In this paper, we examined mixing of various two-fluid flows in a silicon/glass microchannel based on the competition of dominant forces in a flow field, namely viscous/elastic, viscous/viscous and viscous/inertial. Experiments were performed over a range of Deborah and Reynolds numbers (0.36 < De < 278, 0.005 < Re < 24.2). Fluorescent dye and microshperes were used to characterize the flow kinematics. Employing abrupt convergent/divergent channel geometry, we achieved efficient mixing of twodissimilar viscoelastic fluids at very low Reynolds number. Enhanced mixing was achieved through elastically induced flow instability at negligible diffusion and inertial effects (i.e. enormous Peclet and Elasticity numbers). This viscoelastic mixing was achieved over a short effective mixing length and relatively fast flow velocities.

Inkjet printing has proven to be a promising and flexible process methodology for low cost and drop-on-demand pattern formation in small-scale production of micro-electro-mechanical systems. To optimize the micro-patterns formed by inkjet printing, an accurate control of droplet volume is essential and critical. In this study, an inkjet system with a nozzle driven by a circular piezoelectric element was used to explore the impact of different waveforms on droplet volume. The investigation into this study included the impact of unipolar, bipolar, M-shaped and W-shaped waveforms as well as the effects of their amplitudes and pulse durations. The inkjetting behavior of Newtonian and non-Newtonian fluids under different actuating waveforms was studied in order to obtain a maximum reduction in ejected droplet sizes. An effective reduction of droplet volume in the range of 50–80% was demonstrated. The results of inkjetting PEDOT ink on a polished silicon surface showed that a 50% reduction in line width was achieved.

We exploited the viscoelasticity of biocompatible dilute polymeric solutions, namely, dilute poly͑ethylene oxide͒ solutions, to significantly enhance mixing in microfluidic devices at a very small Reynolds number, i.e., ReϷ 0.023, but large Peclet and elasticity numbers. With an abrupt contraction microgeometry ͑8:1 contraction ratio͒, two different dilute poly͑ethylene oxide͒ solutions were successfully mixed with a short flow length at a relatively fast mixing time of Ͻ10 s. Microparticle image velocimetry was employed in our investigations to characterize the flow fields. The increase in velocity fluctuation with an increase in flow rate and Deborah number indicates the increase in viscoelastic flow instability. Mixing efficiency was characterized by fluorescent concentration measurements. Our results showed that enhanced mixing can be achieved through viscoelastic flow instability under situations where molecular-diffusion and inertia effects are negligible. This approach bypasses the laminar flow limitation, usually associated with a low Reynolds number, which is not conducive to mixing.

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We demonstrated rapid mixing of viscoelastic fluids in microchannels constructed based on polymethyl methacrylate. Viscoelastic mixing without diffusion was achieved with an effective mixing length of less than 5mm and a relatively fast flow rate. With an abrupt contraction microgeometry (8:1 contraction ratio), we mixed two different viscoelastic fluids experimentally at very low Reynolds numbers, but enormous Peclet and elasticity numbers. This special geometrical configuration triggers flow instability, leading to turbulent and efficient mixing. This flow regime has negligible inertia effects but significant elastic effects.

Sepsis is an adverse systemic inflammatory response caused by microbial infection in blood. This paper reports a simple microfluidic approach for intrinsic, non-specific removal of both microbes and inflammatory cellular components (platelets and leukocytes) from whole blood, inspired by the invivo phenomenon of leukocyte margination. As blood flows through a narrow microchannel (20 × 20 µm), deformable red blood cells (RBCs) migrate axially to the channel centre, resulting in margination of other cell types (bacteria, platelets, and leukocytes) towards the channel sides. By using a simple cascaded channel design, the blood samples undergo a 2-stage bacteria removal in a single pass through the device, thereby allowing higher bacterial removal efficiency. As an application for sepsis treatment, we demonstrated separation of Escherichia coli and Saccharomyces cerevisiae spiked into whole blood, achieving high removal efficiencies of ∼80% and ∼90%, respectively. Inflammatory cellular components were also depleted by >80% in the filtered blood samples which could help to modulate the host inflammatory response and potentially serve as a blood cleansing method for sepsis treatment. The developed technique offers significant advantages including high throughput (∼1 ml/h per channel) and label-free separation which allows non-specific removal of any blood-borne pathogens (bacteria and fungi). The continuous processing and collection mode could potentially enable the return of filtered blood back to the patient directly, similar to a simple and complete dialysis circuit setup. Lastly, we designed and tested a larger filtration device consisting of 6 channels in parallel (∼6 ml/h) and obtained similar filtration performances. Further multiplexing is possible by increasing channel parallelization or device stacking to achieve higher throughput comparable to convectional blood dialysis systems used in clinical settings.

The ability to infiltrate various molecules and resins into dental enamel is highly desirable in dentistry, yet transporting materials into dental enamel is limited by the nanometric scale of their pores. Materials that cannot be infiltrated into enamel by diffusion/capillarity are often considered molecules with sizes above a critical threshold, which are often considered to be larger than the pores of enamel. We challenge this notion by reporting the use of electrokinetic flow to transport solutions with molecules with sizes above a critical threshold-namely, an aqueous solution with a high refractive index (Thoulet's solution) and a curable fluid resin infiltrant (without acid etching)-deep into the normal enamel layer. Volume infiltration by Thoulet's solution is increased by 5- to 6-fold, and resin infiltration depths as large as 600 to 2,000 µm were achieved, in contrast to ~10 µm resulting from diffusion/capillarity. Incubation with demineralization solution for 192 h resulted in significant demineralization at noninfiltrated histologic points but not at resin infiltrated. These results open new avenues for the transport of materials in dental enamel.

findings agreed with Fromm whereby ejected volume The dimensionless Ohnesorge number (Oh) describes the increases with decreasing Oh value. relative importance of viscous to surface tension effects, Several studies [3][4][5] had been conducted on the effects of which is commonly used to characterize jet breakup. In this Oh on the mechanics of droplet formation, e.g. capillary study, the experimental results have proven that single break-off length and time, droplet volume and satellite droplets can be jetted for 0.02 < Oh < 1.5, for viscosity > 50 formation. Xu and Basaran [5] stated that these parameters mPas, using different mixture compositions of glycerol in depend weakly on Oh when Weber number (We) is water (0 -80 wt%) as the ink. This is contrary to previous sufficiently large. Schulkes [6] and Dong et al. [7] had also published literature [1, 2]. However, the findings are in good investigated the effects of Oh on the creation of satellite agreement with Reis and Derby [2] that the velocity of the droplets due to end-pinching. Experiments and simulations of ejected droplet exhibits a maximum (i.e. inverted 'U' curve) Chen and Basaran [8] studied the effect of Ohnesorge number and is a function of pulse width. This velocity curve is on the size of droplets produced. They stated that a uni-polar apparently governed by the Ohnesorge numbers. From a waveform could lead to satellite formation rather than a single practical standpoint, with the large variety of inkjet printing droplet. With their tailored waveform, droplets smaller than inks having different properties, these results can be useful for the diameter of the nozzle orifice can be produced at waveform tailoring to achieve optimal performance for droplet intermediate Oh (-. 0.1 -0.2), but not when Oh is too low ('. formation control. 0.02) or too high (z 1.0). However, results of Gohari and Introduction Chandra [9] disagreed with this finding by producing smaller Inkjet printing has received enormous attention and drops from a 204 ptm diameter nozzle (Oh = 0.21 -1.73), interetas a mufactugtechnology with the applications using a pneumatic DOD generator. Their results also stated otintertst manvenuionglgyfice/home use in printed graphics that single droplets could not be produced when Oh was too outside itS conventional office/home use in printed graphics lw ..O .8 and text. These include fabrication of polymer electronics lo,ie O .8 aompondtext.ese o nincLuD fabricationof polymponernelctrani Bogy and Talke [10] defined the optimum pulse width of micrompons, forganical screrics cm pnemnt anr d the applied rectangular pulse at which the ejected droplet has mppicrtioar s for biolo a screnting. Forthedmose manufact ur the maximum velocity, due to the pressure wave in the cavity s te i t p g m o ms c y being optimally enhanced. They concluded that this optimum is the piezoelectric drop-on-demand method (DOD). The basic I w i principle of operation is via the use of pressure waves induced Pu in an ink-filled conduit by piezoelectric sleeve actuation, to ...