Microcontact Printing of Protein Patterns

Patterned PDMS stamps were cast from a photoresist-patterned silicon wafer, as previously described.^{23 (link)} Stamp-off templates were cast similarly, but from negative photoresist patterns on the silicon wafer. Flat PDMS stamps were cast from an unpatterned silicon wafer. For microcontact printing, PDMS stamps were inked with protein at 50 μg ml⁻¹ in H₂O (for fibronectin and vitronectin), 50 μg ml⁻¹ in PBS (for bovine serum albumins), or 100 μg ml⁻¹ in 1% (v/v) acetic acid (for collagen type I), all for 1 h at room temperature. The stamps were then thoroughly rinsed in H₂O and blown dry with a stream of N₂. In parallel, the target substrate (a stamp-off template or PDMS cell culture substrate) was treated with ultraviolet ozone for specified times (Jelight Company, Irvine, CA). The stamp was then placed in conformal contact with the target substrate for ~1 s. F127 Pluronics was adsorbed to PDMS surfaces from a 0.2% (w/v) solution for 1 h at room temperature to prevent protein adsorbtion to non-functionalized portions of the PDMS.