Lab on a Chip Blog

This Communication from Nathan B. Crane (University of South Florida) et al. describes new method of droplet transport, combining diode-like conduction and electrowetting on dielectric to achieve continuous electrowetting with a single electrode.

Continuous electrowetting via electrochemical diodes
Christopher W. Nelson, Corey M. Lynch and Nathan B. Crane
Lab Chip, 2011, 11, 2149-2152
DOI: 10.1039/C1LC20196D

In their paper Seok Chung (Korea University) et al. have developed a hydrogel incorporating a microfluidic platform which can mimic the 3D tissue microenvironment for the study of endothelial cell sprouting angiogenesis.  They are able to precisely control the gradient of soluble angiogenic factors, VEGF and ANG-1 and obtain a quantitative response to the assay.

In vitro 3D collective sprouting angiogenesis under orchestrated ANG-1 and VEGF gradients
Yoojin Shin, Jessie S. Jeon, Sewoon Han, Gi-Seok Jung, Sehyun Shin, Sang-Hoon Lee, Ryo Sudo, Roger D. Kamm and Seok Chung
Lab Chip, 2011, 11, 2175-2181
DOI: 10.1039/C1LC20039A

William C. Messner (Carnegie Mellon University) and colleagues have also been working in 3D to achieve dynamic control of 3D chemical patterns in a single 2D microfluidic platform.  They are able to switch between ‘focused’ and ‘defocused’ 3D flow profiles, and to rapidly tune the patterns through feedback control of the inlet pressures.

Dynamic control of 3D chemical profiles with a single 2D microfluidic platform
YongTae Kim, Sagar D. Joshi, Lance A. Davidson, Philip R. LeDuc and William C. Messner
Lab Chip, 2011, 11, 2182-2188
DOI: 10.1039/C1LC20077A

As with all our HOT papers, these are free to access for 4 weeks

Cells labelled with magnetic nanoparticles are useful for a number of applications, ranging from MRI to drug delivery and cancer therapy, and being able to sort said cells based on their magnetic nanoparticle loading is obviously necessary. Continuous flow methods currently exist for separating cells based on the extent of their magnetisation, but only for cells where the nanoparticles have been bound to them via specific surface markers.

Photograph of the microfluidic magnetophoresis chip

In this paper Claire Wilhelm (University of Paris Diderot) and Nicole Pamme (University of Hull) make use of the other mechanism of introducing nanoparticles to the cells  – exploiting the natural ability of monocytes and macrophages to engulf molecules. The team produced a free-flow microfluidic chip with an external magnet to separate the cells through five different exits, depending on the loading of magnetic nanoparticles. They demonstrated successful and efficient separation of the monocytes and macrophages, with monocytes displaying a much weaker endocytotic ability than macrophages, at rates of 10 to 100 cells per second.

For the full details download the article – it’s free to access for 4 weeks:

Cell sorting by endocytotic capacity in a microfluidic magnetophoresis device
Damien Robert, Nicole Pamme, Hélène Conjeaud, Florence Gazeau, Alexander Iles and Claire Wilhelm
Lab Chip, 2011, Advance Article
DOI: 10.1039/C0LC00656D

Identifying drugs that have the potential to cause heart dysfunction as early as possible is crucial for preventing the waste of time and money in drug discovery processes.

Cell-based biosensors using living cells have been applied in pharmacological screening, but current technologies encounter difficulties such as small measurement areas, complicated fabrication procedures and high costs.  However, the rapid development of digital consumer technologies has driven down the cost and created compact imaging sensor modules such as CMOS (complementary field oxide semiconductor) imaging senors.  

In this HOT article, Ali Khademhosseini (Harvard Medical School) and colleagues made use of this development, extracting the CMOS sensor from a webcam and using it with an image processing algorithm to measure cardiotoxicity in cardiomyocytes.  They were able to detect beat-to-beat variability in real-time after treatment with drugs iosprenaline and doxorubicin.

The authors hope this neat system may be useful for a range of cell-based biosensing applications.

Download the article for free for 4 weeks:

A cell-based biosensor for real-time detection of cardiotoxicity using lensfree imaging
Sang Bok Kim, Hojae Bae, Jae Min Cha, Sang Jun Moon, Mehmet R. Dokmeci, Donald M. Cropek and Ali Khademhosseini
Lab Chip, 2011, 11, 1801-1807
DOI: 10.1039/C1LC20098D, Paper

Ju-Hee So and Michael Dickey from North Carolina State University present an extremely simple fabrication route for microfluidic electrodes by using metal alloys with low melting point , such as eutectic gallium indium.

The liquid metal injected into the microchannels is inherently aligned and in direct contact with the fluid, but is neatly prevented from mixing with the fluid by posts with spacings that are too small to allow the metal to easily flow through.  The metal also maintains its shape despite being a liquid, due to the spontaneous formation of a thick oxide skin.  The mechanical stability of the electrodes was demonstrated in operating conditions commonly used in microfluidic applications, and as a proof-of-principle, used for electrohydrodynamic mixing, which requires extremely high electric fields.

The authors believe that this technique is significantly simpler and easier to implement than anything that has been published to date in the literature – why not download the article and see for yourself?  The article is free to access for 4 weeks!

Inherently aligned microfluidic electrodes composed of liquid metal
Ju-Hee So and Michael D. Dickey
Lab Chip, 2011, 11, 905-911
DOI: 10.1039/C0LC00501K

The fabrication  of 3D microstructures for microfluidic devices continues to be a challenge as traditional microfabrication techniques are not suitable for the construction of these devices.  For example, PDMS (polydimethylsiloxane) is one of the most common substrate materials for microfluidic devices, but standard packaging techniques are not able to bond multiple substrate layers with the high precision required.

Tingrui Pan (University of California, Davis) et al. have now come up with an easy and robust technique which they hope will make this problem a thing of the past.  Their new technique, CAP (capillary-driven automatic packaging) uses the interactions between a liquid capillary bridge and the top and bottom substrates to align multiple substrate layers with high precision, and has a bonding strength comparable to standard oxygen plasma processes.  The technique is also transferable to other materials, requires no thermal or mechanical treatment, nor any specialist equipment.

Illustration of the CAP-enabled microdevice fabrication process, including (a) micropatterning of a shadow mask made of dry film, (b) PDMS replica molding, (c) selective oxygen plasma treatment through the shadow mask, (d) DI water loading in the defined hydrophilic regions, and finally (e) self-alignment and self-engagement steps between two chips with identical capillary alignment patterns.

Pan et al. believe that this technique has the ability to be employed in microdevices for point-of-care diagnosis, controlled drug delivery, and combinatorial biological screening – why not take a look and see for yourself – the article’s free to access for four weeks!

Capillary-driven automatic packaging
Yuzhe Ding, Lingfei Hong, Baoqing Nie, Kit S. Lam and Tingrui Pan
Lab Chip, 2011, 11, 1464-1469
DOI: 10.1039/C0LC00710B