Owing to the capability of fabricating a well-defined chemical structure on the surface, self-assembled alkanethiols with a variety of terminal functionalities were prepared on the gold substrate for investigating the interactions between the biological environment and synthetic surface. In this study, we report the synthesis of the sulfonic acid terminated long-chain alkanethiol, 10-mercaptodecane-sulfonic acid, for direct preparation of a self-assembled monolayer (SAM) with -SO(3)H functionality. Nuclear magnetic resonance (NMR) and elemental analysis studies indicated that a high purity of sulfonic acid terminated alkanethiol was obtained. Surface characterization results showed that the -SO(3)H terminated SAM is hydrophilic and has a slightly higher hysteresis value, possibly because of the slower chain mobility of the bound sulfonic acid alkanethiol. Electron spectroscopy for chemical analysis (ESCA) analysis demonstrated that the -SO(3)H terminal group is situated in the outermost layer of the monolayer, as previous alkanethiol SAM structure models proposed. The platelet reactivity of the -SO(3)H SAM was higher than that of -OH SAM but less than the -CH(3) terminated one in vitro, whereas similar platelet reactivity was noticed between the -SO(3)H and -COOH SAMs. The higher platelet reactivity found on the -SO(3)H SAM could be caused by the higher surface functional group density inherent in the SAM structure and/or the composition and conformation state of the adsorbed protein layer.

The mixed self-assembled monolayers (SAM) prepared from long chain alkanethiols, HS(CH(2))(11)NH(2) and HS(CH(2))(10)COOH, on gold are employed as the model surface for investigating the interactions between the biological environment and synthetic surface. A distinctive SAM preparation scheme was utilized in this investigation. The triethylamine was added to the alkanethiol solution during SAM formation and then followed by additional rinsing of SAM with 10% CH(3)COOH or 1% HCl ethanolic solution. The contact angle values of NH(2) + COOH mixed SAMs were between those of the pure SAMs, except that it was prepared with solution mole fraction of amine-terminated alkanethiol at 0.2. X-ray photoelectron spectroscopy (XPS) analysis has indicated that these two distinctive SAM preparation procedures had both resulted in a reduction in oxidized sulfur species on pure --NH(2) terminated SAM. However, the procedure utilizing 1% HCl ethanolic washing solution was more effective in reducing the unbound thiol fraction and to form a pure --NH(2) SAM with better quality. XPS analysis has also revealed that the surface of NH(2) + COOH mixed SAMs was "amine-rich". In vitro platelet adhesion assay has shown that the amount of adherent platelets on pure positive charged --NH(2) terminated SAM is less than that on anionic --COOH terminated counterpart in both acidic ethanolic washing schemes. Moreover, the lowest platelet adhesion density was noted on the mixed SAM surfaces with surface amine mole fraction at 0.51 and 0.57. This finding suggests that the surface charge with near neutrality might be of importance in reducing platelet adhesion and activation on artificial biomaterial.

Despite of its widely uses in various clinical applications, the titanium-based material still faces different challenges, such as hemocompatibility and anti-biofouling characteristics required in various situations. The objective of this investigation was to develop a novel surface modification strategy for titanium-based material to improve the platelet compatibility that is important in rigorous blood-contacting cardiovascular applications. In this work, a series of copolymers, which composed of novel 6-acryloyloxy hexyl phosphonic acid (AcrHPA) and sulfobetaine methacrylate (SBMA) was synthesized. The phosphonic acid group in these copolymers can impart covalent binding to the titanium substrate while the zwitterionic sulfobetaine functionality is considered being able to reduce the platelet adhesion and activation on the modified titanium substrate. NMR analyses suggested that copolymerization reaction is likely not an ideal statistical reaction but to add the monomers in a random order. Studies have shown that the composition of the monomers affected the surface characteristics and platelet compatibility of these covalent-bound AcrHPA-SBMA copolymers on titanium substrate. Contact angle analysis has shown the addition of SBMA can increase surface hydrophilicity of the spun-coated copolymers. In addition, AFM analyses have revealed that the surface roughness of the spun-coated copolymer layer were varied with the ratio of AcrHPA and SBMA. The most platelet compatible surface was noted on the one modified by the highest amount of SBMA added (i.e. 70 mol%) in copolymerization. In summary, the surface modification scheme presented here would be of potential as well as manufacturing process applicable for future development in blood-contacting titanium-based biomedical devices.