In this work, a simple microfluidic junction with a T geometry and coarse (200 μm diameter) capillaries was used to generate monodisperse microbubbles with an alginate polymer shell. Subsequently, these bubbles were used to prepare porous alginate films with good control over the pore structure. The lack of pore size, shape, and surface control in scalable forming of polymeric films is a major application-limiting drawback at present. Controlling the thinning process of the shell of the bubbles to tune the surface of the resulting structures was also explored. Films were prepared with nanopatterned surfaces by controlling the thinning of the bubble shell, with the aid of surfactants, to induce efficient bursting (fragmentation) of bubbles to generate nanodroplets, which become embedded within the film surface. This novel feature greatly expands and enhances the use of hydrophilic polymers in a wide range of biomedical applications, particularly in drug delivery and tissue engineering, such as studying cellular responses to different morphological surfaces.

Microbubbles generated by microfluidic techniques have gained substantial interest in various industries such as cosmetics, food engineering, and the biomedical field. The microfluidic T-junction provides exquisite control over processing parameters, however, it relies on pressure driven flows only; therefore, bubble size variation is limited especially for viscous solutions. A novel set-up to superimpose an alternating current (AC) oscillation onto a direct current (DC) field is invented in this work, capitalising on the possibility to excite bubble resonance phenomenon and properties, and introducing relevant parameters such as frequency, AC voltage, and waveform to further control bubble size. A capillary embedded T-junction microfluidic device fitted with a stainless-steel capillary was utilised for microbubble formation. Furthermore, a numerical model of the T-junction was developed by integrating the volume of fluid (VOF) method with the electric module; simulation results were attained for the formation of the microbubbles with a particular focus on the flow fields along the detachment of the emerging bubble. Two main types of experiments were conducted in this framework: the first was to test the effect of applied AC voltage magnitude and the second was to vary the applied frequency. Experimental results indicated that higher frequencies have a pronounced effect on the bubble diameter within the 100 Hz and 2.2 kHz range, whereas elevated AC voltages tend to promote bubble elongation and growth. Computational results suggest there is a uniform velocity field distribution along the bubble upon application of a superimposed field and that microbubble detachment is facilitated by the recirculation of the dispersed phase. Furthermore, an ideal range of parameters exists to tailor monodisperse bubble size for specific applications.

The application of an electric field on a fluid in motion gives rise to unique features and flow manipulation capabilities. Technologies ranging from bubble formation, droplet generation, fibre spinning, and many others are predicated on this type of flows, often referred to as Electrohydrodynamics (EHD). In this paper, we present a numerical methodology that allows for the

In this work we report a significant advance in the preparation of monodisperse microbubbles using a combination of microfluidic and electric field technologies. Microbubbles have been employed in various fields such as biomedical engineering, water purification and food engineering. Many techniques have been investigated for their preparation. Of these, the microfluidic T-Junction has shown great potential due to the high degree of control it has over processing parameters and the ability to produce monodisperse microbubbles. Two main lines of investigation were conducted in this work-the effect of varying the mixing region distance (Mx) and the influence of altering the tip-tocollector distance (Dx) when an AC-DC field is applied. It was found that when Mx was decreased from 200µm to 100µm, the microbubble size also decreased from 128 ± 3 µm to 88 ± 5 µm due to an increase in shear stress as a result of a reduction in surface area. Similarly, decreasing the tip-tocollector distance results in an increase in electric field strength experienced at the nozzle, facilitating further reduction of bubble size from 111 ± 1 µm to 86 ± 1µm at an AC voltage of 6kV P-P and an applied DC voltage of 6kV. Experiments conducted with the optimal parameters identified from the previous experiments enabled further reduction of the microbubble size to 18 ± 2 µm. These results suggest that a unique combination of parameters can be employed to achieve particular microbubble sizes to suit various applications.

Coronary Artery Stents have been the preferred form of treatment for vascular occlusive disease, due to the minimally invasive surgical procedure, post-operative recovery time and cost, when compared to open coronary bypass surgery. The cellular response upon applying an AC electric field to type 316LM Stainless Steel stent mimics was investigated in this paper. The highest RBC adhesion was observed at voltages higher than 88mV and lower than 74mV.Their unique alignment along the lines of fracture on the stent surface at 88mV was a phenomenon caused by an increase in electrical conductivity in these regions. Being able to control RBC adhesion may have various clinical implications such as inhibition of thrombus formation, and provide a basis to analyse whether electric fields may be applied to cancer therapy as well.2