title: Formation of three-dimensional hydrogel multilayers using enzyme-mediated redox chain initiation.
abstract: Enzyme-mediated redox chain initiation involving glucose oxidase (GOX) was employed in an iterative solution dip-coating technique to polymerize multiple, three-dimensional hydrogel layers using mild aqueous conditions at ambient temperature and oxygen levels. To the best of our knowledge, sequential enzyme-mediated dip-coating resulting in an interfacial radical chain polymerization and subsequent formation of three-dimensional hydrogel layers has not been previously explored. Conformal, micrometer-scale, uniform poly(ethylene glycol) (PEG)-based hydrogel layers were polymerized within seconds and remained securely associated after incubation in water for 16 weeks. Incorporation of either small molecules (i.e., rhodamine-B acrylate, fluorescein acrylate) or fluorescent nanoparticles into crosslinked hydrogel layers during the polymerization reaction was also achieved. The encapsulation of 0.2 microm-diameter nanoparticles into hydrogels during polymerization of a 2-hydroxyethyl acrylate (HEA)/PEG(575) diacrylate monomer formulation, using the GOX-mediated initiation, resulted in minimal effects on polymerization kinetics, with final acrylate conversions of 95% (+/- 1%) achieved within minutes. The temporal control and spatial localization afforded by this interfacial redox approach resulted in the polymerization of uniform secondary layers ranging between 150 (+/- 10) microm and 650 (+/- 10) microm for 15 and 120 s immersion times, respectively. Moreover, increasing the PEG(575)-fraction within the initial hydrogel substrate from 10 to 50% decreased the subsequent layer thicknesses from 690 (+/- 30) microm to 490 (+/- 10) microm because of lowered glucose concentration at the hydrogel interface. The ability to sequentially combine differing initiation mechanisms with this coating approach was achieved by using GOX-mediated interfacial polymerization on hydrogel substrates initially photopolymerized in the presence of glucose. The strict control of layer thicknesses combined with the rapid, water-soluble, and mild polymerization will readily benefit applications requiring formation of stratified, complex, and three-dimensional polymer structures.
authors.affiliation: Department of Chemical and Biological Engineering, ECCH 111 CB 424, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Leah M
authors.initials: LM
authors.lastname: Johnson
authors.forename: Cole A
authors.initials: CA
authors.lastname: Deforest
authors.forename: Aishwarya
authors.initials: A
authors.lastname: Pendurti
authors.forename: Kristi S
authors.initials: KS
authors.lastname: Anseth
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Bowman
mesh_terms: D005456:Fluorescent Dyes / Q000737:chemistry*; D005949:Glucose Oxidase / Q000737:chemistry*; D020100:Hydrogels / Q000138:chemical synthesis* / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D005456:Fluorescent Dyes; D020100:Hydrogels; D005949:Glucose Oxidase