Probe Penetration Method to Characterize Low Solid High Viscous Pharmaceutical Gel Compositions

Objective: The objective was to develop a discriminatory analytical technique to evaluate rheological properties of low solid high viscous gel compositions used in the preparation of semi-solid pharmaceutical dosage forms. Background: Rheological properties of materials are frequently described in terms of viscosity, which is defined as resistance to flow. Compositions displaying strong gel consistency do not flow unless the applied stress exceeds certain value “Yield Stress”. In this study, we propose a Probe Penetration Method for better characterization of gels displaying yield stress when used at very low concentrations. Methods: Different types of carbomer solutions (carbomer homopolymer, copolymer, interpolymer, and polycarbophil) were prepared in water at different concentrations (0.1-1.0% w/w). Using sodium hydroxide, the pH of solutions was adjusted to 5.0-6.0, and the gel strength was measured using CT3-Texture Analyzer for non-neutralized and neutralized samples. The test records sample resistance to a penetrating stainless-steel probe (@ speed of 0.5mm/s). The test starts when the designated trigger load (10mN) is reached (at sample surface), then travelling 25mm distance representing sample center. Results: The control solutions, regardless of their concentrations, showed minimal differences in their gel strength values, 12-31mN. The results after neutralization demonstrated higher values and varied among different concentrations; carbomer homopolymer 18-196mN, copolymer 28-132mN, interpolymer 21-238mN, & polycarbophil 20-118mN. Conclusion: Given its discriminatory capability, the gel strength measurement by probe penetration method can be used in studying the rheological properties of highly viscous gel materials used at less than 1% concentrations. Grants: This study was supported by NSU Grant 33508