Introduction: Poly lactic acid (PLA) obtained from the plant resources, is the most commonly and extensively used biodegradable polymer in the medical fields such as orthopaedics, cardiovascular, oral surgery. PLA offers high mechanical strength and long in vivo degradation time however, its inherent high brittleness limit its use for the medical devices fabrication.
One such medical device where the use of the PLA has caused a revolution is coronary stents. With the fabrication of the bioresorbable stents the drawbacks associated with the metallic stents has been eliminated, such as permanent presence of the stent in the coronary artery for the rest of the patient’s life, restoration of the arterial vasomotion to name a few. The manufacturing of the stent is from the polymeric tube having the desired mechanical properties (specially the radial strength), which are necessary for the proper functioning of the stent. Thus the first step in the polymeric stent manufacturing is fabrication of the polymeric tube with desired mechanical properties such as high strength, high radial strength, longer in vivo degradation time, low elastic recoil.
Material and Methods: In this study, the blends of PLA with PolyCaprolactone (PCL) were made with different wt % (5% and 8%)of PCL. The tubes of PLA/PCL blends were were extruded using two different ways for the tube extrusion 1. Simple extrusion 2. Biaxial expansion of the tube during the extrusion process. Extruded tubes were subjected to radial strength measurement, by subjecting to internal pressure which was increased at a constant rate. For radial strength measurement, the tubes were subjected to internal pressure which increases at a constant rate. Then change in the tube diameter with respect to increase of the internal pressure is reported in this paper. Further Scanning Electron Microscopy(SEM) of the bursted tube samples was performed to get the information about the surface morphology and difference in the fracture mode id any, between the simply extruded and biaxially expanded tubes of different PLA/PCL blends.
Subsequently, fluid structure interaction (FSI) simulation for the radial strength measurement for different PLA/PCL blends tubes is conducted and the results obtained from the simulations are compared with the experimental results.
Results: It has been found that the PLA/PCL tubes manufactured by the biaxial expansion during the extrusion process has better radial stregth as compared to the simply extruded tubes. In the PLA/PCl blends tubes containing 5 wt%PCL biaxially expanded tubes has the highest radial strength followed by the PLA/PCL simply extruded tube containing PCL 8wt%.
Discussion: This increase in the radial strength of PLA/PCL blends tubes containing 5 wt%PCL and biaxially expanded tubes, can be due to the increased alignment of the polymer chains in the radial direction due to biaxial expansion during the extrusion process. PLA/PCL blend tubes with high radial strength resist the radial forces(internal pressure ) acting in that direction. Also higher percentage of PLA in PLA/PCL with 5wt % can be the cause of the higher radial strength as PLA has higher strength as compared to PCL. Also the processing method used for the tube fabrication can be the reason for the increased radial strength.
Conclusion: Among the tested PLA/PCL blends, PLA/PCL with 5wt% PCL and biaxially extruded is better material for the stent manufacturing.The PLA/PCL with 5wt% PCLblend has higher radial strength (burst pressure) which is the most significant property required for the proper functioning of the polymeric stent. Also the brittleness of the pure PLA has been reduced by the addition of the PCL. Another suitable candidate for the polymeric bioresorbable stent manufacturing can be PLA/PCL with 8wt% PCL and simply extrudedas this material has slightly lower radial strength in comparision with the with the PLA/PCL with 5wt% PCL and biaxially extruded. hence, the fabrication method used for the tube manufacturing can manufacture the tubes with different properteis in different directions.