Laser-Engineered Black TiO2/UHMWPE Nanocomposites: Tribomechanical Response and Potential for Biomedical Bearing Applications

Wear of ultra-high-molecular-weight polyethylene (UHMWPE) remains a limitation for long-term orthopedic bearing performance. This study investigated how pulsed laser irradiation in liquid (PLIL)-induced modification of TiO2 affects the mechanical and tribological response of UHMWPE nanocomposites containing 0.1–1.0 wt% TiO2. PLIL changed TiO2 from predominantly irregular/angular particles with an anatase-dominant composition (~56% anatase/44% rutile) to a greater prevalence of rounded particles with a rutile-dominant balance (~41% anatase/59% rutile). TiO2 incorporation produced a statistically significant but moderate microhardness increase, reaching 4.19 ± 0.12 HV0.05 at 1.0 wt% untreated TiO2, approximately 25% above neat UHMWPE. Tribological behavior was formulation dependent: 0.5 wt% PLIL-modified black TiO2 exhibited the lowest mean wear volume (2.06 ± 0.02 mm3), 13.1% below neat UHMWPE (2.37 ± 0.23 mm3), although the difference was not statistically significant (p = 0.739). Maximum microhardness, minimum terminal friction, and minimum mean wear occurred in different formulations, demonstrating that these responses are partially decoupled. Nanoparticle state and concentration jointly governed the tribomechanical response within the investigated low-filler regime.