3D printable insole with TPMS lattice for relieving foot plantar pressure and shear forces

Human feet are subjected to pressure forces during walking or running. However, these pressures are not equally distributed over the entire regions of the foot. The increase of pressure in one area regardless of the others can lead to serious medical issues such as foot ulceration in diabetic patients. Plantar pressure and shear stress are the main components that contribute to this caution. Medical insoles are usually prescribed to prevent this critical situation or to treat the foot by decreasing the feeling of pain. This study proposes a design of 3D printable medical insole that contains lattice structure of triply periodic minimal surfaces (TPMS) unit cells in order to relieve plantar pressure and shear stress on the foot. To test the eligibility of this topology, TPMS specimens were created using nTopology software and subjected to a finite element analysis. Samples from EVA foam and other lattice structures were also tested under compression and elasticity modulus was calculated. After comparisons, the most appropriate combination of cell size and strut diameter of TPMS unit cells was selected for both hard and soft sections of the insole. The resultant unit cells were utilized in the final design of a full insole with TPMS lattice structure, and another insole with Fluorite lattice structure.