Archive for the ‘Chemistry World Highlights’ Category

Channelling deeper to target breast cancer

US scientists have developed a model of the breast ductal system that could be used to discover abnormal cells or deliver drugs at locations further along the ducts than other techniques. The model fits on a slide, enabling on-chip experiments.

The human mammary gland consists of branched ducts with channels of decreasing size that are increasingly more difficult to access to obtain cell samples. This is because the channels get too narrow so the liquid inside them does not move around enough for probes to pass through to collect the cells. Now, a team led by Sophie Lelièvre and James Leary at Purdue University, Indiana, have mimicked the ductal system by making branched channels from polydimethylsiloxane (PDMS). They then moved magnetic particles along the channels through static fluid using a magnet.

The team coated the PDMS with extracellular matrix – a protein scaffold that supports cells. From this, they formed a tubular structure in which to culture mammary epithelial cells. Due to stress from the tube walls, the cells did not survive in straight tubes, so the team engineered U-shaped half channels, or hemichannels, instead. They were then able to culture cells on them, and covered the channels with a PDMS membrane to form tubes.
 

Schematic of the branched channel system 

Link to journal articleBreast on-a-chip: mimicry of the channeling system of the breast for development of theranostics
Meggie M.G. Grafton, Lei Wang, Pierre-Alexandre Vidi, James Leary and Sophie A. Lelièvre
Integr. Biol., 2011, DOI: 10.1039/c0ib00132e

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A tattoo to monitor health

A sensor to be injected into the skin just like a tattoo that measures sodium concentrations in the blood has been developed by US scientists. The sensor could be used to monitor diseases or warn against dangerously low sodium levels during exercise.

Heather Clark from Northeastern University, Boston, and coworkers made plastic nanobeads that fluoresce to different extents with changes in sodium levels. The beads are coated with a biocompatible polymer and are injected just under the skin to allow the fluorescence to be monitored easily.

Technology for determining the amount of sodium in the bloodstream has been available for some time. However, it requires a blood sample from the patient, which limits the measurements to isolated time points. This is a problem for understanding a condition called hyponatremia, where sodium concentrations in blood serum are lower than normal. Hyponatremia can occur after certain types of surgery, with brain trauma or tumours, and has been found in endurance athletes.

The team is developing a sensor to inject into the top layer of the skin that falls off after seven days, like a non-permanent tattoo

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Link to journal article
In vivo sodium concentration continuously monitored with fluorescent sensors
J. Matthew Dubach, Edward Lim, Ning Zhang, Kevin P. Francis and Heather Clark
Integr. Biol., 2011, DOI: 10.1039/c0ib00020e

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Artificially controlling cell division

US scientists have replicated a part of a cell, called a mitotic spindle, to better understand its role in cell division. If the spindle doesn’t function properly, the effect could lead to cell death, Down’s Syndrome or cancer.

William Hancock and team at Pennsylvania State University recreated a step in a process called mitosis using the artificial mitotic spindle. Mitosis is when a cell separates the chromosomes in its nucleus into two identical sets in two nuclei. The mitotic spindle, which consists of microtubules, controls the chromosome movement. Microtubules play an important role in the migration of chromosomes to opposite ends of a dividing cell. ‘This work is the first to organise microtubules in vitro into cell-like arrangements with the proper filament polarity and immobilise them in an experimental chamber,’ claims Hancock.

Microtubules are polymers of the protein tubulin. They are inherently polar and can organise themselves into complex geometries in dividing cells. Key characteristics of a mitotic spindle are two spindle poles, oriented microtubules overlapping at the centre, and motor protein activity along the microtubules. To recreate the spindle, Hancock made microscopic electrodes and coated them with proteins binding to one specific end of microtubules. The microtubules were then guided towards these attachment sites using dielectrophoresis and the attached microtubules were extended by additional polymerisation of tubulin.

The mitotic spindle controls chromosome movement in cells

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Link to journal article
Artificial mitotic spindle generated by dielectrophoresis and protein micropatterning supports bidirectional transport of kinesin-coated beads
Maruti Uppalapati, Ying-Ming Huang, Vidhya Aravamuthan, Thomas N. Jackson and William O. Hancock
Integr. Biol., 2011, DOI: 10.1039/c0ib00065e

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