Towards mimicking biological function with responsive surface-grafted polymer brushes

Abstract

Responsive or smart polymer brushes undergo pronounced changes in their surface properties and conformation in response to changes in their environment, including variation in temperature, solution pH or ionic strength, and presence of light. Because the brush stimulus response resembles the ability of natural systems to react to environmental changes, responsive polymer brushes have been incorporated into a number of soft biomimetic structures. Nonetheless, the ability to design soft matter systems that recreate the complexity of life remains limited. Here, we survey the use of responsive surface-grafted polymer brushes to mimic biological function. We summarize various ways in which surface-grafted brushes respond to stimuli. Next, we highlight examples of biomimetic engineering that mimic specific biological structures, including molecular motors, ion channels, leukocytes, and leaves. Finally, we discuss recent studies that design brushes to generate lifelike behavior and interrogate their response under the non-equilibrium, spatiotemporally heterogeneous conditions in living systems. Specifically, we focus on hysteresis in the brush response, as one example of nonlinear response; slow diffusion, used by biological systems to maintain chemical gradients; self-oscillation, as an example of auto-amplification of stimuli; and patterned responsiveness, as an example of compartmentalization. This focus emphasizes the emerging need to rationally design the response of brushes for use as soft components in dynamic, life-inspired systems.