Effects of hydroxyapatite (HA) particles on the PLLA polymeric matrix for fabrication of absorbable interference screws

Polymeric interference screws, especially poly(L-lactic acid) (PLLA), have gained significant attention for anterior cruciate ligament (ACL) reconstruction. In this study, a polymeric composite of PLLA with hydroxyapatite (HA) particles was made with an internal mixing chamber. A two-stage injection molding machine was used for manufacturing of interference screws. PLLA and the PLLA mixture with hydroxyapatite were used for injection molding. Different characterization techniques were used to study the physical, mechanical and biological properties of the samples. Techniques such as particle size analysis (PSA), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), energy-dispersive spectroscopy (EDS), degradation, pH analysis, and tensile testing were performed. Some in vitro assays such as alkaline phosphatase (ALP), MTT and cell attachment for MG63 osteoblastic cells were investigated. Due to a fast cooling rate of the produced screws after injection in metallic molds, the microstructure crystallinity was reduced for both of PLLA and PLLA–HA screws. The degradation rate of composite screws was 2.58% after 4 weeks. For the same duration, it was 1.16% for PLLA. The tensile strength of PLLA–HA was 21% lower compared to the PLLA screw. According to the results of in vitro cell assays, biocomposite PLLA–HA screws have improved cell attachment, and also no cytotoxic effects were observed for both groups of screws after injection.