Ultrasound-assisted production and optimization of mini-emulsions in a microfluidic chip in continuous-flow

The Evolution of Sonochemistry: From the Beginnings to Novel Applications

Sonochemistry is the use of ultrasonic waves in an aqueous medium, to generate acoustic cavitation. In this context, sonochemistry emerged as a focal point over the past few decades, starting as a manageable process such as a cleaning technique. Now, it is found in a wide range of applications across various chemical, physical, and biological processes, creating opportunities for analysis between these processes. Sonochemistry is a powerful and eco-friendly technique often called "green chemistry" for less energy use, toxic reagents, and residues generation. It is increasing the number of applications achieved through the ultrasonic irradiation (USI) method. Sonochemistry has been established as a sustainable and cost-effective alternative compared to traditional industrial methods. It promotes scientific and social well-being, offering non-destructive advantages, including rapid processes, improved process efficiency, enhanced product quality, and, in some cases, the retention of key product characteristics. This versatile technology has significantly contributed to the food industry, materials technology, environmental remediation, and biological research. This review is created with enthusiasm and focus on shedding light on the manifold applications of sonochemistry. It delves into this technique's evolution and current applications in cleaning, environmental remediation, microfluidic, biological, and medical fields. The purpose is to show the physicochemical effects and characteristics of acoustic cavitation in different processes across various fields and to demonstrate the extending application reach of sonochemistry. Also to provide insights into the prospects of this versatile technique and demonstrating that sonochemistry is an adapting system able to generate more efficient products or processes.

Continuous generation of cross-linked polymer nanoparticles employing an ultrasonic microreactor

In this article, a new system employing an ultrasonic microreactor coupled with a tubular reactor is presented for the continuous generation of polymer nanoparticles. The continuous generation of cross-linked polymer nanoparticles utilizing the monomer butyl methacrylate and the cross-linker ethylene glycol dimethacrylate is demonstrated. Firstly, the miniemulsion polymerization of a monomer-in-water miniemulsion is studied in a batch system. Secondly, a coiled tubular reactor is employed for the continuous polymerization of the miniemulsion generated by an ultrasonic microreactor. Finally, the influence of monomer volume fraction and surfactant concentration on the synthesized polymer nanoparticles is studied. Polymer particles in a size range of 50-250 nm are synthesized and a high polymerization conversion is achieved utilizing the system demonstrated in this article.

Mechanisms of lipid oxidation in water-in-oil emulsions and oxidomics-guided discovery of targeted protective approaches

Lipid oxidation is an inevitable event during the processing, storage, and even consumption of lipid-containing food, which may cause adverse effects on both food quality and human health. Water-in-oil (W/O) food emulsions contain a high content of lipids and small water droplets, which renders them vulnerable to lipid oxidation. The present review provides comprehensive insights into the lipid oxidation of W/O food emulsions. The key influential factors of lipid oxidation in W/O food emulsions are presented systematically. To better interpret the specific mechanisms of lipid oxidation in W/O food emulsions, a comprehensive detection method, oxidative lipidomics (oxidomics), is proposed to identify novel markers, which not only tracks the chemical molecules but also considers the changes in supramolecular properties, sensory properties, and nutritional value. The microstructure of emulsions, components from both phases, emulsifiers, pH, temperature, and light should be taken into account to identify specific oxidation markers. A correlation of these novel oxidation markers with the shelf life, the organoleptic properties, and the nutritional value of W/O food emulsions should be applied to develop targeted protective approaches for limiting lipid oxidation. Accordingly, the processing parameters, the application of antioxidants and emulsifiers, as well as packing and storage conditions can be optimized to develop W/O emulsions with improved oxidative stability. This review may help in emphasizing the future research priorities of investigating the mechanisms of lipid oxidation in W/O emulsion by oxidomics, leading to practical solutions for the food industry to prevent oxidative rancidity in W/O food emulsions.

Nanoemulsification of soybean oil using ultrasonic microreactor: Process optimization, scale-up and numbering-up in series

Ultrasonically-induced nanoemulsions have been widely investigated for the development of functional food, cosmetics, and pharmaceuticals due to ideal droplet sizes (DS), low polydispersity index (PDI), and superior physical stability. However, a series of frequently-used ultrasonic set-ups mainly suffered from a low ultrasonic energy efficiency caused by the large acoustic impedance and energy consumption, subordinately confronted with a low throughput, complicated fabrication with complex structure and weak ultrasonic cavitation. Herein, we employed a typical ultrasonic microreactor (USMR) that ensured the high-efficient energy input and generated intense cavitation behavior for efficient breakage of droplets and continuous production of unified oil-in-water (O/W) nanoemulsions in a single cycle and without any pre-emulsification treatment. The emulsification was optimized by tuning the formula indexes, technological parameters, and numerical analysis using Response Surface Methodology (RSM), followed by a comparison with the emulsification by a traditional ultrasonic probe. The USMR exhibited superior emulsification efficiency and easy scale-up with remarkable uniformity by series mode. In addition, concurrent and uniform nanoemulsions with high throughput could also be achieved by a larger USMR with high ultrasonic power. Based on RSM analysis, uniform DS and PDI of 96.4 nm and 0.195 were observed under the optimal conditions, respectively, well consistent with the predicted values. Impressively, the optimal nanoemulsions have a uniform spherical morphology and exhibited superior stability, which held well in 45 days at 4℃ and 25℃. The results in the present work may provide a typical paradigm for the preparation of functional nanomaterials based on the novel and efficient emulsification tools.

Emulsification mechanism in an ultrasonic microreactor: Influence of surface roughness and ultrasound frequency

An ultrasonic microreactor with rough microchannels is presented in this study for oil-in-water (O/W) emulsion generation. Previous accounts have shown that surface pits or imperfections localize and enhance cavitation activity. In this study cavitation bubbles are localized on the rough microchannels of a borosilicate glass microreactor. The cavitation bubbles in the microchannel are primarily responsible for emulsification in the ultrasonic microreactor. We investigate the emulsification mechanism in the rough microchannels employing high-speed imaging to reveal the different emulsification modes influenced by the size and oscillation intensity of the cavitation bubbles. The effect of emulsification modes on the O/W emulsion droplet size distribution for different surface roughness and frequency is demonstrated. The positive effect of the frequency on minimizing the droplet size utilizing a reactor with large pits is presented. We also demonstrate microreactor systems for a successful generation of miniemulsions with high dispersed phase volume fractions up to 20%. The observed emulsification mechanism in the rough microchannel offers new insights into the utility and scale-up of ultrasonic microreactors for emulsification.

Macro-Batch and Continuously Operated Microfluidic Emulsification—Differences, Similarities and Optimization

In this work, the emulsification of oil-in-water two-phase systems with three emulsifiers (PEG1500, 6000 and 20000) was studied in a batch macro system and in a continuously operated microfluidic system. The effect of emulsifier concentration, oil concentration and mixing rate on zeta potential and average Feret diameter was analyzed for the macro-batch system, while the effect of emulsifier concentration, oil concentration and total flow rate on zeta potential and average Feret diameter was analyzed for the microfluidic system. The emulsions prepared in batch system were more stable, had smaller droplet diameter but higher values of polydispersity index (PDI) compared to those prepared by continuous method. In both cases, batch and continuous, the use of PEG with higher molecular weight resulted in emulsions with lower zeta potential values. In batch emulsification, all three optimization parameters (emulsifier concentration, oil concentration and mixing rate) had a significant influence on the average Feret diameter and zeta potential (depending on the PEG, used for emulsification), while the emulsifier concentration had the most significant influence on the zeta potential and average Feret diameter of emulsions prepared in the continuous microsystem process.

Microfluidic Preparation of Nanoparticles Using Poly(ethylene Glycol)-distearoylphosphatidylethanolamine for Solubilizing Poorly Soluble Drugs

Microfluidic systems have shown promise for the production of nanoparticles from mixtures of aqueous and organic solutions, including liposomes, oil-in-water nanoemulsions, and lipid nanoparticles. They offer important practical advantages, including low reagent consumption, parallelization, and automation, and are ideally suited to high-throughput optimization and scale-up. In this study, we developed a new method for the formulation of nanoparticles of poorly soluble drug compounds. The nanoparticles, prepared by microfluidic mixing using only poly(ethylene glycol)-distearoylphosphatidylethanolamine (PEG-DSPE), were highly stable and uniform in size. By mixing an organic solution of poorly soluble cyclosporine A and PEG-DSPE with water in the microfluidic device, amorphous cyclosporine A nanoparticles (CsA-NPs), with an encapsulation efficiency of approximately 90% and a particle size of 100-200 nm, were obtained. Analysis of the microfluidic process parameters revealed that particle size distribution was significantly controlled by the flow rate ratio. The obtained CsA-NPs were stable for up to 150 days at room temperature, and the pharmacokinetic profile was similar to that of the commercial formulation containing Cremophor EL, which has been reported to induce serious adverse effects after intravenous administration. These findings provide a useful technical platform for the safe solubilization of poorly soluble compounds and their subsequent pharmaceutical development.