Improving rheological characteristics of hydrophilic ointment base by treatment with a high-pressure wet-type jet mill

Background: A high-pressure wet-type jet mill is a powerful equipment used for the dispersion and emulsification of substances. In this study, we investigated its usefulness in the preparation of skin cream formulations. Method: We prepared a hydrophilic ointment base as a typical skin cream base, and then treated it with the wet-type jet mill under different conditions. Controllable factors of the wet-type jet mill included processing pressure, treatment cycle, and temperature of the treatment. Result: Treatment with the wet-type jet mill had a great impact on the rheological characteristics of the hydrophilic ointment base. The hysteresis areas and yield values of the treated ointments were significantly increased by increasing the processing pressure and temperature during the treatment. From scanning electron microscopic observations, the oil droplet size of the hydrophilic ointments decreased after treatment with the wet-type jet mill, suggesting that a decrease in oil droplet size mediates changes in the rheological characteristics. Conclusion: Because we can expect the wet-type jet mill to control the rheological characteristics of the ointment, it is a promising tool for the preparation of skin cream formulations.