A Bioinspired Insole Based on Shear-Stiffening Gel for Plantar Load Modulation: Material Characterization and a...

The human foot adaptively modulates stiffness during walking to balance impact attenuation, arch support, and propulsion, but this function may decline with aging and foot deformity. This study developed a bioinspired insole (bio-insole) for passive rate-adaptive plantar load modulation by embedding shear-stiffening gel (STG) within a Dragon Skin 30 (DS30) silicone elastomer backbone. DS30-STG sandwich specimens were characterized under rate-dependent and cyclic compression. A customized prototype was then evaluated in a preliminary single-case proof-of-concept walking test involving an older adult with sarcopenia, pes cavus, and hindfoot varus tendency, using stock and rigid insoles as comparators. The DS30-STG composite exhibited rate-dependent stiffening, with the apparent compressive modulus increasing from 262.11 to 553.00 kPa as the compression speed increased from 30 to 2000 mm/min, and showed short-term repeatable responses over 100 cycles at 40% strain. Compared with the stock insole, the bio-insole was associated with higher pressure-derived plantar force and peak pressure at the heel, medial arch, and first metatarsophalangeal joint. It also showed lower measured peak electromyography amplitudes of the tibialis anterior and lateral gastrocnemius by 7.8% and 9.3%, respectively, compared with the stock insole. No large observable changes were found in sagittal-plane ankle or knee excursion. These preliminary participant-specific findings suggest that the tested DS30-STG-based insole was associated with altered regional plantar loading and lower-leg muscle activation patterns during walking. Controlled studies with larger cohorts are required to determine reproducibility, tissue-loading safety, functional benefit, and clinical relevance.