Wear and tribocorrosive performance of DLC coating at the screw-rod interface in the Guided Growth Spinal Systems

Early-onset scoliosis poses a particular challenge, as treatment must correct spinal deformity while preserving longitudinal growth, which growth guidance systems (GGS) address through controlled, sliding kinematic mechanisms. However, friction-driven wear and tribocorrosion within these interfaces generate debris and degradation, yet the underlying mechanisms in individual kinematic nodes remain insufficiently characterised. This study expands previous dry-friction research by evaluating the tribological performance of conforming screw–rod interfaces from a Ti-6Al-4V GGS stabilisation system under corrosive conditions. Two surface variants were examined: components with a standard passive layer and those coated with a DLC coating. Tests were conducted in distilled water (simulating physiological conditions) and acid sodium lactate solution (representing an inflammatory environment). Friction coefficients, surface wear, wear debris morphology, surface properties, and pH variations of the surrounding medium were systematically analysed. The quantitative wear analysis and geometric profile characterisation were specifically focused on the sliding screw caps. The results demonstrate that inflammatory conditions significantly intensify frictional and wear processes, particularly in passive layer components. DLC-coated pairs exhibited markedly lower static and kinetic friction coefficients, reduced mass loss, and improved mechanical resistance. Increased microhardness, stable wettability, and defined scratch-resistance thresholds confirmed the protective role of the coating. pH measurements revealed greater tribocorrosion activity in passive layer pairs, whereas the DLC coating mitigated environmentally induced degradation. Overall, the findings substantiate the beneficial effects of DLC coatings in enhancing the tribological durability of GGS kinematic pairs under physiologically relevant corrosive conditions.