Soft lithography

In technology, soft lithography is a family of techniques for fabricating or replicatingstructures using "elastomeric stamps, molds, and conformable photomasks". It is called "soft" because it uses elastomeric materials, most notably PDMS.

PDMS, an amorphous polymer, is favored for the following characteristics:

• Elasticity: the elasticity of PDMS is tuned by (1) adjusting curing conditions (curing agent concentration and temperature) and (2) dispersing particles throughout the polymer matrix. Its elasticity and durability allows the mold to conform to the surface of the substrate without rupture.
• Optical transparency: PDMS transmits ~90% of light from 390 nm to 780 nm, meaning it's optically transparent across the entire visible spectrum. The transparency of PDMS allows the direct observation of biological processes (including the observation of blood flow through the mimicked PDMS-based blood vessels).
• Gas-permeability: PDMS is gas-permeable which is useful in applications such as Microfluidics.
• Isotropic: PDMS is isotropic, meaning its physical properties are identical in every direction, and will thus perform uniformly.
• Chemically-inert: PDMS will not interfere chemically with the substrate.

Following the molding onto the master template, PDMS is cured at high temperatures with a cross-linking agent.

Soft lithography is generally used to construct features measured on the micrometer to nanometerscale. According to Rogers and Nuzzo (2005), development of soft lithography expanded rapidly from 1995 to 2005. Soft lithography tools are now commercially available.