A simple prosthesis allows hundreds of thousands of people with lower limb amputations to get around more easily. And a normal bodily function — sweat — can render the prosthetic limb useless.
The problem has been around for years, accompanying an advance in prosthetic materials technology: the use of silicone liners to create a tight, comfortable seal with a wearer's leg. But the seal is so good that sweat, the result of exercise and higher temperatures, has no place to go.
"So if people are out mowing the grass in the summer they will basically come in and take the prosthesis off and pour water out," said Jon Akins, an assistant professor of biomedical engineering at Widener University. Letting the sweat linger can cause painful sores and blisters, he said, rendering the prosthesis "essentially useless."
Akins will soon be enrolling participants in a clinical trial of a liner infused with what is known as a phase-change material. It absorbs heat in the process of changing from solid to liquid and releases it while changing back to solid later. The silicone liner works normally in both phases, Akins said, and controlling "the micro-climate within a prosthesis socket entails better skin and tissue health."
The study — funded by a $140,000 Department of Defense grant — is part of a $500,000 award to the University of Pittsburgh, which will lead the trial. The vast majority of lower limb amputations are the result of accidents such as motorcycle crashes and falls, and the study will enroll participants regardless of military service. Each site plans to enroll 25 participants in tests of silicone liners with and without the new material. All participants will use each kind of liner for six months and then switch, but they won't know which is which.
The Alpha SmartTemp Liner is already marketed by the Ohio Willow Wood Co., which Akins said had no role in funding the study. He said that Willow Wood had already shown that the liner can reduce temperatures but had not studied the benefits to users.
Participants at Widener and Pittsburgh will be given sensors to measure physical activity and will come in every six weeks to be tested on mobility and fill out questionnaires about the use of the prosthesis with the liner. Enrollment will begin in either January or July to ensure coverage of all seasons, since outdoor temperatures play a role in heat and perspiration. The study will also help determine the extent of the problem.