Assessing mycelium-based blocks utilizing <i>Pleurotus ostreatus</i> versus <i>Trichoderma virens</i>: material characterization and substrate ratios of bamboo residues, spent coffee grounds, and rice husks

Mycelium-based blocks (MBBs) represent an innovative and eco-friendly approach to composite material design, combining fungal mycelium with lignocellulosic biomass to produce sustainable, rapidly regenerating materials with intrinsic hydrophobic properties. This study investigates the fabrication and characterization of MBBs using <italic>Pleurotus ostreatus</italic> (Basidiomycota) as the mycelial binding agent and compares its performance with <italic>Trichoderma virens</italic> (Ascomycota), a non-mushroom mycelial alternative. The performance of both fungal species was assessed using three lignocellulosic substrates: bamboo residues (BRs), spent coffee grounds (SCGs), and rice husks (RHs). Substrates were evaluated individually (100% BRs, SCGs, or RHs) and in binary mixtures at a 50:50 ratio (BRs:SCGs, BRs:RHs, and SCGs:RHs). The physical and mechanical properties—including density, water absorption, compressive strength, and modulus of rupture—were systematically evaluated. Results demonstrated that MBBs composed of BRs and <italic>P. ostreatus</italic> mycelium achieved the highest average compressive strength (0.190 MPa), outperforming <italic>T. virens</italic>-based blocks and other MBB formulations. Additionally, blocks incorporating RHs, SCGs, and <italic>P. ostreatus</italic> exhibited the highest density, reaching 379 kg/m³. In contrast, RH-based blocks with <italic>T. virens</italic> mycelium showed the highest water absorption, at 294.25%. Overall, MBBs utilizing <italic>P. ostreatus</italic> mycelium outperformed those with <italic>T. virens</italic> in key metrics such as density, compressive strength, and modulus of rupture, though water absorption was a notable exception. These findings underscore the potential of MBBs—particularly those incorporating SCGs, BRs, and RHs—as sustainable, non-load-bearing construction materials. Their reduced reliance on conventional resources highlights their promise as eco-friendly alternatives for sustainable applications.