PROJECT SUMMARY Cells are dynamic, multiscale materials. Their ability to sense and respond to a wide variety of stimuli is predicated on the hierarchical construction of the actin cytoskeleton, where individual actin monomers assemble to form filaments, which themselves assemble to form more complicated structures. Therefore, to engineer nano- bio interfaces that can stimulate a specific cellular response, we propose to test a biomimetic approach, where our designer material will exhibit hierarchy and function across the same length scales as the cytoskeleton. This project aims to engineer arrays of spiky gold nanoparticles with spike characteristics that are commensurate with actin filaments and where the particle-particle spacing corresponds to the size of mature focal adhesions. Our fabrication method is biocompatible, high-resolution, and high-throughput. We will investigate the physical effects of topographical features across length scales as well as chemical effects. Since the smallest feature size of the spiky nanoparticles (the tips) have radii of curvature tunable in the 5-10 nm range, we can test whether known nanotopographical sensing pathways occur at length scales similar in size to single proteins as well as the effects on cell phenotype resulting from reduced focal adhesion density. We will evaluate for synergistic effects between nano- and microscale topographical sensing on contact guidance of the cytoskeleton by comparing responses from different spike and nanoparticle array geometries. As a model problem, we aim to manipulate the process of macropinocytosis. While nanoscale curvature is known to promote clathrin-mediated endocytosis, the effects of curvature on macropinocytosis remain unclear. By varying the spike features of the nanoparticles and the DNA-aptamer functionalization of their surfaces, we will test for synergy between two factors: (1) enhanced rates of macropinocytosis via receptor binding to the DNA ligands; and (2) effects of priming the cell membrane for macropinocytosis through nanotopographical curvature. We expect that our biomimetic approach enabled by spiky nanoparticle arrays will have a significant impact on a range of questions in biotechnology, from fundamental mechanisms for early-stage endocytosis to applications such as biofouling-resistant sensors and the use of topographical cues as mechanobiological stimuli.

PROJECT NARRATIVE The intersection of nanomaterials and biology has produced promising tools for selective drug delivery, bio- imaging, and biosensing. This project will design structured nano- and microscale materials with topographical features similar to that of the extracellular matrix. This platform to investigate nano-bio interfaces will allow control over cellular motion, adhesion, and shape that will then enable more targeted diagnostics and therapeutics.