Less is More: Oligomer extraction and hydrothermal annealing increase PDMS bonding forces for new microfluidics assembly and for biological studies

Key determinants in the emergence of complex cellular morphologies and functions are cues in the micro-environment. Primary among these is the presence of neighboring cells as networks form. Therefore, for high-resolution analysis, it is crucial to develop micro-environments that permit exquisite control of network formation. This is especially true in cell science, tissue engineering, and clinical biology. We introduce a new approach for assembling polydimethylsiloxane (PDMS)-based microfluidic environments that enhances cell network formation and analyses. We report that the combined processes of PDMS solvent-extraction (E-PDMS) and hydrothermal annealing create unique conditions that produce high-strength bonds between E-PDMS and glass - properties not associated with conventional PDMS. Extraction followed by hydrothermal annealing removes unbound oligomers, promotes polymer cross-linking, facilitates covalent bond formation with glass, and retains the highest biocompatibility. Our extraction protocol accelerates oligomer removal from 5 to 2 days. Resulting microfluidic platforms are uniquely suited for cell-network studies owing to high bond strengths, effectively corralling cellular extensions and eliminating harmful oligomers. We demonstrate simple, simultaneous actuation of multiple microfluidic domains for invoking ATP- and glutamate-induced Ca2+ signaling in glial-cell networks. These low-cost, simple E-PMDS modifications and flow manipulations further enable microfluidic technologies for cell-signaling and network studies as well as novel applications.