Microstructural imaging of early gel layer formation in HPMC matrices

BAJWA, G. S., HOEBLER, K., SAMMON, C., TIMMINS, P. and MELIA, C. D. (2006). Microstructural imaging of early gel layer formation in HPMC matrices. Journal of pharmaceutical sciences. B, 95 (10), 2145-2157.

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Link to published version:: 10.1002/jps.20656

Abstract

A real-time confocal fluorescence imaging method has been developed which allows the critical early stages of gel layer formation in hydroxypropylmethylcellulose (HPMC) matrices to be examined. Congo Red, a fluorophore whose fluorescence is selectively intensified when bound to -D-glucopyranosyl sequences, has allowed mapping of hydrated polymer regions within the emerging gel layer, and revealed for the first time, the microstructural sequence of polymer hydration during development of the early gel layer. Liquid penetration and swelling can be examined in unprecedented detail. The earliest images revealed an initial phase of liquid ingress into the tablet pore network, followed by the progressive formation of a coherent gel layer by outward columnar swelling and coalescence of hydrated HPMC particles. Salts can markedly affect HPMC matrix behaviour. Gel layer growth in 0.1-0.5 M NaCl was progressively suppressed until at 0.75 M, particles clearly failed to coalesce into a gel layer, although with considerable polymer swelling. The failure to form a limiting diffusion barrier resulted in enhanced liquid penetration of the core, and the swelling of particles that did not coalesce culminated in surface disintegration. This provides direct evidence of physical mechanisms that contribute to salts accelerating drug release from HPMC matrices.

Item Type: Article
Additional Information: © 2006 Wiley-Liss, Inc. and the American Pharmacists Association
Research Institute, Centre or Group: Materials and Engineering Research Institute > Polymers Nanocomposites and Modelling Research Centre > Polymers, Composites and Spectroscopy Group
Identification Number: 10.1002/jps.20656
Depositing User: Ann Betterton
Date Deposited: 29 Jul 2008
Last Modified: 11 May 2010 15:07
URI: http://shura.shu.ac.uk/id/eprint/938

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