Experimental analysis of PDMS surface wettability to improve fluid dynamics within a microfluidic device

This study explores a simple, robust, and long-term polydimethylsiloxane (PDMS) bulk modification approach with the surfactants Brij L4 (BL4) or Poly(dimethylsiloxane-b-ethylene oxide), methyl terminated (PEO). Wettability was assessed through water contact angle measurements, and by capillary flow studies in both open and closed channels. The results demonstrate the superior effectiveness of both bulk modification with BL4 or PEO, over oxygen plasma treatment in achieving long-term hydrophilic surfaces, over 7-month. Long-term stability studies and shelf-life assessments, under different storage conditions (air, water, and phosphate-buffered saline) were also conducted, where PEO or BL4-modified PDMS stored in air showed promising wettability stability over time. Among the tested methods, PEO at 2.5% was the most effective bulk-modified method, reducing the contact angle of PDMS samples to 31 ± 3° while maintaining surface hydrophilicity over 7-month. Finally, the improved PEO-modified PDMS surface was successfully implemented in the fabrication of a microfluidic device, enhancing its fluid flow efficiency and demonstrating the potential for organ-on-a-chip applications. This bulk modification therefore has the potential to improve device standardization and support the adoption of microfluidic platforms as clinical tools for personalized medicine.