Polymer continued implant

The use of polymers in medicine is steadily growing. The synthetic and processing flexibility of polymers continue to permit polymers to be applied in a broad range of medical, biological, and implant applications. Creative polymer synthesis continues to expand the functionality and tunability of polymers for medical applications. There are now excellent biomedical polymers available to address general needs in medidne (the subject of this chapter). Opportunities that present themselves for enhanced or improved biomedical polymers are in the following areas ... 

Protein Adsorption. The development of medical implant polymers has stimulated interest in the use of ATR techniques for monitoring the kinetics of adsorption of proteins involved in thrombogenesis onto polymer surfaces. Such studies employ optical accessories in which an aqueous protein solution (93) or even ex - vivo whole blood (94-%) can be flowed over the surface of the internal reflection element (IRE), which may be coated with a thin layer of the experimental polymer. Modem FT-IR spectrometers are rapid - scanning devices, and hence spectra of the protein layer adsorbed onto the IRE can be computed from a series of inteiferograms recorded continuously in time, yielding ah effective time resolution of as little as 0.8 s early in the kinetic runs. Such capability is important because of the rapid changes in the composition of the adsorbed protein layers which can occur in the first several minutes (97). 

The penetration of a solvent, usually water, into a polymeric implant initiates dmg release via a diffusion process. Diffusion of dmg molecules through non-porous polymer membranes depends on the size of the dmg molecules and the spaces available between the polymeric chains. Even through the space between the polymer chains may be smaller than the size of the dmg molecules, dmg can still diffuse through the polymer chains due to the continuous movement of polymer chains by Brownian motion. 

The discontinuous two phases drug release can be controlled and avoided by manipulating the degradation properties of the polymer so that it is possible for the Zoladex implant to provide continuous release over a 28-day period. 

Historically, polysiloxane elastomers have been reinforced with micron scale particles such as amorphous inorganic silica to form polysiloxane microcomposites. However, with the continued growth of new fields such as soft nanolithography, flexible polymer electronics and biomedical implant technology, there is an ever increasing demand for polysiloxane materials with better defined, improved and novel physical, chemical and mechanical properties. In line with these trends, researchers have turned towards the development of polysiloxane nanocomposites systems which incorporate a heterogeneous second phase on the nanometer scale. Over the last decade, there has been much interest in polymeric nanocomposite materials and the reader is directed towards the reviews by Alexandre and Dubois (4) or Joshi and Bhupendra (5) on the subject. 

In the future, nanotubes and nanofibers can be administered systemically, if the problem of their toxicity is addressed, for example, by appropriate polymer coating. In this respect, the continuous nanofibers are more likely to be used in implants or tissue engineering applications. 

Current research and development efforts have focused on the use of more biocompatible coatings to reduce the biological response of both intravascular and subcutaneous devices. These efforts are based on the expectation that such developments wfllbe critical to the ultimate success in developing implanted sensors that yield continuous analytical results that match closely with conventional in vitro test methods. One new approach in this direction employs novel nitric oxide (NO) release polymers to coat the surface of intravascular sensors.The potent antiplatelet activity of NO has been shown to greatly reduce the formation of thrombus on the surface of implantable electrochemical oxygen sensing catheters, and yield much more accurate continuous PO2 values in animal experiments. 

In many situations, drug transport due to bulk flow can be neglected. This assumption (v is zero) is common in previous studies of drug distribution in brain tissue [17]. For example, in a study of cisplatin distribution after continuous infusion into the brain, the effects of bulk flow were found to be small, except within 0.5 mm of the site of Infusion [24]. In the cases considered here, since drug molecules enter the tissue by diffusion from the polymer implant, not by pressure-driven flow of a fluid, no flow should be introduced by the presence of the polymer. With fluid convection assumed to be negligible, the general governing equation in the tissue. Equation 10-17, reduces to ... 

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