Polymeric drug delivery matrices

Fig. 13 Scheme of a polymeric drug delivery system formed by the simultaneous coalescence of matrix polymer and drug molecules from their common inclusion complex... 

To enhance the desirable properties of a polymer as a matrix for a controlled drug delivery system, efforts have been made to improve its hydrophilicity, biodegradation rate, and drug stability. Hydrophilic blocks play vital role in polymeric drug delivery systems, for example, poly(ethylene oxide)... 

In the recent years, the usage of polymeric materials for drug delivery matrix tablets has become prevalent. Current research into the utilization of the metabolic activity and the colonic environment in the lower gastrointestinal tract has attained immense value in the design of novel colon targeted drug delivery systems by the utilization of natural biodegradable polymers. 

A large variety of drug delivery systems are described in the literature, such as liposomes (Torchilin, 2006), micro and nanoparticles (Kumar, 2000), polymeric micelles (Torchilin, 2006), nanocrystals (Muller et al., 2011), among others. Microparticles are usually classified as microcapsules or microspheres (Figure 8). Microspheres are matrix spherical microparticles where the drug may be located on the surface or dissolved into the matrix. Microcapsules are characterized as spherical particles more than Ipm containing a core substance (aqueous or lipid), normally lipid, and are used to deliver poor soluble molecules... 

Because these types of polymeric matrix systems are the simplest to design and the easiest to obtain approval by the Food and Drug Administration, they have been the most extensively studied in the past two decades. Numerous polymers have been evaluated for these types of drug delivery systems and although it would be impractical to present each of these polymers and its specific application to drug delivery, this chapter will review in general the types of polymers used as matrices for drug delivery (1-4). 

In polymeric membrane and matrix-based micropumps, the membrane or the matrix makes the essential component of the delivery device that controls the rate of release. In matrix controlled delivery, the rate of the hydrolytic breakdown of the matrix is the governing process. In polymeric membrane-controlled release, the rate of hydration of the membrane and the subsequent diffusion of drug are the rate-controlling steps. 

Applications of polymerization in a supercooled state to the immobilization of various biofunctional components is reviewed. Those applications show advantages because in the low temperature biofunctional components such as proteins, drugs and cells are entrapped or adhered effectively in the polymerized matrix. The immobilized composites are used for biomedical and biochemical systems and processes, such as immuno-diagnosis, artificial organs, drug delivery systems and cell cultures. 

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.

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