Surface roughness in microfluidic device fabrication: limitations of conventional methods and a novel solution for multi-material bonding†

Microfluidic devices, especially those utilizing polydimethylsiloxane (PDMS) structures, require reliable bonding methods to achieve durable, leak-proof seals. Current bonding techniques, including O₂ plasma treatment, suffer from limitations related to material compatibility and surface roughness sensitivity, which compromise device stability and scalability in complex designs. In this study, we investigate the impact of surface roughness, wax contamination, and the presence of conductive materials on bonding strength in PDMS-based microfluidics. Additionally, we propose a novel bonding method using a flowable, one-component silicone rubber that forms robust seals without plasma treatment or silanization, effectively overcoming the challenges posed by increased surface roughness and material heterogeneity. The bonding method demonstrated significantly enhanced bond strengths across various substrate combinations (PDMS, copper, and FR4), with notable resilience under high pressure. This approach advances microfluidic fabrication by offering a scalable, versatile solution for multi-material bonding applicable in digital microfluidics and beyond.