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Microfluidic organs-on-chips (OoCs) technology has emerged as the trend for in vitro functional modeling of organs in recent years. Simplifying the complexities of the human organs under controlled perfusion of required fluids paves the way for accurate prediction of human organ functionalities and their response to interventions like exposure to drugs. However, in the state-of-the-art OoC, the existing methods to control fluids use external bulky peripheral components and systems much larger than the chips used in experiments. A new generation of compact microfluidic flow control systems is needed to overcome this challenge. This study first presents a structured classification of OoC devices according to their types and microfluidic complexities. Next, we suggest three fundamental fluid flow control mechanisms and define component configurations for different levels of OoC complexity for each respective mechanism. Finally, we propose an architecture integrating modular microfluidic flow control components and OoC devices on a single platform. We emphasize the need for miniaturization of flow control components to achieve portability, minimize sample usage, minimize dead volume, improve the flowing time of fluids to the OoC cell chamber, and enable long-duration experiments. [ABSTRACT FROM AUTHOR]

Resonant sensors determine a sensed parameter by measuring the resonance frequency of a resonator. For fast continuous sensing, it is desirable to operate resonant sensors in a closed-loop configuration, where a feedback loop ensures that the resonator is always actuated near its resonance frequency, so that the precision is maximized even in the presence of drifts or fluctuations of the resonance frequency. However, in a closed-loop configuration, the precision is not only determined by the resonator itself, but also by the feedback loop, even if the feedback circuit is noiseless. Therefore, to characterize the intrinsic precision of resonant sensors, the open-loop configuration is often employed. To link these measurements to the actual closed-loop performance of the resonator, it is desirable to have a relation that determines the closed-loop precision of the resonator from open-loop characterisation data. In this work, we present a methodology to estimate the closed-loop resonant sensor precision by relying only on an open-loop characterization of the resonator. The procedure is beneficial for fast performance estimation and benchmarking of resonant sensors, because it does not require actual closed-loop sensor operation, thus being independent on the particular implementation of the feedback loop. We validate the methodology experimentally by determining the closed-loop precision of a mechanical resonator from an open-loop measurement and comparing this to an actual closed-loop measurement. [ABSTRACT FROM AUTHOR]

Microfluidic atomic force microscopy (AFM) cantilever probes have all the functionalities of a standard AFM cantilever along with fluid pipetting. They have a channel inside the cantilever and an aperture at the tip. Such probes are useful for precise fluid manipulation at a desired location, for example near or inside cells. They are typically made by complex microfabrication process steps, resulting in expensive probes. Here, we used two different 3D additive manufacturing techniques, stereolithography and two-photon polymerization, to directly print ready-to-use microfluidic AFM cantilever probes. This approach has considerably reduced the fabrication time and increased the design freedom. One of the probes, 564 μm long, 30 μm wide, 30 μm high, with a 25 μm diameter channel and 2.5 μm wall thickness had a spring constant of 3.7 N m−1 and the polymer fabrication material had an elastic modulus of 4.2 GPa. Using these 3D printed probes, AFM imaging of a surface, puncturing of the cell membrane, and aspiration at the single cell level have been demonstrated. [ABSTRACT FROM AUTHOR]

Current wafer-scale fabrication methods for graphene-based electronics and sensors involve the transfer of single-layer graphene by a support polymer. This often leaves some polymer residue on the graphene, which can strongly impact its electronic, thermal, and mechanical resonance properties. To assess the cleanliness of graphene fabrication methods, it is thus of considerable interest to quantify the amount of contamination on top of the graphene. Here, we present a methodology for the direct measurement of the mass of the graphene sheet using quartz crystal microbalances (QCMs). By monitoring the QCM resonance frequency during removal of graphene in an oxygen plasma, the total mass of the graphene and contamination is determined with sub-graphene-monolayer accuracy. Since the etch-rate of the contamination is higher than that of graphene, quantitative measurements of the mass of contaminants below, on top, and between graphene layers are obtained. We find that polymer-based dry transfer methods can increase the mass of a graphene sheet by a factor of 10. The presented mass measurement method is conceptually straightforward to interpret and can be used for standardized testing of graphene transfer procedures in order to improve the quality of graphene devices in future applications. [ABSTRACT FROM AUTHOR]

Microelectromechanical systems (MEMS)-based sample carriers became a breakthrough for in situ inspection techniques, especially in transmission electron microscopy where the sample carrier functions as a microsized laboratory and enables dynamic studies on samples, such as nanoparticles, nanowires, lamellas, and 2-D materials. Microheaters allow for in situ manipulation of samples by applying heat stimuli such that sample properties and interactions can be studied in real time at elevated temperatures. However, currently developed microheaters still suffer from undesired effects such as mechanical deflection and limitations in temperature range, accuracy, and homogeneity. This review discusses advancements in the technological development of microheaters. Methods and results found in the literature are categorized to provide an overview of optimization methods for thermoelectromechanical design aspects. The knowledge from various application fields, including a critical reflection on mesoscopic material properties, is combined into a series of design guidelines. These compose instructions for developing and optimizing microheater characteristics, such as mechanical and thermal stress, temperature accuracy and homogeneity, power consumption, response time, and sample drift. Although this review and guide are applicable to many application fields that require a microheater, an emphasis is laid on aspects most relevant to the microheater as a high-temperature sample carrier for in situ experiments. [2017–0149] [ABSTRACT FROM PUBLISHER]

Recent progress in nano-/micro-fabrication techniques has paved the way for the emergence of synthetic bactericidal patterned surfaces that are capable of killing the bacteria via mechanical mechanisms. Different design parameters are known to affect the bactericidal activity of nanopatterns. Evaluating the effects of each parameter, isolated from the others, requires systematic studies. Here, we systematically assessed the effects of the interspacing and disordered arrangement of nanopillars on the bactericidal properties of nanopatterned surfaces. Electron beam induced deposition (EBID) was used to additively manufacture nanopatterns with precisely controlled dimensions (i.e., a height of 190 nm, a diameter of 80 nm, and interspaces of 100, 170, 300, and 500 nm) as well as disordered versions of them. The killing efficiency of the nanopatterns against Gram-positive Staphylococcus aureus bacteria increased by decreasing the interspace, achieving the highest efficiency of 62 ± 23% on the nanopatterns with 100 nm interspacing. By comparison, the disordered nanopatterns did not influence the killing efficiency significantly, as compared to their ordered correspondents. Direct penetration of nanopatterns into the bacterial cell wall was identified as the killing mechanism according to cross-sectional views, which is consistent with previous studies. The findings indicate that future studies aimed at optimizing the design of nanopatterns should focus on the interspacing as an important parameter affecting the bactericidal properties. In combination with controlled disorder, nanopatterns with contrary effects on bacterial and mammalian cells may be developed. [ABSTRACT FROM AUTHOR]