Macro-scale Systems Research Articles

Mixture model for biomagnetic separation in microfluidic systems

In this paper, we show that mixture model, with algebraic slip velocity relating to the magnetophoresis, provides a continuum-based, and cost-effective tool to simulate biomagnetic separations in microfluidics. The model is most effective to simulate magnetic separation protocols in which magnetic or magnetically labeled biological targets are within a naturally dilute or diluted samples. The transport of these samples is characterized as mixtures in which the dispersed magnetic microparticles establish their magnetophoretic mobility quickly in response to the acting forces. Our simulations demonstrate the coupled particle-fluid transport and the High Gradient Magnetic Capture (HGMC) of magnetic beads flowing through a microchannel. Also, we show that the mixture model and accordingly the modeling of the slip velocity model, unlike with the case with dense and/or macro-scale systems, can be further simplified by ignoring the gravitational and granular parameters. Furthermore, we show, by conducting comparative simulations, that the developed model provides an easier and viable alternative to the commonly used Lagrangian-Eulerian (particle-based) models.

Friction between van der Waals Solids during Lattice Directed Sliding.

Nanometer-scale crystals of the two-dimensional oxide molybdenum trioxide (MoO3) were formed atop the transition metal dichalcogenides MoS2 and MoSe2. The MoO3 nanocrystals are partially commensurate with the dichalcogenide substrates, being aligned only along one of the substrate's crystallographic axes. These nanocrystals can be slid only along the aligned direction and maintain their alignment with the substrate during motion. Using an AFM probe to oscillate the nanocrystals, it was found that the lateral force required to move them increased linearly with nanocrystal area. The slope of this curve, the interfacial shear strength, was significantly lower than for macroscale systems. It also depended strongly on the duration and the velocity of sliding of the crystal, suggesting a thermal activation model for the system. Finally, it was found that lower commensuration between the nanocrystal and the substrate increased the interfacial shear, a trend opposite that predicted theoretically.

Mechanical test method and properties of a carbon nanomaterial with a high aspect ratio.

Superior nanomaterials have been developed and applied to many fields, and improved characteristic of nanomaterials have been studied. Measurement of the mechanical properties for nanomaterials is important to ensure the reliability and predict the service life times of products containing nanomaterials. However, it is challenging to measure the mechanical properties of nanomaterials due to their very small dimensions. Moreover, macro-scale measurement systems are not suitable for use with nanomaterials. Therefore, various methods have been developed and used to in an effort to measure the mechanical properties of nanomaterials. This paper presents a review of various evaluation systems and the measurement methods which are used to determine the mechanical properties of carbon nanotube (CNT) and carbon nanofiber (CNF), representatively. In addition, we measured the tensile strength and elastic modulus of the CNT and CNF in the scanning electron microscope (SEM) installed the nano-manipulator and the force sensor and this measurement system and results would be introduced in detail.

Transfer of motion through a microelectromechanical linkage at nanometer and microradian scales.

Mechanical linkages are fundamentally important for the transfer of motion through assemblies of parts to perform work. Whereas their behavior in macroscale systems is well understood, there are open questions regarding the performance and reliability of linkages with moving parts in contact within microscale systems. Measurement challenges impede experimental studies to answer such questions. In this study, we develop a novel combination of optical microscopy methods that enable the first quantitative measurements at nanometer and microradian scales of the transfer of motion through a microelectromechanical linkage. We track surface features and fluorescent nanoparticles as optical indicators of the motion of the underlying parts of the microsystem. Empirical models allow precise characterization of the electrothermal actuation of the linkage. The transfer of motion between translating and rotating links can be nearly ideal, depending on the operating conditions. The coupling and decoupling of the links agree with an ideal kinematic model to within approximately 5%, and the rotational output is perfectly repeatable to within approximately 20 microradians. However, stiction can result in nonideal kinematics, and input noise on the scale of a few millivolts produces an asymmetric interaction of electrical noise and mechanical play that results in the nondeterministic transfer of motion. Our study establishes a new approach towards testing the performance and reliability of the transfer of motion through assemblies of microscale parts, opening the door to future studies of complex microsystems.

Some Brief Comments on Recent Studies on Quantum Cognition

The emerging discipline of Quantum Cognitive Studies is filled with promise and pitfalls. The rich and detailed formalism of quantum theory must be closely considered in crafting an approach to the field. This essay strikes a cautionary note in assessment of trends which reduce the theory to instrumentalism. A brief accounting of the proper formalism, will correct the problem of “quantum-like” adaptations. The quantum principles which govern the complexities of dynamic object representation may be analogously and fruitfully captured in a schematic adaptation of the Mach Zehnder interferometer. The appropriate brain areas and functions are briefly discussed, and a justification for utilization of quantum features in describing macro-scale biological systems is presented. The problem of maintaining quantum superpositions is delineated inviting people to study and experience by the well known Legget-Garg relation.

A disposable, continuous-flow polymerase chain reaction device: design, fabrication and evaluation

Polymerase Chain Reaction (PCR) is used to amplify a specific segment of DNA through a thermal cycling protocol. The PCR industry is shifting its focus away from macro-scale systems and towards micro-scale devices because: micro-scale sample sizes require less blood from patients, total reaction times are on the order of minutes opposed to hours, and there are cost advantages as many microfluidic devices are manufactured from inexpensive polymers. Some of the fastest PCR devices use continuous flow, but they have all been built of silicon or glass to allow sufficient heat transfer. This article presents a disposable polycarbonate (PC) device that is capable of achieving real-time, continuous flow PCR in a completely disposable polymer device in less than 13 minutes by thermally cycling the sample through an established temperature gradient in a serpentine channel. The desired temperature gradient was determined through simulations and validated by experiments which showed that PCR was achieved. Practical demonstration included amplification of foot-and-mouth disease virus (FMDV) derived cDNA.

Layer-by-layer carbon nanotube coatings for enhanced pool boiling heat transfer on metal surfaces

Micro/nanotextured coatings have enabled the manipulation of thermal characteristics in pool boiling heat transfer such as the heat transfer coefficient (HTC) and critical heat flux (CHF) because of the ability to optimize bubble formations and departures. However, fabricating such coatings on substrates involves high cost-bulky setup, and is limited by the materials and adhesion properties. Herein, we report layer-by-layer (LbL)-assembled polyethylenimine (PEI)-multi-walled carbon nanotube (MWCNTs) coatings on stainless steel (SS316) to enhance HTC and CHF in pool boiling heat transfer. LbL-assembled PEI-MWCNTs coatings (10, 20, 40 bi-layers) on SS316 were fabricated, whereas bare SS316 substrate and vacuum-filtered MWCNTs coating were prepared as controls. Because of the nano-cavities and the inner-nanoporous structures, LbL coatings showed significant enhancement of HTCs and CHFs compared to bare SS316. Furthermore, denser networks of MWCNTs due to electrostatic bonding and hydrophilic nature of PEI in the LbL coatings could enhance the HTCs and CHFs compared to vacuum-filtered MWCNTs coating. LbL-assembled PEI-MWCNTs of 20 bi-layers showed the highest improvement in HTC, whereas the 40 bi-layers coatings achieved the best enhancement ratio of CHF, (∼147%). Further development of the LbL-assembled coatings on metal surfaces would enable potential applications for thermal management, from micro/nanoscale platforms to macroscale systems.

On the oblique collision of gaseous molecules with graphene nanosheets

In this paper, normal and tangential coefficients of restitution for gaseous molecules colliding with layerwise (single and few layers) graphene nanosheets were calculated using non-equilibrium molecular dynamics method. The normal and tangential coefficients of restitution depend on impact angle, velocity and landing position of projectiles. These parameters were evaluated computationally by implementation of several operations. Some differences were observed between proposed problem and macro-scale nature. The most notable difference was proportionality between the restitution coefficients and impact velocity, while in the case of macro-scale systems, they have inverse relation. Number of layers of graphene substrate does not contribute significantly to the normal and tangential coefficients of restitution. On the other hand, except for hydrogen, where its normal coefficient of restitution is approximately unity, the normal coefficient of restitution for other gasses increases as impact angle increases. Furthermore, tangential coefficients of restitution reduce with impact angle. These results can offer additional insights for further understanding the impact mechanisms and bombardment-related phenomena in low-dimensional materials. Presented results could be utilised to optimise some applied operations such as porosity generation via bombardment of layered nanostructures, gas detection process, thermal management and pressure sensor applications.

DNA-Based Drug Carriers: The Paradox of a Classical "Cargo" Material Becoming a Versatile "Carrier" to Overcome Barriers in Drug Delivery.

Drug delivery strategies help cope with drawbacks of classical pharmaceuticals, including increasing their solubility, diminishing side effects and improving biodistribution. A multitude of vehicles have been envisioned to this end, encompassing a variety of materials, architectures, and functionalities. DNA-built carriers are relatively new, yet promising devices to help overcome some of the current barriers in drug delivery. Its easy fabrication, reproducibility and tunability make DNA a unique material for building devices ranging from macro-scale depot systems to nano-scale vehicles tailored as nanoparticles, containers, dendrimers, tubes, etc. Although this DNA application is relatively novel and knowledge is building up, current advances suggest great potential. Intracellular delivery is a promising option, whereby access of cargoes (from small molecules to large biotherapeutics) to the cytosol has been demonstrated in many cell types, without apparent side effects or need for additional actuators. This is paradoxical since "natural" DNA cannot access cells and nucleic acids are among the most difficult cargoes to be delivered within cells; yet this property arises from engineering DNA into particular configurations. Their biocompatibility and safety also holds potential, since this natural material is biodegradable and nucleotides are biological metabolites. Using modified nucleotides and properly designing their sequence, along with classical chemical means, make it feasible to tune the stability and degradation rates of DNA devices. Taken together, although much research is still necessary to understand the in vivo behaviour of DNA-based vehicles, the design parameters ruling their optimization, and the biological pathways regulating their function, DNA represents a unique material to help in future drug delivery applications.

Seismic small-scale discontinuity sparsity-constraint inversion method using a penalty decomposition algorithm

We consider sparsity-constraint inversion method for detecting seismic small-scale discontinuities, such as edges, faults and cavities, which provide rich information about petroleum reservoirs. However, where there is karstification and interference caused by macro-scale fault systems, these seismic small-scale discontinuities are hard to identify when using currently available discontinuity-detection methods. In the subsurface, these small-scale discontinuities are separately and sparsely distributed and their seismic responses occupy a very small part of seismic image. Considering these sparsity and non-smooth features, we propose an effective L 2-L 0 norm model for improvement of their resolution. First, we apply a low-order plane-wave destruction method to eliminate macro-scale smooth events. Then, based the residual data, we use a nonlinear structure-enhancing filter to build a L 2-L 0 norm model. In searching for its solution, an efficient and fast convergent penalty decomposition method is employed. The proposed method can achieve a significant improvement in enhancing seismic small-scale discontinuities. Numerical experiment and field data application demonstrate the effectiveness and feasibility of the proposed method in studying the relevant geology of these reservoirs.

Dynamics of a monolayer of microspheres on an elastic substrate

We present a model for wave propagation in a monolayer of spheres on an elastic substrate. The model, which considers sagittally polarized waves, includes: horizontal, vertical, and rotational degrees of freedom; normal and shear coupling between the spheres and substrate, as well as between adjacent spheres; and the effects of wave propagation in the elastic substrate. For a monolayer of interacting spheres, we find three contact resonances, whose frequencies are given by simple closed-form expressions. For a monolayer of isolated spheres, only two resonances are present. The contact resonances couple to surface acoustic waves in the substrate, leading to mode hybridization and "avoided crossing" phenomena. We present dispersion curves for a monolayer of silica microspheres on a silica substrate, assuming adhesive, Hertzian interactions, and compare calculations using an effective medium approximation to a discrete model of a monolayer on a rigid substrate. While the effective medium model does not account for discrete lattice effects at short wavelengths, we find that it is well suited for describing the interaction between the monolayer and substrate in the long wavelength limit. We suggest that a complete picture of the dynamics of a discrete monolayer adhered to an elastic substrate can be found using a combination of the results presented for the discrete and effective medium descriptions. This model is potentially scalable for use with both micro- and macroscale systems, and offers the prospect of experimentally extracting contact stiffnesses from measurements of acoustic dispersion.

Electrocavitation in nanofluidics: unique phenomenon and fundamental platform.

In this paper, we will highlight one phenomenon unique to nanofluidics: electrocavitation. Electrocavitation is defined as cavitation induced by electric fields. Cavitation in general occurs in a liquid when it is subjected to a pressure below its vapor pressure, where the liquid can break apart and form a cavity (bubble). This is frequently seen in macroscale systems, for example, rotating propeller blades on the turbines of ships or water columns in the xylem of trees. Electrocavitation in nanochannels was first reported when researchers applied electric fields within nanochannels containing electrolytes discontinuous in conductivity and found that bubbles formed within the channel. The reasons to highlight electrocavitation to both the lab-on-a-chip community and those interested in the fundamental understanding of cavitation in general are detailed below.

Multi-scenario modelling of uncertainty in stochastic chemical systems

Uncertainty analysis has not been well studied at the molecular scale, despite extensive knowledge of uncertainty in macroscale systems. The ability to predict the effect of uncertainty allows for robust control of small scale systems such as nanoreactors, surface reactions, and gene toggle switches. However, it is difficult to model uncertainty in such chemical systems as they are stochastic in nature, and require a large computational cost. To address this issue, a new model of uncertainty propagation in stochastic chemical systems, based on the Chemical Master Equation, is proposed in the present study. The uncertain solution is approximated by a composite state comprised of the averaged effect of samples from the uncertain parameter distributions. This model is then used to study the effect of uncertainty on an isomerization system and a two gene regulation network called a repressilator. The results of this model show that uncertainty in stochastic systems is dependent on both the uncertain distribution, and the system under investigation.

A microreactor with phase-change microvalves for batch chemical synthesis at high temperatures and pressures

We present a simple microreactor with dimethyl sulfoxide (DMSO) phase-change valves suitable for performing batch organic chemistry under high temperature and pressure conditions. As a proof of principle, we demonstrate a radiofluorination reaction important in the synthesis of [(18)F]FAC, a new positron emission tomography biomarker for immune system monitoring and prediction of chemotherapy response. We achieved high radioactivity recovery (97 ± 1%, n = 3) and conversion efficiency (83 ± 1%, n = 3), comparable to that achieved with macroscale systems, but with a volume 30× smaller. This platform overcomes the limitations of previously reported phase-change valves in terms of compatibility with organic chemistry, and extends the range of reaction conditions for carrying out harsh batch chemistry at the microscale.

Asymmetric transport of water molecules through a hydrophobic conical channel

Unlike macroscale systems, symmetry breaking could lead to surprising results for nanoscale systems.

Biomolecular motors in nanoscale materials, devices, and systems

Biomolecular motors are a unique class of intracellular proteins that are fundamental to a considerable number of physiological functions such as DNA replication, organelle trafficking, and cell division. The efficient transformation of chemical energy into useful work by these proteins provides strong motivation for their utilization as nanoscale actuators in ex vivo, meso- and macro-scale hybrid systems. Biomolecular motors involved in cytoskeletal transport are quite attractive models within this context due to their ability to direct the transport of nano-/micro-scale objects at rates significantly greater than diffusion, and in the absence of bulk fluid flow. As in living organisms, biomolecular motors involved in cytoskeletal transport (i.e., kinesin, dynein, and myosin) function outside of their native environment to dissipatively self-assemble biological, biomimetic, and hybrid nanostructures that exhibit nonequilibrium behaviors such as self-healing. These systems also provide nanofluidic transport function in hybrid nanodevices where target analytes are actively captured, sorted, and transported for autonomous sensing and analytical applications. Moving forward, the implementation of biomolecular motors will continue to enable a wide range of unique functionalities that are presently limited to living systems, and support the development of nanoscale systems for addressing critical engineering challenges.

Organ‐on‐a‐chip technology and microfluidic whole‐body models for pharmacokinetic drug toxicity screening

Microscale cell culture platforms better mimic the in vivo cellular microenvironment than conventional, macroscale systems. Microscale cultures therefore elicit a more authentic response from cultured cells, enabling physiologically realistic in vitro tissue models to be constructed. The fabrication of interconnecting microchambers and microchannels allows drug absorption, distribution, metabolism and elimination to be simulated, and enables precise manipulation of fluid flow to replicate blood circulation. Complex, multi-organ interactions can be investigated using "organ-on-a-chip" toxicology screens. By reproducing the dynamics of multi-organ interaction, the dynamics of various diseases and drug activities can be studied in mechanistic detail. In this review, we summarize the current status of technologies related to pharmacokinetic-based drug toxicity testing, and the use of microtechnology for reproducing the interaction between multiple organs.

증발 코팅법으로 증착된 광유와 실리콘 오일 윤활제의 마찰 저감 특성

As the size of mechanical components decreases, capillary forces and surface tension become increasingly significant. A major problem in maintaining high reliability of these small components is that of large frictional forces due to capillary action and surface tension. Unlike the situation with macro-scale systems, liquid lubrication cannot be used to reduce friction of micro-scale components because of the excessive capillary and drag forces. In this work, the feasibility of using evaporation to coat a thin film of organic lubricant on a solid surface was investigated with the aim of reducing friction. Petroleum and silicone oils were used as lubricants to coat a silicon substrate. It was found that friction could be significantly reduced and, furthermore, that the effectiveness of this method was strongly dependent on the coating conditions.

Sliding and rolling frictional behavior of a single ZnO nanowire during manipulation with an AFM

The frictional behavior during manipulation of a single ZnO nanowire with a mass of about 18.7 ng placed horizontally on a Si wafer was examined using atomic force microscopy (AFM). The frictional force measured was in the range of 36.4 nN to 69.3 nN, which corresponded to extremely high friction coefficients of 242 and 462, respectively. However, when the adhesion force of the nanowire was considered, the friction coefficients were similar to the values typically encountered in macro-scale systems. During manipulation of the nanowire, both rolling and sliding motions were observed depending on the nanowire-Si frictional interaction. Unlike macro-scale systems, the difference between the frictional forces of rolling/sliding and pure sliding motions of the nanowire was not drastic.

Near-grazing dynamics of base excited cantilevers with nonlinear tip interactions

In this article, nonsmooth dynamics of impacting cantilevers at different scales is explored through a combination of analytical, numerical, and experimental efforts. For off-resonance and harmonic base excitations, period-doubling events close to grazing impacts are experimentally studied in a macroscale system and a microscale system. The macroscale test apparatus consists of a base excited aluminum cantilever with attractive and repulsive tip interactions. The attractive force is generated through a combination of magnets, one located at the cantilever structure’s tip and another attached to a high-resolution translatory stage. The repulsive forces are generated through impacts of the cantilever tip with the compliant material that covers the magnet on the translatory stage. The microscale system is an atomic force microscope cantilever operated in tapping mode. In this mode, this microcantilever experiences a long-range attractive van der Waals force and a repulsive force as the cantilever tip comes close to the sample. The qualitative changes observed in the experiments are further explored through numerical studies, assuming that the system response is dominated by the fundamental cantilever vibratory mode. In both the microscale and macroscale cases, contact is modeled by using a quadratic repulsive force. A reduced-order model, which is developed on the basis of a single mode approximation, is employed to understand the period-doubling phenomenon experimentally observed close to grazing in both the macroscale and microscale systems. The associated near-grazing dynamics is examined by carrying out local analyses with Poincare map constructions to show that the observed period-doubling events are possible for the considered nonlinear tip interactions. In the corresponding experiments, the stability of the observed grazing periodic orbits has been assessed by constructing the Jacobian matrix from the experimentally obtained Poincare map. The present study also sheds light on the use of macroscale systems to understand near-grazing dynamics in microscale systems.