Degradation and osteogenic induction of a SrHPO₄-coated Mg–Nd–Zn–Zr alloy intramedullary nail in a rat femoral shaft fracture model

Magnesium and Mg-based alloys are promising biomaterials for orthopedic implants because of their degradability, osteogenic effects, and biocompatibility. However, the drawbacks of these materials include high hydrogen gas production, unexpected corrosion resistance, and insufficient mechanical strength duration. Surface modification can protect these biomaterials and induce osteogenesis. In this work, a SrHPO₄ coating was developed for our patented biodegradable Mg–Nd–Zn–Zr alloy (abbr. JDBM) through a chemical deposition method. The coating was characterized by in vitro immersion, ion release, and cytotoxicity tests, which showed a slower corrosion behavior and excellent cell viability. RNA sequencing of MC3T3E1 cells treated with SrHPO₄-coated JDBM ion release test extract showed increased Tlr4, followed by the activation of the downstream PI3K/Akt signaling pathway, causing proliferation and growth of pre-osteoblasts. An intramedullary nail (IMN) was implanted in a femoral fracture rat model. Mechanical test, radiological and histological analysis suggested that SrHPO₄-coated JDBM has superior mechanical properties, induces more bone formation, and decreases the degradation rate compared with uncoated JDBM and the administration of TLR4 inhibitor attenuated the new bone formation for fracture healing. SrHPO₄ is a promising coating for JDBM implants, particularly for long-bone fractures.