Area under rheogram as multi-point viscosity characteristic of the sterilized hypromellose hydrogels.

In this work, the cone and plate rheological viscometry readings of the sterilized hydrogels of hypromellose 4000 (60 g/L) were investigated by using of the three-parameter Herschel a nd Bulkley powerlaw and the new empirical two-parameter model. In it, the independent variable of shear rate was transformed by logarithm and the dependent variable of shear stress by square root. The two-parameter model showed only non-significantly lower mean value of the coefficient of determination when compared with the results of the three-parameter power law model being of good promise in other investigation of the near pseudoplastic rheograms of hypromellose hydrogels. To express the influence of the addition of the isotonic concentration of sodium chloride and/or pilocarpine hydrochloride, respectively, on the viscosity of sterilized hydrogels of hypromellose, the area under rheogram (AUR) data was employed as a multi-point theological characteristic. No significant differences were noted between AUR calculated using three parameters of the power law model and those calculated using two parameters of the proposed one. The significant increase in viscosity was observed in the presence of the isotonic concentration of sodium chloride in comparison to the hydrogel without additives. In the opposite, the addition of the isotonic concentration of pilocarpine hydrochloride resulted in the significant viscosity decrease. In conclusion, the proposed empirical two-parameter model could be used as the rheological model in investigation of the near pseudoplastic rheograms of the sterilized hypromellose hydrogels.