Mantis Shrimp-Inspired Quasi Passive Ankle-Foot Prosthesis

Area of Science:

• Biomimetics and Mechanical Engineering
• Prosthetics and Orthotics

Background:

• Biological ankle joints dynamically adjust stiffness for varied walking conditions.
• Current passive ankle-foot prostheses (AFPs) lack variable stiffness, leading to gait abnormalities.
• Powered AFPs are heavy, bulky, and energy-inefficient due to large actuators.

Purpose of the Study:

• To develop a quasi-passive, variable-stiffness ankle-foot prosthesis.
• To mimic the energy-storing saddle spring mechanism of the mantis shrimp.
• To provide adaptive stiffness for improved gait in lower-limb amputees.

Main Methods:

• Developed governing equations to parameterize the mantis shrimp saddle spring geometry.
• Optimized saddle spring curvature and thickness for biological ankle stiffness at normal walking speeds.
• Optimized the moment arm to achieve a range of stiffness for varying walking speeds.

Main Results:

• The designed saddle spring allows adjustable dorsiflexion stiffness from 8.63 to 18.43 Nm/° for a 100 kg user.
• Stiffness adjustment time is rapid, completing the range in 0.3 seconds.
• Theoretical model validated through experimental bench tests.

Conclusions:

• The developed prosthesis offers prompt, user-specific stiffness adjustment.
• This biomimetic design provides a compact, lightweight, and energy-efficient solution for lower-limb prosthetics.
• The variable-stiffness AFP shows promise for enhancing daily living for amputees.