Lower limb amputees (LLA) rely on their prosthetic legs to remain active and lead an independent life. For most LLAs, a well-fitted prosthetic socket is the only option to interface with their prosthetic leg, however, it is a real challenge to make a prosthetic socket to interface with residual limbs accurately. One of the reasons is that there lack of accurate approaches to evaluate the pressure distribution on the residual limb accurately and effectively. To overcome this issue, the research team will develop an innovative sensing system, which permits the prosthetists to track the pressure distribution on the residual limb visually. The capability of the new sensing system will be demonstrated on lower limb amputees.

A novel pressure sensing pad will be tested in the project. The purpose of these tests is to collect the safety and efficacy of the sensing pad. The research team would like to seek a Non-significant Risk claim from Institutional Review Board (IRB).

The pad will be made of materials similar to the normal liner with embedded nanotubes. The nanotubes are filled with gallium alloys, of which resistance will change based on loaded pressure. When constant current passes these tubes, the change of pressure leads to a change in temperatures around, which will excite thermal-sensitive dyes to change color. So the research team could estimate the pressure at a given area based on the color around it.

The experimental procedure includes three sets and requires 3-4 visits from each subject.

Set I procedure includes a standard socket construction, which requires 2-3 visits for the subjects to the office of a local prosthetic company. Then, a certified prosthetist will build a test socket and a customized liner to maximize the socket fit and comfort and conduct the needed alignment of the prosthetic leg. Unless it is necessary, all testing sockets will be duplications of amputees' everyday sockets.

Set II will test the accuracy of the constructed prototype on amputee subjects compared to a commercially available sensor pad, which serves as a reference. First, the research team will mount both sensing systems on the subjects. The reference sensor grid will be mounted on the residual limb directly using medical tape. After the subject dons the ENABLE sensing pad, the research team will register two sensing systems. In the end, the subjects are required to don the testing socket and walk continuously, so the measurement of the developed prototype could be stabilized. Pictures of the ENABLE will be taken and compared with the recorded pressure signals from the reference grid.

Although the reference grid and ENABLE system are designed to be put on easily, brief assistance from experimenters will be needed to ensure that the mounting procedure can be conducted appropriately.

Set III will test whether information from the ENABLE leads to appropriated socket-fit-assessments based on the response of experienced prosthetists when the prosthetists are shown the pressure distribution measured by the ENABLE under different fit conditions. All subjects will be exposed to five socket fit conditions: good and additional foam pads at four different areas shown in a random sequence. The size of the pad at each location is selected by the prosthetists based on the shape and size of the residual limbs.

Under each fitting condition, each subject will go through three trials. In each trial, the subject will walk continuously until the color of the sensing pad is stabilized. After taking high-resolution digital pictures, which cover most of the sensing area of the ENABLE, the research team will let the subject rest until the optical pattern of the ENABLE fades completely before starting a new trial.

After the experiments are finished, the subject will need to fill out a survey about the comfort of the ENABLE system. The survey will be conducted just after the experimental procedure on paper. During Set II and III, a fall prevention harness is available for the participants if it is needed. The participants are requested to self-monitor the pressure and thermal conditions on their residual limbs and encouraged to request the early termination of the experimental procedure.

Inclusion Criteria:

• Unilateral transtibial amputees
• At least 1 year of experience using his/her prosthetic leg
• Has used the current socket for at least 6 months without a significant skin issue or major modification
• Can comfortably walk 3 mins without pausing to rest
• The fibula length on the residual limb must be greater than half of the length of the fibula on the unaffected side

Exclusion Criteria:

• Cognitive or visual impairment that affects the participant's ability to provide informed consent or to follow simple instructions during the experiments
• neuropathy observed on the residual limb
• regnant female

all individual participant data (IPD) that underlie results in the manuscript, which is planned to report the effectiveness of the ENABLE system.

The information will be available 6 months after the end of the experimental procedure.

The statical analysis results will be available to the public with selected images collected from the experimental procedure. The full picture set will be available based on the request to the research team.

When the digital photos are shown to evaluators from external groups, the socket fitting conditions are not disclosed.