Directing and Deciphering Macrophage Polarization through Biologically-Inspired Surface Design of Polymer Brush-Coated Cell Culture Substrates

PROJECT SUMMARY I have presented four research projects to illustrate my vision—harnessing functional polymer synthesis to present and amplify biochemical cues catalyzing cell biological phenomena such as macrophage (Mp) polarization. Dysregulated Mp polarization profoundly alters the trajectories of wound healing, chronic inflam- mation, and tumor progression. Signaling cascades underlying Mp polarization are activated by soluble and substrate-bound ligands that bind and cluster Mp receptors. How do we model the chemical diversity and spati- otemporal complexity of ligand–receptor interactions—individually fragile yet collectively powerful—to advance our fundamental understanding of Mp polarization? Our overarching hypothesis is that polymer brushes will exploit spatially complex patterns of ligand presentation to extract general principles underlying Mp polarization. Polymer brushes—ultra-thin coatings that are tens to hundreds of nm thick—are formed by grafting polymer chains at sufficiently high densities from cell culture substrates. We will interrogate Mps on ligand-functionalized polymer brushes and disclose how ligand identity, density, and spatial distribution sculpt Mp polarization. We will synthesize polymer brushes functionalized with ligands governing Mp phenotypic changes (e.g., glycosaminoglycan(GAG)-mimetic functional groups, phosphatidyl serine (PS), or mannose) and pursue four objectives: (1) GAG-mimetic polymer brushes will clarify how Mps resort to “bet hedging” to diversify polarization responses and cope with environmental uncertainty presented by infections or wounds, (2) PS-functionalized polymer brushes will reveal how Mps decode PS spatial presentation patterns, discriminate between apoptotic and non-apoptotic cells, and improvise phagocytic responses, (3) mannose-functional polymer brushes will reveal how Mps resolve “mixed messages” in tumors, wounds, and other settings where inflammatory and anti- inflammatory signals co-exist, (4) by grafting polymer brushes from multi-compartmental electrospun scaffolds, we will independently control scaffold stiffness, ligand identity, and spatial patterns of ligand presentation. Three- dimensional cell culture platforms with programmable mechanical, topographical, and surface chemical features will elucidate how Mps integrate physical, chemical, and biological stimuli to devise polarization responses. Although we focus on Mp polarization in this initial application to demonstrate proof-of-concept, the toolset we develop here will find broad application. Our long-term research goal is to interrogate fundamen- tal cell biological phenomena beyond Mp polarization via creative surface engineering of cell culture substrates We will establish cell- and disease-agnostic experimental platforms that recapitulate the chemical diver- sity and spatiotemporal complexity of ligand–receptor interactions orchestrating fundamental cell bio- logical phenomena. Building on the platforms established in the first 5 years, and in partnership with collabo- rators, we will interrogate stem cell differentiation, T-cell activation, exosome biogenesis, and other cell biological phenomena in our renewal application.