Molecularly oriented thermoplastic member and process of forming same

Claim 2

The process of forming a self-supporting high strength thermoplastic member comprising the steps of: providing a thermoplastic polymer capable of being absorbed in an animal body; melting the thermoplastic polymer; cooling the thermoplastic polymer to a temperature below its glass transition temperature to cause nucleation and to form a self-supporting member; reheating the self-supporting member to a temperature above the glass transition temperature of the thermoplastic polymer, but below its melting temperature; applying tension to the self-supporting member during said reheating step; cooling the reheated self-supporting member while maintaining the tension applied thereto; and discontinuing the application of tension after the self-supporting member has cooled to permit the self-supporting member to relax.

Claim 3

The process of Claim 1 wherein said thermoplastic polymer is melted by processing it in an extruder.

Claim 4

The process of claim 1 or claim 2 wherein tension is applied to said member during said initial cooling step.

Claim 5

The process of any one of claims 1 to 3 wherein the initial cooling step is performed by exposing the member to a cooling fluid.

Claim 6

The process of Claim 4 wherein said cooling fluid is air.

Claim 7

The process of Claim 4 wherein said cooling fluid is water.

Claim 8

The process of Claim 6 wherein the water is applied by spraying.

Claim 9

The process of Claim 6 wherein the member is cooled by immersing it in a water bath.

Claim 10

The process of Claim 1 wherein said thermoplastic polymer is melted by processing it in an injection molder.

Claim 11

The process of Claim 9 wherein the thermoplastic polymer is molded into the shape of a rod.

Claim 12

The process of claim 10 wherein the ends of said rod are annealed before said reheating step.

Claim 13

The process of any one of claims 1 to 11 wherein said member is preheated during said reheating step prior to the application of tension.

Claim 14

The process of any one of claims 1 to 12 wherein the step of applying tension is performed by effecting relative longitudinal movement between two spaced points on said member at a given rate until a predetermined load is applied, and then gradually reducing the rate of said relative movement.

Claim 15

The process of any one of claims 1 to 13 wherein the final cooling step is performed by exposing the member to a cooling fluid.

Claim 16

The process of Claim 14 wherein the cooling fluid is water.

Claim 17

The process of Claim 3 wherein the tension applied to said member during said initial cooling step is at a draw ratio of 3 or less.

Claim 18

The process of Claim 16 wherein the tension applied to said member during said reheating and final cooling steps is greater than the tension applied during said initial cooling step.

Claim 19

The process of claim 16 wherein the tension applied to said member during said reheating and final cooling step is at a draw ratio of between 3 and 10.

Claim 20

The process of forming a self-supporting high strength thermoplastic member comprising the steps of: melting a high molecular weight polylactide polymer; forming the molten polylactide polymer into a desired shape; immediately cooling the formed member at a controlled rate to a temperature below the glass transition temperature to cause nucleation and to form a self-supporting member; reheating the self-supporting member to a temperature above the glass transition temperature of the polylactide polymer but substantially below its melting temperature; applying tension to the self-supporting member at a controlled rate during at least a portion of said reheating step at a draw ratio of between about 2 to about 12 times the original formed length of the member to thereby obtain a high degree of molecular orientation in the self-supporting member; cooling the reheated self-supporting member to ambient temperature while maintaining the same level of tension that was applied during the reheating step; and discontinuing the application of tension after the self-supporting member has cooled to permit said self-supporting member to relax.

Claim 21

The process of forming a self-supporting high strength thermoplastic member comprising the steps of: melting a high molecular weight polylactide polymer; forming the molten polylactide polymer into a desired shape; immediately cooling the formed member at a controlled rate to a temperature below the glass transition temperature to cause nucleation and to form a self-supporting member; reheating the self-supporting member to a temperature above the glass transition temperature of the polylactide polymer but substantially below its melting temperature; applying tension to the self-supporting member at a controlled rate during at least a portion of said reheating step at a draw ratio of between about 2 to about 12 times the original formed length of the member to thereby obtain a high degree of molecular orientation in the self-supporting member; cooling the reheated self-supporting member to ambient temperature while maintaining the same level of tension that was applied during the reheating step; and discontinuing the application of tension after the self-supporting member has cooled to permit said self-supporting member to relax.

Claim 22

A self-supporting high strength member formed of a thermoplastic polymeric material capable of being absorbed in an animal body, said self-supporting member having a shape defined by final length and cross-sectional dimensions, the final dimensions of said self-supporting member being substantially different than the initial dimensions of a preformed member, the final length of said self-supporting member being at least twice the initial length of said preformed member and the final cross-sectional dimension of said self-supporting member being less than 50% of the initial cross-sectional dimension of said preformed member, said self-supporting member being highly molecularly oriented and having an ultimate tensile strength substantially greater than the ultimate tensile strength of said preformed member.

Claim 23

A self-supporting high strength member formed of a thermoplastic polymeric material capable of being absorbed in an animal body, said self-supporting member having a shape defined by final length and cross-sectional dimensions, the final dimensions of said self-supporting member being substantially different than the initial dimensions of a preformed member, the final length of said self-supporting member being at least twice the initial length of said preformed member and the final cross-sectional dimension of said self-supporting member being less than 50% of the initial cross-sectional dimension of said preformed member, said self-supporting member being highly molecularly oriented and having an ultimate tensile strength substantially greater than the ultimate tensile strength of said preformed member.

Claim 24

A self-supporting member as defined in Claim 20 wherein said member is formed of a polylactide polymer.

Claim 25

A self-supporting member as defined in Claim 20 wherein said member is formed of extruded polylactide.

Claim 26

A self-supporting member as defined in Claim 20 wherein said member is formed of molded polylactide.

Claim 27

A large profile, self-supporting, high-strength bone fixation device formed of a high molecular weight polymer of L(-)lactide capable of being absorbed in an animal body, said bone fixation device having a shape defined by a final length and cross-sectional dimensions, the final dimensions of said bone fixation device being substantially different than the initial dimensions of a preformed member, the final length of said bone fixation device being at least twice the initial length of said preformed member and the final cross-sectional dimension of said bone fixation device being less than 50% of the initial cross-sectional dimension of said preformed member, said bone fixation device being highly molecularly oriented and having an ultimate tensile strength substantially greater than the ultimate tensile strength of said preformed member.

Claim 28

A large profile, self-supporting, high-strength bone fixation device formed of a high molecular weight polymer of L(-)lactide capable of being absorbed in an animal body, said bone fixation device having a shape defined by a final length and cross-sectional dimensions, the final dimensions of said bone fixation device being substantially different than the initial dimensions of a preformed member, the final length of said bone fixation device being at least twice the initial length of said preformed member and the final cross-sectional dimension of said bone fixation device being less than 50% of the initial cross-sectional dimension of said preformed member, said bone fixation device being highly molecularly oriented and having an ultimate tensile strength substantially greater than the ultimate tensile strength of said preformed member.