PDMS microfluidic devices were fabricated using standard replica molding processes,26 with a cross linker to polymer ratio
of 1 : 10, and maintaining 2 h as the curing time for repeatable mechanical measurements. As PUMA, NOA and TPE adhere to SU8 and make demolding impossible, a PDMS master mold with the same polarity as the silicon master was produced as indicated by Kuo et al.,31 using octadecyltricholosilane (Sigma-Aldrich, 0.2% v/v in pure ethanol) to passivate the surface.