Modeling the Photoinduced Reconfiguration and Directed Motion of Polymer Gels

Abstract

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 fi rst 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 reconfi guring the morphology of soft materials and driving the self-organization of multiple reconfi gurable pieces into complex architectures.

Designing biomimetic reactive polymer gels

“…To simulate the dynamic behavior of these SP-containing gels, we derived a model [3] that accounts for the kinetics of the photoinduced isomerization of the SP chromophores, and the corresponding decrease in the hydration of the polymer network caused by the isomerization of the chromophores to their spiro form. The resulting equations were solved numerically using our three-dimensional 'gel lattice spring model' or gLSM [26].…”

“…We begin by describing recent studies [3] on photosensitive polymer gels containing spirobenzopyran (SP) chromophores, which are anchored onto the polymers in the network. In the presence of light, these gels can undergo three-dimensional biomimetic shape-changes.…”

“…Here, we model polymer gels whose shapes can be reconfigured 'on demand' through the application of non-uniform illumination. Furthermore, by repeatedly rastering the light source over the sample, the same system can be driven to exhibit another biomimetic behavior: sustained, directed motion [3]. The underlying impetus for this light-induced motion is distinctly different from that observed in liquid crystal elastomers, where the motion results from light-induced changes in orientational order within the material [13][14][15][16].…”

Self-Oscillating Gels

“…As a result, on-off switching of the soluble-insoluble self-oscillation for the polymer solution is possible by photo-irradiation. Theoretical simulation of chemomechanical behaviors corresponding to this photoregulation system is also demonstrated [47].…”

“…Then theoretical simulation becomes effective tool for understanding the chemomechanical behaviors. Balazs et al [45][46][47][50][51][52][53] developed a mathematical model for simulating chemomechanical behaviors of the selfoscillating gels. Since reported in 2006 [50], they have demonstrated several aspects of the self-oscillating behavior for the gel by theoretical simulation.…”