A Micropatterned Surface for the Assessment of Relative Two-Dimensional Molecular Selectin Kinetics in Flow

Recruitment rate measurements of micro-scale particles, such as cells or microbeads, to biofunctional surfaces is difficult because factors such as uneven ligand distributions, particle collisions, variable particle fluxes, and molecular-scale surface separation distances that combine to obfuscate the ability to link the observed particle behavior with the governing nanoscale biophysics. We report the development of a hydrodynamically-conditioned micropattern catch strip assay to measure microparticle and cellular recruitment kinetics. The assay exploited patterning within microfluidic channels and the mechanostability of selectin bonds to create reaction geometries that confined a microbead flux to within 200 nm of the surface under flow conditions. Systematic control of capillary action enabled the creation of homogenous or gradient ligand distributions. The method enabled the measurement of particle recruitment rates (k_eff, s⁻¹) that were primarily determined by the interaction of the biomolecular pair being investigated. The method may be well suited for analysis of reaction rates between surface-bound molecules in the presence of convective flow patterns.