*1.1. Relevance*

Since the linkage between human consumption behavior and the rapidly increasing global warming becomes evident, life in the 21st century faces an ongoing environmental crisis. The use of conventional building materials in the global industry impacts largely on climate change by destructing more than 45 percent of global resources and emitting up to 40 percent of the energy-related carbon dioxide into the atmosphere [1,2]. Within an ever-growing society, there is and will be a constant need for materials, and consumption prevention is not the optimal choice. Awareness of already existing alternative systems is crucial for achieving sustainability. Waste can only be repurposed as a new resource if the majority of building components can be disassembled and returned to their original material cycles separately [3,4]. Fungal substrates are considered waste products and thus, can be used as compost and in a range of other applications [5]. By decreasing the cradle-to-gate manufacturing in the building sector, construction processes could be optimized to meet the social, ecologic, and economic values of the future generation. While the composting process was absent during the non-regenerative production line of the 18th and 19th centuries, at the present time, reorientation processes take place towards the cultivation of natural resources by breeding, raising, or growing materials. With

**Citation:** Nguyen, M.T.; Solueva, D.; Spyridonos, E.; Dahy, H. Mycomerge: Fabrication of Mycelium-Based Natural Fiber Reinforced Composites on a Rattan Framework. *Biomimetics* **2022**, *7*, 42. https://doi.org/10.3390/ biomimetics7020042

Academic Editors: Andrew Adamatzky, Han A.B. Wösten and Phil Ayres

Received: 15 March 2022 Accepted: 6 April 2022 Published: 8 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

sufficient improvement of the current fabrication methods, which are biologically driven and technologically supported, designing and manufacturing sustainable objects are goals within reach [3,6,7].

### *1.2. Recyclability of Composites*

With an increasing demand for lightweight and durable building materials, fiberreinforced polymer composites are considered a reliable alternative to conventional building materials such as concrete and steel. Determined by their components and fabrication methods, the structural and functional performance of fiber-reinforced polymers (FRC) can be adjusted to match the preferred application. Natural fiber-reinforced polymer (NFRP) composites consist of a high-strength reinforcement and a high-ductility matrix. Cellulosic fibers are highly sustainable and commonly used as reinforcement in composites. They are commonly agricultural residues; hence they enhance the ecological role of renewable resources, can be found in nature, are non-toxic, renewable, cost-effective, and allow bonding with different matrices. Bio-based composites with mineral and petrochemical matrices are widely used. However, their full biodegradability is costly to achieve due to the complex separation of the composites into their initial components, causing limited end-of-life options. Recyclability of composites with bio-based matrices is also limited, as degradation can only take place in specific industrial composting conditions [4,6,8]. Alternatively, mycelium-based matrices are organic matter and fully biodegradable, fulfilling the requirements of the circular material life cycle [8,9]. Since the main constituents of mycelium composites are fibrous substrates, lignocellulosic agricultural or forestry by-products and wastes such as straw and hemp, or porous substrate, e.g., sawdust, the costs of mycelium composites are low and enable waste upcycling [10,11]. The results of the first methods for the disintegration of mycelium-based composites (Ganoderma resinaceum and hemp fibers) in soil have strengthened their biodegradability, with a maximum weight loss of 43% after 16 weeks [12].

### *1.3. Mycelium Based Composites*

Mycelium is the root of fungi, building large thread-like networks, which are made of individual hyphae. Hyphae grow from mycelium fungal strain spores and consume feedstock containing carbon and nitrogen [13]. To create mycelium-based composites, fast and robust colonization of the substrate is required. Among the numerous subordinates of fungi, Dikarya build large and complex structures. These fungi have two special characteristics: Septa—transverse cell wall opening which can close—decreases damage caused to the colony by a rupture; and Anastomosis—the ability of two hyphae fusing together to build large networks and distribute nutrients from high to low concentrated areas. In the presence of hosting materials from agricultural waste products such as hemp or flax, mycelium merges with its environment and absorbs its host. Colonization and growth are highly dependent on the amount of cellulose in the given hosting material, as the nutrition of fungi consists of glucose. Mycelium can break down cellulose into glucose, which means that a high cellulose environment can improve its growth. Apart from compatibility, some natural fibers offer additional protection by a waxy outer layer, preventing contamination by other microorganisms. Generally, the hosting material must be sterilized through the processes of pasteurization, hydrogen-peroxide treatment, and natural composting [8]. The substrate can then be inoculated with the preferred fungal species. There are crucial growing conditions for successful cultivation, including low light, high humidity, medium temperature, and access to oxygen. After sufficient growth, the growing phase can be interrupted or stopped by exposing the cultivated composite to high temperatures over 80 degrees [8,9,13].
