German Engineers Develop 3D Printed Prosthetic Hand That Replicates Intricate Muscle Movement

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Researchers from Saarland University in Saarbrücken, Germany have developed a promising 3D-printed prosthetic hand that incorporates nickel-titanium “smartwires” to deliver a mechanical form of muscle memory unmatched in previous prosthetics prototypes.

The wires are made from a material known as shape-metal alloys, which exhibit interesting behaviors that make them well suited for use in prosthetics. Shape-metal alloy wires remember their original shape, but are light-weight enough to be easily bent without resistance. By applying heat to the wires, in the form of a small electrical current, the wires quickly return to their original shape. Of all shape-metal alloys, nickel-titanium wires are special because they have the highest energy density, which means they exert the most power when returning to their original shape. In a prosthetics design, this means that powerful and accurate muscle-like movements can be achieved without relying on heavy motors.

Small bundles of the hair-thin wires have been routed throughout the prosthetic hand, providing engineers with a lightweight infrastructure that can be used to reliably control gestures and movements by applying an electrical current to manipulate the hand and deliver the desired movements.

Filomena Simone, an engineer and PhD student working on the project explains, "The movement of the hand is done by the wire. This wire, when activated, they contract, and we are able to exploit this contraction to make the finger move. We can move each phalanx independently. We can monitor the position of the finger without adding any other sensor; only exploiting this embedded feature of the wire. This helps us to always preserve a very lightweight structure. This is a big deal because normally prostheses are very heavy.”

While the design is still in its early stages, researchers are hopeful that the technology will one day lead to lightweight, high-performance prosthetics options for patients. Eventually, the researchers imagine that the devices could leverage advances in neuroprosthetics to integrate the motions directly with the nervous system, allowing users to control the hand fluidly with their brains.


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