Theoretical and experimental investigation for interfacial photopolymerization of poly(ethylene glycol) diacrylate

In the present work experimental and theoretical models for the process of cell encapsulation through surface initiated photopolymerization are described. The experimental model involves photopolymerization of poly(ethylene glycol) diacrylate (PEG-DA) hydrogels on the surface of a cell or substrate functionalized with the photoinitiator eosin. The covalent attachment of hydrogels to substrate surfaces allows for 2-D patterning of hydrogels, which is demonstrated here using the microcontact printing (muCP) technique. This method can be easily implemented to form arrays of fluorophores and proteins in situ. The eosin radical-mediated attachment of hydrogels to surfaces has been exploited to construct multilayers through sequential photopolymerization of hydrogel precursors. The sequential deposition of new hydrogel layers that are covalently bonded to the previous layer allows the incorporation of specific functionalities or compositions within each hydrogel layer. The technique could also be modified, through proper surface patterning procedures, to form 3-D hydrogel structures. The mild photopolymerization condition using visible (514 nm), rather than ultraviolet light makes this technique especially attractive for encapsulation of cells and proteins, tissue engineering, drug delivery, biomaterials and biosensor development.; In the theoretical part of this work, the thickness of the hydrogel membrane is predicted with a general polymerization model and compared with experimental measurements. The good correlation of the model with the experimental results is utilized to apply the Numerical Fractionation (NF) technique to the process of cell encapsulation in order to compute many properties that are not possible to measure experimentally. NF is a refinement of the Method of Moments technique that is used in the general model and permits the calculation of such hydrogel membrane properties as crosslink density in both the pre-gel and post-gel regimes. This is accomplished by segregating the polymer molecules into generations based on each molecule's size and degree of clustering.; In conclusion, the experimental and theoretical techniques developed in this study will significantly improve the current encapsulation techniques by allowing the possibility of using chemically crosslinked multilayers of hydrogel membranes each of which could be specifically tailored based on the predictions of the NF model.