It was during routine academic research at the University of Hartford when graduate student Casey Beasley, uncovered an issue in the design of current prosthetic hands that discouraged amputees from wearing them. For her honors project, she set out to develop a more realistic prosthetic finger, which she hoped would improve overall design, and ultimately, the lives of amputees.
Michael Wininger, PhD, assistant professor of the university’s master’s program in prosthetics and orthotics, and supervisor of the student honors project, told O&P Business News of his first encounter with the idea.
“I had been wanting to build a robotic hand since I arrived at the university,” he said. “But I did not have a vehicle for accomplishing that until Casey came to me with her project. She was working in the clinic and identified that [industry prosthetic] hands were just not ideal.”
Initial research showed that drawbacks in the utility and cosmetic design of prosthetic hands cause many upper limb amputees to discard them, or even opt out of using prostheses in some cases.
“Prosthetic hands have a high rate of disuse,” Wininger added. “There is ample evidence of abandonment rates between 20% and 80%, depending on the type of prosthesis. Many of the people who get their first prosthetic hand take it off because it is easier to go without.”
“Given the high rejection rates…we had to ask ourselves: ‘what could be improved to enhance either utility and, or cosmetics?’ And if we could do both…then we owed it to ourselves to try.”
Grasping a solution
The first step in finding a solution was examining the anthropometry, motor control, utility and design specifications of various prosthetic manufacturers.
Their findings showed that one key aspect that could improve the function of prosthetic hands was the design of the finger.
Individually sized fingers are critical for grip, as they provide natural movement of the hand. Yet, many popular commercially available prosthetic hands have a single set of stock phalanges, some of which use only one digit type for all four fingers. No company currently allows customization, Wininger said.
“If you look down at your hand, the fingers are all different sizes. If you go and buy a prosthetic hand…the fingers are all the same,” he said.
“The prosthesis that I wear will have the same fingers as the prosthesis you wear, even though you and I would have naturally different sized hands,” he added.
With this in mind, Beasley and Wininger created a series of 12 working prototypes of a realistic prosthetic finger that could offer more variation.
One unique aspect of the design is its biomimicry, which Wininger described as the ability to imitate the function and aesthetics of a human finger.
Covering the surface of the device is a compliant fat pad simulant, which mimics the texture of a human finger while providing vital characteristics of natural grasp.
Another level of authenticity comes from the phalangeal segments, or bones of the finger. These segments mirror the structure of a natural human finger and can be adjusted using a screw. This would allow manufacturers to produce the device in a range of sizes, while retaining the ability to alter it post-production for individual patient needs.
“It is a simple setscrew,” Wininger said. “You just back up the screw, lengthen or shorten the finger and set the screw again. We anticipate no problem fitting 95% of the population to their exact specs.”
After additional modification over several weeks, Beasley’s honors project had ended, resulting in a device that could address both the utility and cosmetic shortcomings of prosthetic hands.
Beasley is slated to speak about the prosthesis at the American Orthotic and Prosthetic Association National Assembly in September.
“Now that we have made progress toward Casey’s original ambition of improving the prosthetic finger…a bigger goal has emerged,” Wininger said. “Our intention is to [develop a] prosthetic hand, which is going to act, look and feel more like your missing hand than any other hand available.”
With the addition of three new members to the team, each bringing their own expertise, the project expanded from a simple finger design into a full hand prototype. Graduate students Derek Becker and Joseph Cassella specialize in animatronics, signal processing and control and Stephen Sousa concentrates on fabrication and machining.
“We could have stuck to the finger, but…it is far more appealing to be looking at a hand,” Wininger said. “It was a natural outgrowth.”
An initial hand prototype has already been created through combination of 3-D printing and machined plastic. Within a year, they created four additional hand-like prototypes, using 3-D printed versions of the realistic prosthetic finger.
“The current prototype that is on my desk is the best prototype,” Wininger said. “It is built on the backs of some creative, self-starting students, who take initiative and bring ideas to the table.”
Equipped with support from a Women’s Education and Leadership Fund grant and a student project grant from the a Connecticut Space Grant Consortium, the team is now finalizing the device for machining, and developing the electronics to make it work.
The design of the hand is primarily centered on mechanical and anthropomorphic considerations. In its current form the device offers three degrees of freedom, with the subsequent aim of adding more humanlike qualities.
“We are intending to give the consumer a product that looks, acts and feels just like the hand that should not be there, rather than a stock hand that came off the shelf,” he said. “If we are successful on this enterprise, it could change clinical practice.”
Wininger said the novel design offers another option in prosthetic hands and the O&P field overall.
“We hope the lessons learned from this can be applied not only to kind of broader upper limb, but also to lower limb. There is opportunity for more research that is beyond what we can do.”
He believes that with a team of open-minded, enthusiastic and savvy students, growing the dream of a simple finger into a full hand prototype can be accomplished in just a few months. “Hopefully someday into a workable solution for the patient,” he added.
With challenges ahead, accomplishing this will not be simple. Still, the team remains unwavering.
“In engineering, there is a maxim that we operate by, which is that simpler is better,” he said. “If you have a team of students who are motivated, you can accomplish anything. That is the simplest thing on the planet.” – by Shawn M. Carter
Disclosure: The current grant support is through the Women’s Education Leadership Fund (WEL-Fund) and through the CT Space Grant Consortium.