Investigation of the influence of nutrient additives and the role of microstructure on the unconfined compression behaviour of mycelium composites

Abstract Mycelium composites are emerging as low-carbon alternatives to conventional materials, but scalable engineering interventions to enable tailoring of mycelium composite behaviour for different engineering applications are needed. This study investigated the mechanical behahviour of living, non-pressed beechwood-based composites colonised by Pleurotus ostreatus prepared with six different nutrient amendments—wheat bran, oats, barley, rice, corn, and spent coffee grounds—in. The central hypothesis of the study is that mycelium development and ultimately mechanical performance of mycelium composites can be controlled by modifying microstructural properties of the input nutrient amendments. To this end, unconfined compression tests were performed on beechwood-nutrient specimens after four weeks of fungal growth. Oat- and wheat-bran mixtures exhibited the highest mean peak deviator stresses. For all additives four descriptors of surface area were determined via Brunauer–Emmett–Teller (BET), and X-ray computed tomography (XCT) analyses. Of these, the hypha-accessible surface area SA / V s (associated with pores > 10.5 microns) appeared to have the strongest influence on mycelium development and mycelium composite compression behaviour, following the determined mechanical ranking most closely. The use of ground barley (compared to whole barley) increased hypha-accessible SA / V s from 6.7 to 22.8 mm²/mm³ while the mean peak deviator stress increased by approximately 28%; whereas total and connected SA / V s changed little. While higher hypha-accessible surface area was generally associated with higher peak deviator stress, the spent coffee results indicates that the influence of microstructure does not act independently of nutrient chemistry. The results indicate that particle-size reduction is a practical processing variable for tuning the mechanical performance of living mycelium composites because it increases the surface area available for fungal colonisation and binding.