Biomedicine

Mimicking the Building Prowess of Nature

Scientists build new materials using inspiration from complex biological forms.

Joanna Aizenberg, a materials scientist at Harvard University, has scoured the natural world for clues to biological building codes. She aims to decipher some of Mother Nature’s unique designs, including dirt-resistant sea urchins and sea sponges made of super-strong light-conducting glass, to develop novel materials that, like these organisms, can self-assemble and sense and respond to their environment.


“We try to identify biological systems that have unusual and sophisticated properties, such as optical, structural, or magnetic properties, to make extremely sophisticated, efficient, and highly potent devices and materials,” says Aizenberg, who is also a core faculty member at the Wyss Institute for Biologically Inspired Engineering. “Then we take these principles and try to integrate them with what we already know in materials science–incorporating them into existing materials or fabricating a new generation of materials based on biological principles.” The work could result in better fiber optics, paint that changes color in response to temperature or light, and new ways of delivering drugs or clearing arterial plaques.


This collection of striking images explores some of Aizenberg’s new materials, as well as the organisms that inspired them.


Nanodreadlocks: “One specific feature that interests me more than anything else at the moment is how nature creates adaptive materials that optimize performance in response to changing environmental cues,” says Aizenberg. “The systems I am trying to replicate in my lab are the surfaces of sea urchins. They cover their bodies with an array of microflowers that constantly open and close, protecting the body from contamination.”


Taking inspiration from sea urchins, Aizenberg’s team has developed nanobristles that spontaneously curl into a precise array of helical bundles when immersed in an evaporating liquid. Aizenberg likens the phenomena to the way wet, curly hair clumps together and coils to form dreadlocks. The bristles shown here are made of an epoxy resin and are approximately 100 nanometers in diameter–about one-thousandth the width of a human hair.

Nanodreadlocks grabbing: As they twist together, the nanoscale bristles can capture nearby particles, a property that could be used to develop novel adhesives or a method for capturing and releasing drugs at specific sites within the body. The structures could also be used for their optical properties, says Aizenberg. As the distances between the bristles shrinks or expands, the optical properties of the material changes from reflective to nonreflective.
Smart coatings: Shown here is another responsive material, made up of a polymer hydrogel. As the tiny tent-like structures cluster together, they become hydrophilic, or water-attracting. And as they open up again, they become hydrophobic, or water-repulsing. Researchers ultimately aim to turn the material into smart coatings that attract moisture when dry and repel it when wet. The material also changes color as it changes conformation. “You could think about buildings with coatings of this kind,” says Aizenberg. “As humidity changes, the color of the wall would change.”
Crystal blooms: Aizenberg’s team mimics nature’s ability to efficiently create complex inorganic structures, such as bone and mollusk shells, using patterned templates of organic molecules. Changing the arrangement of these proteins and polysaccharides can control the growth of inorganic crystals. “Instead of using top-down manufacturing, such as making a crystal and then etching it, we want to make the material grow in its final form, even if it is highly unusual, sophisticated, and precise,” says Aizenberg. Researchers can grow crystals in any shape they choose, including this flower-like structure, which is made from a thin film of limestone and is about half the width of a human hair.
Flowers from limestone: A protein core at the black center of each of these “flowers” controls its self-assembly. Scientists can use this technique to grow very different types of crystals at the same time, which is very difficult to do using synthetic approaches.
Sprouting cube: In this image, one organic template produces the leafy structure in the top half of the image, while a second template induces the formation of a cube. “It looks like the bush is growing out of a cube,” says Aizenberg. Both are made of calcium carbonate. The structure resembles that of a mollusk shell–the outer part of the shell is made of calcite, like the cube in the bottom part of the image. The inner shell is made of aragonite, which has the same chemical formula as calcite but different properties, and resembles the leafy structure in the top of the image.

The technology could be used to produce high-quality optical photonics devices or engineered tissues. Bone and teeth, for example, are a combination of inorganic and organic materials. “By learning how to grow ordered phases of inorganic material on top of organic material, one can produce synthetic tissues similar in structure and function to biological tissue,” says Aizenberg. The same approach might one day be used to get rid of unwanted inorganic materials in the body, such as kidney stones or the plaques that build up in the arteries and cause heart disease.
A striking sea sponge: Commonly known as the Venus’ Flower Basket, this organism provides inspiration for energy-efficient building materials. The animal exemplifies how nature can optimize one material for multiple purposes–its skeleton is made entirely of glass that is both extremely strong and is optimized to conduct light. “We study how nature assembles this glass at different levels to create a ‘building’ that is so superior to the glass materials that we make,” says Aizenberg. “The same material that makes walls is optimized to bring light and uptake energy from the environment. We still can’t even think about this level of perfection.”
Biological concrete: A close-up of the sponge reveals that each strand is made of bundles of threads, resembling the structure of reinforced concrete. Each square “window” measures about two by two millimeters.
Not-so-smooth glass: An even closer image of the surface of the sponge, captured with electron microscopy, shows multiple layers within the structure. These layers of natural glass fibers add strength and conduct light from the environment. Each thread is about 100 microns wide, or about the width of a human hair. (By Joanna Aizenberg and James Weaver)

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