Initiated Chemical Vapor Deposition of Polymer Thin Films and Coatings for Biological Applications

Initiated chemical vapor deposition (iCVD) is a surface polymerization technique performed under vacuum without the use of solvents. It uses a chemical vapor deposition environment to first activate an initiator in the gas phase, coupled with monomer adsorption onto a cooled substrate followed by a surface reaction by attaching the activated radicals to multiple monomer units to yield long polymer chains. iCVD produces exceptionally clean polymers with stoichiometric compositions, tunable molecular weights, and with no residual monomer or solvents. The overall objective of this work is to utilize iCVD to explore novel iCVD chemistries and resulting iCVD polymers relevant to biological applications and has been accomplished by performing three specific aims. First, iCVD was used to synthesize thick free standing films of poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels and the resultant polymers were found to be free from entrained monomer, resulting in good cell adhesion and noncytotoxicity towards human dermal fibroblasts, and having low nonspecific protein adsorption, thus making them suitable for potential biomedical applications. Additionally, these linear iCVD PHEMA films were found to have ultra high molecular weight with a high degree of physical chain entanglement that imparted greater mechanical strength compared to the chemically crosslinked counterparts, thus eliminating the need for hydrophobic crosslinking groups and retaining greater hydrophilicity. Second, iCVD was used to synthesize poly(ethylene glycol) (PEG) polymers important in biomedical applications. Since PEG is water soluble, iCVD was employed to graft PEG onto surfaces. In addition, a microcontact printing procedure was used to generate PEG patterns with selective grafting. These immobilized PEG substrates were shown to resist non-specific protein adsorption. A fundamental study of iCVD PEG deposition kinetics shows that the rate of polymerization and the kinetic chain length agree with a cationic polymerization mechanism. Third, iCVD was used to conformally apply polymer coatings on non-planar 3D particles to modify surface characteristics. Different iCVD processing strategies were employed to impart barrier properties to slow the release of microparticles of a crop protection compound by coating them with poly(glycidyl methacrylate) (PGMA) and poly(cyclohexyl methacrylate) (PCHMA) to obtain controlled release. In sum, this work has demonstrated that iCVD is a viable and relevant engineering pathway for the design, synthesis, and processing of polymers for biological applications. Success ultimately depends on understanding the fundamental kinetic mechanisms in iCVD polymerization and deposition.