Microfluidics for most bio-related diagnostic applications typically requires single usage disposable chips to avoid bio-fouling and cross-contamination. Individual piece-wise manufacturing of polymeric microfluidic devices has been widely employed in recent years. To significantly lower the manufacturing costs, one possible way is to improve the production yield of polymer microfluidic chips via the hot roller embossing method. This paper discusses the effects of varying the process parameters such as roller temperature, applied pressure and substrate preheating during hot roller embossing (according to a systematic set of experiment designs) and its influence on the corresponding mold to pattern fidelity in terms of normalized embossed depths on the poly(methylmethacrylate) (PMMA) substrate. Concurrently, pattern density studies on the mold were also conducted. Functional testing in terms of fluid flow and micromixing was carried out to evaluate the feasibility of using hot roller embossed PMMA substrates as microfluidic chips.
A microfluidic oscillator is of interest because it converts a stable laminar flow to oscillatory flow, especially in view of the fact that turbulence is typically absent in miniaturized fluidic devices. One important design approach is to utilize hydroelastic effect-induced autonomous oscillations to modify the flow, so to reduce the reliance on external controllers. However, as complex fluid-structure interactions are involved, the prediction of its mechanism is rather challenging. Here, we present a simple equivalent circuit model and investigate the negative-differential-resistance (NDR) mechanism of a hydroelastic microfluidic oscillator. We show that a variety of complex flow behaviors including the onset of oscillation, formation of different oscillation patterns, collapse of the channel, etc can be well explained by this model. It provides a generic approach for construction of microfluidic NDR oscillators, following which a new design is also proposed. Relevant findings give more insights into the hydroelastic instability problems in microfluidics, and enrich the study of microfluidic flow control devices based on the electric circuit theory.
Fluid mixing in micro-wells/chambers is required in a variety of biological and biochemical processes. However, mixing fluids of small volumes is usually difficult due to increased viscous effects. In this study, we propose a new method for mixing enhancement in microliter-scale open wells. A thin elastic diaphragm is used to seal the bottom of the mixing microwell, underneath which an air chamber connects an aeroelastic vibrator. Driven by an air flow, the vibrator produces self-excited vibrations and causes pressure oscillations in the air chamber. Then the elastic diaphragm is actuated to mix the fluids in the microwell. Two designs that respectively have one single well and 2 × 2 wells were prototyped. Testing results show that for liquids with a volume ranging from 10–60 µl and viscosity ranging from 1–5 cP, complete mixing can be obtained within 5–20 s. Furthermore, the device is operable with an air micropump, and hence facilitating the miniaturization and integration of lab-on-a-chip and microbioreactor systems.
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