Hydrogels with Tethered Transcription Circuit Elements for Chemical Communication and Collective Computation

Tissues, robots, and other distributed systems must make decisions about information originating from and then orchestrate responses at different physical locations. Cell-cell communication processes are essential for morphogenesis, immune response, and wound healing. Devising methods for programming analogous distributed behaviors in synthetic materials, such as multi-scale pattern formation or self-assembly, remains a challenge. Here, we devise a design principle for distributed chemical computing and construct a library of transcription circuit elements, termed tethered genelets (TGs), that implement this design principle within networks of 50-micron hydrogel nodes (HNs). TGs exhibit digital behavior in the form of a "distance-response curve" - they switch off in response to signals emanating from an HN within a specific distance but are unaffected by faraway signals. Computational studies show that this property allows HN networks to reliably propagate information without attenuation and to program specific spatiotemporal patterns such as pulses and oscillations with tunable frequencies. In experiments, we verify that TGs send and receive signals as designed and validate the function and modularity of a library of 15 TGs circuit elements. The resulting design principle and library of molecules now provide a means of programming a diverse range of distributed chemical behaviors, allowing for distributed communication and dynamics in soft robots, responsive surfaces, and other bio-materials.