Bioabsorbable PLA/PHA composite pins for orthopedic applications: In vitro and in vivo study

Poly(lactic acid) (PLA) is a bioabsorbable polymer that is commonly used in orthopedic implants. However, PLA implants can refracture owing to their inherent brittleness and inflammation caused by their acidic degradation products. Polyhydroxyalkanoates (PHAs) are biodegradable polyester derived from microorganisms. Some types such as poly (4-hydroxybutyrate) (P4HB), can be molded and processed at 150 ℃. PHAs can exhibit semi-crystalline or amorphous properties, depending on their composition and structure. Furthermore, PHA can be blended with PLA to enhance the stability and flexibility of the implant. In this study, we fabricated a pin-type implant composed of poly(3-hydroxybutyrate- co -4-hydroxybutyrate) (P3HB-4HB) using injection molding and investigated their applicability as an orthopedic implant through in vitro and in vivo tests. Remarkably, the PLA/PHA pin did not exhibit cytotoxicity in in vitro experiments using MC3T3-E1cells. A rat model of long bone fracture was used for the in vivo study. Overall, the brittleness of the conventional PLA was decreased by blending it with P3HB-4HB (PHA). In vivo studies revealed that the bone union rate of PLA/PHA pins was higher than that of PLA pins. The prepared PLA/PHA composite pin offers superior mechanical properties and enhanced bone healing, making them a promising implant for orthopedic applications.