February 16, 2013
Bio-Inspired Materials Leading To Greater Engineering
Lee Rannals for redOrbit.com — Your Universe Online
Bio-inspired, man-made materials may one day offer up designs that are more lightweight, tougher, and stronger than other options out there. A team writing in the journal Science say they have identified characteristics of biological materials they think engineers will be able to emulate in future materials.
"An abalone doesn't grow a shell overnight," Joanna McKittrick said in a statement. However, using something like 3D printing, "you could build a material similar to the abalone shell using principles we learned from nature by printing layer upon layer of mineral deposits–and do it much faster than nature would."
The team has been studying bio-inspired designs for over a decade using an array of advanced tools, such as X-ray diffraction and electron microscopy. They also developed tests of materials' mechanical properties at the nanoscale in order to understand the structure of material found in animals and plants.
"Mother Nature gives us templates," said McKittrick. "We are trying to understand them better so we can implement them in new materials."
Materials in nature use a variety of strategies to deflect cracks, by erecting various obstacles that prevent them from propagating in a straight line.
An abalone shell is made up of thousands of layers of "tiles," made of calcium carbonate. These irregular stacks of thin tiles refract light to yield the characteristic luster of mother of pearl and they are organized in such a way that they provide the toughest configuration theoretically possible.
Marc Meyers, the other engineer on the project, said the key to the strength of the abalone shell is a protein adhesive that binds to the top and bottom surfaces of the calcium carbonate tiles. The glue is strong enough to hold layers of tiles together, but weak enough to permit the layers to slip apart.
Meyers believes design inspired by the structure of the abalone shell could help to improve advanced ceramic materials.
Structures like porcupine quills and bird beaks are made of materials that do not bend, while also being as light as possible. Most of these materials are made of tube-like structures with a fairly large diameter.
The interior of a toucan's beak is rigid "foam" made of bony fibers and drum-like membranes that are sandwiched between outer layers of keratin. This protein helps make up fingernails, hair and horn. According to Meyers, the bio-composite found in the toucan's beak could inspire the design of ultra-light aircraft and vehicle components.
Spider silk has high tensile strength and extensibility, and Meyers says it is stronger than almost any material. The silk is made of pleated sheets of nano crystals connected by weak hydrogen bonds and embedded in protein strands.
Under small amounts of stress, the protein strands uncoil and straighten, but increasing this stress makes the load get transferred to the nano crystals.
"There are a tremendous number of examples of things we can't do with traditional materials," McKittrick said. "It's going to take more time to make these bio-inspired materials. But they will be better."
Last year, researchers wrote in the journal JoVE about the procedures to harvest and process synthetic spider silk from bacteria known as "post-spin". This team devised a mechanical actuator that can stretch fibers to a desired length, mimicking the spider's natural synthetic fibers. Silk fibers have been used in mammalian neurosurgery, and optical fiber communication.
Engineers can always find inspiration from biology, with even Leonardo Da Vinci finding inspiration for his flying machine from birds. Swimsuits built for competitive swimmers have been bio-inspired, built to replicate the ridges that reduce drag on sharkskin. Also, MIT researchers were inspired by the gecko to create a surgical tape. Irregularities found on whale fins are now used to help design turbine blades.