Student adds functionality to 3D-printed prosthetic hands Wednesday, 12 July 2017

Using 3D printers to print prosthetics and tissue as a low-cost option for people is growing at a rapid pace.

From limbs to organs, engineers are teaming up with medical professionals to create products that were once the realm of science fiction.

One student at the University of Sydney is taking that one step further with work on a 3D-printed prosthetic hand that overcomes some of the challenges of traditional prosthetics, such as their high cost and limited usefulness.

Kristina Mahony, a biomedical engineering student, has been working with Dr Justin Bobyn, an orthopaedic registrar at Westmead Hospital, to develop the 3D-printed prosthetic.

Traditional prosthetic hands are attached to an amputee with a harness system, with the prosthetic moving based on abducting their shoulder muscles, which pulls on a cable on the harness to change the grip type of the hand.

Mahony is using this concept to develop a 3D-printed prosthetic that gives users a greater range of grip patterns at a much lower cost than traditional prosthetics.

“We’ve looked at traditional movements such as bi-scapular abduction, which is used to articulate a basic hook hand,” she said.

“But we’ve also looked at different muscle movements such as the lower abdomen and shoulder elevation, and also lateral flexion.”

A harness, which is connected to the prosthetic via a Bowden cable system, fits onto a patient like a figure of eight.

Mahony’s first prototype also has straps that attach from the bottom of the figure eight harness to an abdomen strap to allow for lateral flexion.

Like other 3D-printed prosthetics, Mahony is using open source designs for the hand, and adding alterations, such as creating a hook in the palm of the hand for greater functionality – this would allow the user to hang a shopping bag off their prosthetic, for example.

The grip patterns of her prosthetic include not only the standard open and close type, but also a pinch grip to grab small objects such as a pen.

Another functionality she is working on is rotating the wrist, where the user would be able to move their shoulder to create the pinch grip, and then move their abdomen in a lateral flexion to rotate their wrist.

Creating these different grip patterns has been a challenge. One reason is because the muscle movement of users varies considerably, and there is some difficulty in producing a satisfactory amount of force with different muscle movements.

Mahony said shoulder muscle movements create the most force, but that may still not be enough for some users to grab a heavy object. The amount of force someone can achieve from abdominal movements also doesn’t correlate to the age or size of a person either.

Instead, she said it relates to how much control someone has over their stomach muscles.

This has made it more difficult to create a standard product, so Mahony sees her prosthetic as just another option for amputees.

“We’re looking at a balance between aesthetics as well as functionality. We are exploring allowing the user to choose different grip patterns and have a bigger sense of ownership of the device,” she said.

The first prototype has already been created, as well as the harness, and Mahony is now working on putting the two parts together. But she said she is not trying to solve every single prosthetic problem, due to the complexities and challenges involved in creating a prosthetic.

So far, tests have been carried out by fitting the harness to different people and measuring how much the cables are displaced and if those cable displacements can activate the prosthetic hand.

In the future, Mahony would like users to be able to choose which type of grip patterns are associated with which muscle movements.

Overcoming challenges in biomedical engineering

Mahony has always had a love for solving real-world problems, and she knew she wanted to do engineering.

She wanted to specifically go into biomedical engineering and be able to think practically and logically, but also apply those skills in a humanitarian context to positively change people’s lives.

Over the next six months, she will begin an industry placement project – the Sydney Industry Project Placement Scholarship.

“There are a lot of challenges of a lot of different biomedical technologies, but that’s why we have engineers to research and improve these technologies,” she said. “I think we can definitely overcome these challenges.”