Simple Photografting Method to Chemically Modify and Micropattern the Surface of SU-8 Photoresist

Abstract

SU-8 has gained widespread acceptance as a negative photoresist. It is also finding increasing use as a structural material in microanalytical devices. Consequently, methods to tailor the surface properties of SU-8 as well as to micropattern coatings on the surface of SU-8 are needed. The SU-8 photoresist consists of EPON SU-8 resin mixed with the photoacid generator triarylsulfonium hexafluoroantimonate. This photoacid generator can also serve as a photoinitiator generating free radicals when illuminated with UV light. Under the appropriate conditions, sufficient triarylsulfonium hexafluoroantimonate remains within cured SU-8 to act as a source of free radicals and initiate UV-mediated grafting of polymers onto the surface of the SU-8. UV-mediated grafting was used to coat SU-8 surfaces with poly(acrylic acid) and other water-soluble monomers. The SU-8 surface was chemically micropatterned by placing a mask between the UV light and SU-8. The X-Y spatial resolution of micropatterned poly(acrylic acid) on the SU-8 surface was 2 mum. Three applications of these chemically modified SU-8 surfaces were demonstrated. In the first, poly(ethylene glycol) was used to protect the SU-8 from interactions with proteins, yielding a surface resistant to biofouling. In the second demonstration, the SU-8 surface was micropatterned with a cell-resistant layer to guide cellular attachment and growth. In the final application, SU-8 micropallets were encoded with polymer lines. The bar codes were read by either absorbance or fluorescence measurements. Thus, UV-mediated graft polymerization is an efficient and effective method to micropattern coatings onto the surface of SU-8.

Surface hydrophilization of SU‐8 by plasma and wet chemical processes

“…In particular, for applications such as microsensing, or DNA array technology, the specificity can be enhanced by functional chemical groups, [29] by means of silanization after wet chemical modification, [2,30,31] by direct covalent attachment, [32] or by UVactivated linking. [6,33] The surface chemistry of SU-8 can also be modified by a two-step process employing CAN and polyacrylic acid to enhance cell attachment. [34] Protein resistance is a surface functionality that is often required in biomicrofluidic devices.…”

Bifurcated Mechanical Behavior of Deformed Periodic Porous Solids

“…It has been demonstrated that trace amounts of triarylsulfonium hexafluoroantimonate (initiator) which remains within cured SU8 acts as a source of free radicals, initiating UV-mediated grafting of PAA onto the surface of the SU8. [39] Figure 3 illustrates the surface modification, infiltration of the monomer and subsequent polymerization of the acrylic acid in the pores of the SU8 structure. The slow evaporation of the water from inside of open cylindrical micropores causes the swollen PAA network grafted to the pore walls to shrink significantly, resulting in high compressive stresses.…”

SU-8 Composite Based “Lube-tape” for a Wide Range of Tribological Applications

“…Water-soluble monomers and other polymers like poly(acrylic acid) have been covalently grafted to SU-8 using UV-mediated grafting and also, chemically micro-patterned [13]. Under controlled conditions, the remainder photo acid generator triarylsulfonium hexafluoroantimonate works as a photo initiator and generates free radicals such as C-OO, C-O, -COOH [13].…”