A closed-loop tray bioreactor for online monitoring of mycelium-based composites

Mycelium-based composites are bio-derived structural materials produced by cultivating filamentous fungi through lignocellulosic substrates under solid-state fermentation conditions. Solid-state fermentation remains difficult to control because fungal growth is highly sensitive to local gradients in temperature, humidity, and gas composition. This study presents the design, construction, and experimental validation of a modular tray bioreactor for the controlled cultivation of mycelium-based composites. The system combines closed-loop feedback control of temperature and relative humidity with continuous monitoring of carbon dioxide and oxygen, online calculation of carbon dioxide evolution rate, programmable environmental trajectories, and synchronized multi-unit operation through a primary-secondary architecture. Performance was evaluated in two abiotic and two biotic experiments. Under abiotic conditions, the reactor provided stable regulation within a practical operating range of approximately 26-29°C and 25-50% relative humidity, with a steady-state temperature error below 0.5°C at the established setpoints and a root mean square error of 0.12°C during fixed-set-point operation. During biotic experiments with Ganoderma sessile, environmental regulation remained comparable, while carbon dioxide accumulation and carbon dioxide evolution rate clearly distinguished biological activity from the abiotic baseline and resolved the transition from internal growth in the closed mould to external growth after demoulding. The biotic runs (one dynamic and one constant schedule, conducted without biological replicates) are presented as a proof-of-concept demonstration of the platform rather than a quantitative study of growth kinetics, and the operating envelope and the limited resolution of the electrochemical oxygen sensor for OUR and RQ analysis are reported as current hardware constraints. The platform was also deployed as a synchronized four-unit array across chambers of different sizes. Together, these results establish a reproducible experimental platform for controlled fermentation of mycelium-based composites and for future studies linking environmental regulation with growth dynamics and material performance.