Mechanical Adaptability of Patterns in Confined Hydrogels

Pattern formation and dynamic restructuring plays a critical role in a plethora of natural processes. Controlling pattern formation dynamically in soft synthetic materials would allow one to control an entire range of surface functionalities. Herein, we focus on the dynamic restructuring between different patterns in thermoresponsive poly(N-isopropylacrylamide) membranes constrained between two rigid surfaces. We use three-dimensional gel Lattice Spring Model to simulate the dynamics of constrained hydrogels. Mechanical instability due to the constrained swelling of a polymer network undergoing extensive volume changes in response to external stimuli results in pattern formation in these systems. We show that the wavelength, the amplitude, and the mode of patterns formed could be controlled dynamically by varying the rates of stretching and compression the sample along its width. Furthermore, the sample exhibits bistability, which in turn is controlled by the rates of the stretching and compression. In effect, our results indicate that the sample has an effective memory of previous state. Our results point out that the functionality of soft structured interfaces can be controlled dynamically via mechanical forcing.