Hydrophobic Implant coating

The implant consists of a tablet-shaped ganciclovir reservoir. The drag is initially completely coated with poly(vinyl alcohol) (PVA) and then coated with a discontinuous film of hydrophobic, dense poly (ethylene-co-vinyl acetate) (EVA). Both polymers are nonerodible and hydrophobic (the PVA used in the implant is cross-linked and/or high molecular weight, to ensure it does not dissolve when exposed to water). The entire assembly is coated again with PVA to which a suture tab made of PVA is attached (Figure 4.5). 

Hydrophobic coatings composed of silicon- and fluorine-containing polymeric materials as well as polyurethanes have been studied because of the relatively good clinical performances of Silastic , Teflon , and polyurethane polymers in cardiovascular implants and devices. Polymeric fluorocarbon coatings deposited from a tetrafluoroethylene gas discharge have been found to greatly enhance resistance to both acute thrombotic occlusion and embolization in small diameter Dacron grafts. 

Biodegradable hydrophobic polymers useful for the fabrication or coating of implantable medical devices are summarized in Table 8.12. 

Because of its precision application and enduring features, PPX films have been used in various applications, including hydrophobic coatings (moisture barriers, e.g., for biomedical hoses), barrier layers (e.g., for filter, diaphragms, valves), microwave electronics, implanted medical devices, sensors in hostile environments (automotive fuel/air sensors), electronics for aerospace and military, corrosion protection for metallic surfaces, reinforcement of microstructures, friction reduction (e.g., for guiding catheters, acupuncture needles and microelectromechanical systems) and protection of plastics and rubbers from harmful environmental conditions. 

Polyphosphazenes bearing fluoroalkoxy side groups are among the most hydrophobic synthetic polymers known, and are bioinert. These polymers are as hyrophobic as polytetrafluoroethylene but, unlike Teflon, are flexible or elastomeric, easy to prepare, and can be used as coatings for other materials. They are highly biocompatible and therefore have been proposed as good candidates for use in heart valves, heart pumps, blood vessel prostheses, or as coating materials for pacemakers or other implantable devices. 

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