Durable, light and firm: Three properties help create new materials

( In an extensive technical review inspired by biology and biomimetics in Science magazine published February 15, two engineers at the University of California, San Diego have confirmed. Determine three characteristics of biological materials that they believe engineers must do well to compete with each other in artificial materials: light weight, durability and strength.

Joanna McKittrick and Marc Meyers, from material science programs at Jacobs School of Engineering at the University of California San Diego, tested these three traits in a wide range of materials, from spider silk to lobster shells and shells. abalone, to the mines of toucan birds and porcupine feathers. The two researchers said the lessons learned from these materials could lead engineers to techniques to create better armor panels, lighter and more powerful aircraft, materials. more flexible.

Engineers say 3-D printing creates new opportunities for making these materials, "An abalone doesn't make a shell overnight, " McKittrick said. "But you can build a material similar to abalone shells using the principles we've learned from nature by printing on layers of mineral sediments - and doing that quickly. much more than nature can do '.

Meyers and McKittrick are studying birth-inspired designs for more than a decade, and are authorized to write research comments on this topic for Science magazine. Over the years, they have used a wide array of advanced tools, from X-ray diffraction to electron microscopy; and has developed a test of the mechanical properties of materials at the nanoscale, to understand the basic structure of materials found in animals and plants.

"Mother nature gives us samples," Mr. McKittrick said. "We are trying to understand them more so we can add them in new materials."

"We outline mechanisms that can help us clarify the properties of biological materials," Meyers said.

Meyers said the bio-inspired design has been a part of science and engineering for a long time - from the legend of Icarus, Leonardo Da Vinci's plane, bird-inspired, to the Modern materials like Velcro.

Durable materials deflect cracks by constructing many obstacles to prevent cracks from propagating in a straight line. Materials in nature use different strategies to achieve this result. One is to attach elastic collagen fibers in brittle materials. Another way is to use interfaces between layers of materials to create obstacles.

For example, at the nanoscale, the abalone shell is made up of thousands of layers of "bricks" made of calcium carbonate CaCO ₃ (often called chalk), about 10 micrometers wide and about 0.5 micrometers thick, equivalent to The thickness is about one percent (1%) compared to the thickness of a hair.

Piles of bricks that are not arranged in order will reflect the light to bring out the characteristic of abalone. They are arranged in an orderly, brick-like structure arranged in the most durable configuration possible theoretically.

The key to creating the power of abalone shell is a protein binder that binds to the upper and lower surfaces of CaCO ₃ bricks. This glue is strong enough to hold the layers together, but it is weak enough to allow the layers to slide aside, absorbing the energy of a heavy smash in the process. Abalone quickly reshapes cracks caused by impacts, and they also leave growth bands (organic bands) during the transition periods in shell development. . The growth strip strengthens the shells. Meyers believes that designs inspired by the abalone shell structure can help improve ceramic materials in the future.

Animals develop extremely light structures, durable structures that are compatible with motion, including flight operations. Think of bird feathers, porcupine feathers and bird beaks. These structures are made of materials that do not bend while being as light as possible. Most are made of tube-like structures with quite large diameters. But when the diameter of these tubes reaches a certain size, they become more and more like being bent. To increase resistance to bending, these tubes are then filled with a foam.

For example, the inner material of the toucan beak is a hard "foam" made of bone fibers and drum-like membranes sandwiched between the outer layers of keratin, the protein that makes up nails, hair and horns. The result is a solid "foam" made of sealed cells that makes the beak rigid. Like a house covered by a single roof, the foam layer is covered with overlapping layers of keratin tiles, each about 50 micrometers in diameter and about 1 micrometer thick, attached to each other to form plate.

Meyers said the biologic compound found in the toucan bird beak can be inspired to design aircraft as well as parts of ultra-light transport vehicles.

Researchers also describe other strategies for making lightweight objects. Some bird's wing bones have continuous strut structures. Bamboo is made by burning without cracking.

"Natural systems are built from very few elements, yet they use clever ways to assemble all the different materials to maximize their properties , " McKittrick said. review

Biological polymers, such as collagen, are an important component of natural materials that are natural. At lower pressure levels, they can significantly extend, their non-coiling and non-twisting molecules, without breaking. At higher pressure, this polymer's spine itself spreads out. These bio-polymers are found between hard materials, making up the natural strength of these materials.

For example, spider silk has both high tensile strength and scalability."It's stronger than almost any material ," Meyers said. Spider silk is made of pleated sheets of nanocrystals connected by weak hydrogen bonds and embedded in protein strands.

Under low pressure, protein fibers do not roll and straighten, like biological polymers. Under higher pressure, the load will be transferred to nanocrystals. If necessary, some hydrogen bonds will slip, allowing the structure to extend without breaking.

The strength of spider silk depends on hydrogen bonds, which suggests researchers have a new way to create stronger materials. True coincidence similar structures are also found in bones.

More robust and complex structures can be found in everything from wool to buggy eggs.

Meyers said there are more examples of materials and designs inspired by creatures. In the future, however, researchers will have to spend more time making these materials better.