Fungi are vital to natural ecosystems by breaking down dead organic material and cycling it back into the environment as nutrients. But new research from the University of Utah finds one species, Marquandomyces marquandii, a ubiquitous soil mold, shows promise as a potential building block for new biomedical materials.
In recent years, scientists have examined fungal mycelium, the network of root-like threads—or hyphae—that penetrate soils, wood and other nutrient-bearing substrate, in search of materials with structural properties that could be useful for human purposes, particularly construction.
In a series of lab demonstrations, U mechanical engineering researchers show M. marquandii can grow into hydrogels, materials that hold lots of water and mimic the softness and flexibility of human tissues, according to a recent study .
[caption width="501"] Atul Agrawal, Ihsan Elnunu and Steven Naleway, left to right, observe how fungal tissues perform using an instrument that measures materials' tensile, shear, compression and other mechanical properties. Photo credit: Dan Hixson.[/caption]
Unlike other fungi that struggle with water retention and durability, M. marquandii produces thick, multilayered hydrogels that can absorb up to 83% water and bounce back after being stretched or stressed, according to Atul Agrawal, the lead author of the study. These properties make it a good candidate for biomedical uses such as tissue regeneration, scaffolds for growing cells or even flexible, wearable devices.
"What you are seeing here is a hydrogel with multilayers," said Agrawal, holding a glass flask containing a fungal colony growing in a yellowish liquid medium. "It's visible to the naked eye, and these multiple layers have different porosity. So the top layer has about 40% porosity, and then there is an alternating bands of 90% porosity and 70% porosity."
Looking to nature to innovate materials
Agrawal is a Ph.D. candidate at the John and Marcia Price College of Engineering. His paper is the latest to emerge from the lab of senior author Steven Naleway , an associate professor of mechanical engineering who explores biological substances to develop bioinspired materials with structural and medical applications.
Agrawal and Naleway are seeking patent protection for their discoveries about the Marquandomyces fungus.
"This one in particular was able to grow these big, beefy mycelial layers, which is what we are interested in. Mycelium is made primarily out of chitin, which is similar to what's in seashells and insect exoskeletons. It's biocompatible, but also it's this highly spongy tissue," said Naleway, whose lab is funded by the National Science Foundation. "In theory, you could use it as a template for biomedical applications or you could try to mineralize it and create a bone scaffolding."
Fungi comprise its own kingdom of organisms, with an estimated 2.2 to 3.8 million species, and just 4% have been characterized by scientists. For decades, scientists have derived from fungi numerous pharmacological substances, from penicillin to LSD. Naleway is among a cohort of engineers now looking to fungal microstructures for potential use in other arenas.
Why fungal mycelia have interesting mechanical properties
In collaboration with U mycologist Bryn Dentinger , Naleway's lab has produced a string of papers documenting potentially useful structural properties of various species of fungi. One outlined how fungi that grow short hyphae are more stiff than those that grow longer hyphae. Another catalogued the various ways bracket fungi's high strength-to-weight ratios make them a viable alternative in various applications, including aerospace and agriculture.
The way fungal hyphae grow is the reason why mycelia could have useful structural properties.
"As they grow forward, they lay down these cross walls that then compartmentalize a really long filament into many, many individual cells," said Dentinger, an associate professor of biology and a curator at the Natural History Museum of Utah. "They will grow forever as long as there's enough nutrition around. There's not a developmental stage where they'll stop. That's a fundamentally different strategy to living in the environment than animals have achieved."
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Fungi evolved multicellularity in ways that are much different than what we see in animals and plants, in which cells differentiate and usually remain in differentiated states.
"In fungi, every cell is capable of differentiating and then reverting to the original state. They're just a lot more malleable and adaptable," Dentinger said. "So there's a lot that we could exploit from those behaviors that really haven't been explored fully."
Fortuitous accidents can fuel discovery
Like many discoveries involving fungi, the U hydrogel experiments arose from a happy accident. The group was originally conducting research into what they thought was a hydrocarbon-eating organism commonly called "kerosene fungus," known to contaminate aviation fuel.
But as their cultures grew the scientists noticed they were behaving unexpectedly, growing in strange layers. Dentinger correctly identifying the mystery fungus as Marquandomyces.
"It highlights the state of mycology because we only have a handle on such a small proportion of the fungi," Dentinger said. "There's a lot of misidentification around in culture collections and even in herbarium collections. Misidentifying something is just part of the game. And that's really why I am involved with this work with Steven."
Over the course of the study, the team found these mycelial cultures showed an unusually high degree of hydrophilia, retaining 83% water without losing its shape.
"What was interesting about our research was that the fungus itself created a full-blown structure that was highly organized," Agrawal said. The Marquandomyces outperformed materials made from more commonly studied fungi, such as Ganoderma and Pleurotus, species that exhibit limitations in water retention, restricting their application in hydrogel-based biomedical systems.
In lab experiments, Agrawal's team found the material could recover 93% of its shape and strength after repeated stress.
"For it to be able to hold this structure together, this entire mycelium colony is connected together, and what we saw through optical imaging is that within these layers at the site of transition, it's a functionally graded structure," Agrawal said. "It helps distribute the stress concentration between layers. So when we apply mechanical stress, it distributes that stress evenly and helps with the mechanical performance of these hydrogels."
