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Novel Light-Responsive Biocompatible Hydrogels Produced by Initiated Chemical Vapor Deposition

Unger, Katrin, Salzmann, Paul, Masciullo, Cecilia, Cecchini, Marco, Koller, Georg, Coclite, Anna Maria
ACS Applied Materials & Interfaces 2017 v.9 no.20 pp. 17408-17416
X-ray photoelectron spectroscopy, biocompatibility, biocompatible materials, crosslinking, drugs, hydrogels, infrared spectroscopy, irradiation, polymers, solvents, ultraviolet radiation, vapors
A novel multiresponsive hydrogel has been synthesized by initiated chemical vapor deposition (iCVD). Hydrogels are known for their dynamic swelling response to aqueous environments. A chemical functionalization of the hydrogel surface was performed to add other stimuli-responsive functionalities and obtain a smart material that responds to two stimuli: light irradiation and exposure to aqueous environment. Modifying the hydrogel surface with solution-based methods is often problematic because of the damages caused by the permeation of solvents in the hydrogel. This issue is completely bypassed by the use of solvent-free techniques. Cross-linked polymers of 2-hydroxyethyl methacrylate (HEMA) were functionalized with azobenzene groups, as confirmed by IR spectroscopy and X-ray photoelectron spectroscopy (XPS). Through photoisomerization of the azobenzene, the polarity within the hydrogel is modified and as a consequence the affinity to water. Light irradiation modifies the degree of swelling within thin hydrogel films from 13% before exposure to UV light to 25% after exposure. The possibility of controlling the degree and rate of swelling by light irradiation was never reported before on these time scales and can have exceptional implications for light-induced drug delivery or light-controlled microfluidic systems. The light-responsive hydrogels showed also biocompatibility, which makes them suitable for a great variety of applications as biomaterials.