Polyanhydrides characteristics

Implants in the rabbit corneas exhibited no observable inflammatory characteristics over a period of 6 weeks. Compared to other previously tested polymers, the inertness of these polyanhydrides rivals that of the biocompatible poly(hydroxyethyl methacrylate) and ethylene-vinyl acetate copolymer. Histological examination of the removed corneas also revealed the absence of inflammatory cells (21)... 

Deong, K. W., Brott, B. C., and Danger, R., Bioerodible polyanhydrides as drug-carrier matrices. I. Characterization, degradation and release characteristics, J. Biomed. Mater. Res., 19, 941-955, 1985. 

The past two decades have produced a revival of interest in the synthesis of polyanhydrides for biomedical applications. These materials offer a unique combination of properties that includes hydrolytically labile backbone, hydrophobic bulk, and very flexible chemistry that can be combined with other functional groups to develop polymers with novel physical and chemical properties. This combination of properties leads to erosion kinetics that is primarily surface eroding and offers the potential to stabilize macromolecular drugs and extend release profiles from days to years. The microstructural characteristics and inhomogeneities of multi-component systems offer an additional dimension of drug release kinetics that can be exploited to tailor drug release profiles. 

The release characteristics of polyanhydride systems could be used not only to develop clinical treatments, but also to induce chronic disease states as models for studying immune function. Many current models of chronic diseases are based on induction of acute effects, which do not exhibit the same long-term behavior as the disease being modeled. 

Pharmaceutical research has to date been focused on polyanhydrides derived from sebacic acid (SA) and its copolymers with bis(p-carboxyphenoxy)propane (CPP) [75,113,115,119]. More recently, a new class of polyanhydrides was presented, containing fatty acid dimers (FAD) [ 116,118,258]. Erosion characteristics, microsphere preparation, pH-dependence, release rates, morphology, and in vivo performance of polyanhydrides from SA, CPP, and FAD have been intensely studied [75, 111-115,117, 119, 258-260]. Other unsaturated polyanhydrides have been derived from ricinoleic acid [261] and ricinoleic acid half-es-... 

Typically, homopolymers are not studied because they possess unfavorable characteristics rendering their handling and manufacture difficult. Poly(SA), poly(CPP), and poly (FA) are semicrystalline and thus suffer from either being brittle or having high Tn,. Conversely, poly(FAD) is a liquid. Therefore, polyanhydrides are often prepared as copolymers of aliphatic and/or aromatic monomers. The most common copolymers under investigation in drug delivery applications include poly(FAD-SA) and poly(CPP-SA). 

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. 

Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy have also been used to authenticate polyanhydride structures. Aliphatic polymers absorb at 1740 and 1810 cm while aromatic polymers absorb at 1720 and 1780 cm All the polyanhydrides show methylene bands because of deformation, stretching, rocking, and twisting. Aside from being used to ascertain polyanhydride structures, these techniques can be used to determine degradation progress, by monitoring the area of carboxylic acid peak (1770-1675 cm ) with respect to the characteristic anhydride peaks over time. 

Jiang, H.L. Zhu, K.J. Preparation, characterization and degradation characteristics of polyanhydrides containing poly(ethylene glycol). Polym. Int. 1999, 48, 47-52. 

The present volume comprises five review articles written especially for this series by leading authorities in the field. The first three adresses major structural characteristics of biodegradable polymers. Robert Lenz provides athorough review of biodegradable polymers. Jorge Heller offers a critical analysis of the structure, properties and medical applications of polyorthoesters, whereas Abraham Domb and his associates offer the same critical analysis of polyanhydrides. Eric Doelker discusses the structure and properties of cellulose derivatives. Finally Michael Sefton presents the use of polyacrylates for the microencapsulation of live animal cells. 

The melting point, as determined by differential scanning calorimeter, of these aromatic polyanhydrides is mnch higher than aliphatic polyanhydrides. The melting point of aliphatic-aromatic copolyanhydrides is proportional to aromatic content. For this type of copolymers, there is characteristically a minimnm between 5 and 20mol% of lower-melting component. The introdnction of fatty acids in the copolymer chain lowers the melting point as compared to that of bulk polymer [14]. 

Akbari, H., D Emanuele, A., Attwood, D., 1998. Effect of geometry on the erosion characteristics of polyanhydride matrices. International Journal of Pharmaceutics 160, 83—89. 

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