Lower Limb Prosthesis with Feeling

The David Geffen School of Medicine has developed sensors for a prosthetic foot that detect forces at four important contact points. The electronic control chip for the prosthetic takes the input signals that come in as force and translate them to pressure signals. Those signals are transmitted via wires to a band that is secured around the patient's stump and has little inflatable actuators that relay the force information to the sensory organs in the skin (http://casit.ucla.edu/body.cfm?id=37 ).

Veterans with foot and leg amputations return to the civilian world wanting, and needing, to resume a former life that included not just walking and running, but dancing, climbing, bicycling, golfing, swimming, and snow skiing. Lower limb prosthetics have, in the past allowed the wearer to stand and walk with a cane or other stabilizing assistance. Not being able to feel your foot in contact with the ground injects a hazard level into simple walking that may restrict many users to paved surfaces only. Being able to feel the uneven surface of the ground gives you a chance to adjust your weight and balance before you fall.

Bio-Medical engineering research is continually improving the interface between the prosthetic and the amputee by introducing sensors that can record, translate and transmit pressure information via tactors to the patient. The sense of touch is critical to the understanding of orientation and localization required for balance. Without the situational awareness enabled by the sense of touch, an amputee can be limited in the ability to navigate rough terrain. The patient can learn to balance while standing and walking and the tactile information feedback prevents injuries from falls and shortens the learning curve.

The skin and muscles have groups of receptors that are uniquely designed to detect different types of touch so the bio-mechanics of the actuators can be adjusted to transmit specific information. Each type of receptor requires a set of sensors, relay infrastructure and tactors that can interpret information for force, pressure, and frequency dependent mechanical stimulus.

Tactors can be little inflatable actuators like the ones developed at the UCLA complex, quarter size actuators that vibrate against the skin such as the ones developed by Engineering Acoustics, Inc, or a tapping actuator such as one developed by Kinea designs.

The functional groups of touch receptors vary in adaptation time and frequency sensitivity and each group varies in the percentage of coverage; because each group is best suited to a specific type of stimulation the variety of tactors in development suggest that revolutionary advances are still to be made within the field of prosthetics and the physiology of haptic perception.

References:

www.ucla.edu )

http://www.tactors.com/Products.aspx?productId=01

http://www.kineadesign.com/news/articles/Kim_2009_OnTheDesignOfMiniatureHapticDevicesForUpperExtremityProsthetics.pdf

http://www.eaiinfo.com/Product Data/Tactor Physiology.htm