Biocompatibility evaluation of titanium nitride coating for canine patellar groove implant

Medial patellar luxation is a common orthopedic disorder in dogs, and advanced cases with severe skeletal deformities or femoropatellar osteoarthritis are often unresponsive to conventional techniques. Patellar groove replacement (PGR) has been proposed as an alternative surgical option; however, systematic comparisons of coating technologies for veterinary PGR implants remain limited. This study aimed to evaluate the physicochemical properties, biological compatibility, and functional performance of a newly developed titanium nitride (TiN)–coated PGR system compared with a clinically available amorphous diamond-like carbon (ADLC)–coated device. TiN-coated prototypes were fabricated using Ti-6Al-4V alloy by injection molding combined with arc ion plating, which requires simpler equipment and lower production costs than the vacuum plasma deposition used for ADLC. Physicochemical evaluations, including corrosion resistance, hardness, surface roughness, and coating thickness, were conducted following International Organization for Standardization (ISO) and Korean Industrial Standards (KS) guidelines. In vitro biocompatibility was assessed using MTT and cell adhesion assays with L-929 fibroblasts, while inflammatory cytokine profiling (interleukin [IL]-1β and IL-6) in a rat subcutaneous model was used to evaluate local tissue responses. Functional feasibility was examined in a canine femoral model bilaterally implanted with TiN- or ADLC-coated PGR systems and monitored for one year through clinical, radiographic, computed tomography (CT), magnetic resonance imaging , and micro-CT assessments. Both coatings demonstrated excellent corrosion resistance and absence of cytotoxicity. TiN-coated implants showed slightly greater hardness and coating thickness, with comparable surface roughness and biocompatibility. All implants maintained stable fixation, proper patellar tracking, and satisfactory bone–implant integration. These findings indicate that TiN-coated PGR implants achieve biological and mechanical performance equivalent to ADLC devices while offering advantages in manufacturing simplicity, scalability, and cost-efficiency, supporting their clinical applicability in veterinary orthopedics.