MIT and Shanghai Jiao Tong University’s engineers designed a soft, lightweight, Inflatable Robotic Hand to facilitate amputees to do several highly complex activities like shaking hands and petting a cat. Their work and research have been published in Nature Biomedical Engineering, a journal for engineers, researchers, and clinicians to understand diseases or improve human health.

A prosthetic implant is a robotic device that restores the normal functions of a body component that is lost by trauma, sickness, or a congenital disability. Prosthetics are regulated by neuro activity in the brain to recover motor function to the natural state.

For diverse purposes, numerous types of prosthetic limbs are offered. These purposes usually rely on the amputation site and the patient’s requirements. A prosthesis limb uses various electrodes, which collect tiny electrical signals from the brain when the patient is thinking about moving the arm and directing the robot arm to move accordingly.

Beyond standard models, there is a rising amount of commercial neuroprosthetics. With highly articulated bionic limbs designed to perceive the remaining muscular signals of a user and robotically imitate its desired motions. However, such top-notch capabilities come at a price. Neuroprosthetic products are costly and are built around metal skeletons with heavy and inflexible electrical engines.

Previously, MIT had created a robotic arm that could dress up people using its unique algorithm to help people with disabilities ease their lives.

But this one is different. Amputees have been testing this artificial limb by carrying out complex actions, like moving a suitcase, petting a cat, and pouring a carton of juice as much as those with more stiff neuroprosthetics and, in some cases, better than them.

The researchers identified the prosthetic limb developed with a tactile feedback system that restored a primal feeling in the residual limb. The new shape is also remarkably durable, rebounding rapidly after resisting a hammer or car running over it.

The smart hand is soft and elastic, weighing around half a pound. Its components amount to about $500, a fraction of the material and weight costs involved with rigid and more intelligent limbs.

Xuanhe Zhao, the professor of civil and mechanical engineering plus environmental engineering at MIT, says that this Inflatable Robotic Hand model is similar to the existing neuroprosthetics in performance. However, this soft prosthetic robot hand has the potential to become affordable neuroprosthetics at a reasonable cost for low-income families that have suffered from an amputation.

Researchers of the Inflatable Robotic Hand include MIT postdoc Shaoting Lin, Guoying Gu, Xiangyang Zhu, and other co-authors at Shanghai Jiao Tong University in China.

How is Inflatable Robotic Hand different?

The team’s new, folding design has an uncanny resemblance to a particular inflating robot in the animated movie “Big Hero 6”.

Soft Hand: The team’s prosthetic hand is created from soft stretch material like the squishy android, in this instance, the commercial EcoFlex elastomer. The prosthesis consists of fingers identical to the globes inserted in fiber segments, similar to the joint bones in the genuine fingers. The bendy numbers are joined with a 3-D palm in the form of a human hand.

Computer Model – In order to connect the required position with the matching pressure, Shaoting Lin, the co-researcher, devised a computer model that a pump had to use to reach this position. Using this model, the team has designed a controller to inflate the pneumatic system to imitate five standard grips, including clamping two and three fingers together to ball up the fist and cupping the palm.

EMG sensors – Electromyographic sensors received by the pneumatic system help measure the electrical signal created by the neuron motor to operate the muscles. The sensors are connected to the user’s limb on the prosthetic’s opening. The sensors can receive signals from a ghost body in this setup, for instance, when an amputee envisions making a fist.

Pneumatic System – As most neuroprosthetics do, the researchers have employed a simple pneumatic system to precisely inflate and flex their fingers at specified locations without controlling each finger with mounted electrical motors. This system has a tiny pump and valves that can be worn on the waist to significantly decrease the prothetic’s weight.

Algorithm – The researchers’ team has then employed an existing algorithm that “decodes” muscle signals for typical grasp forms. This algorithm has been used to program the pneumatic system controller. For example, when an amputee thinks about holding a wine glass, the sensors collect remaining muscle impulses that the controller subsequently places on them. The pump is applied to inflate each finger and provide the intended grasp of the amputee.

Tactile Feedback: The researchers went further in their conception and looked at a function not integrated into most current commercial neuroprosthetics is to allow tactile feedback. In this inflatable robot hand, the team of engineers has stitched a pressure sensor at every fingertip, which generates an electrical signal according to the sensed pressure when touched or squeezed. Each sensor is moved to a particular position on the remaining limb of an amputee so that the user may feel pressure when the prosthetic’s thumb is pressed.

Testing of the Inflatable Robotic Hand

For testing the working of the Inflatable Robotic Hand, the team engaged two volunteers, both with upper limb amputations. After being equipped with neuroprosthesis, the volunteers learned to use the hand by tightening the muscles in their arms repeatedly while envisioning five common grasps.

After 15 minutes of training, volunteers were asked to carry out many standardized tasks to show manual strength and skills. Those activities included stacking controls, turning pages, writing a pen, raising heavy balls, and collecting fragile items such as strawberries and bread. The testing was carried out again using a more rigid, market-based bionic hand, and the inflated prosthesis was as excellent, or even better than its stiff counterpart, at most.

One participant could also utilize the soft prosthesis instinctively for daily tasks, including food such as crackers, cake, and apples, and handling items and instruments such as laptops, bottles, hammers, and pinches. The volunteer might also move the soft prosthesis Inflatable Robotic Hand securely, for example, to shake the hand of someone, touch a flower, or pet a cat.

In another testing, the researchers blindfolded the volunteer in a stimulating practice and discovered which predictable finger they were poking and burning. He was also able to “feel” and lift bottles of various dimensions placed in the prosthetic hand. The scientists see these experiments as a positive sign that amputees can regain a type of sensation and real-time hand control.

Through MIT, the research team has submitted a design patent and is improving the Inflatable Robotic Hand’s sensing and motion spectrum. The Inflatable Robotic Hand has four grasp types now, and there will be more in the future as per the research team. The design of the Inflatable Robotic Hand can be enhanced by introducing better decoding technology, higher-density myoelectric arrays, and a more lightweight pump that could be worn on the wrist. 

The researchers plan to tailor the design for mass production so that soft robotics technology can be translated to the advantage of society. The Inflatable Robotic Hand could help amputees to do their daily chores if available on a budget.