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Porous material holds promise for prosthetics, soft robotics

13 October 2015

Cornell researchers have developed a lightweight and stretchable material with the consistency of memory foam that has potential for use in prosthetic body parts.

A soft foam water pump moulded in the shape of a human heart (photo courtesy of the researchers)
A soft foam water pump moulded in the shape of a human heart (photo courtesy of the researchers)

The polymer foam can be formed and has connected pores that allow fluids to be pumped through it. The material starts as a liquid that can be poured into a mould to create shapes, and because of the pathways for fluids, when air or liquid is pumped through it, the material moves and can change its length by up to 300 percent.

While applications for use inside the body will require approval and testing, Cornell researchers are close to making prosthetic body parts with the so-called 'elastomer foam'.

“We are currently pretty far along for making a prosthetic hand this way,” says Rob Shepherd, assistant professor of mechanical and aerospace engineering, and senior author of a paper appearing online and in a forthcoming issue of the journal, Advanced Materials.

The porous channels are made by mixing salt with the rubbery elastomer when it’s still a liquid. Once the elastomer cures and hardens, the salt is removed. To seal an organ or prosthetic so air or fluid can be pumped through it without escaping, Shepherd and colleagues coat the outside with the same polymer but without the salt.

In the paper, the researchers demonstrated a pump they made into a heart, mimicking both shape and function.

The researchers used carbon fibre and silicone on the outside to fashion a structure that expands at different rates on the surface – to make a spherical shape into an egg shape, for example, that would hold its form when inflated.

“This paper was about exploring the effect of porosity on the actuator, but now we would like to make the foam actuators faster and with higher strength, so we can apply more force. We are also focusing on biocompatibility,” Shepherd says.

In a separate study published last month, Shepherd and colleagues developed an elastomer with a 3D printer to create layers and duplicate muscles of an octopus tentacle, with comparable agility and freedom of movement as a real tentacle.

The research was groundbreaking since until now 3D printing methods could not directly print a device with as much agility and degree of freedom as the new method provides.

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