Polymer dispersions drug-delivery systems

Discrete models of release behavior. A schematic cross-section of a drug delivery system is shown in Figure 1 we hypothesize that release of drug occurs as follows. Prior to release, solid particles of the drug are dispersed in a continuous polymer phase. Since the depth of the device is typically 1 mm and each particle is... 

Figure 1 Schematic cross-section of a drug delivery system. A circular slab, cut in half in the plane parallel to release, is shown in the background. The exposed internal face is blown up in the foreground, revealing discrete particles of solid molecule dispersed in a continuous polymer phase. 

This is a method to obtain colloidal drug delivery systems from preformed, well-defined macromolecular materials with known physicochemical and biological properties. Biodegradable nanoparticles from PLA, PLG, PLGA, and poly(E-caprolactone) have been prepared by dispersing the polymers (Vauthier et al. 1991 Couvreur et al. 1995). 

Fig. 13 The controlled release of drug molecules from a (membrane-matrix) hybrid-type drug delivery system in which solid drug is homogeneously dispersed in a polymer matrix, which is then encapsulated inside a polymeric membrane, where D, P, and h are the diffusivity, permeability, and thickness, respectively, and the subscripts p, m, and d denote the drug depletion zone in the polymer matrix, polymer coating membrane, and diffusion layer, respectively.

Fig. 26 Cross-sectional view of a bioerosion-regulated hydrocortisone delivery system, a feedback-regulated drug delivery system, showing the drug-dispersed monolithic bioerodible polymer matrix with surface-immobilized ureases. The mechanism of release and time course for the urea-activated release of hydrocortisone are also shown. (From Ref > 1)...

Poly(propylene oxide) is typically obtained by base catalyzed anionic polymerization of propylene oxide [12]. Both stereospecific and atactic forms are known. The polymer is used as a soft polyether unit in polyurethane elastomers and foams in polymer electrolytes as surfactants (lubricants, dispersants, antistatic agents, foam control agents) in printing inks, as solubilizers in hydraulic fluids, coolant compositions in various medical applications (protective bandages, drug delivery systems, organ preservation, dental compositions), etc. 

Figure 2.3 IgG levels after administration of drug delivery systems in rats. Controlled-delivery systems for antibody class IgG. The insert figures show the release of antibody from the delivery system during incubation in buffered saline. The panel (a) inset shows release from poly(lactic acid) microspheres these spherical particles were 10-100/rm in diameter. The panel (b) inset shows release from a poly[ethylene-co-(vinyl acetate)] matrix these disk-shaped matrices were 1 cm in diameter and 1 mm thick. In both cases, molecules of IgG were dispersed throughout the solid polymer phase. Although the amount of IgG released during the initial 1-2 days is greater for the matrix, the delivery systems have released comparable amounts after day 5. (a) Comparison of plasma IgG levels after direct injection of IgG (open circles) or subcutaneous injection of the IgG-releasing polymeric microspheres characterized in the inset (filled circles). The delivery system produces sustained IgG concentrations in the blood [3]. (b) Comparison of plasma IgG levels after direct intracranial injection of IgG (open squares) or implantation of an IgG-releasing matrix (filled squares) [4]. The influence of the delivery is less dramatic in this situation, probably because the rate of IgG movement from the brain into the plasma controls the kinetics of the overall process.

Another field of biomedical applications in which polyphosphazenes can be used, is the field of drug delivery systems. One can distinguish two types of drug delivery systems. In a first type of systems, the drug to be released, is covalently attached to the polymer backbone. In a second concept, the polymer material is used as matrix system in which the drug is physically dispersed. 

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