Those over a prosthetic foot cannot walk naturally with this in many cases. A new kind of foot prosthesis should change this. The shape and stiffness of this prosthesis is precisely tuned to the wearer's body weight and height, allowing them to use the prosthesis in a much more natural way.
The new foot prosthesis has been developed by the Massachusetts Institute of Technology (MIT). Foot prostheses are constantly being further developed. For instance, prostheses are now available that are equipped with all kinds of sensors and deploy artificial intelligence (AI) to translate signals from users to mimic natural movements of the lower leg. However, such advanced prosthetics are very expensive and therefore out of reach for many users.
Simpler design and lower costs
MIT has therefore developed a new foot prosthesis that is a lot simpler and cheaper than these high-tech prosthetics. It is a passive prosthesis, whose shape and stiffness can be tailored to the wearer's body weight and height. This is important, as these characteristics significantly affect how users cope with their foot prosthesis.
The new prosthesis contains no sensors and also does not use AI. Because of its relatively simple design, the MIT researchers expect that their prosthesis - if produced on a large scale - can be brought to market many times cheaper than existing high-tech prostheses. The researchers expect to reduce the cost of a prosthesis from thousands of dollars to a few hundred dollars.
Adjusting stiffness and geometry to user
The prosthesis is based on a framework developed by researchers at MIT. This framework allows accurate mapping of users' walking behaviour. "Walking is something that is very natural for us humans. However, for the part of the cloud whose lower leg has been amputated, no theory is available that allows us to determine exactly how the stiffness and geometry of a foot should be designed to allow you to walk the way you want," explains Amos Winter, professor of mechanical engineering at MIT. "Now we can do this, which is very valuable."
Winter developed the prosthesis in collaboration with Jaipur Foot, a prosthetic foot manufacturer based in Jaipur, India. This company develops passive foot prostheses aimed at developing countries. "They have been making this foot for over 40 years. It (ed: the prosthesis) is durable, so farmers can use it barefoot outside. Also, the prosthesis looks lifelike, so people can enter a mosque and pray barefoot without being stigmatised in the process," Winter explains. "However, the prosthesis is fairly heavy and the internal structure is made by hand, so there is a wide variation in product quality."
Design lighter foot prosthesis
Jaipur Foot has therefore asked Winter to design a new lower-weight foot prosthesis that can be mass-produced at low cost. Winter points out that many designers of foot prostheses try to mimic movements of human feet and ankles. However, Winter's team points out that amputees have no sensation in their foot prostheses and therefore do not feel what their prosthesis is doing. "One of the critical insights we have gained is that for a user, the foot is like a black box - it is not connected to their nervous system and they are unable to interact with the foot," Winter said.
The team therefore did not focus on designing a foot prosthesis that tries to artificially mimic the movements of a human lower leg, but rather a prosthesis that, thanks to its shape and stiffness, makes the same movements as the human lower leg while walking due to the movements of the upper leg. "Ideally, we perfectly tune the stiffness and geometry of the flaw so that we exactly replicate the movements of the lower leg," says Winter. The professor points out that his team's prosthesis can achieve these natural movements very accurately.
Computer simulations
The ideal shape of a prosthesis to enable natural movements has been determined through computer simulations. This involved creating a large number of digital designs of foot prostheses, which were then analysed using algorithms to map the movements of the lower leg. The designs with the most promising results were then further developed and simulated again, leading to the final design.
MIT team announces collaboration with Vibram, an Italian company that develops rubber shoe soles. This company will develop a 'shell' for the foot prosthesis that should give the prosthesis a lifelike appearance. In addition, the casing should also ensure sufficient grip on muddy or slippery surfaces. The prosthesis and this shell developed by Vibram are expected to be tested on volunteers in India in spring.
Author: Wouter Hoeffnagel
Source: MIT (photo)
