Microfluidic permeation printing of self-assembled monolayer gradients on surfaces for chemoselective ligand immobilization applied to cell adhesion and polarization.

To study complex cell behavior on model surfaces requires biospecific interactions between the interfacing cell and material. Developing strategies to pattern well-defined molecular gradients on surfaces is difficult but critical for studying cell adhesion, polarization, and directed cell migration. We introduce a new strategy, microfluidic SPREAD (Solute PeRmeation Enhancement And Diffusion) for inking poly(dimethylsiloxane) (PDMS) microfluidic cassettes with a gradient of alkanethiol. Using SPREAD, an oxyamine-terminated alkanethiol is able to permeate into a PDMS microfluidic cassette, creating a chemical gradient, which can subsequently be transfer printed onto a gold surface to form the corresponding chemoselective gradient of oxyamine-alkanethiol self-assembled monolayer (SAM). By first patterning regions of the gold surface with a protective SAM using microfluidic lithography, directional gradients can be stamped exclusively onto unprotected bare gold regions to form single cell gradient microarrays. The microfluidic SPREAD strategy can also be extended to print micrometer-sized islands of radial SAM gradients with excellent geometric resolution. The immobilization of a cell adhesive Arg-Gly-Asp (RGD)-ketone peptide to the SPREAD stamped oxyamine-alkanethiol SAMs provides a stable interfacial oxime linkage for biospecific studies of cell adhesion, polarity, and migration.