Mechanically controlled liesegang pattern formation in stretchable polyacrylamide gels for elastic deformation tracking

Pattern formation in nature has been intellectually appealing for many scientists since antiquity. Simultaneous diffusion and reaction of chemicals in gel media may lead to precipitation and complex pattern formation through self-assembly. Periodic precipitations patterns, also known as Liesegang patterns (LP), are one of the stimulating examples of such self-assembling reaction-diffusion systems. So far, it was shown that LP’s periodic band structure and their unique geometry can be controlled by controlling the reaction parameters (e.g. concentration of the reactants) and affecting the reaction medium (e.g. external electrical field). However, so far, the research on LPs have been concentrated mostly around how these patterns are forming, to retrieve information to build a universal mathematical model for them. Although there are studies showing the effect of external fields on the development of these patterns, to the best of our knowledge, so far, there is no example of these systems, used to retrieve information about the changes in the environment as they form. Here, we first show the formation of Liesegang rings by a diffusion-precipitation reaction in a stretchable hydrogel. Then, we present how to use these patterns to ‘read’ the duration, the extent, and the direction of gel deformation. Also, we describe deviations from LP behavior for the patterns (spacing that can be mathematically defined by a geometrical series) formed after the unloading. We believe this first display of such an ‘environmental sensing’ to be a starting point for more investigations on many aesthetically appealing and mathematically challenging self-assembled systems, which have been studied for decades.