Self shortening fastener

Abstract

Disclosed is a fastener that can be mounted to a bone of a patient and can foreshorten and swell of a desired period of time. The fastener can include a head portion and a body portion extending from the head portion. At least one of the head portion and the body portion has a first width that changes to a second width greater than the first width and collectively the head portion and the body portion have a first length that changes to a second length shorter than the first length upon the head portion and the body portion being exposed to a temperature below a glass transition temperature of a polymeric material forming the head portion and the body portion.

1 . A method of manufacturing an implantable fastener, the method comprising:
 injection molding a biocompatible polymeric composition into a polymeric body within an injection mold cavity, wherein at least a portion of said polymeric body is configured to be an implantable fastener; and   removing said polymeric body from said injection mold, wherein said polymeric body has an amount of polymeric molecules oriented in substantially a first direction so that said polymeric body foreshortens and swells upon being introduced into a moist environment having a temperature below a glass transition temperature of the biocompatible polymeric composition.   
     
     
         2 . The method as recited in  claim 1 , wherein said injection molding comprises passing said polymeric composition through an inlet in a master mold that is configured to orientate macromolecules of the biocompatible polymeric composition in substantially a first direction. 
     
     
         3 . The method as recited in  claim 1 , wherein said injection molding comprises passing said polymeric composition through an inlet into said injection mold cavity, said inlet imparting a shear stress to said polymeric composition to orientate macromolecules of said biocompatible polymeric composition in substantially a first direction generally parallel to a longitudinal axis of said polymeric body. 
     
     
         4 . The method as recited in  claim 3 , wherein said inlet has a cross-sectional length from about 10% to about 60% of an average cross-sectional length of said injection mold cavity or a runner. 
     
     
         5 . The method as recited in  claim 3 , wherein said inlet has a cross-sectional length from about 20% to about 50% of an average cross-sectional length of said injection mold cavity or a runner. 
     
     
         6 . The method as recited in  claim 3 , wherein said inlet has a cross-sectional length from about 30% to about 40% of an average cross-sectional length of said injection mold cavity or a runner. 
     
     
         7 . The method as recited in  claim 1 , further comprising orienting the polymeric molecules so that said implantable fastener foreshortens greater than about 2% of an original dimension in 10 days when maintained in a fluid at 37 degrees Celsius. 
     
     
         8 . The method as recited in  claim 1 , wherein said implantable fastener is biodegradable within a fluid medium maintained at 37 degrees Celsius. 
     
     
         9 . The method as recited in  claim 1 , selecting a master mold and one or more sub-molds, each of said one or more sub-molds comprising said injection mold cavity. 
     
     
         10 . The method as recited in  claim 1 , wherein the biocompatible polymeric composition is a biodegradable polymeric composition. 
     
     
         11 . The method as recited in  claim 10 , wherein the biodegradable polymeric composition is comprised of at least one polymer selected from the group consisting of a poly(alpha-hydroxy esters), polylactic acids, polylactides, poly-L-lactide, poly-DL-lactide, poly-L-lactide-co-DL-lacti-de, polyglycolic acids, polyglycolide, polylactic-co-glycolic acids, polyglycolide-co-lactide, polyglycolide-co-DL-lactide, polyglycolide-co-L-lactide, polyanhydrides, polyanhydride-co-imides, polyesters, polyorthoesters, polycaprolactones, polyesters, polyanydrides, polyphosphazenes, polyester amides, polyester urethanes, polycarbonates, polytrimethylene carbonates, polyglycolide-co-trimethylen-e carbonates, poly(PBA-carbonates), polyfumarates, polypropylene fumarate, poly(p-dioxanone), polyhydroxyalkanoates, polyamino acids, poly-L-tyrosines, poly(beta-hydroxybutyrate), polyhydroxybutyrate-hydroxyvaler-is acids, high-density polyethylenes, ultra-high-density polyethylenes, low-density polyethylenes, polypropylenes, polyacrylates, polymethylmethacrylates, polyethylmethacrylates, polysulfones, polyetheretherketones, polytetrafluoroethylenes, polyurethanes, polystyrenes, polystyrene-co-butadienes, and combinations thereof. 
     
     
         12 . The method as in  claim 11 , wherein the biodegradable polymeric composition is comprised of at least one polymer selected from the group consisting of polylactides, poly-L-lactide, poly-DL-lactide, poly-L-lactide-co-DL-lactide, polyglycolic acids, polyglycolide, polylactic-co-glycolic acids, polyglycolide-lactide, polyglycolide-co-DL-lactide, polyglycolide-co-L-lactide, and combinations thereof. 
     
     
         13 . The method as recited in  claim 1 , further comprising at least one of:
 mixing said polymeric composition in a mixer;   extruding said polymeric composition as a thermoplastic extrudate;   heating said polymeric composition before being introduced into said injection mold cavity;   introducing said polymeric composition into said injection mold cavity under pressure;   cooling said polymeric body in said injection mold cavity;   separating said implantable fastener form said polymeric body; or   finishing said implantable fastener.