How the Squid Beak Inspired a Promising Implant Material

Long viewed as a monster of the sea, the squid, whether exceptionally large or small, is also a wonder of nature. For one thing, its razor-sharp beak is exceptionally stiff and is harder to deform than almost all metals and polymers. In fact, the beak of the Humboldt squid is one of the hardest known organic materials. Other squid beaks are nearly as hard. Meanwhile, squids' bodies are remarkably soft and gelatinous. This disparity in material properties has fascinated scientists, who have wondered how squid can use their beak to attack prey, severing spinal cords of fish, without self-inflicting damage. The answer lies in the gradient of material properties that exists along the squid's body; the tip of its tentacles is 100 times softer than its beak, enabling the animal to crush its prey without harming itself.

Drawing inspiration from squid, scientists at Case Western Reserve University are seeking to improve the safety of implantable medical devices.

Many medical implants must maintain rigidity will coming into contact with soft body tissue. The difference in properties in those materials can be uncomfortable for patients at best. At worst, the disparate properties can cause serious injury and implant failure.

The squid is able to forcefully close its parrot-like jaws without harming its body because the base of the beak works like a shock absorber. The researchers were able to replicate these properties in a nanocomposite film featuring a gradual amount of cross-linking.

Publishing their work in the Journal of the American Chemical Society, the researchers report that the material could be used in everything from glucose sensors to prosthetic limbs. The researchers selected tunicate cellulose nanocrystals as a nanofiller, which are functionalized with allyl moieties. They then crosslinked the material, enabling it to exhibit a substantial mechanical contrast when wet. When it is wet, there is a minimal difference in the stiffness along material. The researchers were able to crosslink the material through the use of light. The softest side of the material was subject to no light exposure while increasingly more light was the material's length to create a gradual increase in crosslinking.

In the case of prosthetic limbs, for instance, this gradual transition in material properties could enable prosthetics to be directly connected to metal inserted within bone, buffering the mechanical forces encountered where the metal is positioned against skin. By contrast, conventional prosthetic limbs are connected using a socked of hard plastic. When worn, the prosthetic limbs can cause the bone to damage soft tissue within the body.

The scientists are currently working on improving the material's variability, which is five times harder on one side than the opposite side. Meanwhile, a squid beak is 100 fold harder at the beak than the softest portion of its body.

Brian Buntz is the editor-in-chief of MPMN. Follow him on Twitter at @brian_buntz.