From Conventional Biomaterials to Smart Bioactive Interfaces: Surface Engineering Strategies for Next-Generation Orthopedic Implants

The long-term success of orthopedic implants depends not only on their mechanical performance but also on their ability to establish a stable and biologically active interface with surrounding tissues. Despite the widespread clinical use of metallic, ceramic, and polymeric biomaterials, implant failure remains associated with insufficient osseointegration, bacterial infection, wear, corrosion, and adverse immune responses. This review provides a comprehensive overview of conventional biomaterials used in orthopedic implants and critically examines current surface engineering strategies developed to improve implant performance and longevity. Particular emphasis is placed on coating technologies, including sol–gel processing, electrochemical deposition, plasma spraying, physical and chemical vapor deposition, and CoBlast™, highlighting their influence on coating adhesion, bioactivity, and clinical performance. Recent developments in bioactive, antibacterial, immunomodulatory, and stimuli-responsive coatings are discussed, together with advances in therapeutic ion incorporation, extracellular matrix-inspired functionalization, and smart drug-delivery systems. Furthermore, the emerging role of osteoimmunomodulation, additive manufacturing, and patient-specific implant design is examined as a key driver for the next generation of orthopedic devices. By integrating materials science, surface engineering, and biological mechanisms, this work highlights current challenges and future opportunities in orthopedic implant technology, offering valuable insights for the development of safer, longer-lasting, and more biologically responsive implant systems.