Preparation of a stable phospholipid monolayer grafted onto a methacryloyl-terminated substrate as blood compatible materials

Abstract

We have prepared a surface-grafted phospholipid monolayer by in situ polymerization carried out at the interface between a pre-assembled phospholipid monolayer and a methacryloyl-terminated substrate. The phospholipid containing an acryloyl moiety, 1-stearoyl-2-[12-(acryloyloxy)-dodecanoyl]- sn-glycero-3-phosphocholine (acryloyl-PC), was pre-assembled by vesicle fusion onto methacryloyl-terminated substrates which were silanized with 3-(trimethoxysilyl)propyl methacrylate (TSM). The acryloyl-PC monolayer and methacryloyl-terminated substrates were then polymerized in situ by adding a water-soluble initiator, 2,2-azobis(2-methylpropionamidine) dihydrochloride (AAPD), at 60°C for 15 min. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements indicated that the polymerized phospholipid surface on the TSM-silanized substrates formed a lipid monolayer structure with some defects. The polymerized phospholipid surfaces also showed good stability in methanol due to chemical bonding to solid surfaces. The grafting efficiency of acryloyl-PC monolayer on the TSM substrate, which was calculated by the relative carbon ratio of the polymerized acryloyl-PC monolayer on TSM substrate before and after methanol washing, was 94.5%. For comparative analysis, the acryloyl-PC monolayer was also polymerized onto dimethyl-terminated substrates silanized with dichlorodimethylsilane (DCM). In the absence of surface grafting moieties on solid substrates, the laterally polymerized acryloyl-PC monolayer physically adsorbed on substrates was easily removed in an organic solvent. The surface-grafted phospholipid monolayer was also greatly effective in the prevention of platelet adhesion.