title: Facile preparation of photodegradable hydrogels by photopolymerization.
abstract: Photodegradable hydrogels have emerged as a powerful material platform for studying and directing cell behaviors, as well as for delivering drugs. The premise of this technique is to use a cytocompatible light source to cleave linkers within a hydrogel, thus causing reduction of matrix stiffness or liberation of matrix-tethered biomolecules in a spatial-temporally controlled manner. The most commonly used photodegradable units are molecules containing nitrobenzyl moieties that absorb light in the ultraviolet (UV) to lower visible wavelengths (~280 to 450 nm). Because photodegradable linkers and hydrogels reported in the literature thus far are all sensitive to UV light, highly efficient UV-mediated photopolymerizations are less likely to be used as the method to prepare these hydrogels. As a result, currently available photodegradable hydrogels are formed by redox-mediated radical polymerizations, emulsion polymerizations, Michael-type addition reactions, or orthogonal click chemistries. Here, we report the first photodegradable poly(ethylene glycol)-based hydrogel system prepared by step-growth photopolymerization. The model photolabile peptide cross-linkers, synthesized by conventional solid phase peptide synthesis, contained terminal cysteines for step-growth thiol-ene photo-click reactions and a UV-sensitive 2-nitrophenylalanine residue in the peptide backbone for photo-cleavage. Photolysis of this peptide was achieved through adjusting UV light exposure time and intensity. Photopolymerization of photodegradable hydrogels containing photolabile peptide cross-linkers was made possible via a highly efficient visible light-mediated thiol-ene photo-click reaction using a non-cleavage type photoinitiator eosin-Y. Rapid gelation was confirmed byin situphoto-rheometry. Flood UV irradiation at controlled wavelength and intensity was used to demonstrate the photodegradability of these photopolymerized hydrogels.
authors.affiliation: Department of Biomedical Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University at Indianapolis, Indianapolis, IN 46202 USA.
authors.forename: Chang Seok
authors.initials: CS
authors.lastname: Ki
authors.forename: Han
authors.initials: H
authors.lastname: Shih
authors.forename: Chien-Chi
authors.initials: CC
authors.lastname: Lin
keywords: Photopolymerization; click reaction; photodegradable hydrogels; thiol-ene
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