Facilitating epitaxial growth of ZnO films on patterned GaN layers: A solution-concentration-induced successive lateral growth mechanism

Organ-on-a-chip (OOC) facilitates precise manipulation of fluids in microfluidic chips and simulation of the physiological, chemical, and mechanical characteristics of tissues, thus providing a promising tool for in vitro drug screening and physiological modeling. In recent decades, this technology has advanced rapidly because of the development of various three-dimensional (3D) printing techniques. 3D printing can not only fabricate microfluidic chips using materials such as resins and polydimethylsiloxane but also construct biomimetic tissues using bioinks such as cell-loaded hydrogels. In this review, recent advances in 3D-printing-based OOC are systematically summarized based on materials used for direct or indirect 3D printing of OOC, 3D printing techniques for the construction of OOC, and applications of 3D-printing-based OOC in models of the heart, blood vessels, intestines, liver, and kidney. In addition, future perspectives and challenges in this area are envisioned to inspire researchers to employ 3D printing techniques to accelerate OOC development. 

Recent Advances in 3D-Printing-Based Organ-on-a-Chip

Compound eyes are high-performing natural optical perception systems with compact configurations, generating extensive research interest. Existing compound eye systems are often combinations of simple uniform microlens arrays; there are still challenges in making more ommatidia on the compound eye surface to focus to the same plane. Here, a biomimetic gradient compound eye is presented by artificially mimicking dragonflies. The multiple replication process efficiently endows compound eyes with the gradient characteristics of dragonfly compound eyes. Experimental results show that the manufactured compound eye allows multifocus imaging by virtue of the gradient ommatidium array arranged closely in a honeycomb pattern while ensuring excellent optical properties and compact configurations. Thousands of ommatidia showing a gradient trend at the millimeter scale while remaining relatively uniform at the micron scale have gradient focal lengths ranging from 260 to 450 μm. This gradient compound eye allows more ommatidia to focus on the same plane than traditional uniform compound eyes, which have experimentally been shown to capture more than 1100 in-plane clear images simultaneously, promising potential applications in micro-optical devices, optical imaging, and biochemical sensing.

Biomimetic Compound Eyes with Gradient Ommatidium Arrays.

Although the enormous potential of droplet-based microfluidics has been successfully demonstrated in the past two decades for medical, pharmaceutical, and academic applications, its inherent potential has not been fully exploited until now. Nevertheless, the cultivation of biological cells and 3D cell structures like spheroids and organoids, located in serially arranged droplets in micro-channels, has a range of benefits compared to established cultivation techniques based on, e.g., microplates and microchips. To exploit the enormous potential of the droplet-based cell cultivation technique, a number of basic functions have to be fulfilled. In this paper, we describe microfluidic modules to realize the following basic functions with high precision: (i) droplet generation, (ii) mixing of cell suspensions and cell culture media in the droplets, (iii) droplet content detection, and (iv) active fluid injection into serially arranged droplets. The robustness of the functionality of the Two-Fluid Probe is further investigated regarding its droplet generation using different flow rates. Advantages and disadvantages in comparison to chip-based solutions are discussed. New chip-based modules like the gradient, the piezo valve-based conditioning, the analysis, and the microscopy module are characterized in detail and their high-precision functionalities are demonstrated. These microfluidic modules are micro-machined, and as the surfaces of their micro-channels are plasma-treated, we are able to perform cell cultivation experiments using any kind of cell culture media, but without needing to use surfactants. This is even more considerable when droplets are used to investigate cell cultures like stem cells or cancer cells as cell suspensions, as 3D cell structures, or as tissue fragments over days or even weeks for versatile applications.

Flexible Toolbox of High-Precision Microfluidic Modules for Versatile Droplet-Based Applications

The paper demonstrates an adaptation of a 3D printer (Prusa Mini+) with novel modules to develop a droplet generation system that generates combinatorial droplets from a standard 96 well plate....

Automated Dynamic Inlet Microfluidics System: 3D Printer Adaptation for Cost-Effective, Low Volume, On-Demand Multi-Analyte Droplet Generator

Abstract Reconfigurable modular microfluidics presents an opportunity for flexibly constructing prototypes of advanced microfluidic systems. Nevertheless, the strategy of directly integrating modules cannot easily fulfill the requirements of common applications, e.g., the incorporation of materials with biochemical compatibility and optical transparency and the execution of small batch production of disposable chips for laboratory trials and initial tests. Here, we propose a manufacturing scheme inspired by the movable type printing technique to realize 3D free-assembly modular microfluidics. Double-layer 3D microfluidic structures can be produced by replicating the assembled molds. A library of modularized molds is presented for flow control, droplet generation and manipulation and cell trapping and coculture. In addition, a variety of modularized attachments, including valves, light sources and microscopic cameras, have been developed with the capability to be mounted onto chips on demand. Microfluidic systems, including those for concentration gradient generation, droplet-based microfluidics, cell trapping and drug screening, are demonstrated. This scheme enables rapid prototyping of microfluidic systems and construction of on-chip research platforms, with the intent of achieving high efficiency of proof-of-concept tests and small batch manufacturing. 

3D free-assembly modular microfluidics inspired by movable type printing

n-GaN/i-ZnO/p-GaN double heterojunction diodes were constructed by vertically binding p-GaN wafer on the tip of ZnO nanopencil arrays grown on n-GaN/sapphire substrates. An increased quantum confinement in the tip of ZnO nanopencils has been verified by photoluminescence measurements combined with quantitative analyses. Under forward bias, a sharp ultraviolet emission at ~375 nm due to localized excitons recombination can be observed in ZnO. The electroluminescence mechanism of the studied diode is tentatively elucidated using a simplified quantum confinement model. Additionally, the improved performance of the studied diode featuring an ultralow emission onset, a good operation stability and an enhanced ultraviolet emission shows the potential of our approach. This work provides a new route for the design and development of ZnO-based excitonic optoelectronic devices.

Exciton localization and ultralow onset ultraviolet emission in ZnO nanopencils-based heterojunction diodes

Polarization modulation of electromagnetic waves plays an important role in the field of optics and optoelectronics. Current polarization optics are typically limited to the modulation in a single transverse plane. However, manipulating polarization along the longitudinal direction is also important for full-space polarization modulation. Here, we propose two kinds of all-dielectric terahertz metasurfaces for longitudinally spatial polarization manipulation. The metasurfaces are capable of controlling polarization along the propagation path, namely: i) a longitudinal bifocal metalens with different polarization states at each focal point, and ii) a versatile metalens can simultaneously generate a uniformly polarized focused beam and a vector beam with varying polarization along the propagation path. Furthermore, the measurement of the dielectric thickness is demonstrated based on the polarization modulation feature of the metalens. The proposed metasurfaces allow for effective polarization state alteration along the propagation path, exhibiting significant potential for applications in versatile light-matter interactions, optical communications, and quantum optics.

Longitudinal polarization manipulation based on all-dielectric terahertz metasurfaces.


 The conventional micro/nano-manufacturing techniques can hardly process interior microstructures. The entire fabrication process is complex and requires large-footprint and high-cost equipment. The presented microfluidics assisted optics manufacturing technique is feasible to create the curved surface inside microstructure using various modified materials. The fabrication process is simple. Only small, low-cost devices are needed. In this paper, microfluidics assisted optics manufacturing technique is introduced in detail and compared with the current manufacturing techniques. A diversity of interesting micro-optics, including microlens array and compound eye, are demonstrated. These optical components are all fabricated by the microfluidics assisted manufacturing technique and possess their own outstanding features.

Microfluidics assisted optics manufacturing technique

/pdf/a-3d-printed-standardized-modular-microfluidic-system-for-1jkqevtl.pdf

A 3D-Printed Standardized Modular Microfluidic System for Droplet Generation

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