Page 23 - Improved endothelialization by silicone surface modification and fluid hydrodynamics modulation- Implications for oxygenator biocompatibility Nasim

releasing encapsulated drugs in a sustained manner by changing environmental conditions and transporting drugs across biological membranes [15, 31-33]. A biomaterial surface simultaneously co-immobilized with different liposome-based biomolecules possessing anticoagulant and growth-inducing properties, might
improve both anticoagulation and endothelialization, which may provide a potential 3 application for long-term usage of blood-contacting devices. Biomaterials co- immobilized with different biomolecules have been shown to possess the properties of each individual biomolecule [16-18].
The stability of collagen or collagen-containing conjugate coatings under blood flow forces is still a common limitation to their clinical use [16, 34]. To study the interaction between conjugate coatings and blood constituents or cultured cells, well defined and stable coatings are required [34-36]. Immobilization of conjugate coatings onto a surface can be done by e.g. physical adsorption, encapsulation, entrapment, and covalent or ionic binding [16]. The advantages of covalent immobilization using carbodiimide bonds are that the immobilized biomolecules are robust enough to withstand blood flow shear stresses [16]. For covalent immobilization of conjugate coatings onto polymer surfaces, functional groups such as amine, carboxyl, hydroxyl, isocyanate, or epoxy are required. Since most conventional polymers do not have such functional groups on their surface, they should be modified to allow reactive group formation for covalent immobilization of active molecules [34-36].
Plasma glow discharge and plasma graft polymerization are two effective methods to introduce functional groups to the material's surface and subsequently affect surface properties, e.g. wettability, and charge [22, 37, 38]. Plasma is composed of highly excited atomic, molecular, ionic, and radical species, and creates surfaces with specific oxygen or nitrogen containing groups in the presence of various vapours [8, 37]. Plasma treatment modifies the outermost surface of polymers without changing the bulk characteristics of the material. The chemical composition of gas-plasma modified surfaces depends on both the gas used and the experimental conditions [22]. Plasma graft polymerization is another attractive way of modifying the surface chemistry and chemically immobilize compounds onto the surface of a biomaterial [34-36, 38]. A desired monomer may be polymerized onto the surface of a plasma-treated material resulting in the formation of a grafted layer on the material surface, avoiding drawbacks of monomer detachment by providing long-term stability. The grafted surfaces may then provide active sites for the binding of collagen or collagen-containing conjugate molecules. This method is highly surface selective, where the modification is confined to a depth of a few nanometers without modification of the bulk properties [38].
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