Liquid metal drop, used to make the mini-centrifuge, sits on the channel where...
Liquid metal drop, used to make the mini-centrifuge, sits on the channel where samples will eventually be pumped through.
Source: RMIT University

Organ-on-a-chip: Device simplifies study of blood cells

A simple innovation the size of a grain of sand means we can now analyse cells and tiny particles as if they were inside the human body.

The new micro-device for fluid analysis will enable more tailored experiments in drug development and disease research. It could also transform water contamination testing and medical diagnosis in natural disaster zones, where its low cost, simple use and portability make it a practical tool almost anyone can use. 

Microfluidic or ‘lab-on-a-chip‘ devices are commonly used to analyse blood and other fluid samples, which are pumped through narrow channels in a transparent chip the size of a postage stamp. These miniaturised chips are made using state-of-the-art device fabrication facilities at RMIT’s Micro Nano Research Facility.

This new chip takes that technology one step further by adding a three-dimensional cavity along the channel – think of a narrow tunnel that suddenly opens into a domed vault – which creates a mini-vortex where particles spin around, making them easier to observe. To make this cavity, researchers inserted a liquid metal drop onto the silicon mould when making the chip. The liquid metal’s high surface tension means it holds its form during the moulding process.

Finally the liquid metal is removed, leaving just the channel and a spherical cavity ready to use as a mini-centrifuge, explained RMIT engineer and study co-leader Dr Khashayar Khoshmanesh. “When the fluid sample enters the spherical-shaped cavity, it spins inside the cavity,” he said. “This spinning creates a natural vortex, which just like a centrifuge machine in an analytics lab, spins the cells or other biological samples, allowing them to be studied without the need for capturing or labelling them.”

The device only requires tiny samples, as little as 1 ml of water or blood, and can be used to study tiny bacterial cells measuring just 1 micron, all the way up to human cells as large as 15 microns.

A platform for studying cardiovascular diseases

Study co-leader and RMIT Postdoctoral Research Fellow, Dr Sara Baratchi, said the device’s soft spherical cavities could be used to mimic 3D human organs and observe how cells behave in various flow conditions or drug interactions. “The ability to tailor the size of the cavity also allows for different flow situations to be simulated – this way we can mimic the response of blood cells under disturbed flow situations, for example at branch points and curvatures of coronary and carotid arteries, which are more prone to narrowing,” she said.

This capability will be of interest to Australia’s booming biomedical industry, with medical apparatus being among our top 10 exports in 2018 and worth $3.2 billion. Baratchi said the discovery was only made possible through collaboration, with technologists from the School of Engineering and mechano-biologists in the School of Health and Biomedical Sciences joining forces in RMIT’s Mechanobiology and Microfluidics research group. “Biologists like myself have been struggling to study the impact of flow-associated forces on circulatory blood cells. Now this miniaturised device developed with our engineering colleagues does exactly that,” Baratchi said. “It’s an ingenious solution that really highlights the value of cross-disciplinary research.”

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