Circadian control of colloidal materials

Through billions of years of evolution, biological systems have engineered exquisite sensors, triggers and timers that allow cells and organisms to adapt and respond to external and internal cues, anticipate needs, and maintain homeostasis. This robust circuity leverages cascading molecular interactions to modulate chemical and mechanical properties from the subcellular to organismal level. Here, we demonstrate the ability to harness biological timers to bring complex, life-like behavior to synthetic materials. Specifically, we functionalize circadian clock proteins from cyanobacteria, KaiB and KaiC, to engineer time-dependent crosslinking of suspended colloids. The resulting material self-assembles with programmable kinetics, producing macroscopic changes in material properties, visible to the naked eye, via molecular-level assembly of KaiB-KaiC complexes. We show that colloid crosslinking depends strictly on the phosphorylation state of KaiC, with kinetics that are coupled to KaiB-KaiC complexing. We further show that the stability of colloidal superstructures depends sensitively on the number of Kai complexes linking each pair of colloids. A high concentration of oscillatory complexes allows for robustly timed self-assembly and stabilization against dissolution, while low concentrations allow circadian oscillation of material structure. This work introduces the concept of harnessing biological timers to control synthetic materials; and, more generally, opens the door to using protein-based reaction networks to endow synthetic systems with life-like functional properties.