Medical polymers implants

Carbon matrices are more suitable than polymers ones for applications at temperatures of 250 to 600°C. Above 600°C they are, however, (as are the C-fibers as such) only utilizable in inert atmospheres. C-fiber reinforced carbon matrix composites are particularly used in aircraft brakes, in fusion reactors and as a substitute for monolithic graphite. In addition they are utilized in the medical sector (implants), in furnace construction (heaters) and in energy conversion (heat exchangers). The market for carbon fiber/carbon matrix composites in 1993 was estimated to be ca. 250 t. 

The main requirement imposed on all polymer biomaterials applied in medicine is a combination of their desired physicochemical and physicomechanical characteristics with biocompatibility. Depending on particular applications, the biocompatibility of polymers can include various requirements, which can sometimes be contradictory to each other. Thns, in the case of artificial vessels, drainages, intraocular lenses, biosensors, or catheters, the interaction of the polymer with a biological medium should be minimized for the rehable operation of the corresponding device after implantation. In contrast, in the majority of orthopedic applications, the active interaction and fusion of an implant with a tissne is required. General requirements imposed on all medical polymers consist in non-toxicity and stability. 

As a result of the rejection of implanted material, peroxides are produced inside the body that causes oxidative degradation of medical polymers. The oxidative degradation of medical polymers occurs inside the human body and can be monitored in simulated environments [22, 23]. The reaction is caused by the peroxides produced by the human body against non-accepted implant materials through a rejection mechanism [22, 24]. 

Blood-surface interactions are of great importance when medical polymers, such as those used in heart valves and artificial organs, are implanted into the body. When polymers come into contact with blood, complex reactions take place and can result in the formation of a blood clot. Infrared analysis has shown in ex vivo studies that during the early stages the proteins albnmin and glycoprotein are present, with fibronogen subsequently appearing. As the adsorption process continues, albumin is replaced by other proteins until a blood clot is formed. 

The applications of hydrogels in the production of medical items, resulting materials must have several features, which recommends them non-toxicity, functionability, sterilizability, biocompatibUity [115]. These characteristics are requires for wound dressings, drug delivery systems, transdermal systems, injectable polymers, implants, dental and ophthalmic applications, stimuli-responsive systems, hydrogel hybrid-type organs. 

To date, PLLA has been the most studied and used medical polymer in a wide range of apphcations, such as in bone fixation (Ueda and Tabata, 2003) (under the product name Fixsorb) and as scaffold implants in tissue engineering for bone (Chan et al., 2007 Schofer et al., 2008 Shim et al., 2010 Cai et al., 2010) cartilage (Ju et al., 2007 Tanaka et al., 2010), tendon (Inui et al., 2010), neural (Hu et al., 2010 Wang et al., 2010), and vascular (Francois et al., 2009) regeneration. 

There are several standards that medical polymers must adhere to. One of the most common standards observed for polymeric materials is published by the United States Pharmacopeia (USP), which necessitates using animal models (in vivo) to test toxicity of elastomers, plastics, and other polymeric materials, prior to clinical use. The standard and forms of testing it outlines is considered in the medical industry as the minimum requirement for a polymeric material before it is considered for use in healthcare applications. According to the standard the biological response of the test animals are measured and determined via three main techniques (1) Systemic toxicity test Evaluates the effects of leachables of intravenously or intraperitoneally injected materials on systems such as the nervous or immune system (2) Intracutaneous test Evaluates local response to materials injected under the skin (3) Implantation test Both local tissue microscopic and macroscopic parameters evaluated at material implant sites. 

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. 

Once implanted into the body medical polymers must show specific properties without interaction with surrounding tissues or with the body as a whole. So far there is no recognized definition of biocompatibility since there is no material parameter or biological tests which could be used as a quantitative characteristic of this property of the polymer [1]. 

Christopher, M.B. (2009) Biocompatibility of polymer implants for medical applications. MSc thesis. University of Akron, August 2009. 

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). 

Ikada Y. Surface modification of polymers for medical application. Biomaterials, 1994, 15, 725-736. James SJ, Pogribna M, Miller BJ, Bolon B, and Muskhelishvili L. Characterization of cellular response to silicone implants in rats Implications for foreign-body carcinogenesis. Biomaterials, 1997, 18, 667-675. 

These results open the exciting possibility of using degradable, tyrosine-derived polymers as "custom-designed" antigen delivery devices. On the other hand, our results indicate that the immunological properties of tyrosine-derived polymers will have to be carefully evaluated before such polymers can be considered for use as drug delivery systems or medical implants. 

Polymer coatings responsive to temperature or moisture form the basis for medications delivered transdermally using patches on the skin or internally via inserts implanted in the body. Oral nitroglycerin (Fig. 14.1.4) tablets to prevent... 

The protection of microelectronics from the effects of humidity and corrosive environments presents especially demanding requirements on protective coatings and encapsulants. Silicone polymers, epoxies, and imide resins are among the materials that have been used for the encapsulation of microelectronics. The physiological environment to which implanted medical electronic devices are exposed poses an especially challenging protection problem. In this volume, Troyk et al. outline the demands placed on such systems in medical applications, and discuss the properties of a variety of silicone-based encapsulants. 

Humidity Testing of Silicone Polymers for Corrosion Control of Implanted Medical Electronic Prostheses... 

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