Cross-Kingdom Composites: Fungal Mycelia and Bacterial PHB for Sustainable Biofabrication

Abstract Crafting new materials using microbial biomass, such as fungal mycelium and bacterially synthesized biopolymers as building blocks, can be a very efficient solution for the post-petroleum polymers era, especially if they can be engineered in similar ways to conventional polymers. In this study, we used melt extrusion followed by molding processes to develop a biocomposite of mycelium from the non-pathogenic fungal strain Pleurotus ostreatus, grown on coffee-silverskin, and processed together with the bacterially synthesized polyhydroxybutyrate biopolymer and the bio-based plasticizer epoxide soybean oil methyl ester, the latter being important for efficient melt processing. The different amounts of the bacterial biopolymer and the fungal mycelium biomass affect the structural, mechanical, thermal, barrier, antioxidant, and overall migration properties, as well as the biodegradation of the developed biocomposites. Importantly, based on the TOPSIS performance analysis, we conclude that the most suitable composition to be used for eco-friendly food packaging is the one with 5 wt % mycelium/coffee silverskin biomass introduced in the plasticized polymer matrix. This novel composite biomaterial, derived from the fungal, bacterial, and plant kingdoms and processed using conventional plastic methods, paves the way for low-cost, sustainable biocomposites with broad application potential.