When designing a lower limb prosthesis, an engineer would have to consider several key factors to create a device that restores the function of a lower limb and the mobility it provides. Here are the most important criteria to consider when designing a lower limb prosthesis:

1. Socket design: the socket is the primary link between the patient’s remaining limb and the actual prosthesis. The socket has to be fitted efficiently, have adequate load transmission meaning withstand the body weight of the patient, as well as guaranteeing stability and control. Many patients actually had to stop wearing their prostheses because of socket-related problems.
2. Actuation and control design: These two go hand-in-hand as actuation refers to the mechanism that generates motion, and control design refers to the system that regulates the motion of the prosthesis.
3. Strength, durability, comfort: Of course, the prosthesis should be strong, durable, and comfortable. You don’t want it to break, nor do you want it to slowly break overtime. But you still want it to be comfortable enough so the user can wear it for a long period of time (imagine how much you use your leg). It should resemble the natural movement of a human leg
4. Costs: Economic status shouldn’t be a limiting factor in getting a lower-limb prosthesis. Lower costs also mean more budget for prototypes which in turn will result in a better product. Estimated lifetime prosthetic costs for an individual with unilateral lower limb amputation could range from $0.5-1.8 million, so it isn’t a factor to underestimate

Current Issues with prosthesis

1. Most materials used for prosthetics are high in cost 
2. Desired functionalities:  For intense exercise different appendages are needed 
3. Aesthetics: For running prosthetics their shape is inorganic