STENT FABRICATION VIA TUBULAR CASTING PROCESSES
Tubular casting processes, such as dip-coating, may be used to form substrates from polymeric solutions which may be used to fabricate implantable devices such as stents. The polymeric substrates may have multiple layers which retain the inherent properties of their starting materials and which are sufficiently ductile to prevent brittle fracture. Parameters such as the number of times the mandrel is immersed, the duration of time of each immersion within the solution, as well as the delay time between each immersion or the drying or curing time between dips and withdrawal rates of the mandrel from the solution may each be controlled to result in the desired mechanical characteristics. Additional post-processing may also be utilized to further increase strength of the substrate or to alter its shape.
1 . A method of making a stent body, comprising
immersing a cylindrical member in a solution including a bioabsorbable polymer dissolved in a fluid, wherein the bioabsorbable polymer has an inherent viscosity of about 4.3 to about 8.4 dl/g or has a molecular weight of up to 2,120,000 g/mole,
removing the member from the solution, wherein a portion of the solution remains on the surface of the member upon removal from the solution;
removing solvent from the solution remaining on the member to form a tubular layer of the bioabsorbable polymer on the member;
repeating the immersion step, removal from the solution step, and removal of the solvent step to form a final tubular layer of bioabsorbable polymer on the member of a desired thickness; and
forming a stent body from the final tubular layer.
2 . The method claim 1 , wherein the member is removed from the solution between 15 seconds and 240 minutes.
3 . The method claim 1 , wherein the member is immersed with its cylindrical axis perpendicular to the surface of the solution.
4 . The method claim 1 , wherein the member is rotated 180 degrees prior to repetition of the immersion step.
5 . The method claim 1 , further comprising radially expanding the final tubular layer and forming the stent body from the expanded tube.
6 . The method claim 1 , wherein the solution further comprises a therapeutic agent, and the final tubular layer comprises some of the therapeutic agent.