Surface engineering of bone screws from perspectives of biomechanics and mechanobiology.

Bone screws are widely used in orthopedic and craniofacial surgery. However, adverse outcomes such as screw loosening frequently occur, often attributed to poor biomechanical and mechanobiological integration at the bone-implant interface. Surface engineering has been extensively applied to enhance the bone-implant interface. Although significant progresses has been made in the field of surface engineering, existing research has primarily focused on material characterization and biological evaluation. There is currently a lack of a theoretical framework that can systematically guide the design of bone screw surface engineering based on the biomechanical and mechanobiological requirements of the bone-screw interface, thereby synergistically enhancing both the primary and long-term stabilities of the screw. In this review, we first discussed biomechanical failure mechanisms and mechanobiological responses at the bone-screw interface, and then summarized various surface engineering strategies for designing of different surface characteristics to meet the biomechanical and mechanobiological requirements of the interface, and finally discussed evaluation methods and standards for surface-engineered bone screws. Unlike previous reviews, which primarily classified surface engineering based on material type, manufacturing techniques, or biological function, this review aims to integrate biomechanics, mechanobiology, and surface engineering into a unified framework for rational bone screw surface design.