Use of photolithography to encode cell adhesive domains into protein microarrays.

Protein microarrays are rapidly emerging as valuable tools in creating combinatorial cell culture systems where inducers of cellular differentiation can be identified in a rapid and multiplexed fashion. In the present study, protein microarraying was combined with photoresist lithography to enable printing of extracellular matrix (ECM) protein arrays while precisely controlling "on-the-spot" cell-cell interactions. In this surface engineering approach, the micropatterned photoresist layer formed on a glass substrate served as a temporary stencil during the microarray printing, defining the micrometer-scale dimensions and the geometry of the cell-adhesion domains within the printed protein spots. After removal of the photoresist, the glass substrates contained micrometer-scale cell-adhesive regions that were encoded within 300 or 500 microm diameter protein domains. Fluorescence microscopy and atomic force microscopy (AFM) were employed to characterize protein micropatterns. When incubated with micropatterned surfaces, hepatic (HepG2) cells attached on 300 or 500 mum diameter protein spots; however, the extent of cell-cell contacts within each spot varied in accordance with dimensions of the photoresist stencil, from single cells attaching on 30 microm diameter features to multicell clusters residing on 100 or 200 microm diameter regions. Importantly, the photoresist removal process was shown to have no detrimental effects on the ability of several ECM proteins (collagens I, II, and IV and laminin) to support functional hepatic cultures. The micropatterning approach described here allows for a small cell population seeded onto a single cell culture substrate to be exposed to multiple scenarios of cell-cell and cell-surface interactions in parallel. This technology will be particularly useful for high-throughput screening of biological stimuli required for tissue specification of stem cells or for maintenance of differentiated phenotype in scarce primary cells.