SoftLithography

Soft lithography refers to a set of patterning and replication methods that use elastomeric polymers, typically polydimethylsiloxane (PDMS), to create micro- and nanoscale features. The technique enables the fabrication of structures by stamping, molding, or printing patterns from a master onto a substrate, with the master produced by conventional photolithography.

Core techniques include microcontact printing (μCP), in which an elastomer stamp inking with molecules is brought into contact with a substrate to transfer patterns; replica molding (REM), where PDMS casts reproduce a microstructured master in a polymer; microtransfer molding (μTM) and related methods; and the fabrication of microfluidic devices, where PDMS channels are cast against a master and bonded to glass or other substrates.

Materials and processing typically involve casting PDMS prepolymer against a silicon or glass master, curing, and peeling to obtain a stamp or mold. The patterned elastomer can be used to stamp chemical patterns onto surfaces, or to cast replicas into various polymers or hydrogels. Bonding to substrates such as glass or silicon often requires surface activation (e.g., oxygen plasma). Pattern resolution depends on the quality of the master, and PDMS properties permit handling of delicate biological samples and rapid prototyping.

Impact and limitations: Soft lithography enabled rapid, low-cost prototyping of microfluidic devices and surface patterns, with widespread use in biology, chemistry, and materials science. Limitations include solvent swelling of PDMS, absorption of hydrophobic molecules, and challenges with long-term stability and precise alignment. The field rose to prominence in the 1990s through the work of Whitesides and colleagues, who popularized these approaches.