Effect of Al₂O₃ nanoparticle reinforcement and annealing on PMMA composite performance for prosthetic feet

Polymethyl methacrylate (PMMA) is a biocompatible polymer widely used in prosthetic applications, yet its limited stiffness and strength restrict its performance under the cyclic loads imposed by lower limb prosthetic feet. This study investigates the combined effect of Al₂O₃ nanoparticle reinforcement and post-fabrication heat treatment on the mechanical and structural performance of PMMA-based nanocomposites for prosthetic foot applications. Nanocomposite samples containing 0, 2.5, 5, 7.5, and 10 wt% α-Al₂O₃ nanoparticles were fabricated using a silane-assisted compounding route and subsequently annealed at 80 °C, 110 °C, and 140 °C for 15 min. XRD confirmed the phase stability of the α-Al₂O₃ reinforcement and the absence of new crystalline reaction products, while scanning electron microscopy (SEM) revealed progressive densification of the particle-matrix interface up to 110 °C. The optimal formulation, P7.5 A annealed at 110 °C, in which the optimal Young's modulus and a compressive yield strength have been achieved, representing improvements of + 71.1% and + 22.2%, respectively, over neat PMMA. A finite element model (FEM) of a prosthetic foot was developed in ANSYS. FEM results showed that P7.5 A/110°C reduced total structural deformation by 40.2% relative to neat PMMA. These findings demonstrate that PMMA reinforced with 7.5 wt% Al₂O₃ and annealed at 110 °C offers a well-balanced combination of stiffness, strength, and structural safety suitable for lower limb prosthetic foot applications.