TEXTURAL, VISCOELASTIC AND MUCOADHESIVE PROPERTIES OF PHARMACEUTICAL GELS COMPOSED OF CELLULOSE POLYMERS

This study examined the mechanical/textural, viscoeiastic and mucoadhe sive properties of a range of aqueous gels composed of either hydroxye thylcellulose (HEC) or sodium carboxymethylcellulose (Na CMC). The mec hanical/textural properties of each formulation were determined using texture profile analysis. The viscoelastic properties of each formulat ion were examined over a defined frequency range (0.01-1.0 Hz) using o scillatory rheometry in conjunction with stainless steel parallel plat e geometry. The mucoadhesive properties of the gels were evaluated by measuring the tensile force required to overcome the gel/mucin adhesiv e interaction. Both gel hardness and compressibility, properties that affect the ease of product removal from a container and spreadability, increased as a function of increasing polymer concentrations. This is attributed to the effects of HEC and Na CMC on gel viscosity. Gel adh esiveness, a property related to bioadhesion, also increased as a func tion of polymer concentration and is attributed to the reported adhesi ve nature of these polymers. Increasing frequency of oscillation incre ased the storage and loss moduli yet decreased bath the dynamic viscos ity of each gel type and also the loss tangent of HEC (but not Na CMC) gels. Therefore, following exposure to the range of oscillatory stres ses that may be expected in vivo, HEC gels will be more susceptible th an Na CMC gels to alterations in these rheological properties. Consequ ently, it would be expected that the clinical performance of HEC gels will be modified to a greater extent than Na CMC gels. In general, HEC gels exhibited a greater elastic nature than Na CMC gels over the fre quency range employed for oscillation The storage and loss moduli and dynamic viscosity of both gel types increased, yet the loss tangent of both gel types decreased as a function of increasing polymer concentr ation. Gel mucoadhesive strength was dependent on both the time of con tact of the formulation with mucin and also on polymer concentration. In conclusion, this study has characterised a number of gels containin g either HEC or Na CMC in terms of their mechanical/textural, viscoela stic and mucoadhesive properties. Due to its relevance to the clinical performance, it is suggested that the information derived from these methods may be usefully combined to provide a more rational basis for the selection of polymers and their formulation as topical drug delive ry systems. (C) 1997 Elsevier Science B.V.