Programmable assembly of mechanically robust and functional polymer–spore biocomposites in organic solvent

Microbial biocomposites offer genetically programmable and regenerative functionality, but their mechanical tunability remains limited by the mild conditions required for biological activity and viability. Here, we report the programmable self-assembly of Bacillus subtilis spores with benzalcyanoacetate (BCA)-functionalized polymers to form robust composites exhibiting tunable viscoelastic and tensile properties. Surface-exposed cysteines on the spore coat react with BCA motifs, forming dynamic thia-Michael networks with Young’s moduli of >100 MPa. Systematic variation of BCA reactivity and comonomer-dependent polymer dynamics enabled control over stiffness, stress-relaxation behavior, microscale morphology, and covalent biocontainment. Incorporation of engineered spores confers catalytic function that can be regenerated following solvent-triggered disassembly. This work establishes a modular platform for constructing biocomposites that are both mechanically and genetically programmable, bridging the synthetic and biological domains through molecularly defined interfaces.