Polyphosphazenes drug delivery applications

A final biomedical use for polyphosphazenes is as components in microspheres, vesicles, and micelles for use in drug-delivery applications. Microspheres are pseudo-spherical constructs that range in size from 1 to 600 microns. Vesicles (lipozomes) are hollow, water-filled bilayer spheres with diameters that range from 0.03 tolO microns. Micelles typically have diameters near 1 micron (100 nanometers). Idealized representations of these three structures are shown in Figure 3.23, together with the location of trapped drug molecules. 

Polyphosphazenes are a relatively new class of biodegradable polymers. Their hydrolytic stability or instability is determined not by changes in the backbone structure but by changes in the side groups attached to an unconventional macromolecular backbone. Synthetic flexibility and versatile adaptability of polyphosphazenes make them unique for drug delivery applications. For example, Veronese et al.18 prepared polyphos-phazene microspheres with phenylalanine ethyl ester as a phosphorous substituent and loaded it with succinylsulphathiazole or naproxen. The kinetics of release from these matrices were very convenient in yielding local concentrations of the two drugs that are useful per se or when mixed with hydroxyapatite for better bone formation. Polyphosphazene matrices are also considered as potential vehicles for the delivery of proteins and vaccines.19... 

Aminated polyphosphazenes present amines with a low value of pKa as side groups, and constitute the most studied class of bioresorbable polyphosphazenes. Amino acid ester and imidazole-substituted polyphosphazenes appear to be two good candidates for drug delivery applications, because of their good hydrolysis degradation and low... 

Lakshmi, S., Katti, D. S. Laurencin, C. T. 2003. Biodegradable polyphosphazenes for drug delivery applications. Advanced Drug Delivery Reviews, 55, 467-482. 

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). 

S. Lakshmi, D. Katti, C. Laurencin, Biodegradable polyphosphazenes for drug delivery applications. Adv. Drug Deliv. Rev. 55(4), 467-482 (2003)... 

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. 

This chapter on polyphosphazenes provides the reader an overview of the synthesis and side group chemistry in context to the degradation profile and biocompatibility. In addition, it reviews the medical applications developed using biodegradable polyphosphazenes specifically drug delivery matrices and tissue-engineering scaffolds. 

Abstract A review is presented of the main types of bioresorbable or bioabsorbable materials used in medical applications such as drug delivery. Groups discussed include aliphatic polyesters, polyanhydrides, poly(ortho esters) (POE), polyphosphazenes, poly(amino acids) and pseudo poly(amino acids), polyalkylcyanoacrylates, poly(propylene fumarate) (PPF), poloxamers, poly(p-dioxanone) (PPDO) and polyvinyl alcohol (PVA). 

Polyphosphazenes have already been investigated for biomedical applications, especially in controlling the release of chemotherapeutic agents (Cho and Allcock, 2007) (and thus in the drug delivery field) and in the temporary replacement of body parts (Deng et al., 2010). For example, following... 

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. 

Biomedical Applications. Biomedical applications were investigated by a number of polyphosphazene research groups (181). The most important studies concerned biocompatibility, biodegradation, enz5une immobilization, and drug delivery (182,183). Polyphosphazene implants and prosthe-ses were also examined. Biocompatibility through appropriate manipulation of surface or bulk chemistry was studied extensively (184). Works on the synthesis and cross-linking of amphiphilic polyphosphazenes (94), heparin immobilization (185-187), and other surface functionalizations (4,101) were reported. 

---