NON-TECHNICAL SUMMARY: The biological growth of filamentous fungi cells (hyphae) and their bonding with substrate particles leads to highly sustainable composite materials called fungal composites. Practical approaches to improve fungal composite mechanical properties are necessary to realize this potential fully. A promising approach to improving fungal composite mechanical properties is reinforcing the substrate with rigid fillers, as commonly used for synthetic polymer composites. The fundamental challenge underlying this approach is that hyphae do not bind naturally to synthetic particles to form the composite due to a lack of nutrient elements. This project will support research on understanding mechanisms to promote bonding between fungal hyphae and synthetic particles to obtain improved mechanical properties in fungal composites that rival traditional composites. The findings from this study will support the development of advanced fungal materials that will advance national technological leadership in biological materials and conserve national non-renewable resources, which will result in significant societal and economic benefits. Additionally, the project will contribute to STEM workforce development on biological materials through outreach activities for K-12 students and research opportunities for undergraduate and graduate students. TECHNICAL SUMMARY: This project will support fundamental materials research on understanding the mechanisms that govern t