Self-Cross-Linking p(APM-co-AA) Microstructured Thin Films as Biomimetic Scaffolds

In nature, cells reside within an extracellular matrix (ECM) that provides biophysical and biochemical cues to direct cell development and behavior. Traditional methods for studying cells involve using in vitro models that are convenient and cost-effective, but often use two-dimensional supports that are poor mimics for three-dimensional natural cell microenvironments. In this work, a synthetic polyampholyte, p(APM-co-AA) [poly(N-(3-aminopropyl)methacrylamide hydrochloride-co-acrylic acid)], was coated onto prestressed polystyrene support films that were then thermally shrunken, which concomitantly induced self-cross-linking of the polyampholyte. The cross-linking process involved a two-step sequence of anhydride formation from pairs of adjacent acrylic acid units, followed by amide cross-linking through reaction with primary amines on other chains. Attenuated reflectance infrared spectroscopy (ATR-IR) confirmed the formation of anhydride and amide bonds during heating, and the cross-linked films remained intact in cell culture media and basic solutions. Furthermore, the compressive stress from the shrinking substrate wrinkled the polyampholyte film, producing 3D scaffolds that were used to study the effect of topography on cell cultures. Cell viability tests confirmed the noncytotoxicity of the microstructured polyampholyte films. The surface wettability of the films was tuned by postfunctionalizing with different amines, with decylamine-functionalized films showing decreased fibroblast attachment, and d-glucamine-functionalized films showing reduced fibroblast spreading, compared to the control. Furthermore, the topography of the p(APM-co-AA) scaffolds could be tuned by changing the polyampholyte film thickness. Different topographies of the microstructured films elicited different fibroblast morphologies, with larger structures contributing to less complex cell boundaries, lower cell areas, and higher cell circularities. Overall, this tunable, self-cross-linking p(APM-co-AA) system can be fabricated into microstructured films, which can be used to study the effects of surface chemistry, topography, and other physical properties of biomimetic scaffolds on cell behavior and contribute to the library of existing biomimetic scaffolds.