| This dissertation investigates the use of self-assembled monolayers (SAMs) as a novel technique for attaching and releasing therapeutic drugs directly from metal implants. The two metal/SAMs systems used in this study were titanium/phosphonic acid and gold/thiol systems. In this study, we mainly investigated the following: (a) stability of SAMs, (b) chemical attachment of therapeutics to SAMs, (c) drug release kinetics of therapeutic SAMs and (d) biocompatibility of SAMs and therapeutic SAMs.;First, a hydroxyl-terminated phosphonic acid (PA) SAM was coated on Ti. The stability of the SAM was investigated in tris-buffered saline (TBS) at 37°C, double distilled water (dd-H2O), ambient air, and ultra-violet (UV) light. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au and its stability was also investigated under similar conditions. The specimens were primarily characterized using X-ray photoelectron spectroscopy (XPS) and contact angle measurements were also taken. In TBS or dd-H 2O, a portion of PA SAM molecules were desorbed from the Ti surface over a period of 14 days, while the thiol SAM on Au was stable up to 21 days under similar conditions. In ambient air, the PA SAM on Ti was stable up to 14 days, while the thiol SAM on Au was not stable for even one day. Under UV-radiation exposure, the alkyl chains of the PA SAM were decomposed leaving only the phosphonate groups on the Ti surface after 12 hours. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied with oxidation of thiolates.;Second, therapeutic SAMs (TSAMs) were prepared by chemically attaching flufenamic acid, a model drug, to --OH terminated SAMs coated Ti and Au surfaces. Three different methods of esterification (acid chloride esterification, dry heat esterification, and direct esterification) were explored to attach flufenamic acid to SAMs coated metal surfaces. TSAMs coated metal surfaces were characterized using XPS, fluorescent microscopy and atomic force microscopy (AFM). XPS confirmed the formation of ester bonds between flufenamic acid and SAMs. The distribution of drug molecules on SAMs coated metal specimens was studied using fluorescent microscopy. AFM images showed the change in surface morphology before and after drug attachment.;Third, in vitro drug release kinetics of TSAMs was investigated using high performance liquid chromatography (HPLC). TSAMs coated metal specimens prepared via acid chloride, dry heat esterification, and direct esterification were immersed in TBS at 37°C for 28 days. TBS was analyzed at 1, 3, 7, 14, 21, and 28 days to determine the amount of drug released. The cumulative drug release profiles of TSAMs prepared via different esterification techniques have different types of drug release profiles. Large scatters were observed in the data for the release profiles of both Ti and Au prepared through acid chloride esterification. Burst release profiles with smaller scatters were observed for both Ti and Au prepared through dry heat esterification. Direct esterification produced a controlled drug release profile for Au specimens; however, burst release profiles were observed for Ti specimens. These findings demonstrated that the techniques used to attach drug molecules may significantly affect the drug release profiles.;Fourth, the biocompatibility of SAMs and therapeutic SAMs was investigated. Human aortic endothelial cells (HAECs) were seeded on seven different surfaces, which included control glass, control-Ti, control-Au, SAMs coated Ti, SAMs coated Au, TSAMs coated Ti, and TSAMs coated Au. The viability and proliferation of HAECs were investigated by using the MTT colorimetric assay. The cell adhesion on SAMs and TSAMs coated metal surfaces is comparable to control metal surfaces and better than plain glass surfaces. The highest number of viable cells was observed on SAMs coated metal surfaces and control-Ti surfaces. Cell proliferation was observed on SAMs and TSAMs coated metal surfaces even though the rate of proliferation was slower than control surfaces. The phase contrast microscopic images of HAECs showed spreading cells with typical polygonal shape on SAMs and TSAMs coated surfaces similar to control surfaces. The expression of surface adhesion protein, platelet endothelial cell adhesion molecule-1 (PECAM-1), showed that the phenotype of endothelial cells was preserved on SAMs and TSAMs coated surfaces similar to control surfaces. (Abstract shortened by UMI.). |
