Effect of solvent lamination on roll-to-roll hot-embossed PMMA microchannels evaluated by optical coherence tomography

Manufacturing of microfluidic based diagnostic devices requires small tolerances and uniform quality to guarantee reliable and repeatable test results. This work describes characterization of morphological changes that occur to a hot embossed PMMA microfluidic channel after solvent lamination with a PMMA lid. A non-contact cross-sectional analysis of the lidded microfluidic device was performed by optical coherence tomography (OCT). The solvent induced morphology change led to a porous structure in bottom corners of hot-embossed channels, which allowed a fluid to absorb in the material. The measurements of solvent diffusion showed faster diffusion rate at the corners of the channel, in which the accumulated stress during the embossing process was the highest. The stress profile was verified by simulation of von Mises stresses during a molding phase of a hot embossing process. The porous structure with increased fluid diffusion has an unwanted effect on bioassay result, e.g. when detection molecules leak into the substrate thus leading to unspecific signal on chip. OCT was found to be a valuable, non-destructive imaging method to monitor solvent diffusion process and lamination process quality.