Adsorption of low density lipoproteins to biomedical polymers

The area of blood-lipid interaction with biomedical polymers has not been clearly defined. The purpose of the dissertation was to examine the interaction of the blood lipid, low density lipoprotein (LDL), with a select group of biomedical polymers. The adsorption characteristics of LDL was studied on filler-free poly(dimethyl siloxane) (PDMSO-FF), Biomer, Cardiomat 610, Kraton 1650, poly(hydroxy ethyl methacylate) (PHEMA) and glass as the control material. The low density lipoprotein was chosen because of its high cholesterol and cholesterol ester content which related to past in vitro studies showing steroidal lipid absorption, Low density lipoprotein was also chosen because of its pathophysiological role in atherogenesis. The data from this study suggest that LDL adsorption of polymer surfaces can occur by both electrostatic interactions and apolar or hydrophobic interactions. Adsorption of LDL to charged hydrophilic glass control surfaces occurred rapidly, reaching plateau concentrations within a minute. Adsorption of LDL to polymer surfaces appeared to be dependent upon the polymer hydrophobicity (or apolar nature) and to its flexibility (or dynamic nature) at the interface. Increased surface concentrations of LDL were observed for both hydrophobic and flexible polymer (Biomer versus PHEMA). Temperature was also found to enhance significantly the surface concentration of absorbed LDL at 37°C versus 25°C. This was suggested to be due to the core lipid phase transition at 36°C. Preliminary competitive absorption studies of LDL with albumin and serum suggest the LDL absorption occurs rapidly and preferentially. Preliminary studies on the role of LDL in calcification were not conclusive. The conclusion from this study suggested that LDL adsorption occurs as a function of polymer hydrophobicity, flexibility and temperature. Further studies are necessary to define the role of LDL in lipid absorption, materials compatibility in affecting the material integrity in an in vivo environment.