High-spatioresolved microarchitectural surface prepared by photograft copolymerization using dithiocarbamate: Surface preparation and cellular responses

Self-perpetuating photograft copolymerization based on the photochemistry of an iniferter benzyl N,N-diethyldithiocarbamate was utilized to design two types of microprocessed surfaces using a custom-designed apparatus operated by an X-Y step motor. Cellular adhesion and growth responses wore studied on (1) a surface upon which five different water soluble polymer regions were photografted with micron order precision and (2) three different gradient surfaces with unidirectionally varying thicknesses of a water soluble graft polymer layer. A striped micropatterned surface (width of each region 500 mu m) was prepared by sequential photoirradiation through a photomask with a stripe window on a selected region of a poly(styrene-co-vinylbenzyl N,N-diethyldithiocarbamate)-coated PET film immersed in an aqueous solution of vinyl monomer. The sample stage was moved in a stepwise manner for each change of monomer solution. The monomers studied were N,N-dimethylacrylamide (DMAAm), 2-hydroxyethyl methacrylate (HEMA), N-[3-(dimethylamino)propyl]acrylamide methiodide (DMAPAAmMeI), methacrylic acid sodium salt (MANa), and 3-sulfopropyl methacrylate potassium salt (SMAK). Surface wettability, X-ray photoelectron spectroscopic analyses, and light microscopic visualization by dye staining revealed that five stripe regions, each of which was grafted with a different polymer, were prepared side by side. Seeding and culture of endothelial cells (ECs) on the micropatterned surfaces yielded markedly reduced adhesion on polyDMAAm and palyHEMA, PolyDMAPAAmMeI and polyMANa regions promoted cell adhesion and growth, whereas enhanced adhesion was initially observed but then became markedly reduced over time on polySMAK. Atomic force microscopic (AFM) observation showed that photoirradiation through a photomask in the presence of a monomer solution (DMAAm, DMAPAAmMeI, and MANa) under continuous sample movement yielded a graft-polymer-layer thickness gradient surface. EC adhesion and proliferation gradually decreased with increasing graft layer thickness on the polyDMAPAAmMeI and polyMANa surfaces. In contrast, cell adhesion on the polyDMAAm-grafted surface ceased abruptly above a certain graft thickness. This study shows that, using this photograft copolymerization method, both regional and chemical specific surface modification on the micron level has been achieved, representing a significant advance in the microprocessing of biomedical devices.