fitted in a 2 cm I.D. CO<sub>2</sub> absorption column.</p> Full article ">Figure 6
<p>Enzyme activity assay on extruded PEG-DA/PEO IPNH grids with different NZCA doses: (<b>a</b>) Samples are cut into circles that fit in the wells of a 24-well plate, (<b>b</b>) Long-term stability of the immobilized NZCA over 150 days in buffer and at room temperature subject to repeated wash and testing, (<b>c</b>) Activity recovery of the immobilized NZCA on Day 0, calculated against the activity of a same amount of dissolved NZCA used in the immobilization, (<b>d</b>) Activity retention on Day 150.</p> Full article ">Figure 7
<p>CO<sub>2</sub> gas scrubber test of the assembled PEG-DA/PEO IPNH structured packings: CO<sub>2</sub> capture efficiency (<b>a</b>) as a function of NZCA dose and (<b>b</b>) over 1032 h of continuous solvent recirculation.</p> Full article ">
15 pages, 5974 KiB  
Article
Amidoamine Oxide Surfactants as Low-Molecular-Weight Hydrogelators: Effect of Methylene Chain Length on Aggregate Structure and Rheological Behavior
by Rie Kakehashi, Naoji Tokai, Makoto Nakagawa, Kazunori Kawasaki, Shin Horiuchi and Atsushi Yamamoto
Gels 2023, 9(3), 261; https://doi.org/10.3390/gels9030261 - 22 Mar 2023
Cited by 1 | Viewed by 1859
Abstract
Rheology control is an important issue in many industrial products such as cosmetics and paints. Recently, low-molecular-weight compounds have attracted considerable attention as thickeners/gelators for various solvents; however, there is still a significant need for molecular design guidelines for industrial applications. Amidoamine oxides [...] Read more.
Rheology control is an important issue in many industrial products such as cosmetics and paints. Recently, low-molecular-weight compounds have attracted considerable attention as thickeners/gelators for various solvents; however, there is still a significant need for molecular design guidelines for industrial applications. Amidoamine oxides (AAOs), which are long-chain alkylamine oxides with three amide groups, are surfactants that act as hydrogelators. Here, we show the relationship between the length of methylene chains at four different locations of AAOs, the aggregate structure, the gelation temperature Tgel, and the viscoelasticity of the formed hydrogels. As seen from the results of electron microscopic observations, the aggregate structure (ribbon-like or rod-like) can be controlled by changing the length of methylene chain in the hydrophobic part, the length of methylene chain between the amide and amine oxide groups, and the lengths of methylene chains between amide groups. Furthermore, hydrogels consisting of rod-like aggregates showed significantly higher viscoelasticity than those consisting of ribbon-like aggregates. In other words, it was shown that the gel viscoelasticity could be controlled by changing the methylene chain lengths at four different locations of the AAO. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications)
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Full article ">Figure 1
<p>Chemical structure of alkyl amidoamine oxide. <span class="html-italic">k</span> is the length of the methylene chain of the hydrophobic part, <span class="html-italic">l</span> is the length of the methylene chain between nitrogen atoms of the amide groups, <span class="html-italic">m</span> is the length of the methylene chain between carbonyl groups of the amide groups, and <span class="html-italic">n</span> is the length of the methylene chain between the amide and amine oxide groups. AAO is denoted as <span class="html-italic">k</span>-<span class="html-italic">l</span>-<span class="html-italic">m</span>-<span class="html-italic">n</span> using the length of the methylene chain in four places.</p> Full article ">Figure 2
<p>Photographs of hydrogels of certain AAOs at around 25 °C. (<b>a</b>) 9-2-2-6, (<b>b</b>) 11-2-2-6, (<b>c</b>) 13-2-2-6, (<b>d</b>) 13-3-2-6, (<b>e</b>) 13-4-2-6, (<b>f</b>) 13-5-2-6, and (<b>g</b>) 13-2-3-6.</p> Full article ">Figure 3
<p>Cryo-SEM images of the surfactant aqueous solutions. Typical images of (<b>a</b>) 9-2-2-6 solution quickly frozen from room temperature (&lt;<span class="html-italic">T</span><sub>gel</sub>), (<b>b</b>) 11-2-2-6 solution quickly frozen from room temperature (&lt;<span class="html-italic">T</span><sub>gel</sub>), (<b>c</b>) 9-2-2-6 solution quickly frozen from about 60 °C (&gt;<span class="html-italic">T</span><sub>gel</sub>), and (<b>d</b>) 11-2-2-6 solution quickly frozen from about 80 °C (&gt;<span class="html-italic">T</span><sub>gel</sub>).</p> Full article ">Figure 4
<p>Typical images of 9-2-2-6 (<b>a</b>), and 11-2-2-6 (<b>b</b>) solutions observed by freeze-fracture TEM.</p> Full article ">Figure 5
<p>Negative-staining TEM images of the surfactant aqueous solutions at room temperature. Yellow arrows indicate aggregates. Typical images of (<b>a</b>) 9-2-2-6 solution, (<b>b</b>) 11-2-2-6 solution, (<b>c</b>) 13-2-2-4 solution, and (<b>d</b>) 13-2-2-6 solution.</p> Full article ">Figure 6
<p>Angular frequency dependence of <span class="html-italic">G</span>′ (solid circles) and <span class="html-italic">G</span>″ (open circles) of 13-2-2-<span class="html-italic">n</span> (<span class="html-italic">n</span> = 4, 5, and 6) aqueous solutions at 25 °C.</p> Full article ">Figure 7
<p>The <span class="html-italic">k</span>-dependence of the <span class="html-italic">T</span><sub>gel</sub> of <span class="html-italic">k</span>-2-2-3 (solid triangles), <span class="html-italic">k</span>-2-2-6 (open triangles) [<a href="#B31-gels-09-00261" class="html-bibr">31</a>], and <span class="html-italic">k</span>-3-2-6 (solid circles).</p> Full article ">Figure 8
<p>Angular frequency dependence of <span class="html-italic">G</span>′ (solid circles) and <span class="html-italic">G</span>″ (open circles) of the <span class="html-italic">k</span>-2-2-6 (<span class="html-italic">k</span> = 9, 11, and 13) aqueous solutions at 25 °C.</p> Full article ">Figure 9
<p>Negative-staining TEM images of the surfactant aqueous solutions at room temperature. Red arrows indicate rod-like aggregates, and yellow arrows indicate ribbon-like aggregates. Typical images of (<b>a</b>) 13-3-2-6 solution, (<b>b</b>) 13-4-2-6 solution, and (<b>c</b>) 13-5-2-6 solution.</p> Full article ">Figure 10
<p>Angular frequency dependence of <span class="html-italic">G</span>′ (solid symbols) and <span class="html-italic">G</span>″ (open symbols) of 13-<span class="html-italic">l</span>-<span class="html-italic">m</span>-6 (<span class="html-italic">l</span> = 2–5; <span class="html-italic">m</span> = 2 and 3) aqueous solutions at 25 °C.</p> Full article ">Figure 11
<p>Schematic of the odd–even effect of hydrogen bonding formation. Blue circles indicate hydrogen bonds between neighboring AAO molecules. Red circles indicate amide groups without hydrogen bonds.</p> Full article ">Scheme 1
<p>Synthesis of alkyl amidoamine oxides used in this study.</p> Full article ">
10 pages, 1925 KiB  
Article
Spatial Control over Catalyst Positioning for Increased Micromotor Efficiency
by Shauni Keller, Serena P. Teora, Arif Keskin, Luuk J. C. Daris, Norman A. P. E. Samuels, Moussa Boujemaa and Daniela A. Wilson
Gels 2023, 9(2), 164; https://doi.org/10.3390/gels9020164 - 18 Feb 2023
Cited by 2 | Viewed by 2173
Abstract
Motion is influenced by many different aspects of a micromotor’s design, such as shape, roughness and the type of materials used. When designing a motor, asymmetry is the main requirement to take into account, either in shape or in catalyst distribution. It influences [...] Read more.
Motion is influenced by many different aspects of a micromotor’s design, such as shape, roughness and the type of materials used. When designing a motor, asymmetry is the main requirement to take into account, either in shape or in catalyst distribution. It influences both speed and directionality since it dictates the location of propulsion force. Here, we combine asymmetry in shape and asymmetry in catalyst distribution to study the motion of soft micromotors. A microfluidic method is utilized to generate aqueous double emulsions, which upon UV-exposure form asymmetric microgels. Taking advantage of the flexibility of this method, we fabricated micromotors with homogeneous catalyst distribution throughout the microbead and micromotors with different degrees of catalyst localization within the active site. Spatial control over catalyst positioning is advantageous since less enzyme is needed for the same propulsion speed as the homogeneous system and it provides further confinement and compartmentalization of the catalyst. This proof-of-concept of our new design will make the use of enzymes as driving forces for motors more accessible, as well as providing a new route for compartmentalizing enzymes at interfaces without the need for catalyst-specific functionalization. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications)
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Graphical abstract
Full article ">Figure 1
<p>Schematic representation of the experimental design. (<b>A</b>) Close-up of the ATPS-based microfluidic chip to generate droplet-in-droplet morphology. An aqueous-two-phase jet is formed at the first cross junction, which is emulsified at the second cross junction by a surfactant containing oil. (<b>B</b>) Asymmetric microgels are obtained after UV-polymerization of the droplets generated by the microfluidic chip; upon addition to hydrogen peroxide the catalyst, catalase, will decompose the fuel to water and propelling oxygen. (<b>C</b>) Two methods to position the catalyst, either homogeneously through incorporation in the gel or spatially through adding it to the polysaccharide, templating phase.</p> Full article ">Figure 2
<p>Confocal microscopy images of the different micromotor systems. Catalase was labelled with a fluorescent dye, Alexa 647, to analyse its position inside the motor. Bright field images are shown left, and the corresponding fluorescence images are on the right. The position of the motor is shown in dashed lines and the fluorescence intensity profile (bottom left) was obtained over the solid line going from the opening inside the motor. Spatial control over the catalyst was obtained by dissolving the enzyme in the polysaccharide phase prior to injection into the chip. As a control the catalyst was dissolved in the PEGDA gel phase, and a homogeneous distribution throughout the bead was observed. Scale bar is 20 µm.</p> Full article ">Figure 3
<p>(<b>A</b>) Bright field microscopy overlay of bubble propulsion of the three different polysaccharide systems with an interval of 0.5, 1, and 6 s for dextran 10 kDa, 70 kDa and Ficoll 400 kDa, respectively. (<b>B</b>) Typical trajectories of each motor system. Scale bar is 20 µm.</p> Full article ">Figure 4
<p>(<b>A</b>) The average speed over 10 s of the enzyme-localized systems compared to the previously obtained homogeneous systems [<a href="#B6-gels-09-00164" class="html-bibr">6</a>] for all three polysaccharides at 4% hydrogen peroxide concentration. (<b>B</b>) The instantaneous speed of both systems was analysed over a time-course up to 60 s after addition at 4% hydrogen peroxide concentration.</p> Full article ">

Review

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23 pages, 4870 KiB  
Review
Recent Advances in Stimuli-Responsive Hydrogel-Based Wound Dressing
by Luigia Serpico, Stefania Dello Iacono, Aniello Cammarano and Luca De Stefano
Gels 2023, 9(6), 451; https://doi.org/10.3390/gels9060451 - 30 May 2023
Cited by 11 | Viewed by 3828
Abstract
Polymeric materials have found increasing use in biomedical applications in the last decades. Among them, hydrogels represent the chosen class of materials to use in this field, in particular as wound dressings. They are generally non-toxic, biocompatible, and biodegradable, and they can absorb [...] Read more.
Polymeric materials have found increasing use in biomedical applications in the last decades. Among them, hydrogels represent the chosen class of materials to use in this field, in particular as wound dressings. They are generally non-toxic, biocompatible, and biodegradable, and they can absorb large amounts of exudates. Moreover, hydrogels actively contribute to skin repair promoting fibroblast proliferation and keratinocyte migration, allowing oxygen to permeate, and protecting wounds from microbial invasion. As wound dressing, stimuli-responsive systems are particularly advantageous since they can be active only in response to specific environmental stimuli (such as pH, light, ROS concentration, temperature, and glucose level). In this review, we briefly resume the human skin’s structure and functions, as well as the wound healing phases; then, we present recent advances in stimuli-responsive hydrogels-based wound dressings. Lastly, we provide a bibliometric analysis of knowledge produced in the field. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Skin structure (Figure created with Biorender).</p> Full article ">Figure 2
<p>Wound healing steps: haemostasis, inflammation, proliferation, and tissue remodeling (Figure created with Biorender).</p> Full article ">Figure 3
<p>Ideal features of a wound dressing.</p> Full article ">Figure 4
<p>Double responsive hydrogel network. Reproduced from open access ref. [<a href="#B85-gels-09-00451" class="html-bibr">85</a>].</p> Full article ">Figure 5
<p>Preparation and application of the NIR-responsive nanocomposite. (<b>a</b>) Synthesis of the hydrogel (PDA-HA). (<b>b</b>) Assembling of CaO<sub>2</sub> based nanocomposite. (<b>c</b>) Nanocomposite hydrogel as wound dressing. Reproduced from open access ref. [<a href="#B90-gels-09-00451" class="html-bibr">90</a>].</p> Full article ">Figure 6
<p>Preparation of the glucose-responsive hydrogel. Reproduced from open access ref. [<a href="#B99-gels-09-00451" class="html-bibr">99</a>].</p> Full article ">Figure 7
<p>Data sample collection strategy.</p> Full article ">Figure 8
<p>Annual global publication in transdermal drug delivery.</p> Full article ">Figure 9
<p>Top countries in publishing works about hydrogel-based wound dressing.</p> Full article ">Figure 10
<p>The co-authorship network of Countries.</p> Full article ">Figure 11
<p>The co-occurrence cluster analysis of the top keywords.</p> Full article ">
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