Researchers led by scientists at Case Western Reserve University (CWRU), Cleveland, Ohio, have turned to a squid’s beak to make medical devices, such as prosthetic arms and legs that attach to amputees’ bones, and glucose sensors for individuals with diabetes, safer and more comfortable. Their work was published April 4 in the Journal of the American Chemical Society.
Many medical implants require hard materials that have to connect to or pass through soft body tissue. This can lead to problems such as skin breakdown at abdominal feeding tubes in stroke patients and where wires pass through the chest to power assistive heart pumps. Enter the squid.
The tip of a squid’s beak is harder than human teeth, but the base is as soft as the animal’s Jell-O-like body. In order to connect these two mechanically dissimilar parts of the squid a major part of the beak has a mechanical gradient that acts as a shock absorber so the animal can bite a fish with bone-crushing force yet suffer no wear and tear on its fleshy mouth.
“We’re mimicking the architecture and the water-enhanced properties of the squid to generate these materials,” said Stuart J. Rowan, PhD, the Kent H. Smith professor of engineering in the Macromolecular Science and Engineering Department at CWRU, and the study’s senior author.
Rowan worked with doctoral student Justin D. Fox, CWRU Assistant Professor of Biomedical Engineering Jeffrey R. Capadona, PhD, and Paul D. Marasco, PhD, who, like Capadona, is a principal investigator at the Advanced Platform Technology Center at the Louis Stokes Cleveland Department of Veterans Affairs Medical Center.
Other researchers have shown the structure of the beak is a nanocomposite comprising a network of chitin fibers embedded within increasingly cross-linked structural proteins from mouth to tip. The gradient is present when the beak material is dry, but is dramatically enhanced when in the squid’s natural environment of water. The wet environment inside the body will enhance the gradient just as well, which makes this technology especially attractive for implants, the researchers said.
Needles in insulin pumps, metal stents inserted in blood vessels, and electrodes inserted in muscles or brains could be safer and more effective if materials would remain hard where they need to be but buffer surrounding soft tissues.
“Prosthetic limbs are connected to the arm or leg with a socket of hard plastic that fits over the residual limb,” said Marasco. “But bone moves around under the socket and can damage the soft tissue inside, while the socket can be hard on the skin where it makes contact.” A better solution, he said, would be to run a metal insert into the bone inside the body and attach a prosthesis directly outside the body using this kind of mechanical buffer where the hard metal passes through the soft skin.
The researchers are already working on the next generation of materials and cross-linking strategies to make the buffer gradient steeper. The tip of a squid’s beak is 100 times harder than it’s softest portion, while this first mimic’s hard tip is five times harder than its soft end.
“This is a proof of concept,” Rowan said. “Now that we have shown the concept works we’re now getting a wee bit more complicated and targeting materials that will allow us to move closer to applications.”