Characterizing Recent PDMS Changes in Electrokinetic-Based Microfluidic Devices' Performance and Manufacturing for Cell Sorting Applications.

Understanding cells from complex biological samples is vital to understanding cellular biology and medical applications. One evolving tool for cell sorting is the use of microfluidic devices to achieve higher precision and remove the need for labeling cell subpopulations. However, few microfluidic devices have been translated commercially beyond academic research often due to challenges in larger scale fabrication. Here, we initially investigated a compelling label-free microfluidic device with complex geometries to perform contactless dielectrophoresis (cDEP) for applications in enriching cell subpopulations in oncology, neurology, stem cells, and sample preparation. We began scaling the manufacturing of cDEP devices using Dow Sylgard 184, more commonly referred to as PDMS (polydimethylsiloxane). However, we began observing a new, dynamic bubble formation phenomenon which had significant impacts on device performance. Within just 5 min of exposure at typical experimental values, cell death was nearly 100%. Variables related to manufacturing, environment, equipment, personnel, raw materials sourcing, lithography methods and experimental conditions/parameters were systematically evaluated to find the root cause of the exacerbated bubble formation observed. Further, alternate polymers were sourced for manufacturing and experimental performance comparisons. All variables investigated failed to solve the significant decline in device performance and increase in cell death. Upon completing chemical analysis in this work, we conclude that the decline in device performance was a direct result of changes to the expected PDMS properties and composition. Despite these challenges, our robust quality control combined with experimental protocols to remove bubbles from the cDEP devices achieved consistent experimental performance including 2-3 h run times and >90% cell viability after sorting. These new PDMS behaviors will need to continue to be monitored and controlled to ensure consistency in experimentation, application and commercialization feasibility for a wide variety of microfluidic device designs and applications.