title: Engineering nanoscale surface features to sustain microparticle rolling in flow.
abstract: Nanoscopic features of channel walls are often engineered to facilitate microfluidic transport, for instance when surface charge enables electro-osmosis or when grooves drive mixing. The dynamic or rolling adhesion of flowing microparticles on a channel wall holds potential to accomplish particle sorting or to selectively transfer reactive species or signals between the wall and flowing particles. Inspired by cell rolling under the direction of adhesion molecules called selectins, we present an engineered platform in which the rolling of flowing microparticles is sustained through the incorporation of entirely synthetic, discrete, nanoscale, attractive features into the nonadhesive (electrostatically repulsive) surface of a flow channel. Focusing on one example or type of nanoscale feature and probing the impact of broad systematic variations in surface feature loading and processing parameters, this study demonstrates how relatively flat, weakly adhesive nanoscale features, positioned with average spacings on the order of tens of nanometers, can produce sustained microparticle rolling. We further demonstrate how the rolling velocity and travel distance depend on flow and surface design. We identify classes of related surfaces that fail to support rolling and present a state space that identifies combinations of surface and processing variables corresponding to transitions between rolling, free particle motion, and arrest. Finally we identify combinations of parameters (surface length scales, particle size, flow rates) where particles can be manipulated with size-selectivity.
authors.affiliation: Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, Massachusetts 01003, United States.
authors.forename: Surachate
authors.initials: S
authors.lastname: Kalasin
authors.affiliation: Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, Massachusetts 01003, United States.
authors.forename: Maria M
authors.initials: MM
authors.lastname: Santore
mesh_terms: D004738:Engineering / Q000379:methods*; D008863:Microspheres; D009038:Motion; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties
chemical_list: D012822:Silicon Dioxide
keywords: cell rolling; dynamic adhesion; electrostatic; hydrodynamics; leukocyte; microcapsules; microfluidics; motion signature; neutrophil; particle sorting; polyelectrolyte; renewable surfaces; selective particle capture; self-cleaning surfaces; surface charge