UCSD Jacobs School of Engineering University of California San Diego
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COVER STORY - Biomimetics

Calcium carbonate tiles form the tough abalone shell.
Man-made laminate mimics the shell and survives ballistics tests.

Jacobs School faculty members are increasingly involved in biomimetic research projects designed to mimic the structure and function of mollusk shells, bird bills, sea urchin spines, deer antler, animal tendon, and other biocomposites in the development of new smart materials and devices.

For example, Marc A. Meyers, professor of mechanical and aerospace engineering, described in the Jan. 15 issue of Materials Science and Engineering A how red abalone builds a surprisingly tough helmet-like home with 95 percent calcium carbonate and 5 percent protein adhesive. The layers of brittle calcium carbonate are sandwiched between the stretchy protein adhesive. "We are interested in basic research on new materials," says Meyers. "We have turned to nature because millions of years of evolution and natural selection have given rise in many animals to some very sturdy materials with surprising mechanical properties."

Fellow MAE professor Kenneth S.Vecchio mimicked the architecture of the shell to create a new class of armor-like metal laminates that stop bullets and could potentially be used in demanding aerospace applications such as an environmentally friendly replacement for beryllium, a strong but highly toxic metal.

In the March issue of JOM (the Journal of the Minerals, Metals and Materials Society) Vecchio described how he reacts alternating foils of aluminum and titanium alloy to create the laminate. "The intermetallic phase of titanium aluminide, which is produced in our reaction, is the complement of the mollusk's hard calcium carbonate phase, and the titanium alloy layer mimics the abalone shell's compliant protein layers," said Vecchio.

Vecchio says his laminate composite performed spectacularly in depth-of-penetration ballistics tests, but he thinks the material's greatest potential may derive from its unique ability to have its structure and properties tailored to meet application-specific engineering requirements.

Another MAE professor Robert Skelton is developing so-called tensegrity structures, spider web-like collections of cables and rods that change shape as cable tension is modified. Meanwhile, Vecchio and Meyers are expanding their biomimetic interests. For example, Vecchio is working with orthopedic surgeons to convert sections of mollusk shell, cuttlefish bone, and sea urchin spines into sturdy bonereplacement implants. The Jacobs School 's von Liebig Center for Entrepreneurism and Technology Advancement recently provided $50,000 to help Vecchio refine a new method for creating synthetic bone for biomedical applications such as dental implants and biocompatible prosthetic interfaces.

In addition to studying the shells of mollusks, Meyers is analyzing the strong but lightweight bill of the Toco Toucan, a Central and South American bird that squashes fruit and berries with its banana-shaped bill. The bill is composed of an outer covering of horny plates made of a protein called keratin (the protein that comprises fingernails and hair).The strength-enhancing interior of the toucan bill is filled with a foamy version of keratin, a rigid and highly porous material, which coincidentally has a structure strikingly similar to the interior of the sea urchin spines being investigated by Vecchio.