Prosthetics have been around for much of human history. One of the oldest recorded prosthetics is a big toe, dated around 950-710 B.C.E. During the 15th century, knights were able to continue their fighting careers with handmade iron prosthetics. From these beginnings, steel, wood, plastic, and carbon fiber have taken over.
Humble beginnings: an early human prosthetic toe. Image courtesy of Jon Bodsworth.
Iron arms helped knights of medieval times continue their careers. Image courtesy of Wikipedia.
Whether the prosthetics are for aesthetic purposes or a physical necessity to enable the wearer to continue moving, working, and playing as normal, researchers are constantly looking for ways to improve upon existing designs. Often, the research centers around new textiles, such as graphene, and new capabilities made possible by flexible chips and small motors.
Improving Prosthetic Ability and Reducing Costs
Prensilia created the IH2 Azzurra series (PDF) robotic hand that can be connected to a prosthetic arm. The IH2 Azzurra series are human-sized anthropomorphic hands with embedded actuation, as well as sensory and control systems to replicate real human hand movements. The hand communicates through an RS232 or USB interface and has embedded 1kHz servo-control loops to enable further customization.
For some, however, making a working prosthetic isn't enough. The cost of a prosthetic can run into the tens of thousands and no prosthetic lasts forever. In 2013, Robohand created and released a 3D printable robotic hand with open-source files on Thingiverse. The cost runs around $1,000 USD to create the prosthetic, a fraction of the cost of other prosthetic options.
A completed 3D printed Robohand. Image courtesy Robohand.
They've made hundreds of prosthetics since 2013 with printable aluminum and medical grade hardware and splinting material. All 3D printing designs are available for makers who want to try printing one on their own.
Improving Control with Implantable Chips
This month, imec introduced an implantable, thin-silicon chip for intuitive prosthetics, created in tandem with researchers from the University of Florida’s IMPRESS (Implantable Multimodal Peripheral Recording and Stimulation System) program. The team approached the project with the goal of creating a close-loop system for future prosthetics technology. Recent advancements in prosthetics have given the wearer the ability to grip and manipulate objects—but imec wants to take it a step further by giving the wearer different stimulations and sensations.
The prototype is an ultrathin chip with a bicompatible, hermetic, and flexible packaging. It also includes 64 electrodes (with the possibility of 128). It's this high number of electrodes that allows stimulation and recording.
A needle attached to the chip allows the package to be inserted and attached inside a nerve bundle. By comparison, current technology wraps around a nerve bundle rather than being inserted. Inserting the electrode directly into the nerve bundle will increase the wearer's control over their prosthetic hand or arm.
“A new biocompatible chip encapsulation technology is used, based on the stacking of nanolayers with superior diffusion barrier properties, alternating with very thin polymer layers with excellent mechanical behavior,” explains Maaike Op de Beeck, program manager at imec. “The final result is an ultrathin flexible electronic device with a thickness comparable to that of a human hair, hence ultimately suitable for minimally invasive implantation.”
imec's new ultrathin (35µm) chip. Image courtesy of imec.
Rizwan Bashirullah is an associate professor of Electrical and Computer Engineering at the University of Florida and director of the IMPRESS program. According to him, “this effort aims to create such new peripheral nerve interfaces with greater channel count, electrode density, and information stability, enabled largely by imec’s technological innovation.”
Researchers continue to explore advances in prosthetics in no small part because they can help give the wearer back a sense of autonomy and normalcy. Technological advances ensure continued progression in prosthetic ability.