WO2017219305A1

WO2017219305A1 - Cavity-microfibers, methods and apparatuses for the fabrication of microfibers, threads, and filaments

Info

Publication number: WO2017219305A1
Application number: PCT/CN2016/086829
Authority: WO
Inventors: Ye Tian; Liqiu WANG
Original assignee: The University Of Hong Kong
Priority date: 2016-06-23
Filing date: 2016-06-23
Publication date: 2017-12-28
Also published as: CN109891009A

Abstract

A method for fabricating microfibers including introducing a dispersed phase fluid into a continuous phase fluid to form a combined fluid, wherein the combined fluid includes dispersed phase fluid bubbles or dispersed phase fluid droplets in the continuous phase fluid and spinning the combined fluid to form cavity-microfibers. Said microfibers have cavities and non-homogenous textures.

Description

CAVITY-MICROFIBERS, METHODS AND APPARATUSES FOR THE FABRICATION OF MICROFIBERS, THREADS, AND FILAMENTS

FIELD OF THE INVENITON

The present invention relates to novel microfibers, threads, and filaments. More specifically, the present invention relates to novel apparatuses and methods for fabricating microfibers, threads, and filaments having cavities and non-homogenous structures.

BACKGROUND OF THE INVENTION

Microfibers can be long, thin, flexible, and hollow and can include cavities. Microfibers have attracted interest for a broad range of applications in different fields including biomedical engineering, tissue engineering, chemical engineering, information technology, biomaterials, and sensor technology. Therefore, there is always interest in new types of microfibers, as well as methods and apparatuses for forming different types of microfibers.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include novel microfibers, threads, and filaments and methods and apparatuses for fabricating such novel microfibers, threads, and filaments. More specifically, embodiments of the present invention include apparatuses and methods for fabricating microfibers, threads, and filaments having cavities and non-homogenous textures (i.e., cavity-microfibers) .

An embodiment of the present invention includes a method for fabricating microfibers including introducing a dispersed phase fluid into a continuous phase fluid to form a combined fluid, wherein the combined fluid includes dispersed phase fluid bubbles or dispersed phase fluid droplets in the continuous phase fluid； and spinning the combined fluid to form cavity-microfibers. The spinning may include forcing the combined fluid through a channel or orifice, solidifying the combined fluid in the channel, or a wet spinning method. The fibers may be cured by drying in air, by being submerged in a curing bath, by UV-curing, by thermal curing, or other curing methods. The cavity-microfibers can then be collected in a container or wrapped on a rod or other device. The dispersed phase fluid can be introduced to the continuous phase fluid using a first tube (or syringe) having an orifice within a second tube that contains a flow of continuous phase fluid. The continuous phase fluid flow rate may be 0.1 mL/h to 5.6 mL/h, 0.3 mL/h to 2.8 mL/h or 0.6 mL/h to 1.4 mL/h. The dispersed phase fluid may be a gas or a liquid and it can be supplied at a variety of pressures to produce cavity-microfibers with different properties. For example, the pressure of the dispersed phase fluid may be 0.0 atm to 0.7 atm, 0.1 atm to 0.6 atm, 0.2 atm to 0.5 atm, 0.0 atm to 0.1 atm, 0.1 atm to 0.2 atm, 0.2 atm to 0.3 atm, 0.3 atm to 0.4 atm, 0.4 atm to 0.5 atm, or 0.6 atm to 0.7 atm.

Other embodiments of the present invention include apparatuses for fabricating cavity-microfibers. An apparatus for fabricating cavity-microfibers according to an embodiment of the present invention can include a first tube connected to a first pressure source and having a first orifice, a second tube having a second orifice that is within the first tube, and a second pressure source connected to the second tube. The apparatus can further include a first container suitable for holding a curing fluid to cure cavity-microfibers, a second container suitable for collecting cavity-microfibers, and a roller suitable for collecting cavity-microfibers.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an image of a microfluidic device for cavity-microfiber fabrication according to an embodiment of the present invention.

Figure 2 is an image showing the fabrication of a cavity-microfiber according to an embodiment of the present invention.

Figures 3a, 3c, 3e, and 3g are images of cavity-microfibers produced by embodiments of the present invention. Figures 3b, 3d, 3f, and 3h are images of hydrated cavity-microfibers corresponding to the cavity-microfibers of Figures 3a, 3c, 3e, and 3g, respectively. Figures 3i, 3j, and 3k are images of dehydrated cavity-microfibers under different levels of magnification.

Figures 4a-f are SEM images of cavity-microfibers.

Figure 5 is a graph illustrating the effects of continuous phase fluid flow rate on microfiber diameter.

Figure 6 is a graph illustrating how different types of cavity-microfibers are formed as a function of Cao (capillary number of continuous phase) and Pr (the pressure of dispersed phase fluid gas divided by standard atmospheric pressure) .

Figure 7 shows different types of cavity-microfibers produced by embodiments of the present invention.

Figure 8 is a graph showing the effects of dispersed phase fluid pressure on the volume of gas bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 0.6 mL/h.

Figure 9 is a graph showing the effect of dispersed phase fluid pressure on the distance between bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 0.6 mL/h.

Figure 10 is a graph showing the effects of dispersed phase fluid pressure on the volume of gas bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under flow rate of 1 mL/h of continuous phase.

Figure 11 is a graph showing the effects of dispersed phase fluid pressure on the distance between bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 1 mL/h.

Figure 12 is a graph showing the effects of dispersed phase fluid gas pressure on the volume of gas bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 1.4 mL/h.

Figure 13 is a graph showing the effects of gas pressure of dispersed phase fluid on the distance between bubbles, knots of hydrated cavity-microfiber and knots of dehydrated cavity-microfiber under flow rate of 1.4 mL/h of continuous phase.

Figure 14 is a graph showing the effects of drying time on the diameter of joint parts of cavity-microfibers.

Figure 15 is a graph showing the effects of drying time on the major axis and minor axis of knots of cavity-microfibers.

Figure 16 is a graph showing the effects of drying time on the volume of knots of cavity-microfibers.

Figure 17 is a graph showing mechanical tensile test results for dehydrated cavity-microfibers.

Figure 18a is an image of a tiny-cavity-microfiber, Figure 18b is an image of mixed bubble cavity-microfibers, and Figure 18c includes images of chained microfibers.

Figure 19 is an image of water collection on a single dehydrated cavity-microfiber.

Figure 20 includes images of water collection on a single spindle-knot as a function of collection time.

Figure 21 is a graph showing water collection volume on a single spindle-knot as a function of collection time.

Figure 22 is an image showing that intersections of cavity-microfibers have a greater ability for water collection than that of single knot of cavity-microfiber.

Figures 23a-23f are images of spider-web-like cavity-microfiber webs and their water collection. Figure 23a is an image of a two-beam cavity-microfiber web. Figure 23b is an image of water collection for a two-beam cavity-microfiber web. Figure 23c is an image of a three-beam cavity-microfiber web. Figure 23d is an image of water collection for a three-beam cavity-microfiber web. Figure 23e is an image of a four-beam cavity-microfiber web. Figure 23f is an image of water collection for a four-beam cavity-microfiber web.

Figure 24 is an image of 2D scaffolds built by cavity-microfibers, which can be used for cell cultures and tissue engineering.

Figure 25 is an image of 3D scaffolds built by cavity-microfibers for cell culture and tissue engineering.

Figure 26 is an image showing the formation of bone tissue on 2D scaffolds built using cavity-microfibers.

Figure 27 is an image showing an alizarin red staining test for forming bone tissue.

Figure 28 is a schematic diagram of drug delivery and drug release of cavity-microfibers.

Figure 29 is a schematic diagram of an apparatus used for melt spinning.

Figure 30 is a schematic diagram of an apparatus used for wet spinning.

Figure 31 is a schematic diagram of an apparatus used for electrospinning.

Figure 32 is an image of an apparatus according to an embodiment of the present invention.

Figure 33 includes images demonstrating bubble distance, hydrated knot distance, and dehydrated knot distance.

Figure 34 is schematic diagram of an apparatus according to the present invention.

Figure 35 is a flowchart detailing a method of forming cavity-microfibers according to the present invention.

DETAILED DISCLOSURE OF THE INVENTION

Embodiments of the present invention include methods and apparatuses for fabricating microfibers, threads, and filaments. More specifically, embodiments of the present invention include apparatuses and methods for fabricating fibers, threads, and filaments having cavities and non-homogenous structures. Embodiments of the present invention may include a continuous microfluidic method and apparatuses for efficiently and rapidly fabricating microfibers with cavity structures in a controllable fashion. Embodiments of the present invention can include droplet microfluidic technology combined with a wet spinning method. The cavity-microfibers can have a broad range of applications, including water collection, drug delivery and release, micro-reactors, micro-cultures, and 2D and 3D scaffolds for cell culturing and tissue engineering.

Methods have been developed for microfiber fabrication at the micro-and nanoscale, including wet spinning, melt spinning, electrospinning, direct write drawing, and electro-hydrodynamic co-jetting. However, microfibers produced using these methods generally can only produce homogeneous structures, with cylindrical microfibers being the most prevalent. The functions, applications, and properties of microfibers can be affected by the structures of microfibers, including their anisotropic properties and surface-volume ratio.

Melt spinning is a commonly used method of manufacture for polymeric fibers. The polymer is melted and pumped through a spinneret (die) with numerous holes (one to thousands) . The molten fibers are cooled, solidified, and collected on a take-up wheel. Stretching of the fibers in both the molten and solid states provides for orientation of the polymer chains along the fiber axis. Polymers such as poly (ethylene terephthalate) and

nylon

6, 6 are able to be melt spun in high volumes. Figure 29 is a schematic diagram of an apparatus used for melt spinning.

In solution spinning (wet spinning) , a polymer is dissolved in a solvent and the solution is extruded into a coagulation bath containing a non-solvent (immersion-jet wet spinning) . When the polymer solution is extruded into the air but eventually makes its way into a coagulation bath, the process is known as dry-jet wet spinning. This is because, as the name suggests, the spinning jet (spinneret) is in the dry state, unlike in wet spinning, where the spinning jet is immersed inside the coagulation bath (also referred as immersion jet wet spinning) . Figure 30 is a schematic diagram of an apparatus used for wet spinning.

Electrospinning is a third method for manufacturing microfibers. It involves extruding a charged jet of polymers or other materials to form the microfibers or thread on a rotating collector. A high voltage is generally produced between the extruder (such as a metallic needle) and the rotating collector. Figure 31 is a schematic diagram of an apparatus used for electrospinning.

Embodiments of the present invention can include droplet microfluidic technology combined with a wet spinning method. Embodiments of the present invention include combining two fluids using a microfluidic device to produce cavity-microfibers. According to an embodiment, a method for forming cavity-microfibers includes providing a continuous phase fluid that can be solidified and incorporating a gas or liquid as a dispersed phase fluid, such that the dispersed phase fluid forms bubbles within the continuous phase fluid. The mixture of the dispersed phase fluid and the continuous phase fluid may be referred to as the “combined fluid. ” A pump (e.g., a syringe pump) and/or a gas pressure controller may be used to spin the cavity-microfibers by forcing them through a channel or orifice. The dispersed phase fluid can be introduced into a first tube containing the continuous phase fluid via a second tube having an orifice with the first tube. The combined fluid (or the extruded cavity-microfiber) may be solidified directly in the channel (or the orifice of the first tube) , the combined fluid may be solidified by drying in air or a gas, the combined fluid may be solidified by chemical curing in a bath of a curing fluid, the combined fluid may be solidified by photo or UV curing, or the combined fluid may be solidified by thermal curing. The cavity-microfibers can then be collected in a container or collected on a roller. The continuous phase fluid can include one or more materials known in the art that are suitable for microfiber spinning. The continuous phase fluid may comprise a material selected from the group consisting of polymers of dextrose, sugars, starches, acrylates, polyvinyl alcohol, gum arabic, polyacrylamide, hydroxypropyl cellulose, hydroxypropyl methylcellulose, polyvinyl pyrrolidone, poly (2-acrylamido-2-methyl-1-propanesulfonic acid) , poly (acrylamido-N-propyltrimethylammonium chloride) , polylactic acid, polycaprolactone, polyglycolic acid, polylactic-co-glycolic acid, 1, 3-propanediol polymer, collagen, gelatin, fibrin, silk-fibroin, elastin mimetic peptide polymer, chitosan, modified chitosan, polyvinylidene fluoride, polytetrafluoroethylene, polyurethane, polycarbonate polyurethane, polyether-based polyurethane, silane-modified polyurethane, polyethylene terephthalate, polymethyl methacrylate, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) , poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) , polyphosphate, polyamino formic anhydride, polyesteramide, poly (para-dioxanone) , polycarbonate, cellulose, chondroitin sulfate, heparin, glucosan, alginic acid, alginate, polyethylene gycol, water and combinations thereof. In an embodiments, the amount of each of said material can be determined by one skilled in the art as long as it is sufficient for the forgoing microfiber spinning. The dispersed phase fluid may be a gas or a liquid, and may also be solidifiable. The gas may be air or inert gas, such as hydrogen, nitrogen, helium, argon, carbon dioxide, carbon monoxide, steam, and mixtures thereof. The dispersed phase fluid may also contain an active ingredient for curing or a compound for drug delivery.

Embodiments of the present invention can effectively control a dispersed phase gas or liquid to fabricate different types of cavity-microfibers. Embodiments of the present invention can also result in precisely controlling the structure of fabricated cavity-microfibers by controlling gas pressures, combined fluid flow rates, continuous phase fluid flow rates, and/or dispersed phase fluid flow rates. Therefore, cavity-microfibers with uniform knots and joint parts can be continuously generated in a controlled manner, or non-homogenous cavity-microfibers can be continuously generated in a controlled manner.

The subject invention includes, but is not limited to, the following exemplified embodiments.

Embodiment 1. A method for fabricating microfibers comprising:

introducing a dispersed phase fluid into a continuous phase fluid to form a combined fluid, wherein the combined fluid includes dispersed phase fluid bubbles or dispersed phase fluid droplets in the continuous phase fluid； and

spinning the combined fluid to form cavity-microfibers.

Embodiment 2. The method of Embodiment 1, wherein the spinning includes forcing the combined fluid through a channel or orifice.

Embodiment 3. The method of any of

Embodiments

1 or 2, wherein the spinning includes solidifying the combined fluid in the channel.

Embodiment 4. The method of

Embodiments

1 or 2, wherein the spinning includes a wet spinning method.

Embodiment 5. The method of any of Embodiments 1-4, further comprising collecting the cavity-microfibers in a container.

Embodiment 6. The method of any of Embodiments 1-5, further comprising collecting the cavity-microfibers on a collection roller.

Embodiment 7. The method of any of Embodiments 1-6, wherein the cavity-microfibers have substantially uniform knots and joints.

Embodiment 8. The method of any of Embodiments 1-7, wherein the cavity-microfibers are spun by feeding the dispersed phase fluid through a first orifice that is enclosed within a second tubing that delivers the continuous phase fluid.

Embodiment 9. The method of any of Embodiments 1-8, further comprising providing a pump to drive the continuous phase fluid.

Embodiment 10. The method of any of Embodiments 1-9, further comprising providing a gas pressure controller to drive the dispersed phase fluid.

Embodiment 11. The method of any of Embodiments 1-10, wherein the dispersed phase fluid is a gas.

Embodiment 12. The method of any of Embodiments 1-10, wherein the dispersed phase fluid is a liquid.

Embodiment 13. The method of any of Embodiments 1-12, wherein the continuous phase fluid includes two or more fluids.

Embodiment 14. The method of any of Embodiments 1-13, wherein the spinning includes photo curing or UV-curing the combined fluid.

Embodiment 15. The method of any of Embodiments 1-14, wherein the spinning includes chemically curing the combined fluid.

Embodiment 16. The method of any of Embodiments 1-15, wherein the spinning includes thermally curing the combined fluid.

Embodiment 17. The method of any of Embodiments 1-16, wherein the dispersed phase fluid includes more than one type of fluid.

Embodiment 18. The method of any of Embodiments 1-17, wherein the dispersed phase fluid is a liquid that volatizes during spinning.

Embodiment 19. The method of any of Embodiments 1-18, wherein the dispersed phase fluid is a gas with a pressure of 0.0 atm to 0.7 atm.

Embodiment 20. The method of any of Embodiments 1-18, wherein the dispersed phase fluid is a gas with a pressure of 0.0 atm to 0.1 atm.

Embodiment 21. The method of any of Embodiments 1-18, wherein the dispersed phase fluid is a gas with a pressure of 0.1 atm to 0.2 atm.

Embodiment 22. The method of any of Embodiments 1-18, wherein the dispersed phase fluid is a gas with a pressure of 0.2 atm to 0.3 atm.

Embodiment 23. The method of any of Embodiments 1-18, wherein the dispersed phase fluid is a gas with a pressure of 0.4 atm to 0.5 atm.

Embodiment 24. The method of any of Embodiments 1-18, wherein the dispersed phase fluid is a gas with a pressure of 0.5 atm to 0.6 atm.

Embodiment 25. The method of any of Embodiments 1-18, wherein the dispersed phase fluid is a gas with a pressure of 0.7 atm to 0.8 atm.

Embodiment 26. The method of any of Embodiments 1-25, wherein the spinning is conducted with a pressure such that the dispersed phase fluid is not sheared into bubbles, resulting in cavities that are substantially tubular in shape.

Embodiment 27. The method of any of Embodiments 1-26, further comprising providing a capillary-based microfluidic device to perform the spinning.

Embodiment 28. The method of any of Embodiments 1-27, further comprising providing a PDMS-based microfluidic device to perform the spinning.

Embodiment 29. The method of any of Embodiments 1-27, further comprising providing a PMMA-based microfluidic device to perform the spinning.

Embodiment 30. The method of any of Embodiments 1-27, further comprising popping bubbles (or cavities) of the cavity-microfibers.

Embodiment 31. The method of Embodiment 30, wherein the bubbles are popped by introducing them into a curing fluid.

Embodiment 32. The method of any of Embodiments 1-31, further comprising stretching the cavity-microfiber.

Embodiment 33. The method of any of Embodiments 31-32, further comprising stretching the cavity-microfiber after the bubbles have been popped to form a chained microfiber.

Embodiment 34. The method of any of Embodiments 1-33, further comprising a flow focusing tube.

Embodiment 35. The method of any of Embodiments 1-34, wherein the dispersed phase fluid is a gas with a pressure of 0.3 atm to 0.4 atm.

Embodiment 36. The method of any of Embodiments 2-35, wherein the extruding orifice has a diameter of about 125 microns.

Embodiment 37. The method of any of Embodiments 2-35, wherein the extruding orifice has a diameter between 200 and 500 microns.

Embodiment 100. An apparatus for fabricating cavity-microfibers comprising:

a first tube connected to a first pressure source and having a first orifice；

a second tube having a second orifice that is within the first tube； and

a second pressure source connected to the second tube.

Embodiment 101. The apparatus of Embodiment 100, further comprising a first container suitable for holding a curing fluid to cure cavity-microfibers.

Embodiment 102. The apparatus of any of Embodiments 100-101, further comprising a second container suitable for collecting cavity-microfibers.

Embodiment 103. The apparatus of any of Embodiments 100-102, further comprising a collection roller suitable for collecting cavity-microfibers.

Embodiment 104. The apparatus of any of Embodiments 100-103, wherein the second tube is a syringe.

Embodiment 105. The apparatus of any of Embodiments 100-104, wherein the first tube is a square.

Embodiment 106. The apparatus of any of Embodiments 100-105, wherein the second tube is made of glass.

Embodiment 107. The apparatus of any of Embodiments 100-106, wherein the first pressure source is a syringe pump.

Embodiment 108. The apparatus of any of Embodiments 100-107, wherein the second pressure source is a gas pressure controller.

Embodiment 108. The apparatus of any of Embodiments 100-108, wherein the second pressure source is a gas pressure controller.

Embodiment 109. The apparatus of any of Embodiments 100-108, further comprising a flow focusing tube within the first tube or connected to the first tube, and having a third orifice.

Embodiment 110. The apparatus of any of Embodiments 100-109, further comprising an extruding orifice.

Embodiment 111. The apparatus of any of Embodiments 100-110, wherein the extruding orifice has a diameter of about 125 microns.

Embodiment 112. The apparatus of any of Embodiments 100-110, wherein the extruding orifice has a diameter between 200 and 500 microns.

Embodiment 201. Cavity-microfiber having cavities and non-homogenous structures prepared by the method according any one of the preceding Embodiments.

Embodiment 202. Cavity-microfiber having cavities and non-homogenous structures comprising knots and joint parts, where the knots comprise cavities or bubbles and the joint parts comprise the area between the cavities or knots.

Embodiment 203. The cavity-microfiber according any one of the preceding Embodiments, wherein the bubbles are uniform in size and the distances between the bubbles are uniform.

Embodiment 204. The cavity-microfiber according to according any one of the preceding Embodiments, wherein a drug is impregnated in the cavities or bubbles.

EXAMPLES

The present disclosure is illustrated by the following examples together with figures the which are merely for the purpose of illustration and are not to be regarded as limiting the scope of the disclosure or manner in which it may be practiced. In these examples, an aqueous solution comprising 3wt％alginate, 5 wt％polyvinyl alcohol (PVA) and 5 wt％polyethylene glycol (PEG) was used as the continuous phase fluid, nitrogen was used as the dispersed phase fluid and calcium chloride solution was used as the curing fluid.

Figure 1 is an exemplary embodiment of the present invention including a capillary-based microfluidic device. The exemplary embodiment of Figure 1 was fabricated by co-axially aligning a glass slide 1, two syringe needles 2, and two cylindrical glass capillaries 3 that were glued together with AB glue (two part epoxy, or additive and base glue) . At the orifice of the output channel of the capillary-based microfluidic system, a container filled with a curing fluid can be provided to cure the combined fluid as it is extruded. A rotating collection roller may also be provided for cavity-microfiber collection and may be positioned on or near the curing fluid container, assuming a curing fluid container is provided. The system can be tuned by adjusting the flow rates and pressures of the continuous phase fluid and the dispersed phase fluid. The cavity-microfibers can have uniform knots (the areas of the cavity-microfibers where the cavities or bubbles are located) and uniform joint parts (the areas between the cavities or knots) , or the cavity-microfibers may be non-homogeneous in structure.

Figure 32 is a close-up view of an apparatus according to an embodiment of the present invention. As seen in Figure 32, a first tube 4 is provided that contains a flowing continuous phase fluid and a second tube 5 is provided that contains a flowing dispersed phase fluid. The second tube 5 and a third tube 6 (aflow focusing tube) are positioned within the second tube 5. Because the second tube 5 and the third tube 6 are within the first tube 4, the second tube 5 and the third tube 6 have a smaller outside diameter than the inside diameter of the first tube 4. The second tube 5 can be a syringe or a tube-like structure that comes to a point； however, in other embodiments, the second tube may have a uniform outside and inside diameter or another shape.

In Figure 32, the second tube 5 delivers the dispersed phase fluid and first tube 4 delivers the continuous phase fluid. At the end of the second tube 5 there is an orifice 7, which is an outlet for the dispersed phase fluid. A bubble 8 can be seen forming as shearing forces cause the dispersed phase fluid to separate within the continuous phase fluid. In the embodiment of Figure 32, the orifice 7 of the second tube 5 is near or at the same position as the inlet orifice of the third tube 6, but the orifice 7 of the second tube 5 could alternatively be located within the third tube 6 or upstream from the orifice of the third tube 6. The first tube 4, the second tube 5, and the third tube 6 can be made of any material including, but not limited to, glass, metal, and plastic. In addition, the tubes do not need to be round and can be square or any other shape.

In another embodiment (not illustrated in Figure 32) , the third tube 6 is not present and the apparatus simply includes a first tube 4 and a second tube 5. That is, the second tube 5 delivers the dispersed phase fluid within the first tube 4, which provides a flow of continuous phase fluid, and bubbles are formed at the orifice 7 of the second tube 5 as the dispersed phase fluid shears under the forces of the continuous phase fluid of the first tube 4. Downstream from the orifice 7 of the second tube 5, the first tube 4 may have a section where the dispersed phase fluid bubbles flow within the stream of the continuous phase fluid to stabilize. The first tube may then end with an orifice where the combined fluid (including the bubbles of dispersed phase fluid and the continuous phase fluid) is extrude to form cavity-microfibers.

Figure 34 is a schematic diagram of an embodiment of the present invention. In this embodiment, a second inner tube is enclosed within a first outer tube and a flow focusing third tube is not present. A syringe pump is provided to control the flow of the continuous phase fluid flowing through the first outer tube and a gas pressure controller system is provided to control the flow (i.e., control the pressure) of the dispersed fluid. Instead of a syringe pump, another type of pump may be provided to control the flow of continuous phase fluid. The dispersed fluid may be a gas or a liquid and, instead of a gas pressure controller, a syringe pump or another type of pump may be provided to control the flow of the dispersed phase fluid. At the end of the second inner tube there is an orifice, where the dispersed phase fluid is introduced to the continuous phase fluid inside the first outer tube. As the dispersed phase fluid enters the flow of the continuous phase fluid, the dispersed phase fluid is sheared to form bubbles, resulting in the combined fluid. At the end of the first outer tube there is an extruding orifice through which the combined fluid, including the continuous phase fluid and the bubbles of dispersed phase fluid, is extruded to spin cavity-microfibers.

Figure 34 also illustrates the use of a container with a curing fluid to harden the cavity-microfibers after they have been extruded. Alternatively, the cavity-microfibers may cure by drying in air and may also dry after they have hardened in the curing fluid. The cavity-microfibers may then be collected on a roller. Figure 34 illustrates an experimental setup with a computer, a camera, and a microscope； however, these elements do not directly affect cavity-microfiber formation, but can be used to better observe the process and fine tune the continuous and dispersed phase fluid pressures and flow rates to achieve whatever cavity-microfiber characteristics are desired.

A method for forming cavity-microfibers according to an embodiment of the present invention can include introducing a flow of dispersed phase fluid within a flow of continuous phase fluid. The dispersed phase fluid can be introduced to the continuous phase fluid within a channel and sheared by the continuous phase fluid to form bubbles. The combined fluid, including the continuous phase fluid and bubbles of dispersed phase fluid, can then be extruded through an orifice and spun into cavity-microfibers. One example of this can be seen in Figure 32, in which a first tube 4 is provided that contains a flowing continuous phase fluid and a second tube 5 is provided that contains a flowing dispersed phase fluid. In some embodiments, a third tube 6 may be provided to focus the flow of the combined fluid.

Figure 35 provides a flowchart of a method for producing cavity-microfibers according to an embodiment of the present invention. According to Figure 25, a syringe pump is provided as a driving force for a solidifiable continuous phase fluid and a gas pressure controller is provided as the driving force for the dispersed phase fluid. Bubbles of dispersed phase fluid are then wrapped in the solidifiable continuous phase fluid and then the combined fluid, including the dispersed phase fluid bubbles wrapped in the continuous phase fluid, is solidified in a channel or extruded via an orifice and dried to form cavity-microfibers. As another option, the combined fluid can be extruded via an orifice and then solidified in a container of curing fluid to form cavity-microfibers.

The cavity-microfiber technology of this application can be applied using a range of extruding orifice sizes to make different sized cavity-microfibers. That is, an apparatus according to an embodiment of the present invention (or a method according to the present invention) can have an extruding orifice with a diameter (or long axis, if not circular) of, for example, about any of the following values, at least any of the following values, not more than any of the following values, or within any range having any of the following values as endpoints (with or without “about” in front of one or both of the endpoints) , though embodiments are not limited thereto (all numerical values are in microns) : 1, 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, and 2000. For example, an extruding orifice of the present invention can have a diameter of about 125 microns, between 1 and 2000 microns, between 200 and 500 microns, or not more than 500 microns.

In the proof of embodiments that are discussed throughout this application, a combined fluid including an alginate-based continuous phase fluid and a dispersed phase fluid gas (air or nitrogen) was used. A calcium chloride solution was provided to solidify the cavity-microfibers. The alginate-based combined fluid was continuously extruded into the calcium chloride (CaCl₂) curing solution via a spinning orifice (i.e, an extruding orifice) , where it began to crosslink into a gelatinized cavity-microfiber. The freshly formed cavity-microfibers were allowed to soak in the calcium chloride solution for a few minutes. The orifice used for spinning the cavity-microfibers had a diameter of 125μm. The apparatus used in the experiments, shown in Figure 1, was made by co-axially aligning a glass slide, two syringe needles, and two cylindrical glass capillaries in a square glass capillary glued together with AB glue. At the output channel of the capillary-based microfluidic system, a container was provided containing the calcium chloride solution as seen in Figure 2. After collection, the cavity-microfiber was dried in air for an hour or more.

By applying different flow rates of continuous phase fluid and adjusting the pressure of a dispersed phase fluid, different types of cavity-microfibers having different characteristics can be fabricated, which are suitable for different applications. Examples of the different types of cavity-microfibers that can be obtained include uniform cavity-microfibers, tiny cavity-microfibers, mixed bubble cavity-microfibers, and chained cavity-microfibers. Drying time also affects the structure of the cavity-microfibers, including the diameter of joint parts, the major axis and minor axis of the knots (or cavities) , and the volume of the knots. Therefore, the size of cavity-microfiber knots and the joint parts of the cavity-microfibers can be adjusted by changing the drying time.

Examples of freshly formed (hydrated) microfibers, fabricated via embodiments of the present invention, are shown in Figures 3a, 3c, 3e, and 3g. Dehydrated microfibers with spindle cavity-knot structures were formed by drying the hydrated cavity-microfibers in air. Examples of dehydrated cavity-microfibers formed according to embodiments of the present invention can be seen in Figure 3b, 3d, 3f, 3h, 3i, 3j, and 3k. Further images of dehydrated cavity-microfibers, formed according to embodiments of the present invention, and captured using scanning electron microscopy, can be seen in Figure 4.

The diameter of hydrated cavity-microfibers (Y) is highly dependent on the flow rate of the combined fluid (X) when the diameter of the extruding orifice of the microfluidic device is held constant. As seen in Figure 5, when the flow rate of the continuous phase fluid increased from 0.4 mL/h to 1.6 mL/h, the diameter of hydrated microfiber increased from 132.093μm to 155.768μm almost linearly.

The structure of cavity-microfibers is also affected by the pressure of the dispersed phase fluid gas. Figure 6 is a graph illustrating how different types of cavity-microfibers are formed as a function of Cao (capillary number of continuous phase) and Pr (the pressure of dispersed phase gas divided by standard atmospheric pressure) . When the gas pressure is increased with a fixed flow rate of continuous phase fluid, five different phases will appear in the microchannel of the microfluidic device, as seen in Figure 6 and Figure 7. First, a phase without bubbles appears in Area0 because the pressure of the dispersed phase fluid gas is much less than that of the continuous phases fluid pressure. Then, as the pressure of the dispersed phase fluid gas increases, a critical value is reached and tiny bubbles of around 10 μm diameter start forming as seen in Area1. As the pressure of the dispersed phase fluid gas continues to increase, the system reaches an unstable transition stage in which a mixture of tiny bubbles and larger bubbles are generated in the cavity-microfiber. This phenomenon can be seen in Area2 of Figure 6. As seen in Area3 of Figure 6, as the pressure of the dispersed phase fluid gas continues to increase, cavity-microfibers having bubbles that are larger and uniform in size are generated with uniform distances between the bubbles. As gas pressure increases further, the diameter of bubbles continues to increase and the distance between the bubbles continues to decrease until it reaches zero, as seen in Area4. Finally, when the pressure of the gas reaches a certain point, the continuous phase fluid no longer shears the gas and a gas jet appears, as seen in Area5. Of particular importance is Area3, which is the basis for controllably fabricating cavity-microfibers having uniform sized cavities, uniform distances between cavities, and uniform junctions (or joints) between cavities. Figure 7 shows enlarged pictures of the different types of cavity-microfibers that are formed under the pressures illustrated in Figure 6.

The effect of the dispersed phase fluid gas pressure on the structure of cavity-microfibers, as seen in Area3, was further investigated. Figure 8 is a graph showing the effects of dispersed phase fluid gas pressure on the volume of gas bubbles, knots (or cavities) of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 0.6 mL/h. Figure 9 is a graph showing the effect of dispersed phase fluid pressure on the distance between bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 0.6 mL/h. Figure 10 is a graph showing the effects of dispersed phase fluid pressure on the volume of gas bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase flow rate of 1 mL/h. Figure 11 is a graph showing the effects of dispersed phase fluid pressure on the distance between bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 1 mL/h. Figure 12 is a graph showing the effects of dispersed phase gas pressure on the volume of gas bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers under a continuous phase fluid flow rate of 1.4 mL/h. Figure 13 is a graph showing the effects of dispersed phase fluid gas pressure on the distance between bubbles, knots of hydrated cavity-microfibers and knots of dehydrated cavity-microfibers under a continuous fluid phase flow rate of 1.4 mL/h.

Figure 33 includes three images illustrating bubble distance, hydrated-knot distance and dehydrated knot distance. Bubble distance is the distances between dispersed phase bubbles while they are still in the microchannel and before they are extruded via an orifice (i.e., spun into cavity-microfibers) . Hydrated knot distance is the distance between knots or bubbles before the cavity-microfibers are allowed to dry. Dehydrated knot distance is the distance between knots or bubbles after the cavity-microfibers have had the chance to cure or dry.

With an increase in dispersed phase fluid gas pressure, the volume of gas bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers increases in an almost linear fashion. Generally, the volume of the knots of hydrated cavity-microfibers is greater than those of the gas bubbles in the channel before the combined fluid is extruded. This is because the gas bubbles are compressed by the pressure of the continuous phase fluid in the microchannel of the microfluidic device as bonding occurs in the microchannel of the microfluidic device. When the liquid of continuous phase fluid carrying the dispersed phase gas bubbles is extruded from the orifice, the diameter of the liquid jet and gas bubbles increases as the bonding ceases to exist and the pressure is reduced. In addition, when the dispersed phase gas pressure is lowered, the volume of the knots of the dehydrated cavity-microfibers is greater than the volume of the gas bubbles, but less than the volume of the knots of hydrated cavity-microfibers. This happens because the diameter of gas bubbles increases after the bonding in the microfluidic microchannel ceases to exist. Then, when the cavity-microfibers dry, the decrease in the diameter of the cavity-microfibers has little influence on the volume of the gas bubbles. With an increase in dispersed phase fluid gas pressure, the volume of the gas bubbles increases. Therefore, when the diameter of microfiber decreases, the gas bubble is compressed and the volume of the knots of the dehydrated cavity-microfiber is less than the volume of the gas bubbles.

The dispersed phase fluid gas pressure also has an important effect on the distance between bubbles, knots of the hydrated cavity-microfiber, and knots of the dehydrated cavity-microfiber. With an increase in dispersed phase gas pressure, the distance between bubbles, knots of hydrated cavity-microfibers, and knots of dehydrated cavity-microfibers gradually decreases. Generally, the distance between bubbles is less than the distance between knots of hydrated cavity-microfiber. Also, the distance between knots of hydrated cavity-microfiber is generally less than the distance between knots of dehydrated cavity-microfiber. This is because microfiber elongates when the microfiber is dried so that the distance between knots is also enlarged. In summary, the gas pressure of dispersed phase fluid has a significant influence on the structure of cavity-microfibers, including the distance between knots of cavity-microfibers and the knot volumes of the cavity-microfibers.

The drying time of cavity-microfibers also plays an important role in the structure of the cavity-microfibers. Figure 14 is a graph showing the effects of drying time on the diameter of joint parts of cavity-microfibers. At the beginning of drying, the diameter of joint parts of the hydrated cavity-microfibers decreases rapidly, almost linearly, due to the rapid loss of moisture. After the cavity-microfiber has dried completely, the diameter of the joint part of the cavity-microfibers is fixed. Figure 15 is a graph showing the effects of drying time on the major axis and minor axis of knots of the cavity-microfibers. Due to the rapid loss of moisture in the cavity-microfiber, the major axis and minor axis of the knots of the cavity-microfibers change during the drying process, as seen in Figure 15.

The drying process can make the cavity-microfibers elongate lengthwise and therefore the major axis of the knots continues to change until drying is complete. However, the minor axis (the diameter) of the knots of cavity-microfibers generally does not change much as the cavity-microfibers dry. Figure 16 is a graph showing the effects of drying time on the volume of knots of cavity-microfibers. During the drying process, the volume of the knots of cavity-microfibers also changes with the changes of the major axis and minor axis of the knots of the cavity-microfibers, as seen in Figure 16. First, the volume of knot of cavity-microfiber decreases with the drying time. At the beginning of drying, moisture in the cavity-microfiber is abundant and the change of diameter in the cavity-microfiber is large, and the gas in the knots is compressed. Next, due to the loss of moisture, the cavity-microfiber elongates (meaning the major axis of the knots increases) , but the diameter of cavity-microfibers generally does not change much (meaning that the minor axis of knots changes little) . Therefore, the volume of the knots of the cavity-microfibers increases until all of the moisture in the cavity-microfibers is lost and the knot volume of the cavity-microfibers stops changing.

Figure 17 is a graph showing mechanical tensile test results of dehydrated cavity-microfibers. The equivalent diameter of dehydrated cavity-microfiber used in the testing shown in Figure 17 was 105.94μm and the sample gauge length was 24mm. The off yield stress was 3.709 MPa, the off yield strain was 0.082 MPa, and the equivalent modulus was 0.582 GPa.

As seen in Figures 18a to 18c, other types of cavity-microfibers were generated including cavity-microfibers with a tiny bubble phase, mixed bubble phases and coherent bubble phases. Figure 18a is an image of a tiny-cavity-microfiber, Figure 18b is an image of a mixed bubble cavity-microfibers, and Figure 18c includes images of chained microfibers. In Figure 18a, the size of cavity is around 10μm. Similarly, the mixed bubble cavity-microfibers shown in Figure 18b and the chained microfibers shown in 18c are generated via mixing the bubble phase and a coherent bubble phase respectively. The mixed bubble cavity-microfibers generally have a structure wherein one tiny bubble is followed by several uniform sized larger bubbles. Because the bubbles in the coherent bubble phase are large, the bubbles cannot be encapsulated into cavity-microfibers. That is, when the alginate solution is extruded into the CaCl₂ solution, the bubbles burst out from the microfiber and the cavities of the cavity-microfiber collapse. After being gently stretched, the chained microfibers are formed.

Spider webs have an excellent ability to collect water. Cavity-microfibers produced by embodiments of the present invention have a similar ability to collect water. To investigate the ability of cavity-microfibers to collect water, a single dehydrated cavity-microfiber and a spider-web-like assembled cavity-microfiber were placed in a water mist generated by an ultrasonic humidifier. The process was recorded by a CCD camera as shown in Figures 19 and 20.

Figure 19 is an image of water collection on a single dehydrated cavity-microfiber. Figure 20 includes images of water collection on a single spindle-knot of a cavity-microfiber as a function of collection time. As seen in Figures 19 and 20, a single dehydrated cavity-microfiber absorbs tiny water droplets from the water mist, resulting in a small amount of swelling and deformation of the dehydrated cavity-microfiber. The water continues condensing on the spindle-like knot parts and joint parts of the cavity-microfibers and the water droplets grow larger and larger. Due to the anisotropic surface properties of the cavity-microfiber, different knots of the cavity-microfiber have varying abilities to collect water. As can be seen in Figure 20, one of the knots appears to be the epicenter of water collection. Despite the vertical positioning of the knots, the water condensed on the knots can overcome gravitational forces and move towards the knot most conducive to collecting water. The water droplets can then coalesce to form larger water droplets.

To evaluate the water collection ability of dehydrated cavity-microfibers, the maximum volume of water droplets collected by the domain knot was calculated, which was over 400 times that of the domain knot of the dehydrated cavity-microfiber. The results show that dehydrated cavity-microfibers are excellent for water collection. It was also observed that the intersections between the cavities (or knots) of the cavity-microfibers had a greater ability to collect water than the knots themselves.

The relation between water collection on a single spindle-knot and collection time was also investigated as seen in Figure 20 and Figure 21. Figure 21 is a graph showing water collection volume on a single spindle-knot as a function of collection time. Experiments showed that water collection of the dehydrated cavity-microfiber was roughly 495 times that of the knots of the dehydrated cavity-microfibers. In Figure 21, water droplet volume increases sharply during 90s-100s period and 150s-160s period because the water droplets grow as time passes, then adjacent droplets coalesce quickly to form larger droplets.

Figure 22 is an image showing that intersections of cavity-microfibers have a greater ability for water collection than the cavity-microfiber knots. The intersectional structure increases overall complexity, leading to increased Laplace pressure and mechanical strength, which allows for greater water collection at the intersection. As also seen in Figure 22, intersecting cavity-microfibers have a greater ability to collect water than parallel cavity-microfibers.

Spider-web-like cavity-microfiber structures were fabricated with varying numbers of beams. Figure 23a is an image of a two-beam cavity-microfiber web. Figure 23b is an image of water collection for a two-beam cavity-microfiber web. Figure 23c is an image of a three-beam cavity-microfiber web. Figure 23d is an image of water collection for a three-beam cavity-microfiber web. Figure 23e is an image of a four-beam cavity-microfiber web. Figure 23f is an image of water collection for a four-beam cavity-microfiber web. It can be seen in Figures 23a through 23f that with more beams there are more intersections and greater water collection ability. The results demonstrate the potential of producing complex structure cavity-microfibers with multiple intersections for water collection.

One application for cavity-microfibers is drug delivery, where the drug can be contained in and released through the cavities. One example of such an application is a surgical suture impregnated with a drug. The cavity-microfiber may also be biodegradable so that it does not have to be removed. Another potential application of the cavity-microfibers is for micro-cultures and micro-reactors. In the cavities of a cavity-microfiber, many cell cultures or chemical reactions can be performed. In addition, cavity-microfibers can be used to build 2D and 3D scaffolds for cell culture and tissue engineering.

Figure 24 is an image of 2D scaffolds constructed using cavity-microfibers, which can be used for cell cultures and tissue engineering. Figure 25 is an image of 3D scaffolds constructed using cavity-microfibers for cell cultures and tissue engineering. Figure 26 is an image showing the formation of bone tissue on 2D scaffolds built using cavity-microfibers. Figure 27 is an image showing an alizarin red staining test for forming bone tissue. The results demonstrate that cavity-microfibers have desirable characteristics for building 2D and 3D scaffolds for cell culture and tissue engineering.

Figure 28 is a schematic diagram of drug delivery and drug release using cavity-microfibers. As shown in Figure 28, a drug can be impregnated in the cavities as the dispersed phase and then slowly released over time. An application of such a cavity-microfiber can include surgical sutures, which may be biodegradable. This sort of surgical suture may be particularly useful in wound recovery.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims. In addition, any elements or limitations of any invention or embodiment thereof disclosed herein can be combined with any and/or all other elements or limitations (individually or in any combination) or any other invention or embodiment thereof disclosed herein, and all such combinations are contemplated with the scope of the invention without limitation thereto.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

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Claims

A method for fabricating microfibers comprising:

introducing a dispersed phase fluid into a continuous phase fluid to form a combined fluid, wherein the combined fluid includes dispersed phase fluid bubbles or dispersed phase fluid droplets in the continuous phase fluid；

spinning the combined fluid to form cavity-microfibers.
The method according to claim 1, wherein the introducing the dispersed phase fluid into the continuous phase fluid includes providing a second tube with a second orifice within a first tube, and wherein the first tube delivers the continuous phase fluid and the second tube delivers the dispersed phase fluid.
The method according to claim 2, wherein the spinning includes solidifying the combined fluid in a channel； and/or

wherein the spinning includes a wet spinning method； and/or

wherein the spinning includes forcing the combined fluid through a flow focusing tube； and/or

wherein the continuous phase fluid includes two or more fluids； and/or

wherein the spinning includes photo curing or UV-curing the combined fluid； and/or

wherein the spinning includes chemically curing the combined fluid； and/or

wherein the spinning includes thermally curing the combined fluid； and/or

wherein the dispersed phase fluid is one or more gases； and/or

wherein the dispersed phase fluid is a gas with a pressure of 0.0 atm to 0.7 atm； and/or

wherein the dispersed phase fluid is a gas with a pressure of 0.0 atm to 0.1 atm； and/or

wherein the dispersed phase fluid is a gas with a pressure of 0.1 atm to 0.2 atm； and/or

wherein the dispersed phase fluid is a gas with a pressure of 0.2 atm to 0.3 atm； and/or

wherein the dispersed phase fluid is a gas with a pressure of 0.3 atm to 0.4 atm； and/or

wherein the dispersed phase fluid is a gas with a pressure of 0.4 atm to 0.5 atm； and/or

wherein the dispersed phase fluid is a gas with a pressure of 0.6 atm to 0.7 atm； and/or

wherein the continuous phase fluid comprises a material selected from the group consisting of polymers of dextrose, sugars, starches, acrylates, polyvinyl alcohol, gum arabic, polyacrylamide, hydroxypropyl cellulose, hydroxypropyl methylcellulose, polyvinyl pyrrolidone, poly (2-acrylamido-2-methyl-1-propanesulfonic acid) , poly (acrylamido-N-propyltrimethylammonium chloride) , polylactic acid, polycaprolactone, polyglycolic acid, polylactic-co-glycolic acid, 1, 3-propanediol polymer, collagen, gelatin, fibrin, silk-fibroin, elastin mimetic peptide polymer, chitosan, modified chitosan, polyvinylidene fluoride, polytetrafluoroethylene, polyurethane, polycarbonate polyurethane, polyether-based polyurethane, silane-modified polyurethane, polyethylene terephthalate, polymethyl methacrylate, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) , poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) , polyphosphate, polyamino formic anhydride, polyesteramide, poly (para-dioxanone) , polycarbonate, cellulose, chondroitin sulfate, heparin, glucosan, alginic acid, alginate, polyethylene gycol, water and combinations thereof； and/or

wherein the dispersed phase fluid comprises air or inert gas； and/or

wherein the dispersed phase fluid comprises hydrogen, nitrogen, helium, argon, carbon dioxide, carbon monoxide, steam, or mixtures thereof.
An apparatus for fabricating cavity-microfibers comprising:

a first tube；

a second tube within the first tube, and having a second orifice that is also within the first tube； and

a first means for supplying pressure to the first tube and a second means of supplying pressure to the second tube.
The apparatus according to claim 4, wherein the second tube tapers going towards the second orifice.
The apparatus according to claim 4, further comprising a flow focusing tube that is positioned after the second orifice, and wherein the flow focusing tube is connected to or within the first tube.
Cavity-microfiber having cavities and non-homogenous structures prepared by the method according any one of the preceding claims or comprising knots and joint parts, where the knots comprise cavities or bubbles and the joint parts comprise the area between the cavities or knots.
The cavity-microfiber according to claim 7, wherein the bubbles are uniform in size and the distances between the bubbles are uniform.
The cavity-microfiber according to claim 7 or 8, wherein a drug is impregnated in the cavities or bubbles.