**1. Introduction**

In the past decades, the construction industry has been challenged by the rapidly increasing population and the proportional demand in housing and construction material supply [1]. Concurrently, the excessive energy used, the pollution and the waste generated to produce traditional building materials, such as steel, cement and plastics, impose severe environmental challenges [2]. The majority of greenhouse gas (GHG) emissions results from the processing of materials that are commonly used in the construction industry [3]. The diminution of natural resources and the growing recognition of climate change have been encouraging researchers and companies to seek sustainable alternatives to the currently used materials [4]. The 4R concept of Reduce, Reuse, Recycle and Recover has been

**Citation:** Özdemir, E.; Saeidi, N.; Javadian, A.; Rossi, A.; Nolte, N.; Ren, S.; Dwan, A.; Acosta, I.; Hebel, D.E.; Wurm, J.; et al. Wood-Veneer-Reinforced Mycelium Composites for Sustainable Building Components. *Biomimetics* **2022**, *7*, 39. https://doi.org/10.3390/ biomimetics7020039

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

Received: 17 March 2022 Accepted: 29 March 2022 Published: 31 March 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/).

increasingly becoming more prevalent to reduce waste and promote circular economy models within industries.

Growing biological materials using plant-based waste from industries can be a potential solution [5]. Among these, the development of bio-based composite materials from mycelium has been introduced recently and could potentially transform the construction sector. Indeed, mycelium-based bio-composites could support the transition towards the utilization of the available organic waste resources by binding them through the mycelium network, further facilitating the development of sustainable and circular alternatives to energy- and resource-intensive construction materials and building products.

Mycelium has been proven to deliver a range of properties significant to construction, from good acoustic to mechanical properties, including compressive strength, while being a renewable and low-carbon alternative material with relatively good fire-resistance properties [6]. However, one of the major limitations for its application within the construction industry is caused by its low resistance to tension and bending [7]. On the other hand, wood has been known for centuries for its high structural performance. It is an inherently tension-resistant material due to its fiber arrangement [8]. Therefore, this research aims at combining the advantages of each material: exploiting the intrinsic properties of mycelium and wood veneer, and exploring the development of novel, 100% bio-based mycelium-wood veneer composites with improved mechanical properties.

We explore two methods for increasing material strength: compression with heat and pressure, and the integration of topologically designed reinforcement within the mycelium matrix. While compression improves material strength and Young's modulus by increasing the density of the material [9], an embedded veneer lattice in mycelium is expected to increase the performance of the composite due to the combination of the compressive strength of mycelium and tensile strength of the internal fiber structure of wood. We investigate these two methods through physical prototyping and testing and compare them in terms of effectiveness, advantages and disadvantages. The possibility of combining the two methods and compressing a veneer-reinforced block is also explored. We develop a hybrid fabrication method suitable for this composite material system and test the samples structurally to assess the effect of compression and reinforcement on composite strength.

The focus of this research is to explore ways to improve the structural performance of this composite for architectural use cases, while maintaining satisfactory levels of suitable acoustic performance. The intended application is currently planned for interior use; therefore, the water and pest resistance of the resulting composite was not yet studied. The acoustic and fire performance will be subject to further studies.

### **2. State of the Art**

### *2.1. Mycelium-Based Composites*

The sustainability issues arising from the use of synthetic and non-renewable resins and binders in the engineered wood industry are well known. Thus, new solutions with bio-based resins with a lower environmental impact are being investigated globally [10]. Among the various materials used, mycelium has the potential to be a sustainable and more attractive alternative to most of the available binder matrices. Mycelium is the root part of fungi, composed of filamentous strands of fine white hyphae. When organic substrates, such as wood or natural fibers, are inoculated with specific fungi species, mycelium starts growing by using the substrates' nutrients [11]. By the time mycelium spreads through the whole substrate, a network structure is developed that binds the discrete particles of the substrate together. Therefore, a range of sustainable and green products can be manufactured in an environmentally friendly way without the need for any adhesives, potentially replacing various energy-intensive building materials. One advantage of mycelium-based composites over traditionally engineered wood-based materials is that they can be recycled or composted at their end of life without any negative impact on the environment [12]. No toxic substances or synthetic components are involved; therefore, mycelium-bound

composite materials fit into the model of a bio-circular economy where there is no waste at the end of a product's lifecycle [6,13].

The properties of mycelium-bound materials can be customized to a certain extent by adjusting the parameters of the manufacturing process. A thorough framework of the main parameters influencing mycelium-based composites was presented in various studies recently and identified advantageous material properties, such as low thermal conductivity, high acoustic absorption, and fire protection properties [10–12]. However, challenges generally arise from research knowledge gaps [14] that limit the use of these materials only to non-structural or semi-structural applications.
