In-situ photopatterning of hydrogel microarrays in polished microchips

We present a fabrication method which enables simple and eproducible photopatterning of micron- sized hydrogel arrays inside closed microchips. To achieve this, the glass cover of the microchip is thinned by mechanical grinding and polishing. This procedure reduces the spacing between the photomask and hydrogel precursor and thereby the effects of UV diffraction. We demonstrate the effects of glass cover thickness and roughness, together with different optical lithography recipes on patterning success. The patterning method is tested with two different types of photopolymerizing hydrogels, polyacrylamide and polyethylene glycol diacrylate. The presented method enables in-situ fabrication of welldefined hydrogel patterns for microfluidic platforms