Led by scientists at 黑料吃瓜网, researchers have turned to an unlikely model to make medical devices safer and more comfortable: a squid鈥檚 beak.
Many medical implants require hard materials that have to connect to or pass through soft body tissue. This mechanical mismatch leads 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鈥檚 beak is harder than human teeth, but the base is as soft as the animal鈥檚 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.
Nature鈥檚 technology could make a range of medical devices more comfortable and safer for patients, from glucose sensors for diabetics to prosthetic arms and legs that attach to amputees鈥 bones, the researchers say. Their work is published in the Journal of the American Chemical Society.
鈥淲e鈥檙e mimicking the architecture and the water-enhanced properties of the squid to generate these materials,鈥 said Stuart J. Rowan, the Kent H. Smith Professor of Engineering at 黑料吃瓜网, and senior author.
Rowan worked with PhD student Justin D. Fox and assistant professor of biomedical engineering Jeffrey R. Capadona at 黑料吃瓜网, and Paul D. Marasco, 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 composed of a network of chitin fibers embedded within cross-linked structural proteins. The gradient is present when the beak material is dry, but is dramatically enhanced when in water, the squid鈥檚 natural environment.
Rowan and Capadona were among a team of researchers who previously reported a material that mimics the sea cucumber鈥檚 skin, which is soft and pliable when wet and stiff and hard when dry.
They thought that material, in the form of a film, could be cross-linked with nanofibers to maintain stiffness when wet. They filled the film with functionalized cellulose nanocrystals that, when exposed to light, form cross-links.
To increase stiffness across the film, one end was exposed to no light and subsequent sections to increasingly more light. The longer the film was exposed, the more cross-links formed.
Just like the beak, the grade from soft to hard was steeper when wet. Water switches off the weaker non-covalent bonds that form when the material is dry.
The wet environment inside the body will enhance the gradient just as well, which makes this technology especially attractive for implants, the researchers say.
鈥淭here are all sorts of places in medicine where we鈥檙e using hard materials, but we鈥檙e mostly soft,鈥 Marasco said. The contrast is a recipe for sores and infection, poor performance and implant failure.
Needles in diabetics鈥 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.
鈥淧rosthetic limbs are connected to the arm or leg with a socket of hard plastic that fits over the residual limb,鈥 Marasco continued. 鈥淏ut 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.鈥
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 already are working on the next generation of materials and cross-linking strategies to make the buffer gradient steeper. The tip of a squid鈥檚 beak is 100 times harder than its softest portion, while this first mimic鈥檚 hard tip is five times harder than its soft end.
鈥淭his is a proof of concept,鈥 Rowan said. 鈥淣ow that we have shown the concept works, we鈥檙e now getting a wee bit more complicated and targeting materials that will allow us to move closer to applications.鈥
The Division of Materials Research at the National Science Foundation funded this research.
