Irvine, CA and Arlington, TX, USA. Scientists have confirmed the hypothesis that, in addition to chemical cues, neurons can respond to physical cues (e.g., fluid flow).

The flow of spinal fluid during the development and growth of neurons in a fetus – neurogenesis – can influence how neurons are guided to their destinations.


Michael Berns is the the founding director of the Beckman Laser Institute and Medical Clinic at UC Irvine. He is the coauthor of a paper that appears in the journal Nature Photonics with Samarendra Mohanty, an assistant professor of physics at The University of Texas (Arlington). The study is based on Mohanty's hypothesis of neuron response to physical cues: he had conducted the seminal work and observed that a laser-driven spinning calcite microparticle could guide the direction of neuron growth. Its rotation caused a shearing effect by creating a microfluidic flow.


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A Vaterite particle is rotated anticlockwise and and positioned.Mohanty's work led the Berns UCI team to test the vaterite micro-motors in guiding neurons. "This is the first report to demonstrate that neurons can be turned in a controlled manner by microfluidic flow," said Mohanty. "With this method, we can direct them to turn right or turn left and we can quickly insert or remove the rotating beads as needed. But flow can be generated by any means. In the body, for example, it will be more convenient to use a tube carrying fluids."

The researchers in the UCI experiments used a laser tweezers system to trap a birefringent particle (calcite or vaterite) near axonal growth cones, which are the tips of neurons where connections are made with other neurons or cells. The same laser causes rotation of the particle, which creates the flow, Mohanty said.

The paper reports that the new method successfully turned the growing axon in a new direction up to 42 percent of the time in lab experiments. The authors noted that the method could also be used to funnel growth between two rotating particles. The effects also may be reproducible on a larger scale, they said. "One can envision large arrays of these devices that can direct large numbers of axons to different locations," the authors wrote. "This may have the potential for use in vivo to direct regenerating axons to mediate brain and spinal cord repair."

The discovery could allow for directed growth of neuronal networks on a chip and improve methods for treating spinal or brain injuries. The experiments shed valuable light on the effect of shear or lateral forces on neuron growth and that knowledge may even apply to other forms of cell growth.

His lab at UT Arlington is currently developing a novel optical method that allows long-range optical guidance of neurons with 100 percent efficacy without use of any additional external objects.

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