(549c) Hydrogel Synthesis Via Initiated Chemical Vapor Deposition (iCVD)

In this work, we produced films of poly(2-hydroxyethyl methacrylate) (PHEMA), a hydrogel polymer, as potential skin scaffolds using a unique initiated chemical vapor deposition (iCVD) process. iCVD is a solvent-free polymerization process which uses a chemical vapor deposition environment to thermally activate an initiator in the gas phase by a resistively heated filament array, followed by subsequent polymerization on a cooled substrate by the attachment of multiple monomer units to these activated radicals to form polymer chains. iCVD reaction parameters, including reactor pressure, substrate temperature, filament temperature and monomer and initiator flowrates, were optimized to yield deposition rates of ~1.5 µm/min, which are high compared to typical vapor deposition processes, giving free standing films of ~100 µm. A study of reaction kinetics showed that iCVD polymerization followed a Langmuir-Hinshelwood mechanism for the surface reaction of two adsorbates, in this case between the monomer and the chain forming radical. NMR and FTIR spectroscopies showed iCVD PHEMA films are chemically stoichiometric, indicating linear homopolymers were obtained. Cytotoxicity assays with adult human dermal fibroblasts showed these films are non-toxic, demonstrating a lack of entrained monomer or initiator in the polymer from the iCVD process. iCVD PHEMA also displayed good cell adhesion properties owing to its hydrophilic nature. From Instron and DMA measurements, iCVD PHEMA was found to be mechanically robust, yielding properties that are similar to PHEMA chemically crosslinked with ethylene glycol dimethacrylate. In addition, water uptake studies of the linear and crosslinked films showed comparable diffusion coefficients of 7.2 x 10^-8 cm²/s and 9.8 x 10^-8 cm²/s, respectively. These similarities are attributed to the high molecular weight of iCVD PHEMA as a result of the high deposition rates achieved, yielding linear PHEMA with a high degree of physical chain entanglements that act similarly to chemical crosslinks. Through the control of processing conditions, iCVD is demonstrated as a viable technique for the synthesis of hydrogel biomaterials with desirable biological, mechanical and transport properties.