Surface characterization and platelet adhesion studies for the mixed self‐assembled monolayers with amine and carboxylic acid terminated functionalities

Abstract

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.

Interactions of leukocytes and platelets with poly(lysine/leucine) immobilized on tetraethylene glycol-terminated self-assembled monolayers

“…Previously studies demonstrated that platelet adhesion is higher on positively charged surfaces, such as chitosan, and that this adhesion decreases by almost 50% when the charge is neutralized [16]. Chuang et al [17] also demonstrated that platelet adhesion is elevated on positively charged NH 2 -SAMs, although not as high as on negatively charged COOH-SAMs. They also demonstrated that the lowest platelet adhesion density was obtained on mixed NH 2 /COOHSAMs with surface amine mole fractions of 0.51 and 0.57, which suggests that surfaces with charges near neutrality are important in reducing platelet adhesion and activation.…”

Blood coagulation on biomaterials requires the combination of distinct activation processes

“…The use of self-assembled monolayers (SAMs) of alkyl thiols on gold [37] has been advantageous to address such issues since it allows a variety of model surfaces to be produced with precisely defined characteristics [38,39]. Previous work using SAM surface chemistry focused on plasma protein adsorption [9,40,41] and cell-surface interactions including leukocyte [42,43] and platelet adhesion [9,44,45]. Here we use a set of SAMs exposing different combinations of functional groups to explore the initial coagulation events brought about by blood-material interaction.…”

Electrostatic deposition of polycations and polyanions onto cysteine monolayers

“…Others employ monolayers that contain a mixture of molecules that have both amine and carboxylic acid groups as a mechanism for altering the properties of the interface [9][10][11]. Chuang and Lin report the use of a mixed 11-aminoundecanethiol/11-mercaptoundecanoic acid monolayer for the purpose of developing a surface to study variations in platelet adhesion to synthetic surfaces [9]. By adjusting the mole fraction of -COOH terminated thiols and -NH 2 terminated thiols, they were able to manipulate the degree of platelet adhesion.…”