In 1941, George de Mestral, a Swiss engineer, noticed his dog was covered in burrs after a long walk in the Alps. Fourteen years and many microscope slides later, de Mestral patented the hooked design for Velcro, inspired by the burrs. Velcro is probably the most well-known form of biomimicry, or human-made designs based on natural structures. Since then, slug mucus has inspired surgical glue, lotus leaves have helped create self-cleaning surfaces, and spider silk has been harnessed to create super-strong fibers.
The most recent iteration is a self-healing polymer that mimics human skin and is as hard as artificial tooth enamel, described in a study published today by ACS Nano.
“We have been always amazed by the power of nature to create sophisticated structures using [the] most elegant way,” Ming Yang, the senior author on this study and professor at the Harbin Institute of Technology in China, told me via email. Yang and his co-authors modeled the material they developed after human skin, setting out to create a polymer that is both self-healing and hard.
When the epidermis, the thick outermost layer of skin, is damaged, cells from the softer layer underneath migrate to the top to heal the injury, hardening and becoming dead cells to protect the live layers beneath.
Our skin is not very stiff, however. It is certainly not as hard as tooth enamel, but teeth cannot repair themselves, as anyone who has had a cavity filled knows. Yang and his co-authors created a material that represents the best of both worlds, with a multilayer structure similar to skin to mimic the self-healing process.
They created the layers using polyvinyl alcohol, a synthetic polymer that has been used in everything from fishing to eye drops, and tannic acid, which is used to stain wood and clarify beer. They are both environmentally friendly, Yang told me. He and his co-authors describe this as a “living” layer, and it acts like the live skin layered under your epidermis. The upper layers have high concentrations of graphene oxide, a hard substance also used in battery electrodes.
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