Lyophilised wafers as a drug delivery system for wound healing containing methylcellulose as a viscosity modifier

Lyophilised wafers as a drug delivery system for wound healing containing methylcellulose as a viscosity modifier
January 2005
K.H. Matthewsa, H.N.E. Stevensa, A.D. Auffretb, M.J. Humphreyb and G.M. Ecclestona
aDepartment of Pharmaceutical Sciences, University of Strathclyde, Strathclyde Institute for Biomedical Sciences, 27 Taylor Street, Glasgow G4 ONR, UK
bPfizer Central Research, Sandwich, Kent CT13 9NJ, UK
International Journal of Pharmaceutics Volume 289, Issues 1-2 , 31 January 2005, Pages 51-62
Received 2 July 2004; revised 4 October 2004; accepted 15 October 2004. Available online 30 December 2004.
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Abstract
Lyophilised wafers have potential as drug delivery systems for suppurating wounds. A dual series of wafers made from low molecular weight sodium alginate (SA) and xanthan gum (XG) respectively, modified with high molecular weight methylcellulose (MC) were produced. The swelling and flow properties of these wafers on model suppurating surfaces were both qualitatively and quantitatively investigated. The wafers instantaneously adhered to the surfaces, absorbing water and transforming from glassy, porous solids to highly viscous gels. The rate at which this occurred varied for the series studied with clear distinctions between the behaviour of SA and XG systems. For SA wafers there was a distinct relationship between the flow-rate and MC content. Increased amounts of MC decreased the rate at which the SA wafers flowed across a model gelatine surface. Flow rheometry was used to quantify the effect of increased MC content on both series of wafers and for the SA series, highlighted a substantial increase in apparent viscosity as a function of incremental increases in MC content. These results reflected those from the gelatine model. Observations of the reluctance of a swollen, unmodified XG wafer to flow compared with the relative ease of unmodified, low molecular weight SA was attributed to the yield stress characteristic of xanthan gels. XG is known to exhibit complex, loosely bound network structures in solution via the association of helical backbone structures. The inclusion of sodium fluorescein as a visible model for a soluble drug highlighted the potential of lyophilised wafers as useful drug delivery systems for suppurating wounds.