Bioabsorbable fibers and reinforced composites produced therefrom

Abstract

This invention relates to bioabsorbable fibers, comprising a semicrystalline fiber-forming core polymer and a amorphous sheath polymer, wherein the core polymer and sheath polymer are separately melt extruded and connected to one another through an adhesive bond. The present invention also relates to reinforced composites of the bioabsorbable fibers, and to devices comprising the reinforced composites. The devices are suitable for in vivo implantation. Some embodiments of the present devices can also support high loads, making them useful for fracture fixation and spinal fusion. The invention also relates to methods of making the various materials of the invention.

What is claimed is:  
     
         1 . A bioabsorbable fiber comprising a core of a semicrystalline fiber-forming bioabsorbable core polymer with a crystalline core melting temperature, and a sheath of an amorphous bioabsorbable sheath polymer with a softening point below the crystalline core melting temperature, wherein the core polymer and sheath polymer are separately melt extruded, and the sheath is connected to the core through an adhesive bond.  
     
     
         2 . The bioabsorbable fiber of  claim 1 , wherein the core polymer is selected from the group consisting of poly(L-lactide), polyglycolide, poly(epsilon-caprolactone), polydioxanone, poly(ester-amide)s, any combination thereof, and any copolymers thereof wherein trimethylene carbonate is a comonomer.  
     
     
         3 . The bioabsorbable fiber of  claim 1 , wherein the sheath polymer comprises at least one polymer selected from the group consisting of poly(ester-amide)s, tyrosine-derived polycarbonates, poly(trimethylene carbonate), poly(dl-lactide), polydioxanone, and any copolymer, mixture, or blend thereof.  
     
     
         4 . The bioabsorbable fiber of  claim 1 , wherein the sheath polymer comprises a copolymer which is the product of copolymerization of at least two monomers selected from the group of monomers consisting of epsilon-caprolactone, trimethylene carbonate, L-lactide, dl-lactide, glycolide, and para-dioxanone.  
     
     
         5 . The bioabsorbable fiber of  claim 1  wherein the core polymer is poly(L-lactide) and the sheath polymer is a block copolymer of poly(ester-amide) and L-lactide.  
     
     
         6 . The bioabsorbable fiber of  claim 5 , wherein the sheath polymer is a block copolymer of L-lactide and 1,6-hexanediol terminated poly[2,5-dioxahexane-1,6-di(carbonyloxy)hexane-1,6-di(amidocarbonylpentamethylene)].  
     
     
         7 . The bioabsorbable fiber of  claim 1 , wherein the sheath is bound to the core with sufficient strength that the sheath elongates with the core and does not separate therefrom through hot stretching, elongation, and cooling of the fiber.  
     
     
         8 . A reinforced composite, comprising: 
 a plurality of filaments of a bioabsorbable fiber, the bioabsorbable fiber comprising a core of a semicrystalline fiber-forming bioabsorbable core polymer with a crystalline core melting temperature, and a sheath of an amorphous bioabsorbable sheath polymer with a softening point below the crystalline core melting temperature, wherein the core polymer and sheath polymer are separately melt extruded, and the sheath is connected to the core through an adhesive bond; and    a molding resin reinforced with the plurality of fibers.    
     
     
         9 . The reinforced composite of  claim 8 , wherein the core polymer is selected from the group consisting of poly(L-lactide), polyglycolide, poly(epsilon-caprolactone), polydioxanone, poly(ester-amide)s, any combination thereof, and any copolymers thereof wherein trimethylene carbonate is a comonomer.  
     
     
         10 . The reinforced composite of  claim 8 , wherein the sheath polymer comprises at least one polymer selected from the group consisting of poly(ester-amide)s, tyrosine-derived polycarbonates, poly(trimethylene carbonate), poly(dl-lactide), polydioxanone, and any copolymer, mixture, or blend thereof.  
     
     
         11 . The reinforced composite of  claim 8 , wherein the sheath polymer comprises a copolymer which is the product of copolymerization of at least two monomers selected from the group of monomers consisting of epsilon-caprolactone, trimethylene carbonate, L-lactide, dl-lactide, glycolide, and para-dioxanone.  
     
     
         12 . The reinforced composite of  claim 8 , wherein the molding resin consists of the same polymer as the sheath polymer.  
     
     
         13 . The reinforced composite of  claim 9 , wherein the molding resin is filled with at least 10% and up to 70% of the bioabsorbable fibers by volume.  
     
     
         14 . The reinforced composite of  claim 9 , wherein the molding resin is filled with a reinforcement filler selected from the group consisting of the bioabsorbable fibers, a mineral filler, and a combination of the bioabsorbable fibers and the mineral filler.  
     
     
         15 . The reinforced composite of  claim 14 , wherein the mineral filler comprises hydroxyapatite.  
     
     
         16 . The reinforced composite of  claim 15  wherein the injection molding resin is filled with 10-70% by volume of hydroxyapatite particles that have been treated with a silane coupling agent.  
     
     
         17 . The reinforced composite of  claim 16  in which the silane coupling agent is trimethoxyaminopropyl silane.  
     
     
         18 . A device designed for in vivo implantation, fabricated from a reinforced bioabsorbable composite, the reinforced composite comprising: 
 a plurality of filaments of a bioabsorbable fiber, the bioabsorbable fiber comprising a core of a semicrystalline fiber-forming bioabsorbable core polymer with a crystalline core melting temperature, and a sheath of an amorphous bioabsorbable sheath polymer with a softening point below the crystalline core melting temperature, wherein the core polymer and sheath polymer are separately melt extruded, and the sheath is connected to the core through an adhesive bond; and    a molding resin reinforced with the plurality of fibers.    
     
     
         19 . The device of  claim 18 , wherein the core polymer is selected from the group consisting of poly(L-lactide), polyglycolide, poly(epsilon-caprolactone), polydioxanone, poly(ester-amide)s, any combination thereof, and any copolymers thereof wherein trimethylene carbonate is a comonomer.  
     
     
         20 . The device of  claim 18 , wherein the sheath polymer comprises at least one polymer selected from the group consisting of poly(ester-amide)s, tyrosine-derived polycarbonates, poly(trimethylene carbonate), poly(dl-lactide), polydioxanone, and any copolymer, mixture, or blend thereof.  
     
     
         21 . The device of  claim 18 , wherein the sheath polymer comprises a copolymer which is the product of copolymerization of at least two monomers selected from the group of monomers consisting of epsilon-caprolactone, trimethylene carbonate, L-lactide, dl-lactide, glycolide, and para-dioxanone.  
     
     
         22 . The device of  claim 18 , wherein the reinforced composite is in a configuration suitable for use as a spinal fusion cage implant.  
     
     
         23 . The device of  claim 18 , wherein the reinforced composite is in a configuration suitable for use as an intramedullary rod.  
     
     
         24 . The device of  claim 18 , wherein the reinforced composite is in a configuration suitable for use as a stent.  
     
     
         25 . A method of making a bioabsorbable fiber, comprising the steps of: 
 a. selecting a core polymer which is semicrystalline, fiber-forming, and bioabsorbable, with a crystalline core melting temperature;    b. selecting a sheath polymer which is bioabsorbable, and which forms an amorphous phase on polymerization, with a softening point below the crystalline core melting temperature;    c. separately melt extruding the core polymer and sheath polymer; and    d. forming an adhesive bond between the core polymer and sheath polymer, such that the resulting bioabsorbable fiber comprises a core of the core polymer and a sheath of the sheath polymer.    
     
     
         26 . The method of making the bioabsorbable fiber of  claim 25 , wherein the core polymer is selected from the group consisting of poly(L-lactide), polyglycolide, poly(epsilon-caprolactone), polydioxanone, poly(ester-amide)s, any combination thereof, and any copolymers thereof wherein trimethylene carbonate is a comonomer.  
     
     
         27 . The method of making the bioabsorbable fiber of  claim 25 , wherein the sheath polymer comprises at least one polymer selected from the group consisting of poly(ester-amide)s, tyrosine-derived polycarbonates, poly(trimethylene carbonate), poly(dl-lactide), polydioxanone, and any copolymer, mixture, or blend thereof.  
     
     
         28 . The bioabsorbable fiber of  claim 26 , wherein the sheath polymer comprises a copolymer which is the product of copolymerization of at least two monomers selected from the group of monomers consisting of epsilon-caprolactone, trimethylene carbonate, L-lactide, dl-lactide, glycolide, and para-dioxanone.  
     
     
         29 . The method of making the bioabsorbable fiber of  claim 26 , wherein the adhesive bond between the core and sheath is formed by forcing the separately melting the extruded core polymer and extruded sheath polymer into a single die.  
     
     
         30 . The method of making the bioabsorbable fiber of  claim 26 , wherein adhesive bond between the sheath and the core is sufficiently strong that the sheath elongates with the core and does not separate therefrom through hot stretching, elongation, and cooling of the bioabsorbable fiber.  
     
     
         31 . A method of making a device of a reinforced composite of bioabsorbable fibers, comprising the steps of: 
 a. providing a plurality of bioabsorbable fibers, comprising: 
 a core of a semicrystalline fiber-forming bioabsorbable core polymer with a crystalline core melting temperature, and a sheath of an amorphous bioabsorbable sheath polymer with a softening point below the crystalline core melting temperature, wherein the core polymer and sheath polymer are separately melt extruded, and the sheath is connected to the core through an adhesive bond;  
   b. providing an injection mold having interior walls which define an interior cavity;    c. inserting the plurality of bioabsorbable fibers into the interior cavity of the injection mold; and    d. adding a bioabsorbable injection molding resin polymer to the injection mold at an injection temperature which is lower than the crystalline core melting temperature.    
     
     
         32 . The method of making a device of  claim 31 , wherein the plurality of bioabsorbable fibers provided in step (a) is provided in a form selected from the group consisting of: knitted, woven, braided, and in the form of a fabric constructed from the bioabsorbable fibers.  
     
     
         33 . The method of making a device of  claim 31 , wherein the interior walls of the injection mold define an interior cavity which is tubular in shape.  
     
     
         34 . The method of making a device of  claim 33 , wherein the injection mold further comprises a mandrel, which is present in the interior cavity during the injection step.  
     
     
         35 . The method of making a device of  claim 34 , wherein the plurality of fibers are wrapped or wound about the mandrel in step (c), such that the resulting device has a tubular shape, with bioabsorbable fibers on the internal surface of the tube.  
     
     
         36 . The method of making a device of  claim 34 , retractable are inserted into the mandrel, and the bioabsorbable fibers are wound or woven onto the pins in step (c), such that the bioabsorbable fibers form a cage structure within the interior of the resulting device.  
     
     
         37 . The method of  claim 31 , wherein the interior cavity of the injection mold is configured to provide the device with external threads.  
     
     
         38 . The method of  claim 31 , wherein the core polymer of the bioabsorbable fiber provided in step (a) is selected from the group consisting of poly(L-lactide), polyglycolide, poly(epsilon-caprolactone), polydioxanone, poly(ester-amide)s, any combination thereof, and any copolymers thereof wherein trimethylene carbonate is a comonomer.  
     
     
         39 . The method of  claim 31 , wherein the sheath polymer of the bioabsorbable fiber provided in step (a) is selected from the group consisting of poly(ester-amide)s, tyrosine-derived polycarbonates, poly(trimethylene carbonate), poly(dl-lactide), polydioxanone, and any copolymer, mixture, or blend thereof.  
     
     
         40 . The method of  claim 31 , wherein the sheath polymer comprises a copolymer which is the product of copolymerization of at least two monomers selected from the group of monomers consisting of epsilon-caprolactone, trimethylene carbonate, L-lactide, dl-lactide, glycolide, and para-dioxanone.  
     
     
         41 . The method of making the device of  claim 31 , wherein the core polymer is poly(L-lactide), the sheath polymer is a copolymer of trimethylene carbonate and L-lactide, and the injection molding resin is poly(trimethylene carbonate).