Researchers at Stanford University have created an electrically conductive gel that feels and behaves like biological tissues, but conducts electricity like a metal or semiconductor. The gel can also be printed or sprayed as a liquid before being turned into a gel. The researchers say this combination of characteristics gives the gel enormous promise for developing new biological sensors and energy storage devices.
The jelly-like material was created by Stanford chemical engineering Associate Professor Zhenan Bao, science and engineering Associate Professor Yi Cui and members of their respective labs by binding long chains of the organic compound aniline together using phytic acid, a substance that is the principal storage form of phosphorous in many plant tissues. The acid’s ability to grab up to six polymer chains at once allows an extensively cross-linked network to form.
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Unlike commercially available conducting polymers that form a uniform film without any nanostructures, the new gel’s cross-linking produces a complex, sponge-like structure. Innumerable tiny pores expand the gel’s surface area, increasing the amount of charge it can hold, the rapidity of its electrical response, and its ability to sense chemicals.
And because the material doesn’t solidify until the final step of its creation, it can be easily manipulated. By printing or spraying the material as a liquid, manufacturers could construct intricately patterned electrodes at low cost, before turning it into a gel.
In contrast to most hydrogels, which are tied together by a large number of insulating molecules that reduce the material’s overall ability to conduct electrical current, the new hydrogel is highly conductive because phytic acid is a “small-molecule dopant” that lends polymer chains a charge when it links them.
Cui says the gel’s conductance is “among the best you can get through this kind of process,” with a high capacity to hold a charge and the ability to respond unusually quickly to an applied charge. The researchers say that, with these electrical capabilities, combined with the material’s similarity to biological tissue and large surface area, it is well suited to the creation of devices that communicate between biological and technological hardware. These could include medical probes and laboratory sensors, as well as biofuel cells and high-energy density capacitors.
Perhaps most importantly, the gel is cheap and easy to produce. “All it’s made of are commercially available ingredients thrown into a water solution,” said Bao.
The team’s research appears in the journal Proceedings of the National Academy of Sciences (PNAS).
Source: Stanford University