Surface modification of SU-8 by photografting of functional polymers for lab-on-a-chip applications

Due to the high flexibility and versatility in the process development of microfluidic devices, an epoxy-based, high-aspect ratio photoresist SU-8 is now attracting attention as the main structuring material of the fluidic channels. Manipulation of the surface properties of SU-8 channel wall is critical to attach functional films such as enzyme-immobilized layers or biocompatible layers. We describe a new in situ patterning method to form a hydrogel film on SU-8 by a photografted polymerization procedure. The hydrophobic surface of SU-8 is modified using a surface bound initiator HCPK (1-hydroxycyclohexyl phenyl ketone). A p-HEMA (poly-2-hydroxyethylmethacrylate) hydrogel film is grafted by photopolymerization of solution-phase precursors on the modified surface. The contact angle measurements reveal that the hydrophilicity was increased after the grafting. This is a promising in situ formation method of patterned functional films within a completed microfluidic channel.