Abstract
The objective of this work was to investigate the main rheological features of vaginal hydrophilic polymer gels and to elucidate about the relationship between these characteristics and gels composition, and their general influence in therapeutic/usage purpose. Flow and dynamic oscillatory properties of four commercially available (Conceptrol®, Gynol II®, RepHresh®, and Replens®) and two investigational vaginal gels were determined by cone-and-plate rheometry, at body temperature. Several parameters (apparent viscosity, complex viscosity, storage modulus, loss modulus, critical oscillatory stress, tan δ, thixotropy and yield stress) were measured and/or calculated. Gels presented non-Newtonian, pseudoplastic, thixotropic behavior, with yield stress. Overall viscosities varied between 13500 Pa.s and approximately 80 Pa.s within a biologically relevant shear rate interval (0.01-100 s-1). Yield stress values were variable between different determination methods but coherent in terms of ranking. Also, tested gels showed viscoelastic properties, being characterized by predominant elastic solid-like behavior. Rheological behavior of vaginal gels strongly depended on the type of gelling agent used, which potentially influences their spreading and retention properties when administered in the vaginal canal. Small variations in gels composition can result in substantial changes in their features, namely viscosity, yield stress and thixotropy. Rheological properties of tested gels appeared to be correlated with their therapeutic/usage purpose.
Keywords: Rheology, vagina, gels, polymeric drug delivery systems, viscoelasticity, thixotropy, yield stress
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