Implantable medical device with biaxially oriented polymers

Abstract

Methods and systems for manufacturing an implantable medical device, such as a stent, from a tube with desirable mechanical properties, such as improved circumferential strength and rigidity, are described herein. Improved circumferential strength and rigidity may be obtained by inducing molecular orientation in materials for use in manufacturing an implantable medical device. Methods of inducing circumferential molecular orientation by inducing circumferential flow in a molten polymer are disclosed.

1 - 20 . (canceled) 
     
     
         21 . A biodegradable stent comprising:
 a cylindrically-shaped scaffold comprising a biodegradable polymer including a poly(L-lactide) based polymer, the scaffold being formed by cutting a pattern into a tube at a second diameter,   wherein the scaffold includes a plurality of interconnecting struts,   wherein the scaffold has induced molecular orientation in the circumferential direction induced by radially expanding the tube from a first diameter to the second diameter prior to cutting the pattern, the second diameter being larger than the first diameter,   wherein the induced molecular orientation increases strength in the circumferential direction of the scaffold which increases a radial strength of the scaffold,   wherein the tube is radially expanded at a temperature above a glass transition temperature (Tg) of the polymer at which an onset of segmental mobility of polymer segments occurs,   wherein at the temperature of radial expanding polymer segments have sufficient segmental mobility to move past one another as the tube is radially expanded to achieve a degree of molecular orientation that cannot be achieved at a temperatures below the Tg at which there is no onset of segmental mobility of polymer segments,   wherein the biodegradable polymer is semicrystalline and comprises crystalline domains and amorphous domains, both domains having the induced molecular orientation, and   wherein the scaffold is radially expandable by a balloon in a blood vessel in a body from a crimped state to a deployed state and the increased radial strength enables the scaffold to hold open the blood vessel when radially expanded in the blood vessel by a balloon and the balloon withdrawn.   
     
     
         22 . The stent of claim  1 , wherein the scaffold has biaxial molecular orientation since the scaffold is formed from a tube having induced molecular orientation in both the longitudinal and the circumferential directions. 
     
     
         23 . The stent of claim  1 , wherein the stent is crimped on to a balloon at a diameter less than the second diameter so that the stent can be delivered into the blood vessel.