Peg 6000 diacrylate

A ~10μm thick polyethylene glycoel (PEG) hydrogel can be assembled on the glass cover slip to exclude surface adhesion, or control surface stiffness52 (link). Glass slides were plasma treated (1min, 100W, 1bar Argon, 2bar Oxygen), and immediately coated with TMSMA solution (10ml ethanol, 300μL 1:10 glacial acetic acid:ddw, and 0.5ml 3-(trimethoxysilyl) propyl methacrylate Sigma, 440159), incubated for 1hr, double rinsed with ethanol, dried with Nitrogen and stored in the dark. PEG mixture: Photoinitiator stock solution was prepared as 100mg 2,2-Dimethoxy-2-phenylacetophenone (Sigma, 196118) to 1ml 70% ethanol. PEG solution was prepared as 200mg PEG-6000 diacrylate (Sigma, 701963) to 1ml PBS. The photoinitiator was mixed into the PEG solution to a final 0.1% concentration and stored at 4C. Gel curing: A 2.5 μL drop of PEG mixture was placed on the surface treated slide, and carefully closed from the top with a 18mm diameter circular coverslip. The PEG mixture uniformly spread between the two surfaces, thus reaching an average thickness of ~10μm. The solution was cross-linked by exposure to UV light. The 18mm coverslip is removed gently using tweezers. The PEG coated coverslip is washed and incubated over night with sterile PBS. Before device assembly the slide is dried with nitrogen, and the PEG gel is clearly visible as an opaque disc on the clear coverslip.