Deformation of a polymer tube in the fabrication of a medical article
Methods of manufacturing a medical article that include radial deformation of a polymer tube are disclosed. A medical article, such as an implantable medical device or an inflatable member, may be fabricated from a deformed tube.
1. A method for fabricating an implantable medical device comprising:
treating at least a portion of a tube comprising a polymer with a solvent capable of inducing crystallization in the polymer;
radially and axially deforming the tube including radially deforming the tube between 100% and 400% while the tube has a temperature above the glass transition temperature of the polymer of the tube; and
fabricating the implantable medical device from the deformed and treated tube;
wherein the implantable medical device is a stent and the polymer is PLLA.
2. The method of claim 1 , wherein inducing crystallization of the polymer occurs before the deforming step and lowers the glass transition temperature of the polymer,
wherein the temperature during the radial and axial deformation is above the lowered glass transition temperature.
3. The method of claim 1 , wherein the device is a stent and the inducing crystallization of the polymer modifies the radial strength of the stent.
4. The method of claim 1 , wherein treating at least a portion of the tube with a solvent comprises immersing at least a portion of the tube in the solvent, spraying at least a portion of the tube with the solvent, and/or applying the solvent to at least a portion of the tube.
5. The method of claim 1 , wherein treating at least a portion of the tube with the solvent decreases a crystallization temperature of the polymer of the tube.
6. The method of claim 1 , wherein at least the portion of the tube is treated with the solvent prior to, contemporaneously with, and/or subsequent to deforming the tube.
7. A method for fabricating a stent comprising:
while a polymer tube made from PLLA has a temperature greater than the glass transition temperature of the polymer, biaxially orientating the molecular structure of the polymer including radially deforming the tube between 100% and 400% and axially deforming the tube including applying a tension to produce a controlled rate of axial deformation of the tube;
heat setting the deformed tube above the glass transition temperature including maintaining the between 100% and 400% radial deformation of the tube by maintaining an internal pressure within the tube;
applying a solvent for the polymer of the tube to induce crystallization in the polymer; and
laser cutting the tube to produce a network of interconnected struts, wherein the combination of the biaxially oriented molecular structure and crystallization in the polymer are such as to produce an increase in the radial strength of the stent.
8. The method of claim 7 , wherein radial deforming includes controlling a rate of pressure increase within the tube to produce radially-outward directed force applied to the luminal surface of the tube to produce a controlled rate of radial deformation of the polymer tube.
9. The method of claim 1 , wherein immediately following the radial deformation of the between 100% and 400% maintaining a pressure within the tube and the temperature above the glass transition temperature for between about 2 and 20 minutes.