The Istituto Italiano di Tecnologia (IIT-Italian Institute of Technology) has designed and prototyped a motorless, flexible, waterproof prosthetic foot inspired by the anatomy of the human limb, called the SoftFoot Pro bionic foot. IIT says its design is unique on an international level and aims to serve both as a flexible technological prosthesis for people with limb loss and as a solution for the humanoid robots of the future.
IIT obtained two international patents for some of the device’s key technological solutions, and a third patent is under evaluation by the European Patent Office. SoftFoot Pro is designed to be used on uneven terrain, including slippery grounds, where it is typically more challenging for prosthetic users, and for robots, to maintain balance.
“What prostheses and today’s humanoid robots have in common is the characteristic of having flat or low compliant feet, developed to ensure maximum stability but incapable of adapting to changes in terrain contour, slope, and different positions such as kneeling or bending,” said Manuel G. Catalano, PhD, a researcher in the Soft Robotics for Human Cooperation and Rehabilitation Lab at IIT.
Soft Foot Pro weighs approximately 450 grams and can support loads of up to 100 kilograms. It consists of a mobile arch mechanism in titanium (or aeronautical-grade aluminum alloy) whose ends are connected by five high-strength plastic chains arranged in parallel to simulate the plantar fascia of human feet. These chains are traversed lengthwise by a high-performance, mechanically inextensible cable of 210 millimeters, connected at the heel. Each chain is characterized by multiple modules made of high-strength plastic derived from automotive technologies and linked to each other by pairs of elastics. The arch system and the elastic chains constitute the artificial equivalent of the architecture composed by tarsus, metatarsus, and phalanges of the human foot.
This specific architecture allows the replication of the windlass mechanism, which progressively stiffens the plantar fascia to evenly distribute the force applied on the ground during walking. This aspect is crucial for the gait of those wearing SoftFoot Pro, as it contributes to a more efficient negotiation with the obstacle and, as consequence, to a better forward propulsion during the step together with a better energy efficiency during the final phase of stance. At the same time, the adaptable and elastic feature of the sole helps with absorbing approximately 10-50 percent of the impact on the ground.
Moreover, unlike the rigid prostheses on the market, SoftFoot Pro can change its shape. This allows the foot sole to deform and to adapt to the roughness of the terrain and any obstacles, minimizing them, improving the naturalness of the step, and enhancing the stability of the user. In this sense, the prototype embodies a form of artificial intelligence, enhancing the system’s autonomy and management capabilities in harmony with the sensorimotor characteristics of the human being.
Because of its flexibility, the prosthesis reproduces the natural positions assumed by the human foot and allows for performing simple everyday actions, such as bending down to tie a shoe, or picking something up from the ground, which also improves walking on stairs. Being waterproof makes it adequate to be used outdoors, on grass, beaches, and slippery terrain, avoiding the need for the user to switch to an activity-specific prosthesis.
The prototype was shown to the public for the first time during the G7 Health track technical event about lifelong prevention for healthy and active aging. The event, held in Genoa, Italy, July 11-12, was organized by the Italian Ministry of Health in collaboration with IIT.
The meeting focused on the second priority of the G7 Health track and was embedded within the Third Health Working Group of the G7 presidency and its high-level session on artificial intelligence. The two main themes were lifelong prevention and innovation.
Various SoftFoot Pro prototypes have been tested by individuals with unilateral lower-limb amputations as part of international collaborations with Hannover Medical School, Germany, and the Medical University of Vienna, Austria. The foot has been also successfully tested with the quadruped robot Anymal at the Federal Institute of Technology Zurich and the humanoid robot HRP-4 at the University of Tokyo.
Editor’s note: This story was adapted from materials provided by IIT-Italian Institute of Technology.
To see a video of the device, visit the IIT website.
