Introduction: Poly Lactic Acid (PLA) derived from the natural resources has extensively been used as Biomaterial. It is a Bioresorbable thermoplastic which found its use in, bone plates, stents, bone screws to name a few. However, its use in pure form is limited due to its poor mechanical properties as compared to the metals. Several studies have been undertaken to study the mechanical properties of the PLA and found that, it’s brittle in nature. Thus to improve its mechanical properties, blending it with ductile polymer such as Poly-caprolactone (PCL) has been adopted. One of the major uses of the PLA in medical industry is in the stent manufacturing. Significant studies have been done on the use of the PLA/PCL as a potential material for Bioresorbable stents manufacturing. Among the various manufacturing processes used for the polymeric stent manufacturing, the most significant method is extrusion of the polymeric tube and then subjects it to post processing operations for enhancing its mechanical properties so as to make it a better material for the stent. Further stent profile cutting by cold laser changes the tube into a stent. The modification in extrusion process employed for tube fabrication is an area not adequately reported.
Materials and Methods: This study gives the insight into the effect of the manufacturing process variation on the tensile properties of biodegradable PLA and PLA/PCL blend tubes. In this study the manufacturing process of the tube is modified so that the post processing on the tubes for improving the tensile properties can be eliminated. Three different methods have been used for the tube extrusion 1). Simple Extrusion (SE), 2). Biaxial Expansion (BAE) during extrusion 3). Delayed Crystallization (DC). Further SEM of the fractured tensile surface has been done for phase morphology study.
Results: Simply extruded tubes and delayed crystallized tubes exhibits lower tensile modulus and tensile strength as compared to biaxially expanded tubes for identical wall thickness and tube diameter. Also it was found that the tubes of PLA/PCL containing 8 wt % PCL blend have better tensile properties as compared to PLA/PCL with 5 wt % PCL blend, even though incorporation of PCL increases ductility.
Discussion: This increase in the Young’s modulus can be attributed to the orientation of the polymer chains in the longitudinal and circumferential direction during the extrusion process. Due to the polymer chain alignment more force is required to deform the tube and hence higher Young’s modulus as compared to simply extruded and delayed crystallized tubes. The increase in the tensile strength and tensile modulus is attributed to the polymer chain alignment during the extrusion process. This polymer chain alignment in tube is achieved during the extrusion process in a continuous manner. Hence, further post processing treatments are not required on the tubes for enhancing their tensile properties.
Conclusion: It has been observed that the addition of PCL in PLA causes improved mechanical properties of the blend. Young’s modulus of the PLA/PCL Blend tubes is enhanced as compared to pure PLA polymer. The Young’s modulus of PLA/PCL Blend containing 5wt% PCL tubes ( biaxially expanded during extrusion) is highest and is comparable with PLA/PCL Blend containing 8wt% PCL ( biaxially expanded during extrusion) tubes.
The average tensile strength of PLA/PCL Blend containing 8wt% PCL tubes ( biaxially expanded) is highest among the tested tubes of the PLA/PCL blends closely followed by the PLA/PCL Blend containing 8wt% PCL tube (simply extruded).