Modeling the Photoinduced Reconfiguration and Directed Motion of Polymer Gels

A remarkable feature of certain biological species is their ability to dramatically alter their shape in response to environmental cues. Here, a computational model for photoresponsive polymer gels that contain spirobenzopyran (SP) chromophores is developed, and it is shown that these materials can undergo 3D biomimetic shape changes under non-uniform illumination. The SP moieties are hydrophilic in the dark, but become hydrophobic under illumination with blue light. Hence, with the incorporation of these chromophores into gels in aqueous solutions, light can be harnessed to control the gel's swelling or shrinking and, thereby, dynamically alter the gel's shape. The model is first validated by determining the effects of uniform illumination on the temperature-induced volume phase transitions in these gels, and show good agreement between these results and available experimental data. These gels can also be patterned remotely and reversibly by illuminating the samples through photomasks and, thus, molded into a variety of shapes with feature sizes on the submillimeter length scale. Furthermore, by repeatedly rastering the light source over the sample, the system can be driven to exhibit another biomimetic behavior: sustained, directed motion. The introduction of a temperature gradient provides a means of further controlling this autonomous movement. The results point to a robust method for controllably reconfiguring the morphology of soft materials and driving the self-organization of multiple reconfigurable pieces into complex architectures.