Implantable medical devices Subject

AH implantable medical devices ate complex in design, materials, and implementation procedures. The biocompatibiUty, biodurabiUty, and efficacy of medical devices are the subject of extensive research by biomaterials scientists, device manufacturers, and health care professionals. 

Community-wide regulation of medical devices commenced with the introduction of Council Directive 90/385/EEC of 20 June 1990 on the approximation of the laws of the Member States relating to active implantable medical devices. Two further base directives followed that cover all other medical devices The Medical Devices Directive 93/42/EEC and The In Vitro Diagnostics Directive 98/79/EC. All three base directives are similar in content and structure. However, it should be noted that, in addition to dealing with the particular subject matter, the Medical Devices Directive and the In Vitro Diagnostics Directive also contained amendments to the previous device directives. The Medical Devices Directive amended articles in the Active Implantable Medical Devices Directive, while the In Vitro Diagnostics Directive amended articles in the Medical Devices Directive. 

Self-healing materials should have many applications. The U.S. Air Force, which partially funded the research at UIUC, is interested in using the materials in tanks that hold gases and liquids under pressure. The current materials used for these tanks are subject to microcracks that eventually grow, causing the tanks to leak. Self-healing materials would also be valuable in situations where repair is impossible or impractical, such as electronic circuit boards, components of deep space probes, and implanted medical devices. ... 

Rather than short fibers, monofilaments have length enough to be considered and used as an individual implantable medical device. Used in their most basic form, monofilaments are commonly subjected to tensile and bending stress in order to bring side by side two or more edges of native tissues/organs, whether wounds or sternum closures, for example. 

Carbon nanotubes are the subject of many research studies from drug delivery systems to many other medical applications. Only a few references and examples have been mentioned here. This dmg delivery application by CNTs constitutes in itself the wide potential of fibrous material for smart implantable medical device designing, going beyond just the biological response impact and including physical and mechanical features. 

Many large-scale retrieval studies have been conducted involving hundreds of implants. Although corrosion of the devices is only one of many topics that are the subjects of retrieval analyses, this type of investigation has yielded the majority of the knowledge that has been amassed regarding corrosion in vivo. ASTM F 561, Practice for Retrieval and Analysis of Implanted Medical Devices, and Associated Tissues, governs the performance of implant retrieval analyses. 

For many applications it is desirable that the implantable medical devices remain benign in the subject for the rest of the subject s life to avoid a secondary removal surgery. The intent is to leave the implanted neuromuscular microstimulator in the subject s body for the rest of his/her lifetime, which could be up to 80 or more years [15]. The cochlear implant is now the treatment of choice for children with profound and severe congenital and neonatal hearing loss [84, 85]. The long-term stability of the package for both of these devices is very important. 

Implanted biomaterials or medical devices are subjected to the surrounding host environment, which contains biochemical molecules such as enzymes [41,42], free radicals, peroxides [43], and hydrogen ions secreted by inflammatory cells and infecting microbes [44-46], The phagocytic mechanism of inflammatory cells such as neutrophils and macrophages has naturally evolved as a defense strategy for the body to ensure the removal of undesired foreign objects. Therefore, the potent biochemical actions of the secreted species can result in the unintended breakdown of solid-phase polymeric components of implanted devices over an extended period of time (months or years) [45],... 

Many of the materials incorporated in respiratory medical devices do not directly contact the person using the device. Therefore, materials are not subject to the same biocompatibility constraints as are implantable or surface contact devices. There is a need, however, to be sure that materials are rugged enough to stand up to repeated use under sometimes fiantic circumstances. An endotracheal tube, for instance, must not fail during insertion into the trachea. In addition, materials in the air passage... 

In the medical device community, the surface of a material is extremely important because it is what is in contact with the body. For example, the components of implants may be plasma treated to make their surfaces more biocompatible, which reduces cell adhesion and the formation of fibrous tissue around the implant. Implantable metal devices are often passivated to make the device resistant to corrosion when subjected to the aqueous environment inside the body. 

After a fiber or yam is produced, it is then fabricated into a textile stmcture in order to obtain the desired form, shape, and mechanical properties for a medical device. There are four alternative types of textile stmctures that are typically used for medical devices. They include wovens, knits, braids, and nonwovens. Each stmcture has its own advantages and disadvantages. For example, woven fabrics are usually stronger and more dimensionally stable and can be fabricated with lower porosities, but are stiffer, less flexible, and more difficult to handle. Knits, on the other hand, have higher permeability and flexibility compared to woven fabrics, but may dilate after implantation. Braids have high longitudinal tensile properties, but can be unstable when subjected to torsional loads. Thus, the type of textile stmcture should be carefully selected when designing the biotextile device, and the medical application and the site of implantation should be taken into account. 

The sterihsation of implantable devices is a subject of great concern for the medical industry. Since ionising radiation is preferentially used for this purpose, attention must be paid to possible effects on the structural and mechanical properties of polymers (through chain scission or cross-linking). L. A. Pruitt from UC Berkeley has reviewed the specific behaviour of the different medical polymer classes to y- and high-energy electron irradiation and environmental effects. The biocidal efficiency refies on free radical formation and on the ability to reduce DNA rephcation in any bacterial spore present in a medical device. 

P4HB and P3HB-4HB have been evaluated in preclinical tests reconunended by the FDA for medical devices. These tests include cytotoxicity, sensitization, irritation and intracutaneous reactivity, hemocompatibility, and implantation. Thus for example, P4HB films and sutures were subjected to a complete series of biocompatibility test protocols that were performed in accordance with the FDA s GLP regulations as set forth in 21 CFR, part 58, as well as ISO 10993-1. The test results confirmed that P4HB is nontoxic and biocompatible (Martin DP, personal communication). 

Another novel membrane formation process to yield thin film coatings involves the polymerization of di-para-xylylene onto the desired substrates. This process involves subjecting di-para-xylylene (or a substituted version) to high temperature in a high-vacuum chamber. The di-para-xylylene forms a di-radical that polymerizes and uniformly coats all surfaces in the vacuum chamber. This produa/process termed Parylene has been employed commercially for over four decades to provide protective coatings for electronic devices and medical devices as well as more recendy for micropatterned surfaces in biomedical implants and biosensors. ... 

The development of polymeric drug delivery devices for sustained ophthalmic CsA release is an active area of research for uveitis, vitreous inflammation, dry eye, and prevention of cornea transplant rejection. The use of these specialized CsA-delivering ophthalmic systems (e.g., implants nanoparticle and microsphere injections) cannot be completely reviewed in this chapter and readers are referred to an alternative text. A sample of applicable polymers for delivery of CsA for uveitis and vitreous inflammation is offered in the accompanying table (Table 15.4). The treatment of posterior uveitis and vitreous inflammation usually involves chronic therapy (often years) of topical agents and frequent intravitreal injections for disease control. These therapies are often impractical and subject to medical non-adherence [33]. Polymeric implants or injectable polymer sustained release systems can potentially improve patient outcomes through optimized intraocular drug concentrations. 

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