Simple Method for On-Demand Droplet Trapping in a Microfluidic Device Based on the Concept of Hydrodynamic Resistance.

We demonstrate an innovative method to catch the desired droplets from a train of droplets and immobilize them in traps located in an integrated microfluidic device. To this end, water-in-oil droplets are generated in a flow-focusing junction and then guided to a channel connected to chambers designated for on-demand droplet trapping. Each chamber is connected to a side channel through a batch of microposts. The side channels are also connected to the flexible poly(vinyl chloride) tubes, which can be closed by attaching binder clips. The hydrodynamic resistance of the routes in the device can be changed by opening and closing the binder clips. In this way, droplets are easily guided into individual traps based on the user's demand. A set of numerical simulations was also conducted to investigate the authenticity of the employed idea and to find the optimal geometry for implementing our strategy. This simple method can be easily employed for on-demand droplet trapping without using on-chip valves or complex off-chip actuators proposed in previous studies.

Novel size-based design of spiral microfluidic devices with elliptic configurations and trapezoidal cross-section for ultra-fast isolation of circulating tumor cells.

Investigation and analysis of circulating tumor cells (CTCs) have been valuable resources for detecting and diagnosing cancer in its early stages. Recently, enumeration and separation of CTCs via microfluidic devices have attracted significant attention due to their low cost and easy setup. In this study, novel microfluidic devices based on size-dependent cell-sorting with a trapezoidal cross-section and elliptic spiral configurations were proposed to reach label-free, ultra-fast CTCs enrichment. Firstly, the possibility and quality of separation in the devices were evaluated via a numerical simulation. Subsequently, these devices were fabricated to investigate the effects of the altering curvature and the trapezoidal cross-section on the isolation of CTCs from the peripheral blood sample at varying flow rates ranging from 0.5 mL/min to 3.5 mL/min. The experimental results indicated that the flow rate of 2.5 mL/min provided the optimal separation efficiency in the proposed devices, which was in fine agreement with the numerical analysis results. In this experiment, the purity values of CTCs between 88% and 90% were achieved, which is an indicator of the high capability of the proposed devices for the isolation and enrichment of CTCs. This strategy is hoped to overcome the limitations of classical affinity-based CTC separation approaches in the future.

The Effect of Non-Uniform Magnetic Field on the Efficiency of Mixing in Droplet-Based Microfluidics: A Numerical Investigation.

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power source is utilized to mix two fluids. One of these active methods is magnetic micromixers using ferrofluid. In this technique, magnetic nanoparticles are used to make one phase responsive to magnetic force, and then by applying a magnetic field, two fluid phases, one of which is magneto-responsive, will sufficiently mix. In this study, we investigated the effect of the magnetic field's characteristics on the efficiency of the mixing process inside droplets. When different concentrations of ferrofluids are affected by a constant magnetic field, there is no significant change in mixing efficiency. As the magnetic field intensifies, the magnetic force makes the circulation flow inside the droplet asymmetric, leading to chaotic advection, which creates a flow that increases the mixing efficiency. The results show that the use of magnetic fields is an effective method to enhance the mixing efficiency within droplets, and the efficiency of mixing increases from 65.4 to 86.1% by increasing the magnetic field intensity from 0 to 90 mT. Besides that, the effect of ferrofluid's concentration on the mixing efficiency is studied. It is shown that when the concentration of the ferrofluid changes from 0 to 0.6 mol/m3, the mixing efficiency increases considerably. It is also shown that by changing the intensity of the magnetic field, the mixing efficiency increases by about 11%.

Green synthesis of silica nanoparticles from olive residue and investigation of their anticancer potential.

Aim: To synthesize silica nanoparticles (SNPs) from olive residue with anticancer properties. Methods: SNPs were synthesized from olive residue ash (ORA). After characterization, cytotoxicity of the SNPs was assessed in vitro, with measurement of reactive oxygen species (ROS) levels. Results: The average diameter of the synthesized SNPs was 30-40 nm, and zeta potential analysis suggested they were stable. The synthesized SNPs were less cytotoxic than commercially available SNPs against fibroblast cells, and the cytotoxic effect on breast cancer cells was significantly higher compared with fibroblast cells. SNPs showed greater uptake into cancer cells where there was greater production of free radicals. Conclusion: SNPs synthesized from ORA have potential anticancer applications because they are more cytotoxic toward cancer cells than fibroblast cells.