Tapping into Nature: Materials that matter

Lotus leaf with water droplets
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Wall coatings by StoCoat mimic the way a lotus leaf "cleans" itself by repelling water.

This is an excerpt from the Tapping into Nature report by Terrapin Bright Green.

Materials — with their various strengths, finishes and functions — underpin all industries, even those that involve intangible goods and services. Therefore, creating materials that provide superior performance at minimal cost is important to every business. Organisms, which "manufacture" their tissues at ambient conditions using locally available materials and energy, offer myriad examples of resource-efficient material manufacturing.

Nature constructs these materials with a vast array of functions unsurpassed by many synthetic materials. It accomplishes this through nanoscale precision, using chemical elements in different proportions and atomic arrangements from synthetic materials.

Selected strategies

Multiscale structures

Many biological materials have impressive levels of tensile strength, hardness, toughness and other material properties unmatched by many of today’s engineered materials. This is achieved in part through hierarchical ordering of material. At the nanoscale, seashell nacre is composed of calcium carbonate crystals deposited in a protein and carbohydrate matrix.

These assemblies then form stacked tiles at the microscale. This multiscalar assembly, visible at the millimeter scale as 3mm thick layers, transforms brittle chalk into a tough ceramic. The structure of nacre has inspired tough, deformable glass. Similarly, the waterproof adhesives produced by mussels owe their strength and stickiness to hierarchically crosslinked fibers. This attribute inspired the development of several biodegradable adhesives.

Functional surfaces

Microscopic surface textures and chemical properties imbue biological materials with an astounding array of functions. Lotus leaves have waxy microscopic bumps that allow water to roll off and carry away dirt and particles. This "lotus effect" inspired the self-cleaning paint StoCoat Lotusan Materials, such as the surface layer of the pitcher plant, wick water into microscopic ridges, creating super slick surfaces. These concepts inspired anti-fouling surfaces such as Slippery Liquid-Infused Porous Surfaces (SLIPS) and superwicking surfaces for indirect evaporative cooling. Similarly, Sharklet mimics the scales of sharkskin to repel bacteria.

'Grown' materials

The ability to grow is an attribute of organisms that produces materials of remarkable complexity and functionality. When given the appropriate scaffolding and nutrients, cells replicate and self-assemble into mats, films and various other forms. Using "biofabrication," or biology as a means of production, labs are able to generate valuable materials using relatively little energy. Materials such as packaging foam, bricks, meat and leather are "grown" using bacteria (bioMASON), fungi (Ecovative) and animal tissue cultures (Modern Meadow).

Existing products

StoCoat Lotusan

When it rains, Nelumbo lotus leaves shed water droplets, dirt and other particles with the help of micro- and nanoscale surface structures and gravity. This "lotus effect" is created by multiscaled, waxy bumps on the leaf surface that cause water to bead up and roll away. 

Sto Corp., a Georgia-based manufacturer of building materials, duplicated this effect in the StoCoat Lotusan self-cleaning paint. The acrylic paint has a similar microtexture to the lotus leaf; it too sheds water and dirt, leaving a dry, clean surface on which algae and fungi have difficulty colonizing. Unlike exterior paints that become soiled over time, Lotusan’s self-cleaning property makes it a low-maintenance, long-lasting coating for exterior applications.

Sharklet

Biofouling and antibiotic resistance are major concerns across many sectors, from maritime transportation to healthcare and food service. Sharklet Technologies, a Colorado-based biotechnology company, produces Sharkle, an engineered microscopic topography inspired by sharkskin that reduces the growth of bacteria without the use of biocides. Like sharkskin, Sharklet surfaces feature a microscopic diamond pattern that prevents bacterial growth by up to 90 percent without contributing to antibiotic-resistant bacteria.

Sharklet generated over $1 million in sales in 2012 and is co-developing furniture, medical devices and consumer products with LG International, Cook Medical, Steelcase and other companies. Sharklet is also developing urinary catheters that reduce the likelihood of catheter-related bacterial infections, which account for more than $565 million in healthcare costs in the U.S. annually.

Mushroom materials

Ecovative, a New York-based materials science company, combines fungal mycelium — the vegetative portion of fungi — and agricultural byproducts to make environmentally friendly Mushroom Materials. These compostable materials are alternatives to plastic foam and other petroleum-derived synthetics.

The manufacturing process begins by placing agricultural waste and a mycelium culture in a mold. As the mycelium grows, it binds the waste fibers into a solid mass that fills the mold. The mass is then heat-treated to stop the growing process, creating a material ready for use. Comparable in performance and cost to competing technology, Mushroom Materials are used as packaging and structural materials and as an environmentally responsible replacement for engineered wood. Mushroom Materials are a Cradle to Cradle Certified Gold product.

Products in development

Mussel-inspired adhesive

Blue mussels (Mytilus edulis) produce a biodegradable, waterproof adhesive that attaches to almost any surface, even Teflon. Most manufactured adhesives are not as versatile and contain toxic compounds such as formaldehyde. Aided by Terrapin’s competitive analysis services, researchers at the chemical company SyntheZyme are developing a water-resistant adhesive inspired by the mussel. The adhesive is made of proteins with chemically "sticky" ends that crosslink biopolymers into a strong matrix, chemically analogous to the mussel adhesive.

It also uses a biological catalyst to achieve a low-energy synthesis. The polymers are renewable, nontoxic and biodegradable. With the global adhesive and sealant market projected to reach $43 billion by 2020, and with demand increasing for nontoxic adhesives, this product could have a dramatic impact on the market. Mussel adhesives already have inspired PureBond, a commercially successful glue used in wood panel manufacturing.

Superwicking materials

Conventional vapor-compression air conditioners consume a great deal of energy and rely on refrigerants that are environmentally destructive when released. Terrapin advised Chunlei Guo’s team at the University of Rochester on the market demand for their bioinspired superwicking material technology and assisted them in securing funds to develop materials for energy-efficient indirect evaporative cooling. Leaves of the plants Ruellia devosiana and Alocasia odora have microscopic surface textures that trap water molecules, causing droplets to spread across the surface.

Mimicking this superwicking property, the research team fabricated materials with nano- and microscale features that wick large volumes of water, even up vertical surfaces. Such materials will increase the evaporation efficiency of cooling devices and, unlike the porous materials used in conventional evaporative coolers, they resist biofouling. The research team predicts a five-fold decrease in the energy consumed to cool buildings with this novel air conditioner.

Biocement bricks

Due to the energy-intensive firing process, clay bricks account for an estimated 1.2 percent of the world’s anthropogenic CO2 emissions. North Carolina-based biotech startup bioMASON has introduced Biocement bricks that are "grown" using bacteria. Combining sand, bacteria, water, nutrients and nitrogen and calcium sources together in a mold, bioMASON creates bricks that are comparable in strength to traditional bricks. The bacteria cause calcium carbonate to precipitate between sediment grains, effectively cementing the mixture together into a hardened brick. 

This process takes place at ambient temperature using locally sourced materials and can occur on-site, drastically reducing the carbon emissions and embodied energy of the bricks. To advance this technology, bioMASON received an SBIR Phase I grant from the National Science Foundation and is collaborating with the Biomanufacturing Training and Education Center at North Carolina State University to advance the technology.

Deformable glass

Although composed mainly of chalk, nacre found in seashells has astounding fracture resistance. Researchers at McGill University believe nacre owes its unique properties to a network of microcracks between brittle calcite plates that are filled with sticky polymer. Translating this idea, the team laser-engraved a 3D array of microscopic cracks in glass and filled them with polyurethane. The microcracks inhibit larger cracks from forming by deflecting and dissipating stresses, making this modified glass 200 times tougher than standard glass. 

The researchers believe the polyurethane fill makes little difference; simply engraving microcracks may be enough to toughen brittle materials, which could mean that the carcinogenic polyurethane can be avoided in the future. The engraved glass deforms without shattering, making it ideal for windows, electronics and glassware. The team also believes the same strategy can be applied to other materials that suffer from brittleness, such as ceramics.

Modern Meadow

Livestock production accounted for at least 18 percent of the world’s GHG emissions in 2006. It also requires 33 percent of the world’s arable land and 8 percent of the world’s water. Using novel tissue engineering techniques, Modern Meadow is producing lab-grown food and materials to make products analogous to — and better than — those produced from animals. Instead of using resources to raise and slaughter, the process takes a culture of cells from an animal and prompts the cells to grow into tissues similar to skin and muscle. Compared to current livestock production, this process could reduce the use of arable land by 99 percent, water by 96 percent and energy by 45 percent, while emitting 96 percent less greenhouse gas emissions.

The production process also avoids the heavy use of antibiotics and the ethical dilemmas associated with current livestock operations. Modern Meadow successfully has produced samples of leather in a variety of colors and thicknesses. The company, currently focused on leather production, envisions leather that is customizable by shape, texture and breathability.

SLIPS

Inspired by the Nepenthes pitcher plant, researchers at Harvard University’s Wyss Institute of Biologically Inspired Engineering developed an extremely slippery surface that repels most liquids and biofilms. The slipperiness of the pitcher-shaped leaf is caused by microscopic surface corrugations that hold water, forming a thin film. The researchers adapted this idea, creating a microstructured porous material which holds a specially formulated liquid lubricant. The surface is so slippery that even crude oil and liquid asphalt roll off it. Unlike engineered hydrophobic surfaces, this surface "self-heals" because the lubricant fills scratches as they occur.

The porous medium can be applied onto many surfaces. SLIPS has many potential applications such as anti-fouling, anti-icing, chemical and fluid handling, corrosion prevention, and pest control. SLIPS Technologies, Inc. was founded in 2014 to further develop the many commercial applications explored by the researchers while at the Wyss Institute.