Building a viable prosthetic hand—one that users can trust and integrate into their daily lives—requires that they recognize they have a hand without looking at it. When a user pulls open a door without looking at it, he or she needs to know where each finger is and feel the pressure of the door.
Touch feedback and joint location sensing, known as proprioception, are two key developments in the prototypes for a prosthetic hand developed in the lab of Tim Bretl, an associate professor in aerospace engineering and Beckman faculty member in the Artificial Intelligence Group. The project is led by Aadeel Akhtar, an M.D./Ph.D. candidate in neuroscience.
“Commercial prosthetic hands are severely limited in providing sensory feedback,” said Akhtar, who started working on developing prosthetics in 2013, and has been working on incorporating sensory feedback after the group traveled to Ecuador last summer to test on Juan Suquillo, a patient with a below-elbow amputation sustained during a war injury.
“We have a prototype finger now that has a pressure sensor built in. When you press the finger down, a correlating amount of electrical current will be sent through and across your skin, and your brain will perceive it as an actual feeling. The harder you push down, the stronger the sensation feels.”
Even though the sensation currents are sent through the forearm, Akhtar said the brain is remarkably adaptable and will rewire to associate the sensations in the forearm with movement in the fingers.
We have a prototype finger now that has a pressure sensor built in. When you press the finger down, a correlating amount of electrical current will be sent through and across your skin, and your brain will perceive it as an actual feeling. - Aadeel Akhtar
“The brain is plastic and will rewire itself pretty readily,” said Akhtar. “Prior studies have shown that your brain will start to think it’s your finger that’s feeling it, rather than your forearm.”
The mechanism used to generate the electrical current in the forearm currently requires a power supply connected to a wall outlet. But their newest prototype is battery operated and has been reduced to the size of a credit card, allowing the researchers to embed all of the electronics into the socket between the prosthetic and the arm.
The group also implemented joint sensing into the latest prototype. When users can’t feel how their joints are moving, they often abandon their prosthesis, says Akhtar.
“If you have a prosthetic device, when your eyes are closed and you move it around, you have no idea where it is,” said Akhtar. “That’s a huge problem. In order for people to use their prosthetic, they have to constantly look at it, and because of that, they’ll just use their other hand, often abandoning the prosthetic entirely.”
To combat this problem, the researchers have developed a cost-effective solution. A small contact pad adhered to the skin connects to the finger via a wire that will stretch the skin an amount proportional to the angle of the finger when it moves.
“Through this skin-stretching mechanism, we give proprioception back to the user in a way that is inexpensive, simple, and intuitive. We can apply this mechanism to any existing prosthesis, and we have plans to integrate it with prostheses not only in the United States, but in developing countries as well,” said Akhtar.
Akhtar and one of his undergraduate students in mechanical science and engineering, Patrick Slade, plan to launch a start-up called PSYONIC to sell their prosthetic for $1,000–3,000—a fraction of the cost of prosthetics on the market today, which typically range from $30,000–40,000. This low cost will make it especially accessible to people in developing countries. The group won the overall $15,000 grand prize, as well as the $10,000 Samsung Research Innovation grand prize, in the Cozad New Venture Competition, a program at the University of Illinois designed to encourage students to create new businesses.
To create a stronger and more durable prosthetic, the group will switch from 3D printing and implement injection molding in the manufacturing process, which infuses heated material into the plastic mold. They will also use rubber on the outside of the hand to absorb impact and mold over the sensors used for feedback.
Many of these changes to the prototypes were built with design in mind. The group wanted to make the prosthetic more anthropomorphic—to look and feel like a normal human hand.
Akhtar has been working with Cliff Shin, an assistant professor in industrial design and member of Beckman’s Cognitive Neuroscience Group, to build a model that looks more aesthetically pleasing, with the hope that it is more readily accepted by users. It also has a smooth surface that will allow users to put on silicon gloves to match their skin tone.
After PSYONIC launches, Akhtar hopes the group, comprised of disciplines ranging from computer engineering to graphic design, will be selling their low-cost prosthetic hand to those in need.
Those involved in the group include: Tim Bretl, associate professor, aerospace engineering; Mary Nguyen, M.S. student, aerospace engineering; Patrick Slade, mechanical science and engineering junior; Joseph Sombeck, bioengineering junior; Jesse Cornman, computer engineering sophomore; Michael Fatina, computer engineering sophomore; Edward Wu, computer engineering sophomore; Alvin Wu, computer engineering sophomore; Sam Goldfinger, electrical engineering senior; Daniel Gonzales, electrical engineering sophomore; Hafsa Siddiqui, graphic design senior; and Liz Ochoa-Raya, molecular and cellular biology senior.