Microscale Technologies Research Articles

Emerging Technologies in Medical Applications of Minimum Volume Vitrification

Cell/tissue biopreservation has broad public health and socio-economic impact affecting millions of lives. Cryopreservation technologies provide an efficient way to preserve cells and tissues targeting the clinic for applications including reproductive medicine and organ transplantation. Among these technologies, vitrification has displayed significant improvement in post-thaw cell viability and function by eliminating harmful effects of ice crystal formation compared to the traditional slow freezing methods. However, high cryoprotectant agent concentrations are required, which induces toxicity and osmotic stress to cells and tissues. It has been shown that vitrification using small sample volumes (i.e., <1 µl) significantly increases cooling rates and hence reduces the required cryoprotectant agent levels. Recently, emerging nano- and micro-scale technologies have shown potential to manipulate picoliter to nanoliter sample sizes. Therefore, the synergistic integration of nanoscale technologies with cryogenics has the potential to improve biopreservation methods.

Spontaneous Self-Organization Enables Dielectrophoresis of Small Nanoparticles and Formation of Photoconductive Microbridges

Detailed understanding of the mechanism of dielectrophoresis (DEP) and the drastic improvement of its efficiency for small size-quantized nanoparticles (NPs) open the door for the convergence of microscale and nanoscale technologies. It is hindered, however, by the severe reduction of DEP force in particles with volumes below a few hundred cubic nanometers. We report here DEP assembly of size-quantized CdTe nanoparticles (NPs) with a diameter of 4.2 nm under AC voltage of 4-10 V. Calculations of the nominal DEP force for these NPs indicate that it is several orders of magnitude smaller than the force of the Brownian motion destroying the assemblies even for the maximum applied AC voltage. Despite this, very efficient formation of NP bridges between electrodes separated by a gap of 2 μm was observed even for AC voltages of 6 V and highly diluted NP dispersions. The resolution of this conundrum was found in the intrinsic ability of CdTe NPs to self-assemble. The species being assembled by DEP are substantially bigger than the individual NPs. DEP assembly should be treated as a process taking place for NP chains with a length of ~140 nm. The self-assembled chains increase the nominal volume where the polarization of the particles takes place, while retaining the size-quantized nature of the material. The produced NP bridges were found to be photoactive, producing photocurrent upon illumination. DEP bridges of quantum confined NPs can be used in fast parallel manufacturing of novel MEMS components, sensors, and optical and optoelectronic devices. Purposeful engineering of self-assembling properties of NPs makes possible further facilitation of the DEP and increase of complexity of the produced nano- and microscale structures.

Particle streaming and separation using dielectrophoresis through discrete periodic microelectrode array

This study presents a particle manipulation and separation technique based on dielectrophoresis principle by employing an array of isosceles triangular microelectrodes on the bottom plate and a continuous electrode on the top plate. These electrodes generate non-uniform electric fields transversely across the microchannel. The particles within the flowing fluid experience a dielectrophoretic force perpendicular to the fluid flow direction due to the non-uniform electric fields. The isosceles triangular microelectrodes were designed to continuously exert a small dielectrophoretic force on the particles. Particles experiencing a larger dielectrophoretic force would move further in the perpendicular direction to the fluid flow as they traveled past each microelectrode. Polystyrene microspheres were used as the model particles, with particles of ∅20 μm employed for studying the basic characteristics of this technique. Particle separation was subsequently demonstrated on ∅10 and ∅15 μm microspheres. Using an applied sinusoidal voltage of 20 Vpp and frequency of 1 MHz, a mean separation distance of 0.765 mm between them was achieved at a flow rate of 3 μl/min (~1 mm/s), an important consideration for high throughput separation capability in a micro-scale technology device. This unique isosceles triangular microelectrodes design allows heterogeneous particle populations to be separated into multiple streams in a single continuous operation.

Microscale Technologies and Modular Approaches for Tissue Engineering: Moving toward the Fabrication of Complex Functional Structures

Micro- and nanoscale technologies have emerged as powerful tools in the fabrication of engineered tissues and organs. Here we focus on the application of these techniques to improve engineered tissue architecture and function using modular and directed self-assembly and highlight the emergence of this new class of materials for biomedical applications.

Three-dimensional biodegradable microscaffolding: Scaffold characterization and cell population at single cell resolution

Engineering artificial tissue scaffolds with a similar organization to that of the natural tissue is a key element to the successful recapitulation of function. However, three-dimensional (3-D) fabrication of tissue scaffolds containing complex microarchitectures still remains a challenge. In addition, little attention has been paid to the issue of how to incorporate cells within 3-D tissue scaffolds that contain precisely engineered architectures. Here we report a 3-D biodegradable microscaffolding (3D-BMS) technology and its process characterization as well as a microscale cellular loading technology as an efficient way to massively populate biodegradable polymers with cells at single cell resolution. In this study a particular emphasis was given to characterization of the material properties of the biodegradable polymers undergoing the 3D-BMS processes. Optimal process conditions were identified in order to avoid any unwanted change in material properties, such as crystallinity and scaffold strength, that have a direct impact on the degradation speed and physical integrity of the constructed scaffolds. For precise control of the cell distribution within the microstructured scaffolds a high precision microsieve structure was designed to localize rat hepatocytes and human articular chondrocytes in the biodegradable polymers. Cell suspensions were passed at a predetermined flow rate through biodegradable polymer layers that contained tapered microholes in a massively parallel process. This high resolution cell seeding method allows accurate manipulation of cell placement in thin layers of biodegradable polymers.

NANO/MICROSCALE TECHNOLOGIES FOR DRUG DELIVERY

Nano- and microscale technologies have made a marked impact on the development of drug delivery systems. The loading efficiency and particle size of nano/micro particles can be better controlled with these new technologies than conventional methods. Moreover, drug delivery systems are moving from simple particles to smart particles and devices with programmable functions. These technologies are also contributing to in vitro and in vivo drug testing, which are important to evaluate drug delivery systems. For in vitro tests, lab-on-a-chip models are potentially useful as alternatives to animal models. For in vivo test, nano/micro-biosensors are developed for testing chemicals and biologics with high sensitivity and selectivity. Here, we review the recent development of nanoscale and microscale technologies in drug delivery including drug delivery systems, in vitro and in vivo tests.

Sequential assembly of cell‐laden hydrogel constructs to engineer vascular‐like microchannels

Microscale technologies, such as microfluidic systems, provide powerful tools for building biomimetic vascular-like structures for tissue engineering or in vitro tissue models. Recently, modular approaches have emerged as attractive approaches in tissue engineering to achieve precisely controlled architectures by using microengineered components. Here, we sequentially assembled microengineered hydrogels (microgels) into hydrogel constructs with an embedded network of microchannels. Arrays of microgels with predefined internal microchannels were fabricated by photolithography and assembled into 3D tubular construct with multi-level interconnected lumens. In the current setting, the sequential assembly of microgels occurred in a biphasic reactor and was initiated by swiping a needle to generate physical forces and fluidic shear. We optimized the conditions for assembly and successfully perfused fluids through the interconnected constructs. The sequential assembly process does not significantly influence cell viability within the microgels indicating its promise as a biofabrication method. Finally, in an attempt to build a biomimetic 3D vasculature, we incorporated endothelial cells and smooth muscle cells into an assembled construct with a concentric microgel design. The sequential assembly is simple, rapid, cost-effective, and could be used for fabricating tissue constructs with biomimetic vasculature and other complex architectures.

In vitro platforms for tissue engineering: implications for basic research and clinical translation

Clinical translation of engineered tissues into regenerative medicine applications, and the effort to reduce the use of animals for the screening of drugs and other compounds, result in an increasing demand for human tissues engineered in vitro for implantation, in vitro screening systems and basic research. Further development and optimization of in vitro models for quantitative studies of biophysical stimulation and mass transport in engineered tissues is seen as one of the high research priorities. A recent international symposium held in The Netherlands discussed the state of the art and key challenges in the development of bioreactor platforms and microscale technologies. Here we summarize the current status and future development of in vitro tissue models, based on the findings presented at this symposium.

Cell patterning technologies for organotypic tissue fabrication

Bottom-up tissue engineering technologies address two of the main limitations of top-down tissue engineering approaches: the control of mass transfer and the fabrication of a controlled and functional histoarchitecture. These emerging technologies encompass mesoscale (e.g. cell sheets, cell-laden hydrogels and 3D printing) and microscale technologies (e.g. inkjet printing and laser-assisted bioprinting), which are used to manipulate and assemble cell-laden building blocks whose thicknesses correspond to the diffusion limit of metabolites, and present the capacity for cell patterning with microscale precision, respectively. Here, we review recent technological advances and further discuss how these technologies are complementary, and could therefore be combined for the biofabrication of organotypic tissues either in vitro, thus serving as realistic tissue models, or within a clinic setting.

Adaptive Movable Neural Interfaces for Monitoring Single Neurons in the Brain

Implantable microelectrodes that are currently used to monitor neuronal activity in the brain in vivo have serious limitations both in acute and chronic experiments. Movable microelectrodes that adapt their position in the brain to maximize the quality of neuronal recording have been suggested and tried as a potential solution to overcome the challenges with the current fixed implantable microelectrodes. While the results so far suggest that movable microelectrodes improve the quality and stability of neuronal recordings from the brain in vivo, the bulky nature of the technologies involved in making these movable microelectrodes limits the throughput (number of neurons that can be recorded from at any given time) of these implantable devices. Emerging technologies involving the use of microscale motors and electrodes promise to overcome this limitation. This review summarizes some of the most recent efforts in developing movable neural interfaces using microscale technologies that adapt their position in response to changes in the quality of the neuronal recordings. Key gaps in our understanding of the brain–electrode interface are highlighted. Emerging discoveries in these areas will lead to success in the development of a reliable and stable interface with single neurons that will impact basic neurophysiological studies and emerging cortical prosthetic technologies.

Linking nanotechnology to gigawatts: Creating building blocks for smart PV modules

AbstractCost reduction, expressed commonly as a unit cost/Wp on the level of solar cells, PV modules and systems, is the overarching theme of the major part of worldwide activities in the field of photovoltaics. Obviously, this is the condition sine qua non to be met for reaching economical viability of solar photovoltaic energy. We already outlined 1 earlier that a number of nanotechnologies developed for advanced Si‐based nanoscale CMOS transistors might also be very useful for the race toward crystalline Si solar cells with higher efficiency and lower cost. The focus on this cost parameter might, however, obscure the growing need to add more functionality to the PV system if photovoltaic energy is to play an important role in the electricity generation scenarios of the future 2. In the view of the authors much of this added functionality could be integrated at the module or even within the module by using a number of microscale and nanoscale technologies. This added functionality on PV‐module level might in first instance aim at an increase of energy yield by adding electronic components allowing to minimize the effect of shadowing losses by allowing a certain degree of reconfigurability of the PV module. Eventually, this might also reach out further by integrating the DC–AC inverter with the module (allowing to reduce DC losses) and in the end even other components integrating control and interaction functions with the electricity grid. In this paper we describe the philosophy behind the concept of the “Smart PV module” as well as two crucial technologies to realize this concept: the embedding technology for cells and components in the so‐called U module and the development of a low‐cost technology for reliable high‐power components based on GaN‐on‐Si, enabling the high‐frequency switching transistors in the DC–DC or DC–AC converters or the low‐loss switches in a “reconfigurable” U module. Besides the well‐spread conviction that nanotechnological aspects will lead to advances in terms of solar cell performance and lower cell costs, the message which we would like to convey is the fact that the development of miniaturized components using advances in micro‐ and nanotechnology are also very likely to affect the development of the “smart PV module” concept, providing ground for the statement “linking nanoscale to gigawatts.” Copyright © 2010 John Wiley &amp; Sons, Ltd.

Integration of in silico and in vitro platforms for pharmacokinetic–pharmacodynamic modeling

Importance of the field: Pharmacokinetic–pharmacodynamic (PK-PD) modeling enables quantitative prediction of the dose–response relationship. Recent advances in microscale technology enabled researchers to create in vitro systems that mimic biological systems more closely. Combination of mathematical modeling and microscale technology offers the possibility of faster, cheaper and more accurate prediction of the drug's effect with a reduced need for animal or human subjects.Areas covered in this review: This article discusses combining in vitro microscale systems and PK-PD models for improved prediction of drug's efficacy and toxicity. First, we describe the concept of PK-PD modeling and its applications. Different classes of PK-PD models are described. Microscale technology offers an opportunity for building physical systems that mimic PK-PD models. Recent progress in this approach during the last decade is summarized.What the reader will gain: This article is intended to review how microscale technology combined with cell cultures, also known as ‘cells-on-a-chip’, can confer a novel aspect to current PK-PD modeling. Readers will gain a comprehensive knowledge of PK-PD modeling and ‘cells-on-a-chip’ technology, with the prospect of how they may be combined for synergistic effect.Take home message: The combination of microscale technology and PK-PD modeling should contribute to the development of a novel in vitro/in silico platform for more physiologically-realistic drug screening.

SI traceability: Current status and future trends for forces below 10 microNewtons

Measurements related to nano- and micro-scale science, technology, and manufacturing are pushing the limits of detectable mechanical, electrical, and chemical quantities to ever smaller values, raising questions about traceability on such scales. The case in small force measurement is illustrative. At present, the mechanical unit of force is linked to the International Prototype Kilogram, or a deadweight force of nearly 10 N. Although known with exquisite accuracy on this scale, such a mass-based force standard is of little use to investigators and manufacturers using instruments that can determine quantities twelve orders of magnitude smaller. Recognizing this situation, the world congress of the International Measurement Confederation (IMEKO) convened a round table of researchers from National Metrology Institutes representing the US, Europe, and Asia to provide an overview of the emerging field of low-force metrology. This paper captures the information shared in that round table and amplifies on its content.

Arraycount, an Algorithm for Automatic Cell Counting in Microwell Arrays

Microscale technologies have emerged as a powerful tool for studying and manipulating biological systems and miniaturizing experiments. However, the lack of software complementing these techniques has made it difficult to apply them for many high-throughput experiments. This work establishes Arraycount, an approach to automatically count cells in microwell arrays. The procedure consists of fluorescent microscope imaging of cells that are seeded in microwells of a microarray system and then analyzing images via computer to recognize the array and count cells inside each microwell. To start counting, green and red fluorescent images (representing live and dead cells, respectively) are extracted from the original image and processed separately. A template-matching algorithm is proposed in which pre-defined well and cell templates are matched against the red and green images to locate microwells and cells. Subsequently, local maxima in the correlation maps are determined and local maxima maps are thresholded. At the end, the software records the cell counts for each detected microwell on the original image in high-throughput. The automated counting was shown to be accurate compared with manual counting, with a difference of approximately 1-2 cells per microwell: based on cell concentration, the absolute difference between manual and automatic counting measurements was 2.5-13%.

Microengineered Platforms for Cell Mechanobiology

Mechanical forces play important roles in the regulation of various biological processes at the molecular and cellular level, such as gene expression, adhesion, migration, and cell fate, which are essential to the maintenance of tissue homeostasis. In this review, we discuss emerging bioengineered tools enabled by microscale technologies for studying the roles of mechanical forces in cell biology. In addition to traditional mechanobiology experimental techniques, we review recent advances of microelectromechanical systems (MEMS)-based approaches for cell mechanobiology and discuss how microengineered platforms can be used to generate in vivo-like micromechanical environment in in vitro settings for investigating cellular processes in normal and pathophysiological contexts. These capabilities also have significant implications for mechanical control of cell and tissue development and cell-based regenerative therapies.

Modelling tissues in 3D: the next future of pharmaco-toxicology and food research?

The development and validation of reliable in vitro methods alternative to conventional in vivo studies in experimental animals is a well-recognised priority in the fields of pharmaco-toxicology and food research. Conventional studies based on two-dimensional (2-D) cell monolayers have demonstrated their significant limitations: the chemically and spatially defined three-dimensional (3-D) network of extracellular matrix components, cell-to-cell and cell-to-matrix interactions that governs differentiation, proliferation and function of cells in vivo is, in fact, lost under the simplified 2-D condition. Being able to reproduce specific tissue-like structures and to mimic functions and responses of real tissues in a way that is more physiologically relevant than what can be achieved through traditional 2-D cell monolayers, 3-D cell culture represents a potential bridge to cover the gap between animal models and human studies. This article addresses the significance and the potential of 3-D in vitro systems to improve the predictive value of cell-based assays for safety and risk assessment studies and for new drugs development and testing. The crucial role of tissue engineering and of the new microscale technologies for improving and optimising these models, as well as the necessity of developing new protocols and analytical methods for their full exploitation, will be also discussed.

Tribology in biology

Man has conducted research in the field of tribology for several thousands of years. Nature has been producing lubricants and adhesives for millions of years. Biotribologists gather information about biological surfaces in relative motion, their friction, adhesion, lubrication and wear, and apply this knowledge to technological innovation as well as to the development of environmentally sound products. Ongoing miniaturisation of technological devices such as hard disk drives and biosensors increases the necessity for the fundamental understanding of tribological phenomena at the micro- and nanometre scale. Biological systems excel also at this scale and might serve as templates for developing the next generation of tools based on nano- and microscale technologies. Examples of systems with optimised biotribological properties are: articular cartilage, a bioactive surface which has a friction coefficient of only 0·001; adaptive adhesion of white blood cells rolling along the layer of cells that lines blood vessels in response to inflammatory signals; and diatoms, micrometre sized glass making organisms that have rigid parts in relative motion. These and other systems have great potential to serve as model systems also for innovations in micro- and nanotechnology.

Screening the Cellular Microenvironment: A Role for Microfluidics

The cellular microenvironment is an increasingly discussed topic in cell biology as it has been implicated in the progression of cancer and the maintenance of stem cells. The microenvironment of a cell is an organized combination of extracellular matrix (ECM), cells, and interstitial fluid that influence cellular phenotype through physical, mechanical, and biochemical mechanisms. Screening can be used to map combinations of cells and microenvironments to phenotypic outcomes in a way that can help develop more predictive in vitro models and to better understand phenotypic mechanisms from a systems biology perspective. This paper examines microenvironmental screening in terms of outcomes and benefits, key elements of the screening process, challenges for implementation, and a possible role for microfluidics as the screening platform. To assess microfluidics for use in microenvironmental screening, examples and categories of micro-scale and microfluidic technology are highlighted. Microfluidic technology shows promise for simultaneous control of multiple parameters of the microenvironment and can provide a base for scaling advanced cell-based experiments into automated high-throughput formats.

Heat-Transfer Mechanism of Sample-Probe in Variable-Temperature Scanning Probe Microscope and Influence of Temperature on Tunneling Current

The macroscopical breakage and nature change of material usually originate in nanometer scale, and the nature of some materials depends on temperature strongly. So it is extremely important for the research of heat transfer in micro-scale and nanometer technology to understand and control the influence of temperature on the nature of material, and developing advanced measuring technique can also improve our knowledge on theories involved in such problem. Due to the usage of variable-temperature sample stage, utilizable range of temperature is widely extended, and thus topography images of materials changing with temperature can be observed so that the thermal properties of materials can be studied further. Accordingly, the theoretical basis of heat-transfer and the influence of temperature on tunneling current owing to temperature variation should be presented. In the view of microscale heat-transfer, this paper describes the problem that heat current transfers from surface of sample to tip of probe through layer of air by means of Boltzmann theory, which can be expressed by the hyperbolic equation of heat conduction when the time is nearly equivalent to slack time and the scale is much larger than the characteristic scale of local thermodynamic equilibrium. The mode of heat-transfer on probe is also analyzed and the analytical solution is obtained in the paper. In addition, the influence of temperature increment of sample on tunneling current is discussed in detail and the change trend of tunneling current with temperature is also obtained in a limited temperature range. Due to such factors, which are possible to disturb the topography images of sample, there is no doubt that many difficulties will be brought to developing new technology such as detecting displacement and strain of materials at microscale by using the images of sample heated and unheated. To understand and control such factors has important advantage for making progress in the advanced scientific fields.

1D Canonical and Perturbed Quantum Potential-well Problem: A Universal Function Approach

The limits of the current micro-scale electronics technology have been approaching rapidly. At nano-scale, however, the physical phenomena involved are fundamentally different than in micro-scale. Classical and semi-classical physical principles are no lo