David Sengeh grew up in Sierra Leone, where around eight thousand citizens lost limbs during the 1990s. Growing up he noticed many of his friends and family members had prosthetic limbs but did not wear them. He realized that ill-fitting prosthetics were painful and traced the issue to the prosthetic socket.
In his TED Talk The sore problem of prosthetic limbs David discusses his work with the MIT Media Lab to make the world more comfortable for amputees. Sengeh explains in his talk that the prosthetic socket is the interface where the residual limb is fit into the prosthetic device.
http://www.ted.com/talks/david_sengeh_the_sore_problem_of_prosthetic_limbs#t-261349
The process of fitting the limb to the socket takes at least three weeks in first world nations and can take up to a year in Sierra Leone. Plaster casting and molding processes are still used to create the sockets, and David looked for a process that could take less time while producing better results.
During his PhD residency at the MIT Media Lab David worked to design a more comfortable prosthetic socket. Using Magnetic Resonance Imaging he took the exact contour of a patient's residual limb. This data went to a finite element program to analyze the areas of greatest stress during normal patient use.
The finite element data was sent to a 3d printer to build a multi-material prosthetic socket. Softer materials are used in areas of highest stress to provide comfort for the user. One of the best anecdotes from Sengeh's talk involves a veteran who says that the socket is as soft as walking on pillows.
My go-to definition when asked about the purpose of engineering is that engineers should make the world a better place. David Sengeh takes this idea a step further, stating that he hopes his work not only comforts patients but transforms their sense of human potential.
http://www.ted.com/talks/david_sengeh_the_sore_problem_of_prosthetic_limbs#t-261349