The fit of a lower limb prosthesis (e.g. an artificial leg) degrades over the course of a day due to unavoidable volume loss of the residual (remaining part of) the limb. This can lead to discomfort, pain, skin irritation, blisters, and eventually soft tissue injuries on the residual limb. The associated pain and injury caused by poor socket fit can become debilitating and impair quality of life. The goal of this project is to develop a better understanding of the causes of volume loss, evaluate volume loss in current state-of-the-art prostheses, and develop a smart prosthetic socket that can accommodate for volume loss of the residual limb. The ability to accommodate for volume loss will eliminate the pain and injury due to poor socket fit and help users maintain a high quality of life. The results of this research will have significant societal impact as more than 1.6 million people in the US are living without a limb, and service members of the Vietnam War and Operation Iraqi Freedom and Operation Enduring Freedom conflicts make up a significant portion of that population. The most common prosthetic device problems for these veterans and service members are that the devices are painful to wear and create skin problems, which leads to at least 22% total device abandonment. The planned educational efforts through high school, undergraduate research, as well as mentorship, will have a broad impact on the students by providing them with the unique and valuable experience of applying analysis tools taught in the classroom to a "real-world" problem. Additionally, numerous physical principles and classroom examples can be illustrated directly from the research for educational benefit in undergraduate courses taught by the investigators. The education and outreach plan will provide a broad impact on students' learning through K-12 outreach programs in collaboration with the Center for the Enhancement of Engineering Diversity and Services for Students with Special Disabilities.
Individuals with transfemoral or transtibial (above the knee or below the knee) amputations experience daily changes in the volume of residual limbs while wearing prosthetic limbs. The volume changes lead to poor fitting of the residual limb in the prosthetic socket, and consequently to various levels of discomfort, pain, skin irritation and tissue damage. This project is focused on studying the underlying reasons for volume change in the residual limbs, measuring the resulting limb deformations in the socket, and developing a smart prosthetic socket employing fluidic flexible matrix composite (f2mc) technology that can accommodate for volume loss of the residual limb. The Research Plan is organized under three tasks. The FIRST Task is to develop new, robust measurement techniques for measuring residual limb volume loss and limb deformation during use. The residual limb measurement system will be an integration of digital image correlation for measuring limb deformation, structured light laser scanning for measuring volume change, and piezoresistive pressure sensors for measuring interfacial pressures. The SECOND Task is to achieve a greater understanding of the relationship between facets of socket performance using the measurement system developed under the first task in assessing socket performance in subjects with unilateral transfemoral amputation. Four facets of socket performance will be evaluated before and after volume change of the residual limb: 1) dimensions and volume of the residual limb when not wearing the socket, 2) limb deformation when wearing the socket, 3) interfacial pressure between the socket and the residual limb when wearing the socket, and 4) subjective assessments of socket performance provided by both subjects and prosthetists. These measurements will provide a greater understanding of the correlation between residual limb volume loss, interfacial socket pressure, and comfort score and help clarify the mechanisms that lead to volume change, and residual limb discomfort or pain, and allow predictive relationships between these four facets of performance to be explored. The THIRD Task is to develop and evaluate customized f2mc smart prosthetic sockets with human subjects. The smart sockets are based upon a novel technology, developed by the investigators, that can be used as an actuator with unique and highly-customizable shapes, sizes, and mechanical properties and that have low power requirements. Key components of the f2mc "wafers" are multiple layers of oriented, high performance carbon fibers surrounding a flexible tube, an elastic casting to hold the tubing/fibers in a desired shape/configuration, and an internal working fluid, such as air or water in the tubing. The f2mc technology is actuated by pressurizing the internal working fluid, which will lead to wafer thickening. The wafers can achieve more than 300% increase in volume when pressurized, exhibit stiffness ratios as high as 56 using simple valve control and be fabricated into a variety of shapes and configurations that can be tailored specifically for the user and thus uniquely accommodate for volume loss of the residual limb and improve socket comfort. Socket performance will be evaluated via benchtop testing and in human subjects with unilateral transfemoral amputation. After the smart sockets are customized and optimized for the amputees, the socket's performance will be compared to the subject's current socket suspension method.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
