Surface wettability and platelet adhesion studies on Langmuir-Blodgett films

Because Langmuir-Blodgett (LB) deposition technique is known to be capable of preparing highly ordered monomolecular films with densely packed structure, LB technique is used to prepare films of DPPC, DMPC, cholesterol, octadecylamine (ODA), and stearic acid, with thickness of one molecular layer. The film surfaces were characterized by dynamic contact angle measurement and the interaction between blood and these materials were investigated. The properties of LB films were also compared with the results obtained on continuous films prepared by solution dipping. The results show that the contact angles of water on LB films of the five compounds decreases as the following order: ODA > DMPC ≈ DPPC > stearicacid > cholesterol. The hydrophobic property reflects the highest organization of ODA molecules on the substrate, which is related to its interaction between the molecule and substrate. The advancing contact angle of ODA is equivalent to that of a methyl-terminated SAM, but its receding contact angle is smaller which implies the exposing of hydrophilic pole or glass substrate on LB film. The irregular orientation of molecules on LB film increases with decreasing of contact angle and is especially significant on LB film of cholesterol which has highest hydrophilic property. The plate adhesion experiments on the continuous films show that the hemocompatibility of the five materials decreases as the order: DPPC ≈ DMPC > ODA > cholesterol > stearicacid ≈ glass. This result implies that the lipid has highest blood compatibility, and then -NH₂, and then -OH functionality. On the contrary, the glass surface, -COOH and -CH₃ functionalities have high reactivity to platelet. Due to the possibility of glass exposure on LB films, as estimated from the surface wettability, the LB films have higher platelet reactivity, especially for the cholesterol, compared with the continuous films. Because the interaction of the LB film to the substrate is physical force, the deposited molecules may be peeled off from the substrate by dipping in Hepes-Tyrodes buffer solution. As a consequence, the LB films after equilibrating with Hepes-Tyrodes buffer solution have high platelet reactivity as that on glass surface.