Medical Device Link.

Originally Published MDDI November 2002

R&D DIGEST

For more than 50 years, researchers have attempted to create artificial muscles from various materials, including polymers and, more recently, carbon nanotubes (see R&D Horizons, MD&DI, August 1999, p 42). Triggered by electrical or chemical stimuli, these artificial muscles would act as actuators for such devices as prosthetic limbs and drug pumps. The principal challenges involved in this research have involved maximizing reaction speed, strength, and the degree of response.

Now, a new class of all-organic composites could offer a greater range of performance for a number of medical applications, according to researchers at the Pennsylvania State University Material Research Institute (University Park, PA).

Says Qiming Zhang, PhD, professor of electrical engineering at the institute, "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." A key advantage of using the new materials is that "with new composite these we have reduced the voltage to one tenth of that previously needed," he adds.

The researchers explain that the composite materials, fabricated from an organic filler possessing a high dielectric constant dispersed in an electrostrictive polymer matrix, provide improved properties for use as actuators.

Zhang and his team have worked on the challenges associated with creating synthetic muscle materials for some time. While earlier research centered on the use of irradiated copolymers, current work has focused on developing new polyvinylidene fluoride (PVDF) terpolymers that do not require irradiation (which greatly reduces processing cost Zhang explains), He adds that the new materials "exhibit better performance. The terpolymers have exhibited a strain of more than 7% and elastic energy density of more than 1 J/cm³."

The main advantage of the materials, according to Zhang, is that they "can be operated under a much lower field," meaning voltage. He adds, "The high dielectric constant makes the materials attractive for high-performance capacitors."

The researcher explains that, unlike traditional piezoelectric materials that have a one-to-one relationship between voltage and movement, most electroactive polymers that are capable of creating large shape changes under electric fields have a square relationship between voltage and movement. In some cases, a 10% range of movement is attainable, the reseacher says.

A number of technical and business challenges remain to be addressed, Zhang explains. "The copper-phthalocyanine filler disperses in the polymer matrix. The dispersion is one aspect that we need to work on more, and we are looking at a variety of approaches, including creating nanocomposites." He adds, "To produce small samples in a lab to demonstrate a principle is quite different from producing that material on an industrial scale. In order to produce a material with high quality and reproducibility, we need to understand many of its basic properties and also the scale-up issues. Along the way, we will still need to work on optimization of the material properties. Right now, we'd like to work on using nano-copper-phthalocyanine to produce nanocomposites that exhibit improved electric and mechanical behavior."

Addressing the business challenges involved with the research, Zhang says, "It normally takes 5 to 10 years for a new material to become established in the market. We are working on the commercial source to scale up the terpolymers. One of the issues now is the stock market, which is quite weak, so it is hard to get enough investment to run a start-up company."

Nevertheless, the researchers see promise in a number of areas. Zhang says the group intends "to have a material that will not just be used in some specialized areas. We would like it to be used even in toys." Feng Xia, graduate student in electrical engineering and part of Zhang's team, adds that, "potential applications for this material include a variety of tiny pumps, because the material can be made to pump periodically or in a wave fashion." Xia explains, "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."

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