Small 2020 Feb 27;16(7):e1906565. Epub 2020 Jan 27.
Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, ON, M5B 2K3, Canada.
Higher order emulsions are used in a variety of different applications in biomedicine, biological studies, cosmetics, and the food industry. Conventional droplet generation platforms for making higher order emulsions use organic solvents as the continuous phase, which is not biocompatible and as a result, further washing steps are required to remove the toxic continuous phase. Recently, droplet generation based on aqueous two-phase systems (ATPS) has emerged in the field of droplet microfluidics due to their intrinsic biocompatibility. Here, a platform to generate all-aqueous double and triple emulsions by introducing pressure-driven flows inside a microfluidic hybrid device is presented. This system uses a conventional microfluidic flow-focusing geometry coupled with a coaxial microneedle and a glass capillary embedded in flow-focusing junctions. The configuration of the hybrid device enables the focusing of two coaxial two-phase streams, which helps to avoid commonly observed channel-wetting problems. It is shown that this approach achieves the fabrication of higher-order emulsions in a poly(dimethylsiloxane)-based microfluidic device, and controls the structure of the all-aqueous emulsions. This hybrid microfluidic approach allows for facile higher-order biocompatible emulsion formation, and it is anticipated that this platform will find utility for generating biocompatible materials for various biotechnological applications.
J Colloid Interface Sci 2019 Oct 30;553:382-389. Epub 2019 May 30.
Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada; Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Canada; Institute for Biomedical Engineering, Science and Technology (iBEST)-a Partnership between Ryerson University and St. Michael's Hospital, Toronto, Canada. Electronic address:
Microdroplets have been utilized for a wide range of applications in biomedicine and biological studies. Despite the importance of such droplets, their fabrication is associated with difficulties in practice that emerge from the incompatible nature of chemicals, such as surfactants and organic solvents, with biological environments. Therefore, microfluidic methods have recently emerged that create biocompatible water-in-water droplets based on aqueous two-phase systems (ATPS), most commonly composed of water and incompatible polymers, dextran (DEX) and polyethylene glycol (PEG). However, so far, DEX- and PEG-based water-in-water droplet generation schemes have been plagued with low throughput, and most systems can only generate DEX-in-PEG droplets; PEG-in-DEX droplets have been elusive due to chemical interactions between the polymers and channel walls. Here, we describe a simple approach to generate water-in-water microdroplets passively at a high throughput of up to 850?Hz, and obtain both DEX-in-PEG and PEG-in-DEX droplets. Specifically, our method involves a simple modification to the conventional microfluidic flow focusing geometry, by the insertion of a microneedle to the flow focusing junction, which causes three-dimensional (3D) flow focusing of the dispersed phase fluid. We observe that the 3D flow focusing of the dispersed phase enables excellent control of droplet diameters, ranging from 5 to 65?µm, and achieves a high throughput. Moreover, we report the passive microfluidic generation of PEG-in-DEX droplets for the first time, because in our system the 3D flow focusing of the disperse phase separates the disperse PEG phase from the channel walls, negating the commonly observed wall wetting issues of the PEG phase. We expect this microfluidic approach to be useful in increasing the versatility and throughput of water-in-water droplet microfluidics, and help enable future biotechnological applications, such as microparticle-based drug delivery, cell encapsulation for single cell analysis, and immunoisolation for cell transplantation.
Chemphyschem 2018 08 13;19(16):2113-2118. Epub 2018 Feb 13.
Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria St., Toronto, ON, M5B 2K3, Canada.
Electrospraying is a technique used to generate microparticles in a high throughput manner. For biomedical applications, a biocompatible electrosprayed material is often desirable. Using polymers, such as alginate hydrogels, makes it possible to create biocompatible and biodegradable microparticles that can be used for cell encapsulation, to be employed as drug carriers, and for use in 3D cell culturing. Evidence in the literature suggests that the morphology of the biocompatible microparticles is relevant in controlling the dynamics of the microparticles in drug delivery and 3D cell culturing applications. Yet, most electrospray-based techniques only form spherical microparticles, and there is currently no widely adopted technique for producing nonspherical microparticles at a high throughput. Here, we demonstrate the generation of nonspherical biocompatible alginate microparticles by electrospraying, and control the shape of the microparticles by varying experimental parameters such as chemical concentration and the distance between the electrospray tip and the particle-solidification bath. Importantly, we show that these changes to the experimental setup enable the synthesis of different shaped particles, and the systematic change in parameters, such as chemical concentration, result in monotonic changes to the particle aspect ratio. We expect that these results will find utility in many biomedical applications that require biocompatible microparticles of specific shapes.
Artif Organs 2018 May 23;42(5):516-524. Epub 2017 Nov 23.
Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario, Canada.
Mitral valve percutaneous edge-to-edge repair (PEtER) is a viable solution in high-risk patients with severe symptomatic mitral regurgitation. However, the generated double-orifice configuration poses challenges for the evaluation of the hemodynamic performance of the mitral valve and may alter flow patterns in the left ventricle (LV) during diastole. This in vitro study aims to evaluate the hemodynamic modifications following a simulated PEtER. A custom-made mitral valve was developed, and two configurations were tested: (i) a single-orifice valve with mitral regurgitation and (ii) a double-orifice mitral valve configuration following PEtER. The hemodynamic performance of the valve was evaluated using Doppler echocardiography and catheterization, while the flow patterns in the LV were investigated using particle image velocimetry (PIV). The tests were run at a stroke volume of 65 mL and a heart rate of 70 bpm. PEtER was found to significantly reduce the regurgitant volume (15 vs. 34 mL). There was a good agreement between Doppler and catheter transmitral pressure gradients (peak gradient: 9 vs. 7 mm Hg; mean gradient: 4 vs. 3 mm Hg) as well as an excellent agreement between maximal velocity measured by Doppler and PIV (1.60 vs. 1.58 m/s). Vortex development in the LV during diastole was significantly different after repair. PEtER significantly increased the amplitude of Reynolds and viscous shear stresses, as well as the number of high shear regions in the LV, potentially promoting thromboembolism events.