Dave M. Johnson

Stability of self-assembled monolayers on titanium and gold.

Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.

Drug delivery from gold and titanium surfaces using self-assembled monolayers.

Currently available drug-eluting stents (DES) use polymers for coating and releasing drugs. Increasing evidence suggests that inflammatory and hypersensitive reactions are caused by such polymer coatings. This study focused on developing new techniques for delivering drugs directly from metal implant surfaces. Hydroxyl-terminated self-assembled monolayers (SAMs) were coated on Au and Ti surfaces. Therapeutic self-assembled monolayers (TSAMs) were prepared by chemically attaching the model drug, flufenamic acid, to SAM coated metal surfaces. Three different methods of esterification (acid chloride esterification, dry heat esterification, and direct esterification) were explored to attach flufenamic acid to SAMs. TSAMs were characterized using X-ray photoelectron spectroscopy, fluorescence microscopy, atomic force microscopy, and contact angle goniometry. These techniques collectively confirmed the attachment of drug onto SAM coated metal surfaces. In vitro drug release was investigated by immersing TSAM coated metal specimens in tris-buffered saline (TBS) at 37 degrees C for 28 days. TBS was analyzed at 1, 3, 7, 14, 21, and 28 days for the amount of drug eluted using high performance liquid chromatography. Large data scatter was observed for the release profiles of TSAMs prepared by acid chloride esterification. TSAMs prepared by dry heat and direct esterification methods showed an initial burst release of the drug followed by a sustained slow release for up to 2 weeks. Thus, this study suggests the potential for using self-assembled monolayers as an alternate system for delivering drugs from coronary stents and other metal implants.

Drug loading of nanoporous TiO2 films

The loading of therapeutic amounts of drug on a nanoporous TiO(2) surface is described. This novel drug-loading scheme on a biocompatible surface, when employed on medical implants, will benefit patients who require the deployment of drug-eluting implants. Anticoagulants, analgesics and antibiotics can be considered on the associated implants for drug delivery during the time of maximal pain or risk for patients undergoing orthopedic procedures. Therefore, this scheme will maximize the chances of patient recovery.

Long-term stability of self-assembled monolayers on 316L stainless steel.

316L stainless steel (316L SS) has been extensively used for making orthopedic, dental and cardiovascular implants. The use of phosphonic acid self-assembled monolayers (SAMs) on 316L SS has been previously explored for potential biomedical applications. In this study, we have investigated the long-term stability of methyl (-CH(3)) and carboxylic acid (-COOH)-terminated phosphonic acid SAMs on 316L under physiological conditions. The stability of SAMs on mechanically polished and electropolished 316L SS was also investigated as a part of this study. Well-ordered and uniform -CH(3)- and -COOH-terminated SAMs were coated on mechanically polished and electropolished 316L SS surfaces. The long-term stability of SAMs on 316L SS was investigated for up to 28 days in Tris-buffered saline (TBS) at 37 degrees C using x-ray photoelectron spectroscopy, atomic force microscopy and contact angle goniometry. A significant amount of phosphonic acid molecules was desorbed from the 316L SS surfaces within 1 to 7 days of TBS immersion followed by a slow desorption of molecules over the remaining days. The -COOH-terminated SAM was found to be more stable than the -CH(3)-terminated SAM on both mechanically and electropolished surfaces. No significant differences in the desorption behavior of SAMs were observed between mechanically and electropolished 316L SS surfaces.