Imagine an aircraft that can alter its wing shape in mid-flight and, like a pelican, dive into the water before morphing into a submarine. New research by Cornell University engineering professor Rob Shepherd and his group might help make that futuristic-sounding vehicle a reality.

The key is their development of a hybrid material featuring a combination of rigid metal and soft, porous rubber foam that can be stiff when required and elastic when a change of shape is required. The material also has the ability to self-heal following damage and is described in a paper in Advanced Materials.

"It's sort of like us – we have a skeleton, plus soft muscles and skin," explained Shepherd. "Unfortunately, that skeleton limits our ability to change shape – unlike an octopus, which does not have a skeleton."

The new hybrid material blends the rigidity and load-bearing capacity of a human skeleton with the ability to dramatically alter shape, like an octopus. "That's what this idea is about, to have a skeleton when you need it, melt it away when you don't, and then reform it," Shepherd said.

"That's what this idea is about, to have a skeleton when you need it, melt it away when you don't, and then reform it."Rob Shepherd, Cornell University

The material combines an alloy called Field's metal with a porous silicone foam. In addition to its low melting point of 144°F, Field's metal was chosen because, unlike similar alloys, it doesn’t contain lead.

"In general, we want the things we make in this lab to be biocompatible," said Ilse Van Meerbeek, a graduate student in the field of mechanical engineering and a contributor to the paper.

The elastomer foam is dipped into the molten metal, then placed in a vacuum so that the air in the foam's pores is removed and replaced by the alloy. The foam has pores with sizes of about 2mm, which can be tuned to create a stiffer or a more flexible material.

In tests of its strength and elasticity, the hybrid material showed an ability to deform when heated above 144°F, regain its rigidity when cooled, and then return to its original shape and strength when reheated.

"Sometimes you want a robot, or any machine, to be stiff," said Shepherd. "But when you make them stiff, they can't morph their shape very well. And to give a soft robot both capabilities, to be able to morph their structure but also to be stiff and bear load, that's what this material does."

This story is adapted from material from Cornell University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.