Sequential formation of covalently bonded hydrogel multilayers through surface initiated photopolymerization.

A novel method for the sequential formation of hydrogel multilayers is described. Formation of the first layer is based on surface initiated photopolymerization of hydrogel precursors on eosin derivatized surfaces. In order to attach subsequent layers it is necessary to be able to functionalize intermediate hydrogel layers with eosin. In the present work, this is accomplished by introducing poly(ethylene glycol) amino acrylate (NH2-PEG-Acr) along with other hydrogel precursors such as poly(ethylene glycol) diacrylate (PEG-DA) on the intermediate layers. The pendant amine groups allow functionalization of the intermediate layers with eosin for subsequent photopolymerization of new hydrogel layers. The process can be repeated sequentially to construct multilayered hydrogel membranes. The NH2-PEG-Acr monomer can be formed by coupling cysteamine to PEG-DA by a conjugate addition reaction. The approach to multilayer formation could allow the incorporation of specific functionalities or compositions within each hydrogel layer so that multifunctional membranes can be formed. It could also be implemented, through proper photopatterning procedures, for the formation of 3-D hydrogel structures. The mild photopolymerization conditions employed using visible (514 nm), rather than ultraviolet light would make this technique especially attractive for tissue engineering, drug delivery, biomaterials, biosensor development and other situations where the elements incorporated are sensitive to UV light exposure.