Woodpile structural designs to increase the stiffness of mycelium-bound composites

Mycelium-bound composites are biodegradable, eco-friendly materials grown by fungi onto solid ligno-cellulosic substrates. Mycelium is an interconnected network made of fungal cells that bind the substrates' particulates together. Uncompressed mycelium-bound composites have typically weak mechanical properties, similar to that of expanded polystyrene. In this paper, mycelium is grown onto porous woodpile struts structures to increase the final mechanical properties. The hypothesis is that increase in porosity can increase oxygen diffusion throughout the material and increase the development of dense mycelium network. Mycelium-bound composites grown from P. ostreatus onto bamboo microfibers substrates were studied to test this hypothesis. Constructing porous woodpile structures and monitoring the growth and the mechanical properties under compression, it was found that the porosity obtained through the design was able to increase dense fungal mycelium skin formation. As a result, the stiffness of the porous structures was multiplied by 6 after 28 days of growth. The specific modulus was in turned multiplied by 4 with the addition of 30 % macroscopic porosity. Despite the modest mechanical properties (stiffness about 0.5 MPa), the approach proposed illustrates how appropriate structural design can efficiently increase the properties of grown bio-based materials.