Macro-scale Systems Research Articles

Orthogonal Cell‐Based Biosensing: Fluorescent, Electrochemical, and Colorimetric Detection with Silica‐Immobilized Cellular Communities Integrated with an ITO–Glass/Plastic Laminate Cartridge

This is the first report of a living cell-based environmental sensing device capable of generating orthogonal fluorescent, electrochemical, and colorimetric signals in response to a single target analyte in complex media. Orthogonality is enabled by use of cellular communities that are engineered to provide distinct signals in response to the model analyte. Coupling these three signal transduction methods provides additional and/or complementary data regarding the sample which may reduce the impact of interferants and increase confidence in the sensor's output. Long-term stability of the cells was addressed via 3D entrapment within a nanostructured matrix derived from glycerated silicate, which allows the device to be sealed and stored under dry, ambient conditions for months with significant retention in cellular activity and viability (40% viability after 60 days). Furthermore, the first co-entrapment of eukaryotic and bacterial cells in a silica matrix is reported, demonstrating multianalyte biodetection by mixing disparate cell lines at intimate proximities which remain viable and responsive. These advances in cell-based biosensing open intriguing opportunities for integrating living cells with nanomaterials and macroscale systems.

A time-of-flight flow sensor for the volume measurement of trace amount of interstitial fluid

Transdermal extraction of interstitial fluid (ISF) offers an attractive method for noninvasive blood glucose monitoring. The existing macroscale systems are not suitable for ISF collection, mainly because of the minute volume of the transdermally extracted ISF which scatters on the skin surface. Human skin's low permeability to glucose and its varying permeability exemplify the crucial need to make precise ISF volume measurements in order to calculate blood glucose concentrations accurately. In this paper, we present a novel time-of-flight flow sensor consisting of four electrode pairs fabricated directly into the channel of a polydimethylsiloxane (PDMS) microfluidic device designed to accurately measure the volume of transdermally extracted ISF. As fluid traverses the channel, it bridges each electrode pair and changes its resistance. By measuring the time difference in resistance change between each electrode pair, a precise fluid volume can be measured. In order to verify the suitability of the sensor for biological applications, experiments were conducted using a normal saline solution which is similar to ISF. The stability of the sensor was tested using a fixed volume, and the coefficient of variation for 20 tests was determined to be 0.0041. The consistency of the sensor for varied volume measurements was shown by the high correlation coefficient (R2 = 0.9992) between the tested volume and the volume measured by a commercial micro syringe. The excellent functionality of the flow sensor can be extended toward the measurement of conductive chemical and biochemical buffers and reagents.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation.

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Optimization and characterization of a microscale thermal field-flow fractionation system

A thorough investigation of the design considerations for microscale thermal field-flow fractionation and characterization of a 25μm thin microscale thermal field-flow fractionation system is reported. A 4–50 times volume reduction from mesoscale and macroscale systems warrants customized design and operational conditions for microscale separation systems. Theoretical calculations are done to illustrate the importance of the increased dispersion due to extra-column tubing, off-chip detection and sample injection volume with reduced channel dimensions. An optimized microscale thermal field-flow fractionation (ThFFF) channel is fabricated using rapid and cost effective manufacturing and assembly processes. Specifically, improvements in material selection and arrangement are implemented to achieve higher particle retentions. The new instrument arrangement includes high conductivity silicon as the cold wall and a thin polymer layer with low thermal conductivity as the hot wall which results in high temperature gradients (∼106°C/m) across the microchannel and subsequently high retention. Single particle retention separations are carried out with polystyrene nanoparticle samples in an aqueous carrier to characterize the device and demonstrate the improvements.

Microfluidic Bioreactors for Cell Culturing: A Review

The use of microfluidic bioreactor platforms for cell culturing holds considerable promise for a range of fields which include drug discovery, tissue engineering, bioprocessing optimisation and cell based screening studies. Microflu- idic bioreactor systems have length scales that are well matched to the physical dimensions of most cells and microorgan- isms. In view of this, microfluidic bioreactors have attractive features which make them ideal to study the behaviour of cells and their internal organisation in their native microenvironment. Due to their small footprint microbioreactor plat- forms offer a number of advantages over conventional macroscale systems including improved biological function, higher quality cell-based data, reduced volume of reagents, ease of integration and lower cost. This review highlights the basic concepts, designs and operational requirements of microbioreactors for cell based studies. An illustrative outline of differ- ent applications of microbioreactors and some indication of new trends and progress in recent years are provided. Specific examples of applications of microbioreactors are drawn for cytotoxicity assays, tissue engineering, stem cells, microbial fermentations, single cell analysis and in vitro fertilisation.

Noise influenced elastic cantilever dynamics with nonlinear tip interaction forces

In this work, the authors study the influence of noise on the dynamics of base-excited elastic cantilever structures at the macroscale and microscale by using experimental, numerical, and analytical means. The macroscale system is a base excited cantilever structure whose tip experiences nonlinear interaction forces. These interaction forces are constructed to be similar in form to tip interaction forces in tapping mode atomic force microscopy (AFM). The macroscale system is used to study nonlinear phenomena and apply the associated findings to the chosen AFM application. In the macroscale experiments, the tip of the cantilever structure experiences long-range attractive and short-range repulsive forces. There is a small magnet attached to the tip, and this magnet is attracted by another one mounted to a high-resolution translatory stage. The magnet fixed to the stage is covered by a compliant material that is periodically impacted by the cantilever’s tip. Building on their earlier work, wherein the authors showed that period-doubling bifurcations associated with near-grazing impacts occur during off-resonance base excitations of macroscale and microscale cantilevers, in the present work, the authors focus on studying the influence of Gaussian white noise when it is included as an addition to a deterministic base excitation input. The repulsive forces are modeled as Derjaguin–Muller–Toporov (DMT) contact forces in both the macroscale and microscale systems, and the attractive forces are modeled as van der Waals attractive forces in the microscale system and magnetic attractive forces in the macroscale system. A reduced-order model, based on a single mode approximation is used to numerically study the response for a combined deterministic and random base excitation. It is experimentally and numerically found that the addition of white Gaussian noise to a harmonic base excitation facilitates contact between the tip and the sample, when there was previously no contact with only the harmonic input, and results in a response that is nominally close to a period-doubled orbit. The qualitative change observed with the addition of noise is associated with near-grazing impacts between the tip and the sample. The numerical and experimental results further motivate the formulation of a general analytical framework, in which the Fokker–Planck equation is derived for the cantilever-impactor system. After making a set of approximations, the moment evolution equations are derived from the Fokker–Planck equation and numerically solved. The resulting findings support the experimental results and demonstrate that noise can be added to the input to facilitate contact between the cantilever’s tip and the surface, when there was previously no contact with only a harmonic input. The effects of Gaussian white noise are numerically studied for a tapping mode AFM application, and it is shown that contact between the tip and the sample can be realized by adding noise of an appropriate level to a harmonic excitation.

A microfluidic membrane device to mimic critical components of the vascular microenvironment

Vascular function, homeostasis, and pathological development are regulated by the endothelial cells that line blood vessels. Endothelial function is influenced by the integrated effects of multiple factors, including hemodynamic conditions, soluble and insoluble biochemical signals, and interactions with other cell types. Here, we present a membrane microfluidic device that recapitulates key components of the vascular microenvironment, including hemodynamic shear stress, circulating cytokines, extracellular matrix proteins, and multiple interacting cells. The utility of the device was demonstrated by measuring monocyte adhesion to and transmigration through a porcine aortic endothelial cell monolayer. Endothelial cells grown in the membrane microchannels and subjected to 20 dynes∕cm(2) shear stress remained viable, attached, and confluent for several days. Consistent with the data from macroscale systems, 25 ng∕ml tumor necrosis factor (TNF)-α significantly increased RAW264.7 monocyte adhesion. Preconditioning endothelial cells for 24 h under static or 20 dynes∕cm(2) shear stress conditions did not influence TNF-α-induced monocyte attachment. In contrast, simultaneous application of TNF-α and 20 dynes∕cm(2) shear stress caused increased monocyte adhesion compared with endothelial cells treated with TNF-α under static conditions. THP-1 monocytic cells migrated across an activated endothelium, with increased diapedesis in response to monocyte chemoattractant protein (MCP)-1 in the lower channel of the device. This microfluidic platform can be used to study complex cell-matrix and cell-cell interactions in environments that mimic those in native and tissue engineered blood vessels, and offers the potential for parallelization and increased throughput over conventional macroscale systems.

PCBMEMS as a Flexible Path to Devices and Systems across Spatial Scales

PCB technology based on both rigid and flexible laminates is desirable for miniaturization of mobile devices and systems. The technology provides substantial flexibility in systems design. The ability to use flexible microsystems allows new sensing systems for mobile applications. Using this design, fabrication and construction approach allows lightweight, complex, and space efficient systems. Flex microsystems based on structurable, non-fiber filled laminates permits miniaturization to occur at two levels: at the micro scale with the embedding of microstructures in the substrate, and at the macro scale with the ability to flex the system across millimeter to centimeter lengths of real everyday objects. The macro scale systems further allows ultra large systems with high resolution features permitting novel sensor systems. Examples will be given where the technology has enabled devices, systems and packaging innovation across several spatial scales. Mobile (environmental, medical, portable, embedded) sensor systems all can be realized using this design and fabrication toolbox.

Simulation-Based Robust Design of Multiscale Products

The current research proposes an integrated framework for product design that incorporates simulation-based tools into the early design stage to achieve optimum multiscale systems. The method to determine the appropriate cellular material-property relations for the internal material structures of the system is through a topology optimization technique and a multiscale design process. Specifically, the reliability-based topology optimization (RBTO) and a multi-attribute decision design method are integrated into the inductive design exploration method (IDEM). The RBTO method is introduced to determine optimal topologies at the mesoscale. The multi-attribute decision design method is used for decision support in the design process of the macroscale systems. IDEM offers the capability for concurrent design on multiple scales providing an approach for the integration of the other two methods. An example of the developed multiscale design framework is presented in terms of a hydrogen storage tank used in a hydrogen fuel cell for automotive applications. The multiscale tank design will feature a high strength cellular structured wall, resulting in a large weight reduction.

Integrated microbioreactor for culture and analysis of bacteria, algae and yeast

We introduce a micro-scale bioreactor for automated culture and density analysis of microorganisms. The microbioreactor is powered by digital microfluidics (DMF) and because it is used with bacteria, algae and yeast, we call it the BAY microbioreactor. Previous miniaturized bioreactors have relied on microchannels which often require valves, mixers and complex optical systems. In contrast, the BAY microbioreactor is capable of culturing microorganisms in distinct droplets on a format compatible with conventional bench-top analyzers without the use of valves, mixers or pumps. Bacteria, algae and yeast were grown for up to 5days with automated semi-continuous mixing and temperature control. Cell densities were determined by measuring absorbances through transparent regions of the devices, and growth profiles were shown to be comparable to those generated in conventional, macro-scale systems. Cell growth and density measurements were integrated in the microbioreactor with a fluorescent viability assay and transformation of bacteria with a fluorescent reporter gene. These results suggest that DMF may be a useful new tool in automated culture and analysis of microorganisms for a wide range of applications.

Biased transportations in a spatially asymmetric system at the nano-scale under thermal noise

Under the theory of ratchet effect for meso- and macro-scale systems, the additional perturbation with a long time correlation and the breaking of spatial inversion symmetry are two main ingredients to bring unidirected transportations. With the help of a simple model system, we show that a spatially asymmetric system of the nano-scale length may induce biased transportations under thermal noise.

Perspectives on Utilizing Unique Features of Microfluidics Technology for Particle and Cell Sorting

Sample preparation is often the most tedious and demanding step in an assay, but it also plays an essential role in determining the quality of results. As biological questions and analytical methods become increasingly sophisticated, there is a rapidly growing need for systems that can reliably and reproducibly separate cells and particles with high purity, throughput and recovery. Microfluidics technology represents a compelling approach in this regard, allowing precise control of separation forces for high performance separation in inexpensive, or even disposable, devices. In addition, microfluidics technology enables the fabrication of arrayed and integrated systems that operate either in parallel or in tandem, in a capacity that would be difficult to achieve in macro-scale systems. In this report, we use recent examples from our work to illustrate the potential of microfluidic cell- and particle-sorting devices. We demonstrate the potential of chip-based high-gradient magnetophoresis that enable high-purity separation through reversible trapping of target particles paired with high-stringency washing with minimal loss. We also describe our work in the development of devices that perform simultaneous multi-target sorting, either through precise control of magnetic and fluidic forces or through the integration of multiple actuation forces into a single monolithic device. We believe that such devices may serve as a powerful "front-end" module of highly integrated analytical platforms capable of providing actionable diagnostic information directly from crude, unprocessed samples - the success of such systems may hold the key to advancing point-of-care diagnostics and personalized medicine.

On-chip cooling by superlattice-based thin-film thermoelectrics

There is a significant need for site-specific and on-demand cooling in electronic, optoelectronic and bioanalytical devices, where cooling is currently achieved by the use of bulky and/or over-designed system-level solutions. Thermoelectric devices can address these limitations while also enabling energy-efficient solutions, and significant progress has been made in the development of nanostructured thermoelectric materials with enhanced figures-of-merit. However, fully functional practical thermoelectric coolers have not been made from these nanomaterials due to the enormous difficulties in integrating nanoscale materials into microscale devices and packaged macroscale systems. Here, we show the integration of thermoelectric coolers fabricated from nanostructured Bi2Te3-based thin-film superlattices into state-of-the-art electronic packages. We report cooling of as much as 15 degrees C at the targeted region on a silicon chip with a high ( approximately 1,300 W cm-2) heat flux. This is the first demonstration of viable chip-scale refrigeration technology and has the potential to enable a wide range of currently thermally limited applications.

A prototype microfluidic chip using fluorescent yeast for detection of toxic compounds

A microfluidic chip has been developed to enable the screening of chemicals for environmental toxicity. The microfluidic approach offers several advantages over macro-scale systems for toxicity screening, including low cost and flexibility in design. This design flexibility means the chips can be produced with multiple channels or chambers which can be used to screen for different toxic compounds, or the same toxicant at different concentrations. Saccharomyces cerevisiae containing fluorescent markers are ideal candidates for the microfluidic screening system as fluorescence is emitted without the need of additional reagents. Microfluidic chips containing eight multi-parallel channels have been developed to retain yeast within the chip and allow exposure of them to toxic compounds. The recombinant yeast used was GreenScreen™ which expresses green fluorescent proteins when is exposed to genotoxins. After exposure of the yeast to target compounds, the fluorescence emission was detected using an inverted microscope. Qualitative and quantitative comparisons of the fluorescent emission were performed. Results indicated that fluorescent intensity per area significantly increases upon exposure to methyl-methanesulfonate, a well known genotoxic compound. The microfluidic approach reported here is an excellent tool for cell-based screening and detection of different toxicities. The device has the potential for use by industrial manufacturers to detect and reduce the production and discharge of toxic compounds, as well as to characterise already polluted environments.

Modeling multiscale diffusion processes in random heterogeneous media

A simple stochastic up-scaling strategy is presented for incorporating the effects of micro-scale variations of thermal conductivity in the thermal analysis of macro-scale systems. Incomplete characterization of the fine-scale variation necessitates posing the thermal conductivity as a stochastic multiscale random field. A data-driven approach coupled with a non-linear dimension reduction algorithm is used to construct a low-dimensional stochastic descriptor of the fine-scale variation of the stochastic conductivity. A representative volume element (RVE) argument is utilized to construct a simple model for up-scaling the stochastic thermal conductivity. In this model, the effective stochastic thermal conductivity is estimated by virtually interrogating the stochastic RV. A realistic example of the proposed stochastic multiscale diffusion strategy is illustrated utilizing limited experimental data.

A Point-Wise Model of Adhesion Suitable for Real-Time Applications of Bio-Inspired Climbing Robots

Bio-inspired climbing robots relying on adhesion systems are believed to become essential tools for several industrial applications in the near future. In recent years, research has mainly focused on modeling micro-scale adhesion phenomena; a macro-scale adhesion model has however to be developed for the design of macro-scale systems. In this paper a macro-model of adhesion suitable for real-time applications is presented; it relies on a continuous representation of adhesion. An extension of the von Mises criterion is proposed as failure adhesion criterion in order to estimate the occurrence of detachment at any point of the contacting surface. An experimental set up has been designed in order to define the parameters of the model. A semi-automatic process has been developed to ensure repeatability and accuracy of the results. Polydimethylsiloxane (PDMS), which has revealed promising adhesive features for robotic use, has been used during the experimental phase. The macro-model of adhesion has been implemented in a multi-body dynamics environment based on Open Dynamics Engine (ODE) to simulate a spider-inspired robot. Simulations based on this model are suitable to represent the behaviour of climbing robots and also to optimize their design.

Miniaturisation of analytical steps: necessity and snobbism

Automation and miniaturization were two widespread trends implicitly included in the research priorities of most scientific fields in the last few decades of the twentieth century. One result of the latter trend was the development of microtechnology, which has by now been superseded by nanotechnology by virtue of the advantages of small devices over macroscale systems. Analytical chemistry has also taken advantage of these trends in general and of nanotechnology in particular. The advantages thus gained include accurate spatial control over reagents and samples, increased throughput, automatability—which is absolutely mandatory, the ability to handle picoliter volumes of undiluted reactants—which saves reagents and sample, compatibility with a wide range of detection systems, the availability of a variety of materials for manufacturing at relatively low cost, design flexibility, the ability to perform multiple tasks (e.g. for the simultaneous development of several sample-preparation steps such as dissolution, extraction, or preconcentration) and improvements derived from the reduced dimensions used (e.g. in nanochromatography or chip-based separations). The development of portable miniaturized devices has facilitated the decentralization of analyses, a primary goal for this century, by enabling real time, in situ, on-line, in-vivo monitoring of processes without the need for skilled operators or special equipment [1]. There is no doubt that miniaturization and nanotechnology have contributed enormously to the emergence and development of new research areas which have brought about true revolutions, particularly in bioanalysis.

Chip integrated strategies for acoustic separation and manipulation of cells and particles

Acoustic standing wave technology combined with microtechnology opens up new areas for the development of advanced particle and cell separating microfluidic systems. This tutorial review outlines the fundamental work performed on continuous flow acoustic standing wave separation of particles in macro scale systems. The transition to the microchip format is further surveyed, where both fabrication and design issues are discussed. The acoustic technology offers attractive features, such as reasonable throughput and ability to separate particles in a size domain of about tenths of micrometers to tens of micrometers. Examples of different particle separation modes enabled in microfluidic chips, utilizing standing wave technology, are described along a discussion of several potential applications in life science research and in the medical clinic. Chip integrated acoustic standing wave separation technology is still in its infancy and it can be anticipated that new laboratory standards very well may emerge from the current research.

Chitosan: a soft interconnect for hierarchical assembly of nano-scale components.

Traditional microfabrication has tremendous capabilities for imparting order to hard materials (e.g., silicon wafers) over a range of length scales. However, conventional microfabrication does not provide the means to assemble pre-formed nano-scale components into higher-ordered structures. We believe the aminopolysaccharide chitosan possesses a unique set of properties that enable it to serve as a length-scale interconnect for the hierarchical assembly of nano-scale components into macro-scale systems. The primary amines (atomic length scale) of the glucosamine repeating units (molecular length scale) provide sites to connect pre-formed or self-assembled nano-scale components to the polysaccharide backbone (macromolecular length scale). Connections to the backbone can be formed by exploiting the electrostatic, nucleophilic, or metal-binding capabilities of the glucosamine residues. Chitosan's film-forming properties provide the means for assembly at micron-to-centimetre lengths (supramolecular length scales). In addition to interconnecting length scales, chitosan's capabilities may also be uniquely-suited as a soft component-hard device interconnect. In particular, chitosan's film formation can be induced under mild aqueous conditions in response to localized electrical signals that can be imposed from microfabricated surfaces. This capability allows chitosan to assemble soft nano-scale components (e.g., proteins, vesicles, and virus particles) at specific electrode addresses on chips and in microfluidic devices. Thus, we envision the potential that chitosan may emerge as an integral material for soft matter (bio)fabrication.

Utilising μ-PIV and pressure measurements to determine the viscosity of a DNA solution in a microchannel

There is currently considerable interest in the development of micro-scale polymerase chain reaction (PCR) systems. Smaller sample volumes are required than for macro-scale systems, and faster process times are feasible. Although much attention has focused on the output of micro-PCR (μ-PCR), little attention has been devoted to the detailed fluid mechanics of such devices. There are many technical challenges associated with systems of these length scales. In this paper the effect of PCR on biofluid viscosity is examined. A theoretical expression for viscosity in PCR is derived. Transmission electron microscopy is used to determine the geometry of a 240 base pair segment of an Escherichia coli ( E. coli) DNA molecule and the results are used to predict the effect of PCR on biofluid viscosity. Micro-particle image velocimetry (μ-PIV) and pressure transducer measurements of water, amplified and unamplified E. coli DNA solutions flowing in a polycarbonate microchannel are recorded. In a novel application of these established measurement techniques, the results are combined with curve fitting of a theoretical prediction for channel flow to estimate the viscosity of the E. coli solutions. The viscosity results are compared to the theoretical prediction for PCR viscosity and to measurements in a commercial viscometer. Viscosity measurements indicated no increase in fluid viscosity after PCR for a low molecular weight molecule.