We compare current bioprinting technologies for their effective resolutions in the fabrication of micro-tissues towards construction of biomimetic microphysiological systems.

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Capturing airborne particles from air into a liquid is a critical process for the development of many sensors and analytical systems. A miniaturized airborne particle sampling device (microimpinger) has been developed in this research. The microimpinger relies on a controlled bubble generation process produced by driving air through microchannel arrays. The particles confined in the microscale bubbles are captured in the sampling liquid while the bubbles form, are released and travel in a millimetre-scale sealed liquid reservoir. The microchannel arrays in the impinger are fabricated using a soft-lithography method with polydimethylsiloxane (PDMS) as the structural material. To prevent air leakage at the connections, a PDMS-only sealing technique is successfully developed. The hydrophobicity of the microchannel surface is found to be critical for generating continuous and stable bubbles in the bubbling process. A Teflon layer is coated on the walls of a microchannel array by vapor deposition which effectively increases the hydrophobicity of the PDMS. The collection efficiency of the microimpinger is measured by counting different sizes of fluorescent polystyrene latex particles on polycarbonate membrane filters. Collection efficiencies above 90% are achieved. Furthermore, the particle capturing mechanisms during the injection, formation and rise of a single microbubble are investigated by a computational fluid dynamics (CFD) model. The Navier-Stokes equations are solved along with the use of the volume-of-fluid (VOF) method to capture the bubble deformations and the particles are tracked using a Lagrangian equation of motion. The model is also employed to study the effect of bubble size on the collection efficiency of the microimpinger.

The United States produces more than 10 million tons of waste oils and fats each year. This paper aims to establish a new biomanufacturing platform that converts waste oils or fats into a series of value‐added products. Our research employs the oleaginous yeast Yarrowia lipolytica as a case study for citric acid (CA) production from waste oils. First, we conducted the computational fluid dynamics (CFD) simulation of the bioreactor system and identified that the extracellular mixing and mass transfer is the first limiting factor of an oil fermentation process due to the insolubility of oil in water. Based on the CFD simulation results, the bioreactor design and operating conditions were optimized and successfully enhanced oil uptake and bioconversion in fed‐batch fermentation experiments. After that, we investigated the impacts of cell morphology on oil uptake, intracellular lipid accumulation, and CA formation by overexpressing and deleting the MHY1 gene in the wild type Y. lipolytica ATCC20362. Fairly good linear correlations (R2 > 0.82) were achieved between cell morphology and productivities of biomass, lipid, and CA. Finally, fermentation kinetics with both glucose and oil substrates were compared and the oil fermentation process was carefully evaluated. Our study suggests that waste oils or fats can be economical feedstocks for biomanufacturing of many high‐value products.

A high throughput manufacturing process to magnetically assembling nanowire (NW) network into paraffin was developed for enhancing conductivity in phase change materials (PCMs) used in energy storage applications. The prefabricated nickel NWs were dispersed in melted paraffin followed by magnetic alignment under a strong magnetic field. Measuring electrical conductivity of the nanocomposite, as well as observing cross section of the sample slice under an optical microscope characterized the alignment of NWs. As a comparison, nickel particles (NPs) based paraffin nanocomposites were also fabricated, and its electrical conductivity with and without applied magnetic field were measured. The effects of aspect ratio of fillers (particles and NWs) and volume concentration on percolation threshold were studied both experimentally and theoretically. It was found that the NW based paraffin nanocomposite has much lower percolation threshold compared to that of particle based paraffin composite. Furthermore, the alignment of particles and NWs under magnetic field significantly reduces the threshold of percolation. This work provides solid foundation for the development of a manufacturing technology for high thermal conductivity PCMs for thermal energy storage applications.

Numerical simulation of particle collection in a newly developed microfluidic air sampling device is presented in this study. In the simulations, the air carrying the particles is injected into a liquid column to form a bubble. The bubble then releases from the air inlet following with interface deformations and rises in the liquid column carrying the particles inside. During this bubbling process, the particles having impact with the bubble interface are collected in the extraction liquid. For the simulations, Navier-Stokes equations are solved along with piecewise-linear Volume-of-Fluid (VOF) method for tracking the interface deformations. The particle trajectories are predicted on a Lagrangian frame of reference by integrating the force balance on each particle. To validate the numerical model, the results for bubble terminal velocity and shape, and particle removal rate are compared with the available experimental data in the literature. Finally, particle removal from different bubble sizes is studied.

Quartz crystal microbalance (QCM) device is a highly sensitive mass sensor (sensitivity: 0.5 ng/cm2) with a wide range of applications including biosensing, thin film deposition, surface chemistry, volatile organic compounds (VOC) and gaseous analytes detection. A recent study shows that several orders of magnitude improvement in sensitivity can be achieved by attaching microscale Polymethyl methacrylate (PMMA) pillars onto the surface of the QCM (QCM-P) to form a two-degree of freedom coupled resonant system. In this research, the effects of residual layer from the nanoimprinting process of micro-pillars and polydispersity index (Pd) of PMMA molecules on the sensitivity of QCM-P devices are investigated both experimentally and theoretically. The results show the residual layer behaves as an additional mass and significantly reduces the frequency shift of QCM-P sensor while a low polydispersity of PMMA improves the sensor responses. The outcome of this research leads to an in-depth understanding of the effects of material and fabrication process on QCM-P sensors which will build a solid foundation for the further improvement of QCM-P devices for a variety of applications such as protein binding measurement in drug discovery, gas detection for environmental monitoring and protection.

A high throughput manufacturing process to magnetically assembling nanowire (NW) network into paraffin was developed for enhancing conductivity in phase change materials (PCMs) used in energy storage applications. The prefabricated nickel nanowires were dispersed in melted paraffin followed by magnetic alignment under a strong magnetic field. Measuring electrical conductivity of the nanocomposites, as well as observing cross-section of the sample slice under an optical microscope characterized the alignment of nanowires. As a comparison, nickel particles (NPs) based paraffin nanocomposites were also fabricated and its electrical conductivity with and without applied magnetic field were measured. The effects of aspect ratio of fillers (particles and nanowires) and volume concentration on percolation threshold were studied both experimentally and theoretically. It was found that the nanowire based paraffin nanocomposite has much lower percolation threshold compared to that of particle based paraffin composite. Furthermore, the alignment of particles and nanowires under magnetic field significantly reduce the threshold of percolation. This work provides solid foundation for the development of a manufacturing technology for high thermal conductivity phase change materials (PCM) for thermal energy storage applications.