Tailoring structure-property relationships of fungal mycelium for material applications: A process engineering approach for pure mycelium-based biomaterials

Pure mycelium materials (PMMs) offer sustainable alternatives to traditional animal and synthetic polymer-based leather and petroleum-based packaging materials, by using innocuous fungi and agri-food biomass residues. Fungi respond readily to growth conditions and produce mycelia with tunable material properties to yield a diverse array of products. Additionally, these properties can be further modified through various post-processing techniques. This critical review examines how process engineering approaches, such as manipulating the fungal microenvironment, via optimal growth conditions, substrate selection, and bioreactor design, as well as post-processing techniques, can be effectively employed to engineer the properties of PMMs. It specifically describes the structure-property relationships of mycelium as governed by substrate assimilation and fermentation process parameters, and their impact on the fungal phenotype. To this, a comprehensive discussion on the role of fermentation conditions to mediate changes in fungal hyphal structure, composition, orientation, and cell wall composition - all of which determine the final mycelium material properties - is provided. By examining these relationships, this review aims to provide process insights that could guide the design and implementation of PMM production systems with enhanced yield and productivity along with the provision of tuneable material properties. Finally, the review highlights other considerations such as life cycle assessment and regulatory requirements, and their relationships with process engineering, which are important for PMM development and their industry exploitation.