When you lose a limb, the loss involves more than just the aesthetics of being one appendage down. It's everything you may have taken for granted that was easily available before, whether from the mobility of a leg, or the deftness of a trained hand. For decades, bionic limbs have advanced to offer progressively wider ranges of movement, and even basic sensation. But the gap between synthetic and original limbs has remained, staggering, sobering, real. And scientists are beginning to understand how to close the experiential gap, with the next generation of bionic prosthetics.
Scientists have come "one step closer" toward offering higher-performance bionic prosthetics capable of not only supplementing, but replacing the functionality of lost limbs, according to a new study published in the journal Biomedical Engineering.
Amputees report what they want in bionic, prosthetic limbs
The goal of prosthetics is to substitute the functional loss in human motion after losing a limb or other extremity with a technological device of some kind. If you've lost a limb, you may experience a serious impairment in motion, in addition to your capacity to manipulate your surrounding environment. Paired with the loss of sensation, the functional loss in one's body can also alter or reduce your autonomy, or your ability to perform daily tasks expected by society and various activities. Consequently, the requirements and expectations for upper- vs. lower-limb prostheses differ broadly.
For example, lower limbs typically assist in cyclical or locomotor tasks, so creating prostheses for these is much more a matter of practical function, alone. But upper limbs support a much wider array of more dextrous activities. People who use prosthetics as a substitute upper-limbs report function, durability, comfort, appearance, and cost as the primary factor for a prosthetic's effectiveness, and all of these qualities together alter the look of a prosthetic device, in addition to body language, and the potential for manipulating objects of the external world.
A survey of amputees in the U.S. and Europe found that the most highly-desired qualities for upper-limb prosthetics include separate fingers, the ability to grasp objects without letting them slip, and a measured, proportional strength of grip. Users of upper-body prosthetics also desired an increase in range of motion, in addition to the movement speed of the wrist, a more organic, natural appearance, "improvement in the socket temperature and transpiration management, reductions in weight and noise, and increased sensory feedback," read the study.
Engineering functional, satisfying prosthetics is a multivariable engineering problem
However, lower-limb prosthetics don't get off easy. While most lower-limb amputees feel confident about walking forward on flat ground, keeping your balance and walking on disturbed ground or up slopes is still a difficult proposition. "This is especially prominent in patients with above-knee amputations, with reduced mobility or with insufficient access to rehabilitation," read the study. "Additionally, skin problems caused by wearing a socket affect lower-limb amputees to a greater extent, and results in substantially reduced walking distance and in prosthetic abandonment," when users decide the pain of prosthetics isn't worth the gain of increased functionality.
The creation of a viable substitute for amputees is one of the most complex engineering challenges in the medical world. Recently, a neural implant enabled a person to use a robotic arm with tactile feedback, literally feeling the world with a synthetic replacement for a lost arm. Range of motion, side effects, appearance, and some fidelity to the sense of physical connection to the world through a prosthetic limb are all paramount in the advancement of bionic arms and legs. In time, we may come to see the most advanced prosthetic limbs depicted in sci-fi as quaint, perhaps even primitive.