Jumpy Insects Make the Leap to Implantable Rubber

R&D Digest

The protein molecule that gives fleas the ability to jump from dog to dog may soon be used to create a biomimetic resin for device materials. Several insects have a molecule called resilin that helps wings to flex without causing damage to the tissue that connects the wing to the body.

Chris Elvin, PhD, is a principal researcher with CSIRO Livestock Industries, a government research organization in St. Lucia, Australia. He was working on parasitic insects that plague livestock when he began reading papers on resilin, an elastic substance made up of di- and trityrosine. The proteins are cross-linked into randomly coiled chains.

Elvin initially became intrigued by the substance because it seemed to be much more resilient than other rubbers. “The molecules can be stretched many times without losing elasticity,” he says.

The other property that makes resilin exciting is its high fatigue resistance. “A bee that lives for 7 days will go through about 500 million cycles of flapping its wings because it has resilin,” Elvin says. “A spinal implant would need to last 100 million cycles in a human.” Elvin's team discovered this fatigue resistance by analyzing genetic patterns. They demonstrated that resilin is only produced in the pupal stages of insects and, therefore, must last a lifetime.

Longevity is the key. Resilin can last through the 100 million cycles needed for spinal implants. It can also spring back to about 97% of its initial form. (The team was able to test resilience at nanoscale using an atomic force microscope.) By contrast, the elasticity of human tissue such as skin, heart, lungs, tendons, and ligaments can only recover up to about 90%.

To create the synthetic resilin, the research team drew samples from the resilin gene of the fruit fly Drosophila melanogaster and inserted the gene into E. coli bacteria. The bacteria produced several grams of the precursor to resilin, called proresilin. “At that point the substance was still a liquid,” Elvin says. “And we had to figure out a way to turn it into a solid.”

To do so, Elvin mixed the proresilin with a ruthenium catalyst under a light to bond the tyrosine amino acids. A substance similar to a rubber band emerged. The group then began in vivo and in vitro testing to explore the material's properties.

The goal of the multidisciplinary team is to make the material stronger and make it able to withstand degradation. “At this point, the material is still a little too soft, so we are trying to stiffen the elastic module,” Elvin explains. “In addition, we are looking at an organic chemistry approach to reassemble the proteins and slow the degrading of the rubber.” Ultimately, Elvin says, the material structure will be different—more like a peptide.

“There are 15–16 people from various disciplines working on the substance to make it viable for use, and I'm not always entirely sure what they are doing,” he says, laughing.

Once the team thoroughly understands the material and is able to manipulate it for certain properties, Elvin says it could be used for several different applications. He is currently exploring how to adapt resilin for spinal implants, drug and therapeutic protein mechanisms, or artificial blood vessels, among others.

“We are keen to establish collaborative relationships with companies,” he says. “Once we know what those companies want to use it for, we will be able to adapt it to fit their needs.”

The team has two patents in the works and one provisional patent for the material and the processes.

The work is supported by an Emerging Sciences Initiative (Nanotechnology) grant from CSIRO, the Australian Research Council, and the Commonwealth government through a Department of Education Science and Training grant.—Heather Thompson

Copyright ©2006 Medical Device & Diagnostic Industry