title: Experimental and numerical models of three-dimensional gravity-driven flow of shear-thinning polymer solutions used in vaginal delivery of microbicides.
abstract: HIV/AIDS is a growing global pandemic. A microbicide is a formulation of a pharmaceutical agent suspended in a delivery vehicle, and can be used by women to protect themselves against HIV infection during intercourse. We have developed a three-dimensional (3D) computational model of a shear-thinning power-law fluid spreading under the influence of gravity to represent the distribution of a microbicide gel over the vaginal epithelium. This model, accompanied by a new experimental methodology, is a step in developing a tool for optimizing a delivery vehicle's structure/function relationship for clinical application. We compare our model with experiments in order to identify critical considerations for simulating 3D free-surface flows of shear-thinning fluids. Here we found that neglecting lateral spreading, when modeling gravity-induced flow, resulted in up to 47% overestimation of the experimental axial spreading after 90 s. In contrast, the inclusion of lateral spreading in 3D computational models resulted in rms errors in axial spreading under 7%. In addition, the choice of the initial condition for shape in the numerical simulation influences the model's ability to describe early time spreading behavior. Finally, we present a parametric study and sensitivity analysis of the power-law parameters' influence on axial spreading, and to examine the impact of changing rheological properties as a result of dilution or formulation conditions. Both the shear-thinning index (n) and consistency (m) impacted the spreading length and deceleration of the moving front. The sensitivity analysis showed that gels with midrange m and n values (for the ranges in this study) would be most sensitive (over 8% changes in spreading length) to 10% changes (e.g., from dilution) in both rheological properties. This work is applicable to many industrial and geophysical thin-film flow applications of non-Newtonian fluids; in addition to biological applications in microbicide drug delivery.
authors.affiliation: Department of Mechanical Engineering, University of Kansas, Lawrence, KS 66045, USA.
authors.forename: Vitaly O
authors.initials: VO
authors.lastname: Kheyfets
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Kieweg
mesh_terms: D000282:Administration, Intravaginal; D000890:Anti-Infective Agents / Q000008:administration & dosage* / Q000378:metabolism; D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry; D003198:Computer Simulation; D004337:Drug Carriers / Q000737:chemistry*; D004848:Epithelium / Q000378:metabolism; D005260:Female; D006112:Gravitation; D006801:Humans; D057446:Hydrodynamics; D012996:Solutions; D013499:Surface Properties; D014621:Vagina / Q000166:cytology
chemical_list: D000890:Anti-Infective Agents; D004337:Drug Carriers; D012996:Solutions; D002482:Cellulose; C002283:hydroxyethylcellulose