Biological, physical and morphological factors for the programming of a novel microbial hygromorphic material

Abstract The urgency for energy efficient, responsive architectures has propelled smart material development to the forefront of scientific and architectural research. This paper explores biological, physical, and morphological factors influencing the programming of a novel microbial-based smart hybrid material which is responsive to changes in environmental humidity. Hygromorphs respond passively, without energy input, by expanding in high humidity and contracting in low humidity. Bacillus subtilis develops environmentally robust, hygromorphic spores which may be harnessed within a bilayer to generate a deflection response with potential for programmability. The bacterial spore-based hygromorph biocomposites (HBCs) were developed and aggregated to enable them to open and close apertures and demonstrate programmable responses to changes in environmental humidity. This study spans many fields including microbiology, materials science, design, fabrication and architectural technology, working at multiple scales from single cells to ‘bench-top’ prototype. Exploration of biological factors at cellular and ultracellular levels enabled optimisation of growth and sporulation conditions to biologically preprogramme optimum spore hygromorphic response and yield. Material explorations revealed physical factors influencing biomechanics, preprogramming shape and response complexity through fabrication and inert substrate interactions, to produce a palette of HBCs. Morphological aggregation was designed to harness and scale-up the HBC palette into programmable humidity responsive aperture openings. This culminated in pilot performance testing of a humidity-responsive ventilation panel fabricated with aggregated Bacillus HBCs as a bench-top prototype and suggests potential for this novel biotechnology to be further developed.