Cavitation technology - a greener processing technique for the generation of pharmaceutical nanoemulsions

Novel nanoemulsion-based drug delivery systems (DDS) have been proposed as alternative and effective approach for the delivery of various types of poorly water-soluble drugs in the last decade. This nanoformulation strategy significantly improves the cell uptake and bioavailability of numerous hydrophobic drugs by increasing their solubility and dissolution rate, maintaining drug concentration within the therapeutic range by controlling the drug release rate, and reducing systemic side effects by targeting to specific disease site, thus offering a better patient compliance. To date, cavitation technology has emerged to be an energy-efficient and promising technique to generate such nanoscale emulsions encapsulating a variety of highly potent pharmaceutical agents that are water-insoluble. The micro-turbulent implosions of cavitation bubbles tear-off primary giant oily emulsion droplets to nano-scale, spontaneously leading to the formation of highly uniform drug contained nanodroplets. A substantial body of recent literatures in the field of nanoemulsions suggests that cavitation is a facile, cost-reducing yet safer generation tool, remarkably highlighting its industrial commercial viability in the development of designing novel nanocarriers or enhancing the properties of existing pharmaceutical products. In this review, the fundamentals of nanoemulsion and the principles involved in their formation are presented. The underlying mechanisms in the generation of pharmaceutical nanoemulsion under acoustic field as well as the advantages of using cavitation compared to the conventional techniques are also highlighted. This review focuses on recent nanoemulsion-based DDS development and how cavitation through ultrasound and hydrodynamic means is useful to generate the pharmaceutical grade nanoemulsions including the complex double or submicron multiple emulsions.