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Process Devised for Sensor-Fitted Personal Prosthetics

Josie Fraticelli and Blake Honson

Josie Fraticelli, right, with her personalized prosthetic hand, and engineering professor Blake Johnson (Virginia Tech)

5 April 2019. Biomedical engineers developed techniques to produce low-cost personalized electronic-enabled prosthetic devices for people with limb loss. A team from Virginia Tech in Blacksburg describes its process for design and production of prosthetic devices with integrated sensors in the 28 March issue of the journal PLoS One.

A similar prosthetic hand is on display at the National Museum of American History in Washington, D.C. today through Sunday, 7 April, as part of the ACC Smithsonian Creativity and Innovation Festival, a joint undertaking of Virginia Tech and the Smithsonian Institution.

Researchers from the Virginia Tech’s Advanced Biomanufacturing and Biosensing Laboratory, led by industrial and systems engineering professor Blake Johnson, is seeking to make personalized prosthetic devices more accessible and useful for people with limb loss. The authors cite data from a 2008 study showing some 1.6 million people in the U.S. are living with the loss of at least one limb, a number that’s expected to grow to 3.6 million by 2050. While techniques for personalized limb prosthetics have advanced, their design and manufacture still makes them prohibitively expensive for many in need, particularly children as they quickly outgrow their devices.

Johnson and colleagues devised techniques that combine advances in computer-aided design and three-dimensional printing into a process for designing and fabricating low-cost prosthetic devices with built-in electronic sensors that match the individual’s personal anatomy. To demonstrate the process, the team designed a prosthetic hand for Josie Fraticelli, the teen-age daughter of a colleague born with an malformed hand, as a result of amniotic band syndrome, a rare condition caused during pregnancy by strands of the amniotic sac that separate and entangle digits, limbs, or other parts of the fetus.

The Virginia Tech team, comprised mainly of graduate and undergrad students, first created a soft plastic mold of Fraticelli’s hand, which has little development beyond the knuckles. They then used a technique called structured light 3-D scanning to create a fine, 60 millimeter grid of the hand from the plastic mold. The researchers fed that grid into computer-aided design software, based on a freely-available model for malformed hands as a result of amniotic band syndrome.

That model, however, has a generalized design, not personalized to a person’s specific anatomy. The team used the scan of Fraticelli’s hand to modify the model’s design for pinpointing the placement of sensors in the prosthetic device to increase exposure of those sensors to the exact shape and pressure points of the hand. The resulting device, say the researchers, increases the contact area of human tissue to the prosthetic device by 408 percent compared to the generalized model. To validate the technique, the team repeated the design process with other human body parts, a foot and an ear, as well as a kidney from a pig.

To produce the prototype prosthetic hand, the researchers used conformal printing, a 3-D printing technique for depositing material on uneven and curved surfaces. Conformal printing also allows for integrating different materials, such as electronic sensors and actuators. The team printed the personalized prosthetic hand for Fraticelli with carbon nanotube-based polymer inks that make it possible to build in the electronics. Tests of the prosthetic hand show the device senses the uneven pressure from her natural malformed hand, then redistributes that pressure through the device when grasping an object.

The researchers believe the prototype hand’s design and production techniques can be extended to other low-cost personalized prosthetics, even at home and on demand. “Hopefully,” says doctoral student and first author Yuxin Tong in a university statement, “every parent could follow the description from the paper we published and develop a low-cost personalized prosthetic hand for his or her child.”

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