Affordable Inflatable Bionic Hand Offers Real-Time Tactile Control for Amputees

Prosthetics enable a wide range of everyday tasks, including shaking hands, stroking cats, and zipping up bags.

Over 5 million people worldwide have had their upper limbs amputated, and prostheses have advanced significantly. A growing number of commercial neuroprosthetics, which are highly articulated bionic appendages designed to pick up a person’s residual muscle signals and robotically mimic their desired movements, are available instead of the traditional mannequin-like appendages.

This refined dexterity, though, has a price. With possibly heavy and stiff electric actuators, neuroprosthetics can cost tens of thousands of dollars and are built around metallic skeletal systems.

Engineers from Shanghai Jiao Tong University and MIT have created a flexible, lightweight neuroprosthetic hand that may be available for a reasonable price. Amputees who used the artificial arm performed commonplace chores like zipping a bag, serving a carton of juice, and petting a cat just as well as—and sometimes even better than—those using stiffer neuroprosthetics.

The researchers found that if the prosthetic was designed with a tactile feedback system, the volunteer’s residual arm could regain some basic sensitivity. The innovative design is also remarkably durable, quickly recovering from a hammer blow or being run over by a vehicle.

Although the “Bionic Hand” is still a prototype, according to MIT professor Xuanhe Zhao of mechanical engineering and civil and environmental engineering, its performance is already on par with or better than that of contemporary neuroprosthetics, which is fantastic news for the team. For low-income families who have battled with amputation, soft prosthetics have a huge potential to become very affordable, says Xuanhe Zhao.

Their research was reported in Nature Biomedical Engineering by Zhao and his colleagues. Co-authors include Guoying Gu, Xiangyang Zhu, and associates from Shanghai Jiao Tong College in China in addition to Shaoting Lin, a researcher at MIT.

Big Hero hand

The adaptable new design by the team is strikingly identical to a specific inflatable robot in the animated film “Big Hero 6.” The group’s artificial hand is constructed of soft, elastic EcoFlex, the same material used to make the soft android. The prosthetic comprises of five fingers that resemble balloons and are each embedded with fiber segments that are comparable to the articulated bones in real fingers. A 3-D-printed palm with human-like finger shapes is connected to the flexible digits.

The bulk of neuroprosthetics use built-in electric motors to individually control each finger, but the researchers controlled each finger individually with a straightforward pneumatic system.

Lin created a computer model to connect the pressure a pump would need to apply to position a finger in the desired location. Using this model, the team created a controller that tells the pneumatically-driven system to inflate the fingertips into imitations of five common grasps, including pinching two and three fingers together, balling up the fist, and cupping the hand.

Electromyography sensors, or EMG sensors, which detect the electric signals produced by motor neurons to control muscular tissues, provide signals to the pneumatically powered system. The sensors are put where the prosthesis joins the user’s arm—at the prosthetic’s opening. In this configuration, the sensors can pick up signals from a residual limb or leg, such as when an amputee imagines clenching their fist.

The team then put into use an already-in-use algorithm that “translates” muscle impulses and links them to typical grasp types. They programmed the controller for their pneumatically powered device using this algorithm. The sensors read residual muscle signals when an amputee imagines, for instance, holding a wine goblet, and the controller then converts those signals into the appropriate pressures. The pump then uses those pressures to inflate each finger and create the grip that the amputee wants.

The researchers took their design one step further by incorporating tactile feedback, a feature that is not present in the bulk of commercial neuroprosthetics. To accomplish this, they affixed a pressure sensor to the tip of each finger, which, when pressed, produces an electric signal corresponding to the pressure detected. Each sensor is linked to a specific area on the residual limb of an amputee, allowing the person to “feel” pressure exerted by the artificial finger, for example, against the forefinger.

Good grip

Two volunteers who had both had their upper limbs amputated were chosen by the researchers to try the inflatable prosthetic hand. After receiving the neuroprosthetic, the participants were instructed on how to use it by repeatedly contracting their arm muscles while picturing five common grasps.

These included picking up fragile objects like strawberries and bread, stacking checkers, turning pages, writing with a stylus, and lifting big spheres. They conducted these tests again using a stiffer bionic hand that was commercially available, and they found that the inflatable prosthetic performed most tasks just as well as, if not better than, its rigid version.

Additionally, one participant was effortlessly able to use the soft prosthetic for activities of daily living, such as eating food like crackers, cake, and apples and handling objects and tools like laptop computers, bottles, hammers, and pliers. Additionally, this volunteer was able to safely manage the soft prosthetic by shaking hands, petting a cat, and touching flowers.

In a fascinating experiment, the researchers blindfolded the subject and found that he could tell which prosthetic finger they were brushing and touching. Additionally, he was able to “feel” bottles of different sizes placed in the prosthetic hand and responded by lifting the bottles. These studies, according to the researchers, provide encouraging evidence that amputees can regain some degree of sensitivity and in-the-moment control by using the inflatable hand.

The team is working to improve the design’s sensing and variety of movement, and they have filed a patent application through MIT.

The team currently has four different grip variations, but Zhao indicated that there may be more in the future. Zhao continued, “Better decoding technology, higher-density myoelectric arrays, and a more compact pump that could be worn on the wrist could enhance the team’s concept.” The design will also be customized for mass production so that the Bionic Hand can communicate with soft robotic systems to benefit society.

Originally published on: Scitechdaily.com

Reference: “A soft neuroprosthetic hand providing simultaneous myoelectric control and tactile feedback” by Guoying Gu, Ningbin Zhang, Haipeng Xu, Shaoting Lin, Yang Yu, Guohong Chai, Lisen Ge, Houle Yang, Qiwen Shao, Xinjun Sheng, Xiangyang Zhu and Xuanhe Zhao, 16 August 2021, Nature Biomedical Engineering.
DOI: 10.1038/s41551-021-00767-0