Microfluidic-based wet spinning of individual solid polymer fibers

Abstract

A method for producing an individual solid polymer fiber from a precursor liquid (L1) including aggregatable, polymerizable and/or cross-linkable polymer precursors, especially from a precursor liquid comprising polymerizable and/pr cross-linkable polymer precursors, by microfluidic-based wet spinning includes: a) introducing the precursor liquid (L1) into a first capillary tube coaxially protruding into a second capillary tube; b) producing a liquid fiber with core-shell structure in the second capillary tube; c) guiding the liquid fiber with core-shell structure, as produced in step b) through a stationary liquid phase (SP); d) curing the liquid sheet of the fiber with core-shell structure in step c) to provide a fiber having a liquid core embedded in a cured shell; e) collecting the fiber; f) after step e), solidifying the liquid core of the fiber; g) removing the cured shell from the solid core to obtain the solid polymer fiber.

1 . A method for producing an individual solid polymer fiber from a precursor liquid comprising aggregatable, polymerizable and/or cross-linkable polymer precursors, or from a precursor liquid comprising polymerizable and/or cross-linkable polymer precursors, by microfluidic-based wet spinning comprising the steps of:
 a) introducing the precursor liquid (L 1 ) through a first inlet into a first capillary tube, whereby-wherein at least a downstream end of the first capillary tube coaxially protrudes into a second capillary tube , and injecting the precursor liquid (L 1 ) into the second capillary tube , to obtain a core flow of the precursor liquid in the second capillary tube;   b) producing a liquid fiber with core-shell structure in the second capillary tube by simultaneously introducing a shell liquid (L 2 ) into the second capillary tube through a second inlet such that the shell liquid (L 2 ) forms a tubular and coaxial shell flow around the core flow of the precursor liquid;   c) guiding the liquid fiber with core-shell structure as produced in step b) through a stationary liquid phase (SP);   d) curing the liquid shell of the fiber with core-shell structure step c), by using a curing agent as the stationary liquid phase (SP) in step c), to provide a fiber having a liquid core embedded in a cured shell;   e) collecting the fiber from the stationary liquid phase (SP) in the form of the fiber having a liquid core ( 22 ) embedded in the cured shell;   f) after step e), solidifying the liquid core of the fiber having a liquid core embedded in a cured shell by aggregation, polymerization and/or crosslinking, to obtain a fiber with a solid core within the cured shell);   g) removing the cured shell from the solid core to obtain the solid polymer fiber.   
     
     
         2 . The method according to  claim 1 , wherein the precursor liquid (L 1 ) comprises one or more of the following substances:
 polyols as well as diisocyanates, triisocyanates and/or polyurethane prepolymers, capable of forming polyurethane polymers;   epoxy resins, with or without hardeners;   crosslinkable siloxane polymers, or polydimethylsiloxane polymers;   ethylenically unsaturated monomers, or alkenes, vinyl monomers, alkenyl monomers and/or (meth) acrylates,   monomers having amine, carboxyl and/or acyl groups, or amino acids, capable of forming polyamides,   monomers and/or oligomers containing active groups for click-chemistry and capable of forming polymers, or monomers and/or oligomers containing groups that react in azide-alkyne cycloaddition reactions, thiol-ene reactions, and/or amino-yne reactions,   monomers selected from α-hydroxy acids, or lactic acid or its cyclic di-ester lactide, glycolic acid, mandelic acid, and/or citric acid;   aggregatable polymers, or polylactic acid (PLA) and/or polycaprolacton (PCL).   
     
     
         3 . The method according to  claim 1 , wherein the precursor liquid (L 1 ) further comprises a solvent, a crosslinking agent, a thermal polymerization initiator, a photopolymerization initiator, a chain transfer agent, a functional molecule and/or a molecular weight regulator. 
     
     
         4 . The method according to  claim 1 , wherein the shell liquid (L 2 ) is a solution of a solvent, or water, and a solvent-soluble non-crosslinked polymer, or wherein the shell liquid is a solution of water and a homopolymer and/or a copolymer formed from one or more of the following monomers: ethylene oxide, vinyl pyrrolidone, vinyl alcohol, vinyl acetate, vinyl pyridine, methyl vinyl ether, acrylic acid and salts thereof, methacrylic acid and salts thereof, hydroxyethyl methacrylate, acrylamide, N,N-dimethyl acrylamide, N-hydroxymethyl acrylamide, alkyl oxazolines, saccharide monomers, polysaccharides, dextran, alginate, amino acids, hydrophilic polypeptides, proteins and/or gelatin. 
     
     
         5 . The method according to  claim 1 , wherein the shell liquid (L 2 ) is an aqueous hydrogel precursor solution, or an aqueous polysaccharide solution, or an aqueous alginate solution, or an aqueous alkaline metal alginate solution. 
     
     
         6 . The method according to claim  19 , wherein the third liquid (L 3 ) or the stationary liquid phase (SP) in step c) is a curing agent for the shell liquid (L 2 ) selected from an aqueous solution of a salt of a divalent metal cation, or selected from of Ca 2+ , Mg 2+ , Zn 2+ , Fe 2+ , Cu 2+ , and/or Ba 2+ . 
     
     
         7 . The method according to claim  19 , further comprising using a curing agent for the shell liquid selected from an aqueous solution of a salt of divalent metal cation, or selected from of Ca 2+ , Mg 2+ , Zn 2+ , Fe 2+ , Cu 2+ , and/or Ba 2+ , wherein the stationary liquid phase in step d) is an aqueous solution, or water. 
     
     
         8 . The method according to  claim 1 , wherein, with respect to an upstream end, at least an outer diameter, or an inner and the outer diameter, of the first capillary tube tapers at the downstream end, to form a first capillary nozzle; and, with respect to an upstream end, at least an outer diameter, or an inner and the outer diameter, of the second capillary tube tapers at the downstream end to form a second capillary nozzle. 
     
     
         9 . The method according to claim  19 , wherein, the sheet liquid is introduced into the second capillary tube at the upstream end face of the second capillary tube, through an annular opening formed by the downstream end of the first capillary tube coaxially protruding into the second capillary tube and, the third liquid (L 3 ) is introduced into the third capillary tube at the upstream end face of the third capillary tube, through an annular opening formed by the downstream end of the second capillary tube coaxially protruding into the third capillary tube. 
     
     
         10 . The method according to claim  19 , wherein a ratio of the flow rates of core flow: shell flow is from 1:0.1-10, or 1:(0.5-1.5), or 1:(0.8-1.2); and a ratio of the flow rates (volume per time) of core flow:shell flow:sheeth flow is from 1:(0.1-10):(1-50), or 1:(0.5-1.5):(2-15), or 1:(0.5-0. 9):(5-12). 
     
     
         11 . The method according to claim  19 , wherein a diameter of the first, the second and the third capillary tube and/or the flow rates of the core flow, the shell flow and the sheath flow are selected such that the solid polymer fiber obtained in step g) has a diameter 1-5'000 μm, or 10-2'500 μm, or 100-1'500 μm. 
     
     
         12 . The method according to  claim 1 , wherein solidifying the liquid core of the core-shell fiber in step f) is affected by irradiation with electromagnetic radiation and/or heating. 
     
     
         13 . The method according to  claim 1 , wherein removing the cured shell from the solid core is effected by dissolving the cured shell in a solvent, or an aqueous solution, or in an aqueous alkaline metal salt solution, or an NaCl solution. 
     
     
         14 . The method according to  claim 1 , wherein steps f) and/or g) take place outside the stationary liquid phase (SP) and/or in time after steps a) to d). 
     
     
         15 . The method according to  claim 1 , wherein in the liquid fiber with core-shell structure produced in the second capillary tube, the shell liquid (L 2 ) and the precursor liquid (L 1 ) in the liquid fiber with core-shell structure are separated by the first capillary tube when flowing through the second capillary tube. 
     
     
         16 . The method according to  claim 15 , wherein the first capillary tube extends completely through the second capillary tube, and the downstream end of the first capillary tube, in flow direction of the liquid fiber, is located further downstream the downstream end of the second capillary tube. 
     
     
         17 . A microfluidic-based wet spinning device for producing an individual solid polymer fiber from a precursor liquid (L 1 ) comprising aggregatable, polymerizable and/or cross-linkable polymer precursors, or from a precursor liquid comprising polymerizable and/or cross-linkable polymer precursors, with a method according to  claim 1 , wherein the device comprises:
 a) a first inlet for introducing the precursor liquid (L 1 ) into a first capillary tube, at least a downstream end of the first capillary tube coaxially protrudes into a second capillary tube, for injecting the precursor liquid (L 1 ) into the second capillary tube, to obtain a core flow of the precursor liquid in the second capillary tube;   b) a second inlet configured for introducing a sheet liquid (L 2 ) into the second capillary tube such that the sheet liquid forms a tubular and coaxial shell flow around the core flow of the precursor liquid, wherein a liquid fiber with core-shell structure is producible in the second capillary tube ;   c) a receptacle for providing a stationary liquid phase (SP) for guiding through the liquid fiber with core-shell structure, optionally having a sheath, as producible in the second capillary tube;   d) a device for collecting the fiber from the stationary liquid phase (SP) in the form of a fiber having a liquid core embedded in a cured shell;   e) a device for solidifying a liquid core of the core-shell fiber by aggregation, polymerization and/or crosslinking, or by polymerization and/or crosslinking, to obtain a fiber with a solid core within the cured shell; and   f) a device for removing the cured shell from the solid core to obtain the solid polymer fiber, or a further receptacle for immersing and/or guiding through the fiber having a solid core embedded in the cured shell.   
     
     
         18 . The microfluidic-based wet spinning device according to claim  20 , wherein the first capillary tube extends completely through the second capillary tube, and the downstream end of the first capillary tube, in flow direction of the liquid fiber, is located further downstream the downstream end of the second capillary tube; and the downstream ends of the first and the second capillary tubes are located inside the third capillary tube, within the first half, or within the first quarter, of the third capillary tube. 
     
     
         19 . The method according to  claim 1 , further comprising: injecting the liquid fiber with core-shell structure produced in step b) into a third capillary tube to obtain a core-shell flow in the third capillary tube, wherein at least a downstream end of the second capillary tube coaxially protrudes into the third capillary tube, and simultaneously introducing a third liquid (L 3 ) into the third capillary tube through a third inlet, such that the third liquid forms a tubular and concentric sheath flow around the core-shell flow in the third capillary tube a liquid fiber with core-shell-sheath structure is produced. 
     
     
         20 . The device according to  claim 17 , further comprising: a third capillary tube, wherein at least a downstream end of the second capillary tube coaxially protrudes into the third capillary tube, such that the liquid fiber with core-shell structure producible in the second capillary tube can be injected in the third capillary tube, to obtain a core-shell flow in the third capillary tube, wherein the third capillary tube has a third inlet for introducing a third liquid (L 3 ) into the third capillary tube, such that the third liquid forms a tubular and concentric sheath flow around the core-shell flow in the third capillary tube, a liquid fiber with core-shell-sheath structure is producible.