Tissue-device interaction

On the other hand, retrieval studies in animals permit detailed monitoring of biocompatibility, biofunctionahty and biostabiUty of the implants at any desired and prescheduled interval of time. They also allow detailed studies of tissue-device interactions at the surface of the biotexthe since the surrounding tissue can be removed as appropriate. Animal models facilitate the study of certain complications such as caldfication in an accelerated time frame. Moreover, experimental conditions can be held constant in animal studies. However, animal models do not rephcate exact human physiological behavior, particularly for iU and injured patients with particular pathologies. 

The interaction of the host tissue with the polymer depends on the implantation site. For example, a pH sensitive suture that exhibits no degradation at a subcutaneous location may exhibit rapid degradation at an acidic location such as the stomach. A material may therefore demonstrate a toxic response at one implantation location but not at another. Similarly, the issue of patient diversity (age, gender, health status, physical condition, size, etc.) lends itself to distinctive device interactions specific to patient characteristics. 

Dee KC, Puleo DA, Bizios R (2002) An introduction to tissue-biomaterial interactions. Wiley-Liss, Hoboken Horbett TA, Brash JL (1995) Proteins at interfaces II fundamentals and applications. American Chemical Society, Washington, DC Contact Ai le and Hydrophobicity Adamson AW, Gast AP (1997) Physical chemistry of surfaces, 6th edn. Wiley, New York Shaw DJ (1992) Introduction to colloid and surface chemistry, 4th edn. Butterworth-Heinemann, Oxford Biological and Medical Applications of Microfluidic Devices... 

A classification often used to distinguish the different typologies of intracorporeal medical devices is that considering their localization into the vascular system (intravascular devices) or not (extravascular devices). It is clear how these two classes of devices interact very differently with the host. Indeed, intravascular devices are destined to interact with the blood components while extravascular devices interact with the surrounding tissues or interstitial fluids. 

Extensive studies of blood-material and tissue-material interactions ate not available in the literature, but Mason el aL (7] repotted PVDF to have inletmcdiale characteristics of blood compatibility as determined through an in vitro lest system. Irreversible loss of remanent polarization occurs above 7IPC. with a quasi linear decrease in residual pyro- and piezoelectric response approximating 1%TC (8]. This must be taken into account in device sterilization, which can be achieved by exposure to ethylene oxide, or by irradiation with an electron beam from a radiouctive source, with a dose of the order of US Mrad. PVDF films retain their polarization fully below 23-Mrad irradialioa from a °Co source (9). According to data provided by Dynamit Nobel. PVDF shows no appreciable chemical attack from ethylene oxide up to a temperature of lOtTC... 

Hyaluronic acid Non-sulfated glycosaminoglycan found in the connective tissue. Strong interaction with endocytic receptors (such as CD44). FDA approved as injectable cosmetic device (wrinkle filler). [38-40]... 

Multiple species of bacteria, protozoa, and fungi can inhabit a human body. Their biological relationship with the host can be described as symbiosis (mutualism), commensalism, and parasitism, while the medium modification can trigger a relationship change. For example, an infection or an invasive procedure can inflict the embedded microbes to shift the microbiotic balance some diseases and treatments promote immune variations embedding devices into the body often causes a tissue alteration. The nature of a device interaction with medium and microbiota is evidently crucial for both device functioning and microbiota behavior. 

As better materials and more sophisticated devices are implanted in humans, new problems in the biocompatibility of these materials and devices will appear as a result of the improved functional longevity of the materials and devices. These so-called second generation problems will be recognized and solved by a better understanding of the tissue/implant interaction. 

Interactions at surfaces and interfaces also play an essential role in the design and function of clinical implants and biomedical devices. With a few recent exceptions, implants do not attach well to tissue, and the resulting mobility of the tissue-implant interface encourages chroitic inflammation. The result can be a gathering of platelets at the site, leading to a blood clot or to the formation of a fibrous capsule, or scar, around the implant (Figure 3.3). 

The interaction in an interface of device/tissue is limited by two factors. There is the corrosive environment, such as biological fluid, which contains salts and proteins among other cellular structures in which the sensor device must survive [47, 48], Second, there is the encapsulation material which may induce a toxic reaction due to poor biocompatibility and hemocompatibility [49, 50], It is crucial to use a biomaterial that can overcome both limiting factors to maintain the lifetime of the sensor device and protect the body [51, 52],... 

By varying the nature of the side chain, R, various elastomers, plastics, films, and fibers have been obtained. These materials tend to be flexible at low temperatures, and water and fire resistant. Some fluoroalkoxy-substituted polymers (R = CHXFJ are so water repellent that they do not interact with living tissues and promise to be useful in fabrication of artificial blood vessels and prosthetic devices. 

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