Hydrogels are networks of polymer in which water is the dispersion medium. They are superabsorbent (can contain over 99% water) natural or synthetic polymers. At the solid-liquid interface hydrogel layers are promising because of their “smart” adsorption properties.
Thin films of hydrogels with stimuli-responsive behavior receive growing attention in the development of advanced in-vitro cell carriers for regenerative medicine. Such hydrogels are
exposing or hiding surface functionalities and changing integral characteristics (hydrophilicity, charge) related to varied degrees of swelling in the aqueous medium.
Schmaljohann et al. (2004) demonstrated a number of advantages of imaging ellipsometry for the characterization of a patterned hydrogel. The gel was immobilized on a polymer substrate using a low-pressure argon plasma treatment via a masking technique. The micropatterned, thermoresponsive hydrogel film has been characterized with imaging ellipsometry. The characterization was carried out on the dry film as well as on a swollen sample in water. The thermoresponsive behavior was studied in deionized water by temperature-dependent measurements in a solid-liquid cell. Through imaging ellipsometry, it was possible to distinguish the different regions of interest on a micrometer scale, to follow the swelling of the hydrogel part as a function of the temperature, and to visualize the swelling as 3D profiles of Δ at various temperatures. Long-term changes of the sample could also be detected, which cannot be observed with conventional ellipsometry.
References:
Schmaljohann D., Nitschke M., Schulze, R., Eing A., Werner C., Eichhorn K.-J (2005) In Situ Study of the Thermoresponsive Behavior of Micropatterned Hydrogel Films by Imaging Ellipsometry. Langmuir 21, 2317-2322
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Microcontact printing (mCP) has been used by Zhou et al. (2004) to introduce temporary hydrophobic barriers on carboxymethylated dextran (CMD) hydrogels on gold. Imaging ellipsometry was used as one method in the characterization of the overall fabrication process.
Reference:
Zhou Y., Andersson O., Lindberg P., Liedberg B. (2004) Protein Microarrays on Carboxymethylated Dextran Hydrogels: Immobilization, Characterization and Application. Microchimica Acta 147, 21–30
Application Note: Functional Coatings on Cantilevers