Polymers for Controlled Drug Release

At the initial dissolution phase, the pores closer to the matrix surfaces can be filled by water rapidly. A burst release of drug will take place unless rapid matrix swelling and gelling occur. 

The release kinetics of drug from a swellable and erodible matrix has been described by Ritger and Peppas [17] through the following mathematical model  

I indicates Case II (Zero order) release and n 1 indicates Super Case II release. Case 

II release refers to transport of drug solute via the erosion of polymeric matrix due to relaxation of polymer chains, whereas Anomalous release refers to the summation of both drug diffusion and polymer erosion or swelling-controlled drug release. Super Case II release denotes drug dissolution which is controlled by polymer relaxation and is characterized by a sigmoidal release pattern [9,15-19]. 

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Hashizoe, M., Ogura, Y., Kimura, H. etal. (1994) Scleral plug of bideogradable polymers for controlled drug release in the vitreous. Archives of Ophthalmology, 112 1380-1384. 

O-carboxymethy Ichitosan is also used to develop a water-soluble matrix polymer for controlled drug release. OCM-chitosan microspheres containing antibiotic drug pazufloxacin mesilate were prepared by the emulsion method and successively crosslinked with glutaraldehyde [52]. 

Noteable are recent studies on the generation of polymer particles as carriers for controlled drug release [333] and of cationic solid lipid micro-particles as synthetic carriers for the targeted delivery of macromolecules to phagocytic antigen-presenting cells [334]. The industrial interest, although rarely disclosed, is evident from the patents filed in the field (see, e.g., [335, 336]). 

With continuous development of systems for controlled drug release, new materials are being used whose influence on peptide stability must be carefully examined. Thus, the model hexapeptide Val-Tyr-Pro-Asn-Gly-Ala (Fig. 6.30) embedded in poly (vinyl alcohol) and poly(vinyl pyrrolidone) matrices had rates of deamidation that increased with increasing water content or water activity, and, hence, with decreasing glass transition temperature (Tg). However, the degradation behavior in the two polymers differed so that chemical reactivity could not be predicted from water content, water activity, or T% alone. Furthermore, the hexapeptide was less stable in such hydrated polymeric matrices than in aqueous buffer or lyophilized polymer-free powders [132],... 

Pekarek KJ, Jacob JS, Mathiowitz E (1994) Double-walled polymer microspheres for controlled drug release. Nature 367 158-260... 

Abidian, M. R., et al. (2006), Conducting-polymer nanotubes for controlled drug release, Adv. Mater., 18,405-409. 

Examples of biomaterials include sodium hyaluronate, a naturally occurring biopol3nner used to reduce the incidence of postsurgical adhesions polymer-based materials for controlled-drug release and tissue engineered scaffolds to... 

Figure 15.5 Left SEM image ofPEDOT nanotubes on a neural probe tip Right mass release of dexamethasone from poly(lactide-co-glycolide) (PLGA) fibers (black), PEDOT-coated PLGA nanoscale fibers without electrical stimulation (red), and PEDOT-coated PLGA nanoscale fibers with electrical stimulation of 1 Vat the times with the circled data. (Reprinted with permission from Advanced Materials, Conducting-polymer nanotubes for controlled drug release by M. R. Abidian, D.-H. Kim and D.C. Martin, 18, 4, 405-409. Copyright (2006) Wiley-VCH)...

Price JC. Diffusion controlled release systems Polymeric microcapsules. In Tarcha PJ, ed. Polymers for Controlled Drug Delivey. Boca Raton, FL CRC Press, Taylor Francis Group, LLC 1990. pp. 1-14. 

Herrero-Venrell, R. Rincon, A.C. Alonso, M. Reboto, V. Molina-Martinez, I.T. Rodriguez-Cabello, J.C. Self-assembled particles of an elastin-like polymer as vehicles for controlled drug release. J. Contr. 

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