Study of engineered low-modulus Mg/PLLA composites as potential orthopaedic implants: An in vitro and in vivo study

Low molecular weight poly-lactic acid (PLLA) is a polymer matrix of orthopaedic implants. The PLLA matrix incorporating bioactive magnesium ion (Mg²⁺) enhances bone regeneration. But the optimal ratio of Mg²⁺ to PLLA matrix has not been well reported and is worthy of study. We synthesized silane-coated Mg/PLLA composites containing 1%, 2%, 3%, 4% and 5% Mg micro-particles. The mechanical properties, in vitro cytocompatibility, cell viability and osteogenesis differentiation and in vivo performance of silane-coated Mg/PLLA composites were evaluated. These results showed that the bending and tensile strength of PLLA matrix was reduced by incorporation of Mg micro-particles. Mg/PLLA composites with higher Mg micro-particles ratio showed higher Mg²⁺ leaching rate and pH value in immersion solutions. MC3T3-E1 pre-osteoblasts incubated with Mg/PLLA composites containing higher ratio of Mg micro-particles showed higher cytocompatibility, cell viability, osteogenesis differentiation and migration. In vitro cellular responses showed that MC3T3-E1 pre-osteoblasts had the highest cell viability at 50 ppm Mg²⁺. In vivo animal studies showed there was no change in serum Mg²⁺ concentration after implanting Mg/PLLA composites comparing with control and the implants of silane-coated Mg/PLLA composites accelerated bone formation. In summary, our study revealed the feasibility of silane-coated Mg/PLLA composites as orthopaedic implants. Silane-coated Mg/PLLA composites with Mg micro-particles ratio of 3% ∼ 5% were optimal substitutes for bone regeneration.