(662b) Applications of Thin Films of pH-Responsive Hydrogels Synthesized by Initiated Chemical Vapor Deposition

Thin functional films of ionic hydrogels have been grafted to silicon and glass substrates by initiated chemical vapor deposition (iCVD). Prior to iCVD, the substrates were primed with 3-aminopropyldimethylethoxysilane, imparting the surface with a free amine group. Three monomers vapors were introduced into the reactor along with the initiator: 0.6 sccm of maleic anhydride (MA), 6 sccm of N,N-dimethylacrylamide (DMAA), and 0.4 sccm of di(ethylene glycol) divinyl ether (DEVE). At a filament temperature of 235 ºC and an initiator flow of 0.4 sccm, the polymer film deposited at a rate of 16 nm/min. The DEVE crosslinker created a network by linking all of the polymer chains together, while maleic anhydride groups at the interface between the substrate and hydrogel film formed a covalent bond with the amine to tether the network to the substrate. Covalent linkages prevented the film from delaminating upon exposure to aqueous solutions; the films undergo 11-fold swelling in pH 7 buffer. The carboxylic acids that formed upon hydrolysis of maleic anhydride imparted anionic character to the film. In pH 1 buffer, the swelling ratio was 7. The composition of the film was 76% DMAA, 14% MA and 10% DEVE, as determined by X-ray photoelectron spectroscopy (XPS).

The anhydride groups were reacted with 2-aminoethanethiol prior to placing the films in water to create free sulfhydryl groups at the surface. The functionalized films were soaked in a dispersion of CdSe/ZnS core-shell quantum dots in tetrahydrofuran, and stable linkages formed between sulfhydryls and the quantum dot surfaces, imparting fluorescence to the hydrogel. Three-dimensional implants for biomedical applications have also been coated with the hydrogel in order to improve biocompatibility. Additional examples of using iCVD to create conformal hydrogel coatings on complex structures will be described, along with their applications. In all cases, the chemical functionalities of hydrogel components were maintained and further exploited for applications. Nanoscale thicknesses of the coatings were precisely controlled.