Publication

Abstract : Surface modification using supported monolayers of phosphorylcholine containing phospholipids has been an accepted strategy for developing blood-contacting materials. We present a detailed study of the blood compatibility of the supported monolayers of phospholipid, glycolipid, and cholesterol (Chol) binary and ternary lipid combinations using in vitro techniques. The packing and orientation of these monolayers have been correlated with the blood compatibility. We have used phosphatidylcholine (PTC) for phospholipid, galactocerebroside (Gal) for glycolipid, and Chol based on the headgroup structure to represent the major lipid components of the endothelial luminal cell membrane. The interfacial behavior of various combinations of PTC, Gal, and Chol monolayers have been studied at the air/water interface and deposited on hydrophobic polycarbonate (PC) polymer substrates with the help of the Langmuir−Blodgett trough. The packing and orientation of the supported monolayers have been varied by means of changing the lipid composition rather than the deposition parameters. This approach seems to be more similar to the in vivo conditions. The different supported monolayer surfaces prepared accordingly are (1) a closely packed ordered hydrophobic surface, PC modified with the combination PTC/Chol/Gal (1:0.35:0.125), (2) a loosely packed ordered hydrophobic surface, PC modified with the combination PTC/Chol (1:0.35), and (3) a closely packed ordered hydrophilic surface, PC modified with the combination PTC/Chol (1:0.7). An optimized modified surface (PTC/Chol/Gal, 1:0.35:0.125) has been identified on the basis of the maximum transfer ratio from the air/water interface and characterized by using atomic force microscopy. The concentration of Chol has been found to be an important parameter, which influences the transfer ratio. The Gal improves the monolayer integrity under a reduced Chol concentration. The blood compatibility of these supported monolayers was studied by protein adsorption, blood cell adhesion, and calcification. The tightly packed ordered hydrophobic surface (PTC/Chol/Gal, 1:0.35:0.125), has been found to be more blood compatible because of reduced blood cell adhesion and calcification. This surface also promotes albumin adsorption and may be the reason for the reduced platelet activation, while in the case of the loosely packed ordered hydrophobic surface (PTC/Chol, 1:0.35) the protein adsorption also has been reduced along with the blood cell adhesion and calcification. When the ordered hydrophilic surface (PTC/Chol, 1:  0.7) of the monolayer has been exposed, the blood cell adhesions as well as the overall protein adsorption were significantly reduced. However, the packing of the phosphorylcholine moieties of the polar headgroup has been affecting the calcification on the surface. We have observed an increase in calcification to the surface modified with the loosely packed polar headgroup, from a relative study on chitosan and chitosan modified with the monolayer of PTC. These findings are helpful for the surface modifications for blood-contacting materials using this strategy.