Fabrication of medical footwear for suitable distribution of stress and strain and reduction of plantar pressure by numerical and experimental approaches

Abstract

Medical insoles and orthopedic shoes are responsible for reducing the force exerted by the ground to the plantar region of the feet. This combination is designed to develop a suitable distribution of stress and strain in the plantar region. In the present study, attempts have been made to design a prototype of medical footwear which can provide a proper stress and strain distribution in the plantar region while reducing pressure in comparison with current orthopedic footwear. For this purpose, the hyper-elastic behavior materials, including styrene-butadiene rubber, silicon, Plastazote foam, polyfoam, ethylene-vinyl acetate foam, polyurethane foam, and polyurethane, have been investigated, with different degree of hardness as well as one layer of composite with Kevlar fiber, whose effect is reducing the pressure exerted to the feet. A combination of materials was used to construct an insole sample, and uniaxial pressure tests were performed for testing its mechanical properties. Then, these properties were used in finite element analysis, whereby the best type of insole for the footwear was chosen and fabricated. The results of finite element analysis were validated using Pedar system and after performing the experimental tests both statically and dynamically. Experimental and numerical investigations suggested that the sole material of orthopedic shoe should be selected as styrene-butadiene rubber. The internal layers of styrene-butadiene rubber frame from top to bottom should be comprised of Plastazote-polyurethane with Kevlar fiber-silicon shore A6, which can be a suitable orthopedic boot in terms of proper stress and strain distribution. Generally, it could reduce the pressure exerted to the sole by 79% compared with barefoot.