Archive for the ‘Hot Articles’ Category

New microfluidic system for intracochlear drug delivery

William Sewell at Massachusetts Eye and Ear Infirmary and Harvard Medical School and Jeffrey Borenstein at the Charles Stark Draper Laboratory in Massachusetts have developed an automated micropump device for direct delivery of drugs into the perilymph fluid within the cochlea. This has potential for use in the treatment of sensorineural hearing loss and would remove the toxicity issues that are common when drugs are administered systemically. This is one of the most common forms of hearing loss and is caused by damage to the sensory hair cells or to the auditory nerve.

Components of the device and process flow for one drug delivery cycle

Due to the small volumes of perilymph fluid within the cochlea (~ 0.2 mL) and the sensitivity of the ear, the authors have developed a reciprocating delivery system, where an accurate volume of the concentrated drug can be infused and, once given time to distribute, the same volume of fluid can be withdrawn, resulting in zero overall net increase in cochlear fluid. The specific design also minimised the dead volume present in the device in order to reduce the amount of pumping needed, and by incorporating capacitors, prevented high flow rates during pumping, which can lead to cochlear damage.

The authors emphasise the need for a device that is small and lightweight enough to be implanted near to the cochlea and that is also able to administer precise sub-microliter volumes of fluid over several days or months. The microfluidic device presented in Lab on a Chip has been fabricated onto a ~4 x 3 cm chip and is capable of delivering accurate and repeatable volumes of fluid over more than 1000 pump strokes. The authors highlight that by incorporating the device onto a head mount, this particular design could be used in animal models for preclinical drug characterisation, where extensive studies are required.

All the fluidic components of this system have been incorporated into the chip, so that, if battery operated, it could be used as a stand-alone device. In this design, a separate controller was used; however, it is stated that the control circuitry could also be miniaturised and incorporated into the chip, for use with a battery. Efforts were also made to minimise the power consumption of the pump for this purpose. The main components of the device are a drug reservoir, a fluid storage capacitor which contains artificial perilymph for flushing the system, an infuse-withdraw line, and multiple valves to control the different steps of the drug delivery process, as shown in the diagram.

Dose control was successfully demonstrated by loading the pump with fluorescein as the test drug and monitoring the fluorescence of the aliquots collected following different dosage schemes. Several studies were also carried out on guinea pigs using a glutamate receptor antagonist as the test drug. This compound reversibly suppresses compound action potentials (CAPs) in the cochlea – monitoring changes in CAP amplitude and threshold can be used to test for hearing loss.

The results showed that fully reversible hearing loss was induced and this was used to estimate the optimum wait time between infusion and withdrawal for the reciprocating delivery. The distribution of the drug in the ear was also monitored by measuring changes to CAPs at different frequencies and comparing these to the known tonotopic organisation of the cochlea. To test for cochlear damage, the authors monitored another hearing response (distortion product otoacoustic emission) that was not expected to change, and determined that there was no acute mechanical damage.

This drug delivery system has excellent potential for use in clinical and preclinical trials and also for long term treatment of hearing loss using existing drugs. The potential for battery operation is particularly important, and is an aspect that the authors are now focusing on for future work.


To download the full article for free* click the link below:

Microfabricated reciprocating micropump for intracochlear drug delivery with integrated drug/fluid storage and electronically controlled dosing
Vishal Tandon, Woo Seok Kang, Tremaan A. Robbins, Abigail J. Spencer, Ernest S. Kim, Michael J. McKenna, Sharon G. Kujawa, Jason Fiering,  Erin E. L. Pararas, Mark J. Mescher, William F. Sewell, Jeffrey T. Borenstein
Lab Chip, 2016, 16, 829-846
DOI: 10.1039/C5LC01396H

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About the webwriter

Claire Weston is a PhD student in the Fuchter Group, at Imperial College London. Her work is focused on developing novel photoswitches and photoswitchable inhibitors.

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*Access is free until 05/04/2016 through a registered RSC account.

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Optimising the conditions for biocrude formation using microfluidics

If the Lab on a Chip HOT articles are anything to go by, using microalgae as a feedstock for biofuel is definitely a flourishing research area.  Microalgae is a particularly attractive feedstock as it grows rapidly, has a large oil content, and can be grown pretty much anywhere.

David Sinton and co-workers at the University of Toronto have previously published in Lab on a Chip on this topic and have now reported their work on optimising the conditions for converting microalgae ‘biomass’ into crude biofuel (‘biocrude’). The process by which this is achieved is known as hydrothermal liquefaction. High temperatures and pressures are employed to break down the organic compounds from the biomass into the oils that make up biocrude.

a) Fluorescence images at increasing reaction time; b) Fluorescence and dark-field imaging of fluids at inlet and outlet.

The Sinton lab have developed a microfluidic chip in order to accurately control the reaction conditions of this process and also to study the effect of changing conditions on the biofuel that is formed. The continuous flow and small volume of the chip allow very fast heating of the algal slurry so reaction times can be accurately studied – in fact the heating rate achieved is the fastest reported to date. The slurry was analysed in situ by fluorescence imaging and changes to the fluorescence signature were monitored. Over the course of the reaction, the fluorescence signal due to chlorophyll disappeared and a new peak developed, indicating the formation of the aromatic compounds that are a characteristic component of crude oil and plant based oils.

Further analysis of the samples collected from the chip outlet found that the energy content (measured by the elemental composition) of the biocrude reached saturation after short reaction times – much before the fluorescence signal stopped changing. In addition to this, non-fluorescent droplets could be seen inside the reaction chamber, as shown in the diagram on the left, which were presumed to comprise of aliphatic oils. These findings indicate that analysis of the elemental composition alone is insufficient to measure chemical conversion to biocrude and methods such as fluorescence imaging should also be employed.

This work is the first example of using a microfluidic platform in hydrothermal liquefaction research and just goes to highlight the versatility of lab-on-a-chip systems.

To download the full article for free* click the link below:

Biomass-to-biocrude on a chip via hydrothermal liquefaction of algae
Xiang Cheng, Matthew D. Ooms and David Sinton
Lab Chip, 2016, 16, 256-260
DOI: 10.1039/C5LC01369K

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About the webwriter

Claire Weston is a PhD student in the Fuchter Group, at Imperial College London. Her work is focused on developing novel photoswitches and photoswitchable inhibitors.

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*Access is free through a registered RSC account until 29/02/2016.

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Differentiation of stem cells into beating cardiac tissues on paper!

The Biomicrofluidics System Group at the Dalian Institute of Chemical Physics in China have published an exciting paper in Lab on a Chip where they have used paper as a material to grow and differentiate human pluripotent stem cells.

Recently, there has been much research into generating biocompatible materials for creating microenvironments for the growth of stem cells, with the aim of improving their regenerative potential. Using paper as the material has several advantages over the conventional polymers – it is cheap and readily available, it is biocompatible, and the bundles of cellulose microfibers that make up paper provide a porous 3D structure.

Identification of cardiomyocytes derived from pluripotent stem cells on paper

The authors used three different types of paper to identify which were best for stem cell growth – printing paper, filter paper, and nitrocellulose membrane. The paper was pre-coated with the required gels and the stem cells were seeded onto the surface. Initially, the stem cells were differentiated into cardiomyocytes prior to being added to the paper to test if the differentiated cells were able to grow on the different types of paper. The cells aggregated on both printing and filter paper and demonstrated spontaneous beating function, but not on the nitrocellulose membrane. These tissues also maintained their beating function for up to three months. The stem cells were then added to the paper prior to differentiation and the required cardiac differentiation procedures were carried out. The cells differentiated to the cardiomyocytes on all three paper types, however the cardiac-specific marker was only expressed weakly on the nitrocellulose membrane. Within two weeks a strong beating function was observed for the printing paper, but not the other paper types. The authors suggest the printing paper had a better pore size to support the cells than the filter paper, while the nitrocellulose membrane didn’t have a favourable microstructure to support growth of cardiac tissue.

Along with this article, there are some impressive videos showing the cardiac tissue beating that are well worth a watch!

To download the full article for free* click the link below:

Human induced pluripotent stem cell-derived beating cardiac tissues on paper
Li Wang, Cong Xu, Yujuan Zhu, Yue Yu, Ning Sun, Xiaoqing Zhang, Ke Feng and Jianhua Qin
Lab Chip,
2015, 15 , 4283-4290
DOI:
10.1039/C5LC00919G

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About the webwriter

Claire Weston is a PhD student in the Fuchter Group, at Imperial College London. Her work is focused on developing novel photoswitches and photoswitchable inhibitors.

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*Access is free through a registered RSC account until 18/12/2015  – click here to register

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Microscopic pumps made from trapped bacteria

Scientists in China have trapped bacteria in 3D-printed structures and used them to pump materials along customised paths.

Transporting materials in the microscopic world is complex. Conventionally, macroscopic pumps drive motion, but pumps are bulky and not ideal for miniaturisation. Now, Hepeng Zhang and colleagues at Shanghai Jiao Tong University have tackled this problem using native inhabitants of the microscopic world – motile bacteria. Not only are they already present in the media, but their energy conversion efficiency is estimated to be greater than existing man-made micro-motors.

Please visit Chemistry World to read the full article.

Using confined bacteria as building blocks to generate fluid flow
Zhiyong Gao, He Li, Xiao Chen and H. P. Zhang
Lab Chip, 2015, Advance Article
DOI: 10.1039/C5LC01093D

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New method for studying microalgal growth

The device

The study and optimisation of microalgal growth is a hot topic at the moment due to the use of microalgae in many industrial processes, as well as its potential use as biofuel. Previously, I have written about a Lab on a Chip article from the Sinton lab on optimising microalgal growth by varying irradiance conditions.

Now Mingming Wu’s group, from Cornell University, have published an article focused on the effect of nitrogen concentration on cell growth rates. Wu has developed a platform based on agarose gel, as shown in the diagram. The nutrient media can flow through this gel while the cells can’t, maintaining separate microhabitats.

The authors decided to study the effect of nitrogen concentration gradients on the microalgae (C. reinhardtii), using ammonium as the nitrogen source. Nitrogen is essential for microalgae, as it is required for protein and nucleic acid synthesis, and ammonium is the preferred source for this particular strain.

An ammonium gradient was obtained by flowing ammonium-containing media through the source channel, and ammonium-free media through the sink channel (diagram C). As expected, increasing the concentration (within the micromolar range) increased the microalgal growth rates. Fluorescence imaging allowed the authors to quantify the growth kinetics using the Monod equation (similar to the Michaelis-Menten equation for enzyme kinetics). This is the first time this has been achieved for this particular microalgal strain with nitrogen concentration as the variable.

Another interesting find was that when the microalgae were subjected to millimolar ammonium concentrations, growth inhibition was seen. The standard medium for microalgae contains 7.5 mM ammonium, so these results suggest that these concentrations need to be reduced by several orders of magnitude in order to maximise growth rates!

Wu and co-workers have nicely demonstrated the capablilty of their agarose-based platform in quantifying growth kinetics and they highlight that it is 50-fold faster, and more cost effective, than the standard chemostat system. They also observed cell heterogeneity during their experiments and plan to use their system to study this further, along with other aspects of cellular behaviour such as quorum sensing.

To download the full article for free* click the link below:

An array microhabitat system for high throughput studies of microalgal growth under controlled nutrient gradients
Beum Jun Kim, Lubna V. Richter, Nicholas Hatter, Chih-kuan Tung, Beth A. Ahner and Mingming Wu
Lab Chip, 2015,15, 3687-3694
DOI: 10.1039/ C5LC00727E

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About the webwriter

Claire Weston is a PhD student in the Fuchter Group, at Imperial College London. Her work is focused on developing novel photoswitches and photoswitchable inhibitors.

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*Access is free until 19/10/2015 through a registered RSC account – click here to register

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A wireless chemical sensor for long-term monitoring

For effective treatment of many illnesses, in particular cancer, long-term monitoring of certain biomarkers is required. A needle probe with a chemically sensitive tip can be used, however this is invasive as it has to be inserted every time a new measurement is taken. There are also issues with tissue heterogenicity, as it is possible that changes in the measurements are solely due to a different local environment within the tissue.

Size of sensor

Previously the Cima lab at MIT reported an improved alternative for long-term in vivo monitoring. A capsule containing an NMR contrast agent was inserted in vivo and measurements were recorded using an MRI scanner. They have now done one better and eliminated the need of very costly MRI equipment by developing a small NMR sensor that simply requires a small external reader coil.

Both the sensor and reader contain a circuit with a coil and when both are in range magnetic inductance occurs, causing field amplification inside the chamber of the sensor.  This effectively means that a reading is taken only from tissue within the sensor, rather than surrounding tissue, and this is responsible for the high selectivity seen.

Different components of the system

In order to test their wireless sensor, Cima and coworkers separately measured pH and oxygen tension, both in vivo and in vitro. For the pH experiments, a polymer gel was used as the NMR contrast agent that had an exchangeable H atom with an appropriate pKa value. Using a tumor mouse model, pH readings were found to be lower when the sensor was nearer the tumor, as expected from the acidic nature of tumors. For the oxygen experiments, silicone was used as the contrast agent. The paramagnetic nature of molecular oxygen alters the relaxation time and this can therefore be used to determine the concentration of oxygen in the sensor.

From the success of their experiments, the authors conclude that they have demonstrated the flexibility of the sensor with these two measurements, and indeed there is huge potential for this NMR probe to greatly simplify in vivo monitoring.


To download the full article for free* click the link below:

Miniaturized, biopsy-implantable chemical sensor with wireless, magnetic resonance readout
C. C. Vassiliou, V. H. Liu and M. J. Cima
Lab Chip, 2015, 15, 3465-3472
DOI: 10.1039/C5LC00546A

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About the webwriter

Claire Weston is a PhD student in the Fuchter Group, at Imperial College London. Her work is focused on developing novel photoswitches and photoswitchable inhibitors.

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*Access is free until 01/10/2015  through a registered RSC account.

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A closer look at erythrocytes in motion

Blood analysis is usually the first step involved in the diagnosis of various diseases, such as typhoid and malaria. The biochemical and cellular equilibrium of blood is very sensitive to physiological variations occurring in the body at various disease stages. Thus, a fast and accurate examination of blood properties is essential. The morphological and biochemical changes in erythrocytes are used as  the pathological signatures of various diseases.

Flow cytometry is used  to examine blood cells, which requires hydrodynamic sheath flow alignment and fluorescence antibody labelling, making it time-consuming and expensive. Advanced light scattering techniques (such as digital holography) are often seen as suitable alternatives, as they provide fast and label-free measurements.

In a recent Lab On A Chip articleNetti et al. from the Italian Institute of Technology, in collaboration with scientists from Germany and Russia, presented a camera-based light scattering approach, coupled with a viscoelasticity -induced cell migration technique. This new system is used to characterise the morphological properties of erythrocytes in microfluidic flows.

They obtained light scattering profiles (LSPs) of individual living cells in microfluidic flows over a wide angular range and matched them with scattering simulations to characterise their morphological properties. A healthy erythrocyte diameter lies between 6 and 9 µm. The diameter values obtained from the experiment lie between 7 and 8.3 µm, which is in good agreement with the existing literature.

‘The results demonstrate the ability of a rapid and cost effective way to measure the average dimensions of an erythrocyte population which can be easily related to the health of a patient,’ concludes Netti.



To gain deeper insight into LSP acquisition and simulation, you can read the full article for free* by following the link below.
Optical signature of erythrocytes by light scattering in microfluidic flows
D. Dannhauser, D. Rossi, F. Causa, P. Memmolo, A. Finizio, T. Wriedt, J. Hellmers, Y. Eremin, P. Ferraro and   P. A. Netti
Lab Chip, 2015,15, 3278-3285
DOI: 10.1039/C5LC00525F

*Access is free until 27/09/2015 through a registered RSC account.
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Cell pinballs in microfluidic channels

Researchers from the Kaneko Higashimori Lab at Osaka University and the Arai Lab at Nagoya University have observed an interesting phenomenon when studying red blood cells in microfluidic channels. Instead of flowing along the channel in a smooth motion as expected, some cells bounce back and forth between the channel walls in a pinball-like motion at much slower speed. In addition to these ‘cell pinballs’, there are also cells that move at a similar reduced speed, but don’t hit the channel walls.

This altered behaviour could have detrimental effects on microfluidic devices, caused by non-uniform movement of the cells in the channels. In order to prevent these potential problems, the authors have investigated the cause of this behaviour. They noted that cell pinballs only occur when the saline medium is hypotonic, as this causes the cells to inflate due to intake of water. By attaching microbeads to the cells and using a high speed camera, the motion of the cells were studied in more detail. The pinball cells rotated clockwise as they moved to the left of the channel and anticlockwise as they moved to the right of the channel (relative to the direction of the flow).

This observation, combined with the knowledge that the cells were inflated in the hypotonic solution, led the authors to believe that the pinball-motion was occurring due to both the shape of the red blood cell and contact with the channel walls. 3D images obtained using confocal microscopy showed that the upper and lower surfaces of the cells were flattened, confirming that the cells were in contact with the walls.

By studying the different possible deformations of the inflated red blood cells when subjected to flow, the authors found that the contact line (between the cell and wall) and the centre line of the cell were not the same. This explains both types of unexpected cell motion – if the contact line is downstream of the centre line, the cell is unstable to rotational motion and this causes it to move at an angle to the flow, leading to the pinball cells, whereas if the contact line is upstream of the centre line the cell is stable to rotational motion and no displacement occurs, leading to the slow moving non-pinball cells.

From these studies, the authors were able to propose mechanisms that successfully explained the two types of altered red blood cell behaviour in hypotonic solutions, and hopefully in the future this should allow microfluidic systems to be used which will avoid this pinball-motion occurring.



To download the full article for free* click the link below:
Cell pinball: phenomenon and mechanism of inertia-like cell motion in a microfluidic channel
Ryo Murakami, Chia-Hung Dylan Tsai, Makoto Kaneko, Shinya Sakuma and Fumihito Arai
Lab Chip, 2015, 15, 3307-3313
DOI: 10.1039/ c5lc00535c

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About the webwriter

Claire Weston is a PhD student in the Fuchter Group, at Imperial College London. Her work is focused on developing novel photoswitches and photoswitchable inhibitors.

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*Access is free until 06/09/2015  through a registered RSC account.

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3D Bio-etching is here!

3D technology has revolutionised the entertainment industry by offering viewers the experience of being part of the action, going on in a movie rather than simply watching it. Thanks to 3D technology, we can sky walk hand in hand with George Clooney in ‘Gravity’.

Microfluidics setup for 3D bioetching

The history of 3D technology can be drawn all the way back to the invention of the stereoscope by David Brewster in 1844. Last two decades have seen 3D technology replacing 2D in all walks of life, ranging from entertainment, physics, microelectronics, tissue engineering and regenerative medicine. For e.g., microelectromechanosensors (MEMS) are 3D devices produced by using soft lithography techniques. MEMS installed in air-bags in the cars have saved thousands of lives by sensing pressure levels during accidents.

Can we use 3D technology to have a better look at the complex events happening at cellular level? One of the major challenges in tissue engineering is that the conventional approaches are mainly limited to 2D monolayers systems and do not allow manipulation of complex multilayer tissue. Cells grown on 2D substrates may respond and differentiate distinctly than those in more physiologically relevant 3D environments. The emergence of 3D technology has enabled scientists to mimic the exact cellular environments and helped to provide better insights into the cell signalling, migration and differentiation in cells.

One of the ways of mimicking the cellular architectures is bio-etching which involves subtractive manufacturing. Bioetching of monolayers of cells in response to laser cuts or scratch assays is achieved by using 2D cell culture studies. But the actual biological systems such as tissues and organs are much more complex and cannot be mimicked using simple monolayers. For long time, scientists have been working on developing better technologies to address this problem. One of the ways to achieve this is 3D bio-etching.

William C. Messner et al. from Tufts University in a recent article in Lab on a Chip explain the utility of 3D bioetching technique to create and shape 3D composite tissues using a microfluidics based approach. The ability to shape the 3D form of multicellular tissues and to control 3D stimulation will have a high impact on tissue engineering and regeneration applications in bioengineering and medicine as well as provide significant improvements of highly complex 3D integrated multicellular biosystems.


Can 3D bio-etching help us to design tissue architecture of our choice mimicking different biological events? Find out by reading the full paper for free* using the link below:

3D bio-etching of a complex composite-like embryonic tissue
Melis Hazar, Yong Tae Kim, Jiho Song, Philip R. LeDuc, Lance A. Davidson and William C. Messner
Lab Chip, 2015, Advance Article
DOI: 10.1039/C5LC00530B


*Access is free through a registered RSC account.

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Recognition of danger in single cells

For more than a century, researchers have been studying how the body detects and defends itself against foreign invaders.1 This process relies on a series of cell-to-cell signaling, starting with the detection of common pathogen components by receptors of immune cells. For example, macrophages, a surveillance immune cell, recognize bacteria using the Toll-Like receptor 4 (TLR4), which binds to lipopolysaccharide (LPS) found in the membrane of gram-negative bacteria.

Upon recognition of danger signals, immune cells engulf and degrade the invaders and activate NF-κB, an intracellular protein that, when activated, migrates into the nucleus and turns on inflammatory response genes. For immune cells, this initiates the secretion of signaling mediators such as tumour necrosis factor (TNF), which helps remove invaders by dilating local blood vessels and recruiting other immune cells.

Although our understanding of the immune system has skyrocketed in the past two decades,2 researchers are still lacking the tools needed to study the signaling of inflammation in a highly controlled manner. Most approaches rely on bulk population measurements, in which important spatial and temporal patterns of signaling are obscured by biological noise from neighbouring cells. To address this challenge, Tino Frank and Prof. Savas Tay from ETH Zurich developed a microfluidic system that can propagate inflammatory signals from a single immune cell (sender cell) and to a population of fibroblast cells (receiver cells).3

The microfluidic device, formed from polydimethylsiloxane (PDMS), comprises a deflectable membrane sandwiched between a flow layer and a control layer. The flow layer houses supply channels and cell culture chambers, while the control layer regulates input, output, and segregation of these chambers using solenoid-actuated valves.

As shown in picture 1, the chambers for the sender cell (chamber A) and receiver cells (chamber B) can be segregated for mono culture or connected for co-culture, depending on the state of the reversible separation valve. In mono culture mode, the sender cell can be stimulated independent of the receiver cells, whereas in co-culture mode, the signaling mediators secreted by the sender cell can be broadcasted to the receiver cells via diffusion.

Valve PDMS microfluidic device for mono and co-culture

Using this system, the researchers implemented a single-cell model of inflammation arising from bacterial infection (picture 2). This model begins in mono culture mode, with a single macrophage seeded in chamber A and a population fibroblasts seeded in chamber B. Inflammation was initiated by stimulating the macrophage with short pulses of bacterial LPS, leading to the activation of NF-κB and TNF secretion. Subsequently, the device was switched to co-culture mode, allowing the secreted TNF to diffuse across the fibroblasts and activate their NF-κB signaling.

One-way communication chain mimicking an inflammatory process, with macrophage as sender and fibroblasts as receiver.

By tracking the movement of NF-κB in the nucleus of individual cells, the researchers, for the first time, mapped the spatiotemporal distribution of immune response to bacterial infection. They demonstrate that a single macrophage can activate and control over 100 fibroblasts up to 1 mm away, and that fibroblasts located farther away exhibited a time-delayed activation profile and fewer NF-κB oscillations (between the nucleus and cytoplasm). Furthermore, they observed that the NF-κB signaling in some fibroblasts can linger for up to 10 hours, demonstrating that a brief exposure to pathogenic signal can induce long-term inflammatory response in nearby cells.

In summary, Tino Frank and Prof. Savas Tay developed a microfluidic platform to study spatiotemporal dynamics of immune response in single cells. The continued investigation of these dynamics will be important for understanding of the inflammatory process and modeling of relevant signaling pathways.4


To download the full article for free* click the link below:
Automated co-culture system for spatiotemporal analysis of cell-to-cell communication
Tino Franka and Savaş Taya
Lab Chip, 2015, 15, 2192-2200
DOI: 10.1039/C5LC00182J


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References:

1. K. M. Murphy, Janeway’s immunobiology, Garland Science, 2011.
2. L. A. J. O’Neill, D. Golenbock and A. G. Bowie, Nat Rev Immunol, 2013, 13, 453-460.
3. T. Frank and S. Tay, Lab on a Chip, 2015, 15, 2192-2200.
4. M. Junkin and S. Tay, Lab on a Chip, 2014, 14, 1246-1260.

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About the webwriter

Alphonsus Ng is a postdoctoral fellow under the supervision of Dr. Aaron Wheeler in the Department of Chemistry and the Institute of Biomaterials and Biomedical Engineering at the University of Toronto. His research focuses on the development of microfluidic methods for heterogeneous immunoassays, cell-based assays, enzymatic catalysis, sample preparation for proteomics, and chemical synthesis.

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*Access is free until 24/08/2015  through a registered RSC account.

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