The Subterranean Substance With Surprising Superpowers

small green seedlings sprout from rich dark soil

Biological Strategy

Fungi

Mary Hoff

Image: Hans Braxmeier / Pixabay / Free non-commercial use

Manage Compression

When a living system is under compression, there is a force pushing on it, like a chair with a person sitting on it. When evenly applied to all sides of a living system, compression results in decreased volume. When applied on two sides, it results in deformation, such as when pushing on two sides of a balloon. This deformation can be temporary or permanent. Because living systems must retain their most efficient form, they must ensure that any deformation is temporary. Managing compression also provides an opportunity to lessen the effects of other forces. Living systems have strategies to help prevent compression or recover from it, while maintaining function. For example, African elephant adults weigh from 4,700 to 6,048 kilograms. Because they must hold all of that weight on their four feet, the tissues of their feet have features that enable compression to absorb and distribute forces.

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Manage Mechanical Wear

A living system is subject to mechanical wear when two parts rub against each other or when the living system comes in contact with abrasive components in its environment, such as sand or coral. Some abrasive components are a constant force, such as finger joints moving, while others occur infrequently, such as a sand storm moving across a desert. Living systems protect from mechanical wear using strategies appropriate to the level and frequency of the source, such as having abrasion-resistant surfaces, replaceable parts, or lubricants. For example, human joints like shoulders and knees move against each other all day, every day. To protect from mechanical wear, a lubricant reduces friction between the cartilage and the joint.

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Prevent Deformation

When a living system undergoes compression, tension, shear, bending, or twisting, its internal inter-molecular forces can often resist these forces and even change shape temporarily, returning to the original shape when the forces stop. However, if the force is too strong or lasts too long, permanent deformation or structural failure can occur, resulting in death. Therefore, living systems have strategies to resist deformation or help ensure limited deformation. For example, bones have thin crystals and proteinaceous fibers that provide strength and flexibility, protecting them from forces that would otherwise cause deformation on a daily basis.

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Fungi

Kingdom Fungi: Mildews, molds, mushrooms, rusts, smuts, and yeasts

Once thought to be more closely related to plants, fungi have been found to contain chitin in their cell walls, indicating a closer evolutionary relationship to animals. Fungi are decomposers, using digestive enzymes to break down their surroundings, making them an essential part of ecosystems worldwide, as new soil is formed from rotting matter. Almost all fungi reproduce through spores (mushrooms, molds) or asexual budding (some yeast). There are estimated to be more than 2 million species, but only about 140,000 have been described. Fungi have great importance in culture, food, and medicine (including being the source of penicillin) worldwide.

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Fungi create a strong but lightweight material by producing a random network of tiny threads.

Introduction

Pick up a handful of soil. At first glance, it might seem simply like a lot of brown stuff. Look closer and you’ll see every particle tells a story. Dig a little deeper and you’ll see that woven through just a single shovel-full are literally miles of fibers created when fungi break down plant material to make tissue for themselves. The fibers, collectively known as mycelium, reach far and wide to harvest food for the fungi.

In the process, they create a physical network with remarkable mechanical properties. Organic, lightweight, durable, and moldable, mycelium not only offers inspiration for the design of manufactured materials, but also can be used directly to make a wide range of objects with desirable traits.

The Strategy

Fungi grow from spores just as plants grow from seeds. When a spore sprouts, it puts out a microscopic rootlike structure called a hypha. As it grows, the hypha branches, eventually creating a network of tube-shaped threads called mycelium that can stretch for miles underground, fusing with other hyphae to create a dense web.

Each thread consists of several types of chemicals. On the inside are proteins and chitin fibers held together with sugars that provide mechanical rigidity and strength. On the outside, beta-glucans form a gel-like material that give flexibility and expandability. In which direction the fibers grow and how dense the network becomes depends on the physical and chemical traits of the environment as well as the food available within it.

The combination of the materials that make up individual hyphae and the structure of the mycelium as a whole, composed of both fibers and the spaces between them, give the overall material some highly desirable traits. It is at the same time strong and flexible. It can be compressed and bounce back. It slows the spread of heat and sound. And because the shape of the space and amount of food available influence the degree and direction the hyphae grow, a mycelium mat can take a variety of shapes and density characteristics.

The Potential

Mycelium provides inspiration for making lightweight containers, construction panels, furniture, clothing, and other objects with a wide range of beneficial traits such as padding, durability, thermal insulation, soundproofing, and the ability to wick moisture.

In addition to serving as a source of inspiration, mycelium can be produced and used as a raw material itself. Because it is organic, mycelium made by fungi offers additional benefits. It can be produced from waste materials. It is biodegradable. And when it burns it doesn’t produce harmful gases as do plastics and other manmade materials.

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Last Updated June 15, 2021

References

“Mycelium has a filamentous network structure with mechanics largely controlled by filament elasticity and branching, and network density. We report the morphological and mechanical characterization of mycelium through an integrated experimental and computational approach. The monotonic mechanical behavior of the mycelium is non-linear both in tension and compression. The

material exhibits considerable strain hardening before rupture under tension, it mimics the open cell foam behavior under compression and exhibits hysteresis and the Mullins effect when subjected to cyclic loading.” (Islam et al., 2017:1)

Journal article

Morphology and mechanics of fungal mycelium

Scientific Reports | October 12, 2017 | M. R. Islam, G. Tudryn, R. Bucinell, L. Schadler, & R. C. Picu

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Reference

“Wood-decay species can degrade cellulose, hemicelluloses and lignin by enzymatic or non-enzymatic mechanisms, of which selectivity is both species-specific and environmentally determined. The substrate matrix thus is forced and penetrated by the hyphae, which develops inside as an increasingly tight net. Over time,the substrate is replaced partially by the fungal biomass and the resulting mycelium is able to strongly cement the substrate itself, resulting in a biocomposite material.” (Girometta et al., 2019:2)

“Altogether, mycelium-based materials have demonstrated their potential to replace the use of less environmentally friendly materials, such as bioplastics or wood composites. The resulting materials are fully natural and compostable, thus potentially supporting the transition toward a circular economy, where the value of materials and resources is maintained in the economy for as long as possible and the generation of waste is minimized. Moreover, a unique feature of mycelium-based composites is the wide diversity of technical and aesthetic properties that can be achieved through minimal variations in the fabrication process, such as the substrate or fungal strains employed.” (Girometta et al., 2019:3)

Journal article

Physico-Mechanical and Thermodynamic Properties of mycelium-based biocomposites: A review

Sustainability | January 8, 2019 | Carolina Girometta 1 , Anna Maria Picco, Rebecca Michela Baiguera, Daniele Dondi, Stefano Babbini, Marco Cartabia, Mirko Pellegrini, and Elena Savino

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