This research investigates the dynamic behavior of microelectromechanical systems (MEMS) containing curved electrodes, under a combined loading of electrostatic force, axial force, mechanical shock loading and squeeze-film damping (SQFD). The dynamic governing equation of a curved microbeam (micro-arch) is solved by utilizing a nonlinear finite element method, while the effect of the fluid film damping on the microbeam is modeled by the nonlinear Reynolds equation. The response of the micro-arch under different loading conditions and the influence of the MEMS device parameters on its behavior are studied and discussed in detail. In particular, the snap-through and pullin instabilities of the curved microbeam are thoroughly investigated, and the maximum deflections of the micro-arch subjected to different types of loadings are analyzed. Finally, the phase diagram of the curved beam under various loading conditions is presented for guiding the design and analysis of the MEMS in the future.
Over the course of the COVID-19 pandemic, wastewater surveillance has become a useful tool for describing SARS-CoV-2 prevalence in populations of varying size, from individual facilities (e.g., university residence halls, nursing homes, prisons) to entire municipalities. Wastewater analysis for SARS-CoV-2 RNA requires specialized equipment, expensive consumables, and expert staff, limiting its feasibility and scalability. Further, the extremely labile nature of viral RNA complicates sample transportation, especially in regions with limited access to reliable cold chains. Here, we present a new method for wastewater analysis, termed exclusion-based sample preparation (ESP), that substantially simplifies workflow (at least 70% decrease in time; 40% decrease in consumable usage compared with traditional techniques) by targeting the labor-intensive processing steps of RNA purification and concentration. To optimize and validate this method, we analyzed wastewater samples from residence halls at the University of Kentucky, of which 34% (44/129) contained detectible SARS-CoV-2 RNA. Although concurrent clinical testing was not comprehensive, student infections were identified in the 7 days following a positive wastewater detection in 68% of samples. This pilot study among university residence halls validated the performance and utility of the ESP method, laying the foundation for future studies in regions of the world where wastewater testing is not currently feasible.
In this study, simulation, design, and fabrication of a Micro PCR based on MEMS and LoC are done. The designed PCR has 2 temperature zones. In fact, in this PCR, the second and third stages of the experiment are merged inside one temperature zone. In the first step, a proper design based on genetic studies is considered. Then, to find the location of the heaters, the system is numerically studied via COMSOL Multiphysics. The designed PCR in this study has 2 temperature zones of 95 and 60 centigrade. After that, the heat transfer analysis is validated. The dimensions of the chip are 80 mm in length and width and 7 mm in height. There are 64 channels on the chip which means the PCR has 32 cycles. The length of each microchannel is 33 mm and each temperature cycle is 68 mm. The width of the microchannels is 500 mm and the depth of it is 400 µm (following Mohr et al. study (30)). Different methods for fabrication of the microchannel has been used, which in the end, laser engraving was chosen. Isopropyl Alcohol (IPA) is used for the bonding. Also, the thickness of the cap is considered 2 mm to strengthen the chip. Heater and Peltier (thermoelectric cooler) is used to reach the desired temperatures. The reason to use the Peltier is that the 95 centigrade zone can affect the 60 centigrade zone which increases the temperature at this zone. A PID controller is used to control the temperatures. The main advantage of this research is the very fast, easy, and low-cost method for producing PCR chips. It can be useful in critical situations, such as COVID-19 pandemic conditions where there is an urgent need for PCR chips to diagnose this disease.
Molecular diffusive membranes play crucial roles in the field of microfluidics for biological applications e.g., 3D cell culture and biosensors. Hydrogels provide a range of benefits such as free diffusion of small molecules, cost-effectiveness, and the ability to be produced in bulk. Among various hydrogels, Pluronic F127 can be used for cell culture purposes due to its biocompatibility and flexible characteristics regarding its environment. Aqueous solutions of Pluronic F127 shows a reversible thermo-thickening property, which can be manipulated by introduction of ions. As a result, controlled diffusion of ions into the solution of Pluronic F127 can result in a controlled gel formation. In this study, the flow of immiscible solutions of Pluronic and sodium phosphate inside a Y-shaped microchannel is simulated using the level set method, and the effects of volume flow rates and temperature on the gel formation are investigated. It is indicated that the gel wall thickness can decrease by either increasing the Pluronic volume flow rate or increasing both volume flow rates while increasing the saline volume flow rate enhances the gel wall thickness. Below a critical temperature value, no gel wall is formed, and above that, a gel wall is constructed, with a thickness that increases with temperature. This setup can be used for drug screening, where gel wall provides an environment for drug-cell interactions.Article Highlights Parallel flow of Pluronic F127 and saline solutions inside a Y-shaped microchannel results in formation of a gel wall at their interface. The numerical analysis reveals the impact of each inlet flow rate and temperature on gel wall thickness and movement. The findings indicate that the gel wall has a low but steady velocity toward the saline solution. Graphical abstract
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