Design of novel orthotic insoles based on partition infilling of TPMS structures

Abstract

Introduction – Excessive plantar pressure has been recognized as a key risk factor for diabetic foot ulceration. Methods – To address this problem, a partition-infilled functional insole based on triply periodic minimal surface (TPMS) lattice structures was proposed and systematically investigated. First, the mechanical responses of three representative TPMS structures, namely Gyroid, Diamond and Primitive, were characterized by compression experiments and finite element (FE) analysis. Subsequently, a partition infilling strategy was designed according to distribution of the plantar pressure. Under additive manufacturing constraint of minimal thickness of 0.2 mm, different TPMS lattices were assigned to specific plantar regions. Results – Gait experiments and FE results demonstrated that, compared to a uniformly Gyroid-infilled insole and a single-lattice gradient-infilled insole, the partition-infilled insole achieved significant reductions in both peak and mean pressures. A Primitive lattice in the heel region exhibited superior pressure-relief performance, whereas Gyroid and Diamond lattices in the forefoot and midfoot balanced cushioning with overall structural stability. Owing to the mathematical definitions of different TPMS structures, smooth topological transitions between lattices were enabled, further improving comfort and manufacture ability. An integrated design-manufacturing framework for personalized diabetic insoles was established. Discussion – The potential of TPMS partition infilling for redistributing plantar loads and reducing ulceration risk was verified, providing theoretical and experimental support for subsequent clinical applications and large-scale additive manufacturing.