The multilayer coatings on polylactic acid implants spatiotemporally regulates the microenvironment to enhance antibacterial and osseointegration capacity

Absorbable implants such as polylactic acid (PLA), which obviate the need for secondary removal surgery and avoid stress shielding, have emerged as promising alternative internal fixation systems compared to conventional metallic implants. However, some issues hinder their widespread applications including implant-related infection, subsequent poor osseointegration and poor radiopacity, potentially resulting in implant failure or related complications, particularly in the osteoporotic patients. Herein, we constructed a multilayer coating by radiofrequency magnetron sputtering technologies to modify the PLA surface with magnesium oxide (MgO) in the outer layer, cerium dioxide (CeO₂) in the middle layer and platinum (Pt) in the inner layer. In the initial stage, the rapid degradation of MgO created a strong alkaline microenvironment to inhibit bacteria. In the later stage, as the MgO was depleted, CeO₂ and magnesium ions (Mg²⁺) acted synergistically to induce M2 macrophage polarization, suppress the senescence of bone marrow mesenchymal stem cells, and ultimately enhance osseointegration. Pt functioned as a radiopaque agent. The osteo-inductive efficacy of the Pt@CeO₂/MgO coating implants was further assessed using a femoral condyle implantation model in ovariectomy rats, which demonstrated significantly enhanced osseointegration at eight weeks post-implantation, thereby indicating their great potential as biomaterials for musculoskeletal applications.