Haptic Feedback: New Direction for Prosthetics

In the quest to build bionic hands that can “feel,” vibrotactile feedback is starting to generate significant buzz.

Researchers at multiple universities have had recent success in clinical trials with prosthetic limbs that simulate the sense of touch via buzzers. By transmitting signals from bionic fingertips to the surface of the wearer’s residual limb, these devices help upper-limb amputees manipulate objects with greater precision and less mental effort than conventional prostheses demand. And because they don’t require surgery or other major interventions, vibration-based sensory feedback systems are more affordable and easier to master than alternatives such as targeted muscle reinnervation (TMR) or peripheral nerve stimulation.

A team at Florida Atlantic University achieved a breakthrough earlier this year by connecting a bionic hand to users’ nervous systems by means of a soft robotic armband. According to findings published in Nature Scientific Reports, the system enabled users to execute a range of complex manual tasks, even when they couldn’t see their bionic digits and had to operate solely on feel. One participant was able to grasp a ball with three fingers while flicking a light switch on and off with the pinky. Another used the bionic thumb and pinky to unscrew the lid of a water bottle while simultaneously using two other fingers to maintain a steady grip on a playing card. 

“Our researchers are addressing the loss of tactile sensations, which is currently a major roadblock in preventing upper-limb-absent people from multitasking or using the full dexterity of their prosthetic hands,” Florida Atlantic’s Stella Batalama told Science Daily. “Enabling refined dexterous control necessitates not only the interpretation of human grasp control intentions, but also complementary haptic feedback of tactile sensations.”

A similar project is underway at the University of Cincinnati, led by psychologist Charles Moore. In an initial trial of that system, able-bodied participants wore a vibrating armband to guide an artificial hand in virtual reality. By working with non-amputees in virtual reality, the researchers were able to directly compare natural sensory inputs with simulated ones—and they found no difference in either perception or the ability to execute manual tasks. 

“These findings might have a large impact on the future of prosthetics,” Moore and his fellow authors concluded in Frontiers in Neurorobotics. “Vibrotactile feedback is less invasive and risky than neural connection. . . [and] is a low-cost solution that may be added to existing prosthetic systems by simply retrofitting (or creating new ones) using relatively simple technology.”

The same principle can be applied in prosthetic legs. One recent case study published in the journal Medicine described how a vibrotactile feedback system improved balance, gait, and walking speed in a below-knee amputee. A larger clinical study is in progress at the Cleveland Clinic, with the goal of developing new socket designs.

The Florida Atlantic study holds particular promise, as it demonstrated users’ ability to exercise fine motor control over all five digits independently. Will refinements allow future upper-limb amputees to type on a keyboard, tie shoelaces, and the like? Stay tuned.

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