25 December 2009

Virtual microfluidics

The inner surface of organs such as the trachea and intestines is covered with constantly moving tiny hairs – microvilli, which ensure the movement of mucous secretions, cells, nutrients and other small particles in a certain direction.

Researchers at the Massachusetts Institute of Technology, working under the leadership of Professor Alfredo Alexander-Katz, in collaboration with colleagues from Germany and the University of Boston, have developed a method for controlling the movement of microscopic objects suspended in a liquid that can not only revolutionize the creation of biochips, but also help in studying the patterns of cell movement. and other objects inside the body.

The main component of the system proposed by the authors are superparamagnetic beads (tiny polymer beads with inclusions of magnetic material). Due to the weight of the magnetic material, the beads sink to the bottom of the container containing the sample being studied. When a rotating magnetic field is applied, the beads spontaneously form short rapidly rotating chains that create fluid flows capable of moving the particles contained in it, and the size of these particles can be 100 times the size of the beads themselves.

Alexander-Katz calls his beads, whose diameter is only a few microns, "micromurts", because of their ability to move objects much larger than them in size. The article "Controlled surface-induced flows from the motion of self-assembled colloidal walkers", which describes their creation and functioning, was published on December 18 in the preliminary on-line version of the journal Proceedings of the National Academy of Sciences.

Chains of super-magnetic particles, rotating, form fluid flows, the size of which is much larger than the size of the chains themselves, which allows them, like ants, to move objects many times their size.

The new method may provide a simpler and cheaper alternative to existing microfluidic devices, the development of which is currently in the initial stages. For the functioning of such devices, micro-components made with high precision are necessary: channels, valves and pumps that provide controlled movement of liquids and particles suspended in them. The new system, in which flow control is carried out exclusively by changing the characteristics of the applied magnetic field, can provide similar opportunities.

Rotating chains of suspended beads move along the surface of the liquid.

In other words, the new approach, which Alexander-Katz dubbed "virtual microfluidics", allows you to change the properties and configuration of chips using software, rather than by changing their physical structure. This will reduce the cost and increase the functionality of chips that can be used for biomedical screening, as well as for detecting trace amounts of environmental pollutants or toxic substances. Perhaps the new method will allow achieving even greater accuracy of spatial control of particle motion than the channels of microfluidic chips allow.

Chains of tiny plastic beads rotate in a magnetic field.
When viewed from above, the rotating chains look like thin lines.
Their movement causes fluid flows to move, dragging cell layouts (round objects) with them.
Changing the characteristics of the magnetic field allows researchers to control this movement with a high degree of accuracy.

The authors believe that their development can help in studying the movement of microvilli, the mechanism of hydrodynamic synchronization of which is currently a mystery to scientists. In the future, similar systems may also be used in medical diagnostics. With their help, it will be possible to control the movement of particles in the patient's body, located, for example, in a magnetic resonance tomograph.

Portal "Eternal youth" http://vechnayamolodost.ru according to the Massachusetts Institute of Technology: "'Micro-ants': Tiny conveyor belts for the 21st century"25.12.2009

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