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. 2008 Jan 1;18(4):450131-450137.
doi: 10.1088/0960-1317/18/4/045013.

Enhanced wettability of SU-8 photoresist through a photografting procedure for bioanalytical device applications

Zhan Gao  1 , David B Henthorn, Chang-Soo Kim
Affiliations

Enhanced wettability of SU-8 photoresist through a photografting procedure for bioanalytical device applications

Zhan Gao et al. J Micromech Microeng. .

Abstract

In this work, we detail a method whereby a polymeric hydrogel layer is grafted to the negative tone photoresist SU-8 in order to improve its wettability. A photoinitiator is first immobilized on freshly prepared SU-8 samples, acting as the starting point for various surface modifications strategies. Grafting of a 2-hydroxyethylmethacrylate-based hydrogel from the SU-8 surface resulted in the reduction of the static contact angle of a water droplet from 79 +/- 1 degrees to 36 +/- 1 degrees , while addition of a poly(ethylene glycol)-rich hydrogel layer resulted in further improvement (8 +/- 1 degrees ). Wettability is greatly enhanced after 30 minutes of polymerization, with a continued but more gradual decrease in contact angle up to approximately 50 minutes. Hydrogel formation is triggered by exposure to UV irradiation, allowing for the formation of photopatterned structures using existing photolithographic techniques.

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Figures

Figure 1
Figure 1
Schematic diagram for the photoinduced graft polymerization of monomer onto a SU-8 surface.
Figure 2
Figure 2
Static water contact angle decreases with increasing percentage of HEMA in prepolymerization mixture.
Figure 3
Figure 3
Influence of polymerization reaction time on surface wettability for 95% HEMA hydrogel on SU-8.
Figure 4
Figure 4
ATR-FTIR spectra: pHEMA photo-grafting on SU-8 surface: a.) Reference spectrum of hydrogel (95% HEMA, 5% TEGDMA). b.) Surface after 50 minutes of polymerization. c.) Surface after 10 minutes of UV initiated polymerization. d.) Unmodified SU-8 surface.
Figure 5
Figure 5
ATR - FTIR spectra: PEGDMA hydrogel on SU-8 surface: a) Unmodified SU-8 surface after development and hard bake b) Scan of initiator HCPK bound SU-8 surface c) Surface after 30 minutes of polymerization of PEGDMA on SU-8 surface
Figure 6
Figure 6
ATR - FTIR subtraction spectra: PEGDMA hydrogel on SU-8 surface: a) Subtraction spectrum of PEGDMA (reference spectrum of initiator HCPK bound SU-8 surface). b) Polymerized PEGDMA hydrogel (99%PEGMA+1% HCPK) c) PEGDMA monomer (Mn=875)
Figure 7
Figure 7
ATR - FTIR subtraction spectra: PEGMA hydrogel on SU-8 surface: a) Subtraction spectrum of PEGMA (reference spectrum of initiator HCPK bound SU-8 surface). b) Polymerized PEGMA hydrogel (99%PEGMA+1% HCPK) c) PEGMA monomer (Mn=475)
Figure 8
Figure 8
Scanning electron micrographs of PEGDMA(Mn=875) gel microstructures on SU-8 surface. (a) Wheel-like PEG microstructure consists of 50 μm wide rod (at outer side) (b) SEM image of wheel-like PEG microstructure (tilt angle=60°) (c) SEM image of photopatterned grafted layer on SU-8 surface (tilt angle=30°)
See this image and copyright information in PMC

References

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