3D printing has the potential to significantly change the field of microfluidics. The ability to fabricate a complete microfluidic device in a single step from a computer model has obvious attractions, but it is the ability to create truly three dimensional structures that will provide new microfluidic capability that is challenging, if not impossible to make with existing approaches. This critical review covers the current state of 3D printing for microfluidics, focusing on the four most frequently used printing approaches: inkjet (i3DP), stereolithography (SLA), two photon polymerisation (2PP) and extrusion printing (focusing on fused deposition modeling). It discusses current achievements and limitations, and opportunities for advancement to reach 3D printing's full potential.

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3D printed microfluidic devices: enablers and barriers

Microorganisms move in challenging environments by periodic changes in body shape. In contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realize continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microswimmers. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies.

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Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots

Review on battery thermal management system for electric vehicles

Bioengineered and biohybrid bacteria-based systems for drug delivery.

This review aims to concisely chart the development of two individual research fields, namely nanomedicines, with specific emphasis on nanoparticles (NP) and microparticles (MP), and microneedle (MN) technologies, which have, in the recent past, been exploited in combinatorial approaches for the efficient delivery of a variety of medicinal agents across the skin. This is an emerging and exciting area of pharmaceutical sciences research within the remit of transdermal drug delivery and as such will undoubtedly continue to grow with the emergence of new formulation and fabrication methodologies for particles and MN. Firstly, the fundamental aspects of skin architecture and structure are outlined, with particular reference to their influence on NP and MP penetration. Following on from this, a variety of different particles are described, as are the diverse range of MN modalities currently under development. The review concludes by highlighting some of the novel delivery systems which have been described in the literature exploiting these two approaches and directs the reader towards emerging uses for nanomedicines in combination with MN.

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Microneedles: A New Frontier in Nanomedicine Delivery

The retinal arterial network is the only source of the highly nutrient-consumptive retina, thus any insult on the arteries can impair the retinal oxygen and nutrient supply and affect its normal function. The aim of this work is to study the influences of vascular structure variation on the flow and pressure characteristics via microfluidic devices. Two sets of micro-channel were designed to mimic the stenosed microvessels and dichotomous branching structure in the retinal arteries. Three working fluids including red blood cell (RBC) suspension were employed to investigate the pressure drop in the stenosed channel. The flow behaviors of RBC suspensions inside the micro channels were observed using high speed camera system. Pressure drop of different working fluids and RBC velocity profiles in the stenosed channel were obtained. Moreover, hematocrit levels of RBC suspensions inside the bifurcated channels were analyzed from the sequential images of RBC flow. The results of the flow in the stenosed channel show that RBCs drift from the center of the channels, and RBC velocity is influenced not only by the inlet flow rate but also the interaction between RBCs. The measured pressure drops in the stenosed channel increase notably with the increase of fluid viscosity. Furthermore, the dimensionless pressure drop due to the stenosis decreases with Reynolds number. On the other hand, the results of flow through the bifurcated channels show that as the ratio of the daughter-branch width to the mother-channel width increases, the ratio of hematocrit in two connected branches (Ht/Hd) decreases, which is in favorable agreement with the available analysis results.

Microfluidic analysis of pressure drop and flow behavior in hypertensive micro vessels

Analysis of a lithium-ion battery cooling system for electric vehicles using a phase-change material and heat pipes

The surface tension of some high-carbon alcohol aqueous solutions increases as the temperature rises above a certain temperature. There have been attempts to use such special solutions in thermal devices to promote heat transfer. In this study, the authors analyzed the temperature dependence of surface tension of these solutions to investigate this peculiar characteristic in detail. The test fluids were butanol and pentanol aqueous solutions as peculiar solutions, while pure water and ethanol aqueous solution were normal fluids. First, the authors adopted Wilhelmy's method to measure the surface tension during heating, but found that the influence of evaporation of the solution could not be completely eliminated. In this study, the maximum bubble pressure method was employed, which made it possible to isolate the measured solution from ambient air and eliminate the influence of evaporation of the solution. The authors succeeded in measuring the temperature dependence of surface tension, and obtained more reasonable data.

https://www.jstage.jst.go.jp/article/jtst/4/2/4_2_284/_pdf

Measurement of Temperature Dependence of Surface Tension of Alcohol Aqueous Solutions by Maximum Bubble Pressure Method

Electrical vehicles equipped with lithium-ion batteries (LiBs) have been increasing in popularity on the market. LiBs have high energy density and high electric current; however, their lifetimes and performance are known to be strongly influenced by temperature rise due to heat generation, and thermal runaway may occur when the battery temperature exceeds 80 °C. Hence, the development of LiB thermal-management technology is essential. In this study, an A4-sized LiB was short circuited in a prototype cooling system with phase-change material (PCM) and heat pipes (HPs), and the performance of the cooling system was evaluated. To compare the cooling performances, four experimental conditions were adopted: a combination of PCM and HP; PCM only; HP only; and not using the cooling system. In addition, a simulation was conducted under the experimental conditions using a scale model of the cooling system. Thus, we confirmed that the temperature increase of the LiB, especially up to 80 °C, was extended by the effects of PCM. The combination of PCM and HP suppressed the temperature of LiB to be about 80 °C.

Performance evaluation of a battery-cooling system using phase-change materials and heat pipes for electric vehicles under the short-circuited battery condition

Aqueous solutions of some alcohols such as butanol show peculiar temperature dependence of surface tension. Contrary to ordinary liquids or solutions, the surface tension increases with temperature at the range of high liquid temperature. So at the triple-phase point on a heated surface, the thermo-capillary force acts for the liquid to wet the heated surface, so the solutions are sometimes called as “self-wetting liquids”. Self-wetting liquids may prohibit the dry-out of a heated surface so that the heat transfer performance would be enhanced. For this reason, applications of self-wetting liquids to heat transfer devices such as heat pipes are actively studied in recent years. However, the heat transfer characteristics of boiling of self-wetting liquids are not fully understood. In the present research, a boiling experiment of butanol aqueous solution was performed on a heated fine wire in order to make clear the fundamental heat transfer characteristics. A heated wire configuration is easy to observe the phenomena and easy to address the fundamental issues of boiling. In the present experiment, nucleate boiling heat transfer were investigated with special attention to critical heat flux (CHF), by changing solution concentration and temperature. Bubbling aspects were observed by high-speed video camera. It is found from the experiment that CHF is generally enhanced 20 to 50% when compared to the case of pure water. It is also found that at a certain concentration and at a certain liquid temperature, peculiar boiling takes place where very small bubbles are emitted from the heated wire and CHF enhancement becomes very large from 2 to 3 times higher than CHF of pure water. The temperature when the peculiar boiling takes place is close to boiling temperature of the solution. These results suggest the possibility of application of aqueous solution to high-performance cooling devices utilizing micro-scaled channels because generating bubbles are small enough so that the pressure loss of the flow passage is small and heat transfer rate is very large.Copyright © 2008 by ASME

Naoki Ono

Papers

Microfluidic analysis of pressure drop and flow behavior in hypertensive micro vessels

Analysis of a lithium-ion battery cooling system for electric vehicles using a phase-change material and heat pipes

Measurement of Temperature Dependence of Surface Tension of Alcohol Aqueous Solutions by Maximum Bubble Pressure Method

Performance evaluation of a battery-cooling system using phase-change materials and heat pipes for electric vehicles under the short-circuited battery condition

Critical Heat Flux of Butanol Aqueous Solution