Implantable medical devices catheters

Segmented polyurethane elastomers, prepared from diisocyanates, macrodiols and chain extenders, are frequently used in the construction of implantable medical devices, such as cardiac pacemakers, heart valves, catheters, and heart assist devices, because of their excellent mechanical properties and haemocompatibility. Polyether macrodiols, such as poly(tetramethylene oxide) (PTMO), are used to prepare polyurethanes for implant, since they offer an increased resistance to enzymatic hydrolysis compared with polyester-based polyurethanes. 

One simple but smart example of a fibrous implantable medical device that uses the high surface ratio feature of fibers is embolization coil. Such devices are intended for many endovascular treatments of aneurysms, hemorrhages of peripheral lesions, and arteriovenous malformations. The procedure involves the threading of thin coils through a catheter into the affected area of the brain, filling the weakened portion of the vessel. Once in place, the body responds by forming a clot around the coil, further reducing the pressure and risk of rupmre. 

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. 

Biomedical Applications. In the area of biomedical polymers and materials, two types of appHcations have been envisioned and explored. The first is the use of polyphosphazenes as bioinert materials for implantation in the body either as housing for medical devices or as stmctural materials for heart valves, artificial blood vessels, and catheters. A number of fluoroalkoxy-, aryloxy-, and arylamino-substituted polyphosphazenes have been tested by actual implantation ia rats and found to generate Httle tissue response (18). 

In general, a medical device is defined as follows a medical device is an implant and equipment to be used either to achieve disease diagnosis, medical treatment, or disease prevention for human and animals, or to influence the physical structure and function of human and animals. Medical devices for humans may also be classified based on whether and how long the device is in contact with tissue or cells and on the degree of disjunction induced by the device when in a disabling situation. The term covers various categories, such as scissors and tweezers, with small risk to human function, to central venous catheters, artificial dialysis (human kidney), and pacemakers, with high risk to human function. 

Silicone-nylon 12IPN is a candidate material for self-supporting medical devices such as implantable pumps, catheter guides, and connectors. 

Phthalate esters are widely used in the production of plastics, particularly vinyl plastics, to add flexibility to products made with these materials. DEHP is commonly used in medical devices, including cardiac catheters, endotracheal tubes, and certain implanted devices, while DINP is more often found in wires and cables, hoses, and plastic toys. DEHP is also used in plastic containers, such as those used for food. These phthalates are not bound chemically to the plastic but are physically dissolved in it. 

Medical PUs are another subset of PU elastomers. Segmented PUs were first suggested for use in a biomedical application in 1967. ° Early work with PU elastomers showed that these materials could be used for implants without causing a large, unwanted inflammatory response. The first medical devices made of PUs, however, were found to be susceptible to hydrolysis and degraded faster than desired. ° From that time, new biostable materials have been developed for use as pacemaker leads, catheters, vascular grafts. 

Despite the sophistication of today s medical devices, the materials used often result in undesirable complications, including bacterial infections, blood clots, tissue trauma due to device insertion, and friction and wear of implants. This is especially true for such devices as catheters, guidewires, stents, probes, and prosthetic implants. 

Gram-positive opportunistic pathogens such as Staphylococcus epidermidis, S. aureus, E. faecalis and E. faecium have the capacity to form biofilms on foreign medical devices such as catheters, and surgical implants [52, 53], These microorganisms are normal inhabitants of healthy humans, in recent years, however, the bacteria emerged as a common cause of nosocomial infections [54], Interestingly,... 

Silicone elastomers, with their low surface energies, hydrophobicities, as well as chemical and thermal stabilities, are widely used throughout the medical device industry (for component fabrication) and in pharmaceutical applications (tubings for fluid-handling), as a hybrid material (in catheter applications), and as implants. 

The types of medical devices that require biornaterials arc wide ranging across most medical disciplines. " Artificial heart valves, contact lenses, drug delivery implants. urinary catheters, and replacement hip joints are just a few examples that demonstrate where biomaterials can be employed in the body. 

Blood-contacting materials have to fulfill particular requirements, as they are immediately exposed to all host defense mechanisms of the body. Thus, the contact of blood with foreign surfaces induces several cascade reactions and activation phenomena. These complex and highly interconnected reactions potentially create clinically significant side effects in the application of medical devices (e.g., cardiovascular implants, extracorporeal circulation, catheters) and interfere with the success of the medical treatments [64]. In certain cases, even the formation of thromboemboli or systemic inflammatory reactions were reported to occur as a consequence of the activation of coagulation enzymes and thrombocytes and/or the activation of the complement system and leukocytes (immune response) at the biointerfaces of the applied materials [65]. 

The final consideration to be addressed in this chapter on the choice of a polymer fortrsein medical devices is cost. Biomedical polymers can range from inexpensive (PVC, polyethylene) to extremely expensive (e.g., polymers with peptide components). A disposable catheter intended for minutes or hotus use in the body will not jrrstily an expensive polymer. On the other hand, a device implanted with the intent of a lifetime of acceptable performance might rrse an expensive polymeric component if long-term performance benefit can be demonstrated. Also, a higher priced polymer might be justified based on reduced complications. For example, as catheter-related bloodstream infections can add over 56000 to a hospital stay, a more expensive antibacterial catheter should be justified. ... 

To avoid missing out on unexpected opportunities, you may want to brand yourself broadly in the area of your interests and capabilities (for example, a specialist or generalist in medical devices ), yet with a marketable depth (for example, cardiovascular implantable technologies, but not too specific such as a specialist in patent foramen ovale catheters, unless it is absolutely necessary). 

Tubular, sheet, plate, and film forms of PVC have been used in medical devices such as blood bags and catheters. Implants of PVC are not encouraged. 

Silicone elastomers have a long history of use in the medical field. They have been applied to cannulas, catheters, drainage tubes, balloon catheters, finger and toe joints, pacemaker lead wire insulation, components of artificial heart valves, breast implants, intraocular lenses, contraceptive devices, burn dressings and a variety of associated medical devices. A silicone reference material has been made available by the National Institutes of Health to equate the blood compatibility of different surfaces for vascular applications. This material is available as a silica-free sheet. Contact the Artificial Heart Program, NHBLI, NIH, Bethesda, Md. for further information. 

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