Of bioerodible polymers

Poly(orthoesters) represent the first class of bioerodible polymers designed specifically for dmg deUvery appHcations (52). In vivo degradation of the polyorthoester shown, known as the Al amer degradation, yields 1,4-cydohexanedimethanol and 4-hydroxybutyric acid as hydrolysis products (53). 

Kohn, J., and Langer, R., A new approach to the development of bioerodible polymers for controlled release applications employing naturally occurring amino acids, in Proceeding of the ACS Division of Polymeric Materials. Science and Engineering. American Chemical Society, 1984, Vol. 51, pp. 119-121. 

Use of Bioerodible Polymers in Self-Regulated Drug Delivery Systems... 

Polyanhydrides are a class of bioerodible polymers that have shown excellent characteristics as drug delivery carriers. The properties of these biomaterials can be tailored to obtain desirable controlled release characteristics. Extensive research in this promising area of biomaterials is the focus of this entry. In the first part of the entry, the chemical structures and synthesis methods of various polyanhydrides are discussed. This is followed by a discussion of the physical, chemical, and thermal properties of polyanhydrides and their effect on the degradation mechanism of these materials. Finally, a description of drug release applications from polyanhydride systems is presented, highlighting their potential in biomedical applications. 

Mathiowitz, E. Ron, E. Mathiowitz, G. Amato, C. Langer, R. Morphological characterization of bioerodible polymers. 1. Crystallinity of polyanhydride copolymers. Macromolecules 1990, 23, 3212-3218. 

Lee DA, Leong KW, Panek WC, et al. The use of bioerodible polymers and 5-fluorour-acil in glaucoma filtration surgery. Invest Ophthalmol Vis Sci 1988 29 1692-1697. 

The main family of bioerodible polymers is represented by poly(alkylcya-noacrylate)s (PACA). These polymers have a long history since 1947 as adhesives, especially in areas where a fast cure rate is needed. Polymerisation of alkylcyanoacrylates (ACA) can be initiated in the presence of bases as weak as the hydroxyl ions of water. The propagation rate decreases when the size of the lateral alkyl chain increases. As polymerisation can be very fast, ACAs have been used as surgical glue, as tissue adhesive and for embolisation purposes. As shown in Section 4.4.6, ACAs have also been used extensively for preparing nanospheres and nanocapsules for drug delivery. 

Surface Characterization of Bioerodible Polymers Using XPS, SIMS and AFM... 

SURFACE CHARACTERISATION OF BIOERODIBLE POLYMERS USING XPS, SIMS AND AFM... 

For the analysis of bioerodible polymers, the atomic force microscope (AFM) is more suited than the STM because its imaging mechanism is independent of electron conduction and hence insulating organic materials can be directly visualized (Burnham and Colton, 1993). The basic components of an AFM are shown in Figure 7. The sample is mounted onto a piezoceramic scanner device capable of moving the sample in all three-dimensions. Above the sample surface is the AFM probe unit, which is composed of a sharp probe positioned on the end of a flexible cantilever. The cantilever is microfabricated in a V-shape with the two arms of the V attached to a stationary support. 

The potendal of the AFM to enhance the characterization of bioerodible polymers, and biomaterials in general, stems from ability of the instrument to obtain veity high resolution images from uncoated polymer. samples within aqueous environments. Therefore, it has become possible to image dynamic processes like surface erosion and protein adsorption which are fundamental to the mechanisms of drug delivery and biocompatibility. 

Table 2 I.iterature examples of surface characterisation of bioerodible polymers...

SURFACE SPECTROSCOPIES OF BIOERODIBLE POLYMER BLENDS AND COPOLYMERS... 

This review has outlined the use of surface analytical techniques in the study of bioerodible polymers. Both the chemical information obtainable from XPS and SIMS, and the analysis of topographical changes provided by AFM can supply... 

Mathiowitz, E., Jacob, J., Pekarek, K. and Chickering III, D. (1993) Morphological characerization of bioerodible polymers. 3. characterization of the erosion and intact zones in polyanhydrides using scanning electron microscopy. Macromolecules, 26, 6756-6765. 

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