3D-Printed Insole Designs for Enhanced Pressure-Relief in Diabetic Foot Based on Functionally-Graded Stiffness Properties

To effectively reduce the incidence of foot ulcerations in people with diabetes, a novel workflow was proposed to design, manufacture, and evaluate the offloading insoles for diabetic foot. In this study, the stiffness and morphological aspects of the insole were altered to accommodate the diabetic foot and four types of insoles were designed, namely the ordinary flat insole, flat insole with graded-stiffness, total contact insole (TCI) and TCI with graded-stiffness. Porous elements with different elastic moduli were designed and used in different sub-regions of the insoles to realize functionally-graded stiffness properties. The relationship between structural parameters and its modulus was determined through mechanical tests and finite element analysis. The insoles were manufactured using a fused deposition modelling (FDM) 3D-printing technology and its unloading capacities were evaluated using patient-specific plantar pressure analysis. The results revealed that the TCI with graded-stiffness reached the optimal offloading effects by reducing the peak pressure of the foot by 52.8% in static standing state and pressure-time integral by 18.43% in gait conditions. The methodology framework built in the study can serve as a useful foundation to produce functional insole designs to meet patient-specific needs. Such functional-graded-stiffness insoles can potentially be made as an off-the-shelf product, which are critical for the prevention and treatment of foot ulcers in people with diabetes.