Balancing comfort and safety in transfemoral prosthetic sockets through finite-element modelling of interface mechanics

The mechanical interaction at the limb–socket interface is a critical determinant of user comfort and skin integrity; however, the specific contributions of the coefficient of friction (μ) and Poisson’s ratio (ν) have not been quantitatively established. Objective: The objective of this work is to evaluate how μ modulates stresses in the residual limb and its potential association with socket safety, and to determine how ν governs socket maximum stress and structural safety margins. Methods: Above-knee finite-element (FE) model (elastic-plastic socket/base, first-order Ogden limb, rigid femur; C3D4H mesh) with parametric sweeps of μ (0.30–1.00) and ν (0.10–0.49) across polyethylene (PE), polyethylene terephthalate glycol (PETG), and high-performance carbon-fiber-reinforced polymers (HCFRPs). Results: Residual limb soft-tissue maximum Von Mises stress showed a U-shaped dependence on μ with a minimum near 0.7; the socket stress-to-yield ratio was largely insensitive to μ but differed by material (largest margin for HCFRPs, intermediate for PETG, smallest for PE). Increasing ν reduced socket maximum Von Mises stress by ~16–18% from 0.10 to 0.50 for all materials, with the ranking of safety margins (HCFRPs > PETG > PE) consistent with that observed in the μ analysis. Conclusions: Specifying a mid-range μ (~0.7) together with socket materials of higher ν (0.40–0.50) constitutes an effective strategy to reduce soft-tissue stresses while preserving structural safety, thereby offering biomechanical criteria for liner selection and material specification.