Design of a bio-inspired foot based on the functional anatomy and biomechanics of the natural human foot

BACKGROUND: Prosthetic foot users often face secondary physical complications such as lower back pain [1] and osteoarthritis in the hips and knees. Individuals with an amputation are particularly susceptible to knee osteoarthritis in their intact limb due to asymmetrical gait and resulting abnormal joint kinematics and kinetics [2]. Limited range of motion (ROM), comfort, and energy handling in the current prosthetic feet contribute to these issues, prompting a need for prosthetic foot designs that better mimic natural foot biomechanics.

AIM: The aim of this study was to develop a bio-inspired foot which is based on the functional anatomy and biomechanical principles of the natural human foot, with a specific focus on enhancing ROM (flexibility and adaptability) and energy handling (storage and return).

METHOD: A comprehensive literature review was conducted to understand the functional anatomy and biomechanics of the natural human foot. This knowledge was used to design a first prototype of the bio-inspired foot (Figure 1A), which was fabricated from PLA. Gait was simulated manually in a gait lab and motion tracking and force plate data were acquired to assess performance and functionality using different spring stiffnesses, thereby measuring e.g. ROM and energy handling.

RESULTS: The bio-inspired foot demonstrated plantarflexion and dorsiflexion angles of 14 and 21 deg, respectively, during stance. Maximum ROM tests, with low spring stiffness configurations, showed 21 deg of plantarflexion and 23 deg of dorsiflexion in the talocrural joint. The talocalcaneal joint reached 9 deg of eversion and 13 deg of inversion, whereas the first MTP joint reached a maximum ROM of 18 deg. In addition, the bio-inspired foot demonstrated varying energy storage across spring stiffness configurations (Figure 1B & 1C).

DISCUSSION AND CONCLUSION: This study resulted in the design of a bio-inspired foot with arches, plantar fascia, Achilles tendon and primary motion axes of the natural human foot by replicating the talocrural axis, talocalcaneal axis and MTP axes. The bio-inspired foot demonstrated notable ROM and storage of energy with adjustable spring stiffnesses for adaptability. Further research is needed to validate its performance under real-world conditions.