Finger-powered fluidic actuation and mixing via MultiJet 3D printing

Advancements in the research of finger-actuated POCT chips

Microfluidic point-of-care testing (POCT) chips are used to enable the mixing and reaction of small sample volumes, facilitating target molecule detection. Traditional methods for actuating POCT chips rely on external pumps or power supplies, which are complex and non-portable. The development of finger-actuated chips has reduced operational difficulty and improved portability, promoting the development of POCT chips. This paper reviews the significance, developments, and potential applications of finger-actuated POCT chips. Three methods for controlling the flow accuracy of finger-actuated chips are summarized: direct push, indirect control, and sample injection control method, along with their respective advantages and disadvantages. Meanwhile, a comprehensive analysis of multi-fluid driving modes is provided, categorizing them into single-push multi-driving and multi-push multi-driving modes. Furthermore, recent research breakthroughs in finger-actuated chips are thoroughly summarized, and their structures, driving, and detection methods are discussed. Finally, this paper discusses the driving performance of finger-actuated chips, the suitability of detection scenarios, and the compatibility with existing detection technologies. It also provides prospects for the future development and application of finger-actuated POCT chips.

Micropatterning of functional lipid bilayer assays for quantitative bioanalysis

Interactions of the cell with its environment are mediated by the cell membrane and membrane-localized molecules. Supported lipid bilayers have enabled the recapitulation of the basic properties of cell membranes and have been broadly used to further our understanding of cellular behavior. Coupled with micropatterning techniques, lipid bilayer platforms have allowed for high throughput assays capable of performing quantitative analysis at a high spatiotemporal resolution. Here, an overview of the current methods of the lipid membrane patterning is presented. The fabrication and pattern characteristics are briefly described to present an idea of the quality and notable features of the methods, their utilizations for quantitative bioanalysis, as well as to highlight possible directions for the advanced micropatterning lipid membrane assays.

3D printed microfluidics: advances in strategies, integration, and applications

The ability to construct multiplexed micro-systems for fluid regulation could substantially impact multiple fields, including chemistry, biology, biomedicine, tissue engineering, and soft robotics, among others. 3D printing is gaining traction as a compelling approach to fabricating microfluidic devices by providing unique capabilities, such as 1) rapid design iteration and prototyping, 2) the potential for automated manufacturing and alignment, 3) the incorporation of numerous classes of materials within a single platform, and 4) the integration of 3D microstructures with prefabricated devices, sensing arrays, and nonplanar substrates. However, to widely deploy 3D printed microfluidics at research and commercial scales, critical issues related to printing factors, device integration strategies, and incorporation of multiple functionalities require further development and optimization. In this review, we summarize important figures of merit of 3D printed microfluidics and inspect recent progress in the field, including ink properties, structural resolutions, and hierarchical levels of integration with functional platforms. Particularly, we highlight advances in microfluidic devices printed with thermosetting elastomers, printing methodologies with enhanced degrees of automation and resolution, and the direct printing of microfluidics on various 3D surfaces. The substantial progress in the performance and multifunctionality of 3D printed microfluidics suggests a rapidly approaching era in which these versatile devices could be untethered from microfabrication facilities and created on demand by users in arbitrary settings with minimal prior training.

Numerical Study of the Coalescence and Mixing of Drops of Different Polymeric Materials

In this study, we employ direct numerical simulation (DNS) to investigate the solutal hydrodynamics dictating the three-dimensional coalescence of microscopic, identical-sized sessile drops of different but miscible shear-thinning polymeric liquids (namely, PVAc or polyvinyl acetate and PMMA or polymethylmethacrylate), with the drops being in partially wetted configuration. Despite the ubiquitousness of the interaction of different dissimilar droplets in a variety of engineering problems ranging from additive manufacturing to understanding the behavior of photonic crystals, coalescence of drops composed of different polymeric and non-Newtonian materials has not been significantly explored. Interaction of such dissimilar droplets often involves simultaneous drop spreading, coalescence, and mixing. The mixing dynamics of the dissimilar drops are governed by interphase diffusion, the residual kinetic energy of the drops stemming from the fact that coalescence starts before the spreading of the drops have been completed, and the solutal Marangoni convection. We provide the three-dimensional velocity fields and velocity vectors inside the completely miscible, dissimilar coalescing droplets. Our simulations explicate the relative influence of these different effects in determining the flow field at different locations and at different time instances and the consequent mixing behavior inside the interacting drops. We also show the non-monotonic (in terms of the direction of migration) propagation of the mixing front of the miscible coalescing drops over time. We also establish that the overall mixing (on either side of the mixing front) speeds up as the Marangoni effects dictate the mixing. We anticipate that our study will provide an important foundation for studying miscible multi-material liquid systems, which will be crucial for applications such as inkjet or aerosol jet printing, lab-on-a-chip, polymer processing, etc.

Biomedical Applications of Microfluidic Devices: A Review

Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

Investigating the mechanotransduction of transient shear stress mediated by Piezo1 ion channel using a 3D printed dynamic gravity pump

Microfluidic systems are widely used for studying the mechanotransduction of flow-induced shear stress in mechanosensitive cells. However, these studies are generally performed under constant flow rates, mainly, due to the deficiency of existing pumps for generating transient flows. To address this limitation, we have developed a unique dynamic gravity pump to generate transient flows in microfluidics. The pump utilises a motorised 3D-printed cam-lever mechanism to change the inlet pressure of the system in repeated cycles. 3D printing technology facilitates the rapid and low-cost prototyping of the pump. Customised transient flow patterns can be generated by modulating the profile, size, and rotational speed of the cam, location of the hinge along the lever, and the height of the syringe. Using this unique dynamic gravity pump, we investigated the mechanotransduction of shear stress in HEK293 cells stably expressing Piezo1 mechanosensitive ion channel under transient flows. The controllable, simple, low-cost, compact, and modular design of the pump makes it suitable for studying the mechanobiology of shear sensitive cells under transient flows.

Design and fabrication of micro/nanofluidics devices and systems

This chapter provides an overview of the science, engineering, and design methods required in the development of micro/nanofluidic devices. Section 2 provides the scientific background of fluid mechanics and physical phenomena in micro/nanoscale. Section 3 gives a brief overview of the existing fabrication techniques employed in micro/nanofluidics. The techniques are grouped into three categories: (1) subtractive manufacturing, (2) formative manufacturing, and (3) additive manufacturing. The advantages and disadvantages of each manufacturing technique are also discussed. Implementation of the fluidic devices beyond laboratory demonstrations is not trivial, which requires a good understanding of the problems of interest and the end-users. To that end, Section 4 introduces the design thinking approach and its application to develop micro/nanofluidic devices. Finally, Section 5 concludes the chapter with future outlooks.