| A surface modification approach was performed to generate a nonthrombogenic surface through a dense gas process. This modification was achieved by incorporating phosphatidylcholine, a phosphatide which is one of the most common constituents of biological membranes, into the polymeric substrate. Supercritical fluid was employed as the reaction medium for such surface modification due to its gas like diffusivity, excellent solvating properties and ability to “wet” all types of surfaces and yet offer the same advantages as organic solvents. During the surface modification process, polymeric substrates were exposed to phosphatidylcholine which were previously solvated in the supercritical CO2. These molecules with phosphorylcholine moieties were interacting with the polymers in SCCO2 through molecular entanglement between the hydrocarbon chains of phosphatidylcholine and the surface molecules of the polymer. Consequently, these phosphatidylcholine molecules were immobilized on the surface of the polymer via an extensive molecular entanglement during the surface modification process. After the carbon dioxide molecules were removed, phosphatidylcholine would be anchored onto the surfaces of the polymer and attached to the substrate permanently leaving the desired phosphorylcholine moieties on their surfaces. These phosphatidylcholine molecules were strongly attached to the substrate, and did not detach even after extensive rinsing in distilled water. Thus, a polymeric substrate with the phosphorylcholine moieties incorporated on its surfaces was then generated and it provides surfaces with biomembrane-like structure. This new surface modification approach can be used to develop a great variety of promising materials to produce a very useful blood-contacting surface for various biomedical applications. |
