Simple additive-based modifications of PDMS for long-term hydrophilic stability†

Abstract

Polydimethylsiloxane (PDMS) is widely used in microfluidic systems due to its ease of fabrication and versatile properties; however, its inherent hydrophobicity limits its utility. In this study, we fabricated hydrophilic PDMS in a one-step process by incorporating a PDMS–poly(ethylene glycol) block copolymer into two commercially available PDMS formulations (Sylgard 184 and KE-106), requiring only mixing, without additional steps such as plasma treatment or chemical coating. The contact angles of the modified PDMS and the surrounding glass surfaces assembled with PDMS gradually increased over the assembled period, but the overall hydrophilic properties were retained for up to two months, enabling stable fluid flow within microfluidic channels as small as 3 μm in height. Interestingly, our hydrophilic PDMS exhibited dynamic wettability transition, which varied between the two PDMS formulations, with KE-106 showing a faster and more extensive hydrophilic transformation compared to Sylgard 184. Gas chromatography-mass spectrometry analysis confirmed a higher release of hydrophobic PDMS compounds, namely D4 and D5, from Sylgard 184 compared to KE-106. Based on these results, we suggest that differences in PDMS compounds affect the efficiency and performance of the block copolymer-mediated hydrophilization of PDMS. These findings provide crucial insights into designing hydrophilic PDMS-based microfluidic devices, particularly for long-term biomedical applications requiring reliable fluid flow and hemocompatibility.