Impact of process parameters in the generation of novel aspirin nanoemulsions – Comparative studies between ultrasound cavitation and microfluidizer

In the present investigation, the operating efficiency of a bench-top air-driven microfluidizer has been compared to that of a bench-top high power ultrasound horn in the production of pharmaceutical grade nanoemulsions using aspirin as a model drug. The influence of important process variables as well as the pre-homogenization and drug loading on the resultant mean droplet diameter and size distribution of emulsion droplets was studied in an oil-in-water nanoemulsion incorporated with a model drug aspirin. Results obtained show that both the emulsification methods were capable of producing very fine nanoemulsions containing aspirin with the minimum droplet size ranging from 150 to 170 nm. In case of using the microfluidizer, it has been observed that the size of the emulsion droplets obtained was almost independent of the applied microfluidization pressure (200–600 bar) and the number of passes (up to 10 passes) while the pre-homogenization and drug loading had a marginal effect in increasing the droplet size. Whereas, in the case of ultrasound emulsification, the droplet size was generally decreased with an increase in sonication amplitude (50–70%) and period of sonication but the resultant emulsion was found to be dependent on the pre-homogenization and drug loading. The STEM microscopic observations illustrated that the optimized formulations obtained using ultrasound cavitation technique are comparable to microfluidized emulsions. These comparative results demonstrated that ultrasound cavitation is a relatively energy-efficient yet promising method of pharmaceutical nanoemulsions as compared to microfluidizer although the means used to generate the nanoemulsions are different.