New Class Of Composite Organic Material Could Put The Muscle In Artificial Body Parts

"Electroactive polymers have been around for a long time, but the energy input required for them to do enough work to be of value was very high," says Dr. Qiming Zhang, professor of electrical engineering. "With this new composite we have reduced the voltage to one tenth that previously needed."

The researchers report in today's ( Sept. 19 ) issue of the journal, Nature that a new class of composites, fabricated from an organic filler possessing very high dielectric constant dispersed in an electrostrictive polymer matrix, has much improved properties for the manufacture of actuators.

"These all-organic actuators could find applications as artificial muscles, smart skins for drag reduction, toys and in microfluidic systems for drug delivery," says Zhang. "In addition, the high dielectric constant makes this material attractive for high performance capacitors."

The dielectric constant is a relative measure of a materials ability to store electric charge. The dielectric constant is related to the chemical structure of the material and the higher the dielectric constant, the better the material will store an electric charge. Unlike traditional piezoelectric materials, which have a one-to-one relationship between voltage and movement, most electroactive polymers which are capable of creating large shape changes under electric fields have a square relationship between voltage and movement. In some cases, a 10 percent range of movement is attainable.

The researchers looked at the electrostrictive poly(vinylidene fluoride-trifluoroethylene), a known electroactive copolymer which was developed recently at Zhang's Penn State laboratory, for the matrix in the composite. For filler, they used an organic semiconductor, copper-phthalocyanine, because it has a high dielectric constant.

"The copper-phthalocyanine disperses in the polymer matrix," says Zhang. "The dispersion is one aspect that we need to work on more and we are looking at a variety of approaches including creating nanocomposites."

The composite has electrical properties more suitable to low voltage operation. The composites are also nearly as flexible as the copolymer alone which has the appearance of a slightly more rigid plastic bag.

"Potential applications for this material include a variety of tiny pumps because the material can me made to pump periodically or in a wave fashion," says Feng Xia, graduate student in electrical engineering and part of the team working on a variety of approaches to electrostrictive materials in Penn State's Materials Research Institute. "Small insulin or other pharmaceutical pumps could be powered by a low voltage battery and an electroactive composite. Other applications include pumping fluids through the channels in a diagnostic chip array or as smart skins that would reduce drag."

For artificial muscles and tendons, the flexible, elastic nature of the material may provide a more natural motion for mechanical musculature. Multiple, very thin layers stacked and then rolled and flattened could simulate muscles.

The team consists of Zhang; Xia; Hengfeng Li, post doctoral fellow in materials; Z.-Y Cheng, research associate; Haisheng Xu, post doctoral fellow; and Cheng Huang and Martin Poh, graduate student in materials research. This work was supported by the National Institutes of Health, the Office of Naval Research and the Defense Advanced Research Project Agency. A patent has been filed on this research.