Views: 4 Author: Li Bo Publish Time: 2023-06-29 Origin: China Popular Science Expo
Speaking of mushrooms, people can't help but associate it with eating for the first time. Although traditionally considered vegetables by the general public, mushrooms are not plants, but fungi. Moreover, these parts that we usually regard as food are not all of the mushrooms. Under the ground (or in the decayed wood) where they grow, there is also a hyphae network composed of countless cells, called mycelium.
Mycelium is the basic structural unit of fungi, generally in the shape of a tube, with a fixed cell wall, mostly colorless and transparent, with a diameter of 1-30 μm, responsible for absorbing, transporting and storing nutrients. In order to obtain nutrients, the fungi will continue to radiate and extend the mycelium outward during growth, penetrate into the gaps between the soil and decayed wood, and continue to produce branches, eventually forming a huge mycelium network underground.
The mycelium seen with the naked eye (top) and the mycelium observed under the electron microscope (bottom)
The main components of mycelial cell wall include chitin, glucan and protein. The outer layer of the cell wall is mainly protein and glucan, while the inner layer is chitin interwoven with other polysaccharides in the form of microfibrils to form a strong skeleton. Chitin has a tensile strength comparable to that of carbon fibers and has excellent thermal stability and flame retardancy. And glucan, like a binder, can help the mycelium network to bind more closely with the substrate it grows in, so that it can better absorb nutrients from it. It is precisely because of these outstanding characteristics that mycelium has gradually entered the field of vision of material scientists.
Structural composition of mycelium
In view of the structure and characteristics of mycelium, some innovative scientists try to apply it to the development and manufacture of new biomass materials, and apply it to various design fields. By establishing suitable culture conditions, the hyphae of mushrooms gradually grow into a single tubular hyphae, and then artificially induced to make the tubular hyphae aggregate into a dense sheet-like structure by intertwining each other. Since the entire formation process is achieved through the natural growth of mycelia without chemical synthesis, this material is also called a bio-assembly material.
The growth of purple Ganoderma lucidum mycelium exhibits different structural characteristics after adding different cellulose substrates
At present, there are mainly two types of mycelium materials: pure mycelium materials and mycelium composite materials. Pure mycelium material exists in a flat form and is naturally grown from pure mycelium. Its texture is similar to animal leather. It has been widely used in clothing, shoe and hat processing and other fields. In recent years, many internationally renowned luxury brands have launched products made of mycelium leather. Compared with raising livestock to produce leather, the carbon emission of mycelium leather production is much smaller than that of the former. It is also for this reason that keen luxury giants see the huge business opportunities hidden in it. After all, environmental protection is the most concerned and popular fashion element nowadays.
With the deepening of research, scientists have discovered that pure mycelium materials have interactive characteristics that can be printed, dyed, and sewed. At the same time, they can also allow mycelium to continue to grow on other fabrics to further form mycelium composite fabrics. Moreover, the material has tensile resistance due to the intertwining and compression of mycelium, and when they are treated with glycerin, the stretchability can be further enhanced to achieve rubber-like properties. This kind of foam rubber produced by using mycelium has many advantages such as lightness, breathability, flame retardancy, and waterproof.
Packaging foam material (a), packaging board (b), leather-like material (c) and flexible sponge material (d) made of mycelium
In addition, scientists have discovered that by mixing pure mycelium leather materials with natural or synthetic polymers to form composites, their fatigue and abrasion resistance can be further improved. This material is soft and wear-resistant. What's even more commendable is that, as pure natural products, they have excellent biocompatibility, will not cause skin irritation and allergic reactions, and are quite safe to use, so they are made into facial masks, eye masks and cosmetic puffs and other medical and beauty products have huge market application potential.
Compared with pure mycelium materials, mycelium composite materials mainly exist in a three-dimensional form, which is a composite material formed by combining mushroom mycelium with agricultural waste such as rice husks, corncobs, straw, and wood chips. In the process of mixed cultivation with these wastes, the mycelium decomposes the wastes to obtain nutrients for its own growth, and at the same time tightly combines the wastes as the attachment of its own growth.
Features of mycelium composites under different magnification scales: surface features under the naked eye scale (a); longitudinal section features under the naked eye scale (b); longitudinal section features after magnification of 5mm scale (c); after 50uM scale magnification under the scanning electron microscope Mycelium characteristics of (d)
Depending on the incubation time, the color of the material changes from white to brown. The color difference is mainly caused by the amount of mycelium growing on the surface of the material. Usually, the whiter the color, the more vigorous the mycelium growth. The biggest advantage of this composite material lies in its super plasticity, which can be made into any shape according to the different growth molds. Moreover, this material combines the characteristics of mycelium, plant fiber, straw and other substrates, and has excellent properties such as light weight, strong compression resistance, heat insulation, sound insulation and noise reduction, flame retardant and waterproof. Therefore, mycelium composite materials are mainly used to make cushioning packaging, building bricks, soundproof wall panels, lampshades, tables and chairs, and interior decoration materials for cars.
The "growth hall" (a) using mycelium material as the building surface material and the space tree branch structure (b) built with mycelium bricks displayed at the Dutch Design Week in 2019
In addition to the application of mycelium materials in the fields of leather and packaging, construction and other materials. Scientists have also applied it to research on alternative protein foods. Based on the technology of pure mycelium leather material, a new type of mycelium artificial meat was born. Compared with artificial meat made of soy protein, it not only has no beany smell, but also tastes closer to real meat. Not only easy to digest and absorb, but also rich in more vitamins and minerals. Therefore, it is favored by more and more vegetarians.
In addition, due to the differences in the main components such as chitin and glucan in the mycelium cells of different mushrooms, scientists can select different types of mushrooms as culture objects according to different needs in the production of mycelium materials. For example, using the hyphae of edible fungi such as Pleurotus ostreatus to produce artificial meat can effectively avoid food safety risks, and using mushrooms with a high degree of lignification such as Ganoderma lucidum to produce rubber materials and building materials can significantly improve their strength and toughness. In nature, there are more than 20,000 species of macrofungi known as mushrooms. These abundant species resources provide almost unlimited possibilities for the production and application of mycelium materials.
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