Improved Polydimethylsiloxane (PDMS) Double Casting via Silicone Oil Treatment for Densely Packed Microstructure Replication

Polydimethylsiloxane (PDMS) double casting is widely used for replicating microscale structures, including microfluidic channels and biomedical microdevices such as Bio-MEMS. Despite its versatility, strong interfacial adhesion between PDMS layers often results in incomplete replication or structural damage, particularly in densely packed microfeatures. Conventional approaches to reduce adhesion, such as plasma or chemical surface modification, require specialized equipment and can be time-consuming and costly. To address these limitations, we present an improved demolding strategy that combines thermal aging with the application of a thin silicone oil layer as a non-adhesive release barrier. A critical step in the protocol involves sweeping a tensioned thread across the surface to distribute the oil and promote even PDMS penetration between micropillars. This enhances mold release and preserves structural integrity without compromising delicate microstructures. The method is demonstrated using densely packed hole-array patterns, achieving clean replication with minimal dimensional deviation. This simple, reproducible, and cost-effective approach is well-suited for fabricating PDMS-based microsystems, including multilayer devices and geometrically complex features in soft lithography applications.