Polyphosphazene , bioerodible

Laurencin CT, Koh HJ, Neenan TX, Allcock HR, and Longer R. Controlled release using a new bioerodible polyphosphazene matrix system. J Biomed Mater Res, 1987, 21, 1231. 

Polyphosphazenes can be considered as biomaterials in several different ways, depending on the type of utilization one can predict for these substrates. In this regard, we will consider three different topics concerning water-soluble POPs and their hydrogels, bioerodible POPs for drug delivery systems and for tissue engineering, and the surface implications of POP films. 

The first bioerodible polyphosphazenes synthesized possessed amino acid ester side groups (25). The structure and preparation of one example is shown in Scheme V. The ethyl glycinato derivative shown... 

A substantial number of bioactive molecules, such as polypeptides, N-acetyl-DL-penicillamine, p-(dipropylsulfamoyl)benzoic acid, and nicotinic acid, contain a carboxylic acid function, and this provides a site for linkage to a polyphosphazene chain. A number of prototype polymers have been synthesized in which pendent amino groups provide coupling sites for the carboxylic acid (34). The amide linkages so formed are potentially bioerodible, but the use of a hydrolytic sensitizing cosubstituent would be expected to accelerate the process. 

It has been demonstrated that a variety of different polyphosphazenes can be developed as biomaterials, membranes or hydrogels, bioactive polymers, and bioerodible polymers. As with most new areas of polymer chemistry and biomaterials science, molecular design forms the basis of most new advances, but the rate-controlling step is the testing and evaluation of the materials in both in vitro and in vivo environments. This is particularly true for polyphosphazenes where the availability of research quantities only has limited the... 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

The main class of bioerodible polyphosphazenes that have been developed so far are polymers with amino acid ester side groups. They are prepared by the reaction of poly(dichlorophosphazene) with the ethyl or propyl esters of amino acids such as glycine, alanine, phenylalanine, and so on (reaction (57)).196 The ethyl or propyl ester of the amino acid must be used as the nucleophile in this reaction for two reasons. First, a free carboxylic acid unit would provide a second nucleophilic site that could lead to... 

Protection and Deprotection of Pendent Hydroxyl Groups. The presence of hydroxyl oups in the side chains of polyphosphazenes is required for a variety of purposes, including the preparation of water-soluble or bioerodible polymers, and for the introduction of sites for the linkage of biologically active or electro-optical units to the polymer. Two typical approaches are shown in Scheme V. 

MAJOR APPLICATIONS Polymers have shown promise as bioerodible materials capable of (controlled degradation and sustained drug delivery for therapeutic cmd other related uses/ Polyphosphazenes have been evaluated for approximately two decades, but resecirch has become more focused in recent years. 

N.R. Krogman, et al., MiscibiUty of bioerodible polyphosphazene/ poly0aclide-co-glycolide) blends. Biomacromolecules 8 (4) (2007) 1306-1312. 

A wide range of polyphosphazenes have been used for a number of biomedical applications. Examples are inert biomaterials for cardiovascular and dental uses, bioerodible and water soluble polymers for controlled drug delivery applications (Allcock et al, 1990). 

Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming, and bioerodable materials (1). 

A further major field of investigation for bioerodihle polymers is their use as scaffolds for tissue engineering. Tissue engineering is the use of a bioerodible polymer as an artificial extracellular matrix, supporting cell growth and organisation and will he discussed in Chapter 4, as it represents a major focus of polyphosphazene research. 

Allcock, H.R., Morozowich, N.L. Bioerodible polyphosphazenes and their medical potential. Polymer Chemistry 3(3), 578-590 (2012). doi 10.1039/clpy00468a... 

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