A bit reminiscent of the Terminator T-1000, a new material created by Cornell researchers is so soft that it can flow like a liquid and then, strangely, return to its original shape.
Rather than liquid metal, it is a hydrogel, a mesh of organic molecules with many small empty spaces that can absorb water like a sponge. It qualifies as a "metamaterial" with properties not found in nature and may be the first organic metamaterial with mechanical meta-properties.
Hydrogels have already been considered for use in drug delivery - the spaces can be filled with drugs that release slowly as the gel biodegrades - and as frameworks for tissue rebuilding. The ability to form a gel into a desired shape further expands the possibilities. For example, a drug-infused gel could be formed to exactly fit the space inside a wound.
Dan Luo, professor of biological and environmental engineering, and colleagues describe their creation in the Dec. 2 issue of the journal Nature Nanotechnology.
The new hydrogel is made of synthetic DNA. In addition to being the stuff genes are made of, DNA can serve as a building block for self-assembling materials. Single strands of DNA will lock onto other single stands that have complementary coding, like tiny organic Legos. By synthesizing DNA with carefully arranged complementary sections Luo's research team previously created short stands that link into shapes such as crosses or Y's, which in turn join at the ends to form meshlike structures to form the first successful all-DNA hydrogel. Trying a new approach, they mixed synthetic DNA with enzymes that cause DNA to self-replicate and to extend itself into long chains, to make a hydrogel without DNA linkages.
"During this process they entangle, and the entanglement produces a 3-D network," Luo said. But the result was not what they expected: The hydrogel they made flows like a liquid, but when placed in water returns to the shape of the container in which it was formed.
"This was not by design," Luo said.
Examination under an electron microscope shows that the material is made up of a mass of tiny spherical "bird's nests" of tangled DNA, about 1 micron (millionth of a meter) in diameter, further entangled to one another by longer DNA chains. It behaves something like a mass of rubber bands glued together: It has an inherent shape, but can be stretched and deformed.