Guiding light: Gentle, noninvasive process steers cells, researchers find

August 1, 2009
Bob Roehr
Bob Roehr

Bob Roehr is a medical writer based in Washinton, D.C.

The brute force of lasers to kill targeted cells has become an important tool for dermatologists. Now, research presented at an optics conference in June may be opening the door to a gentle, new way to promote healing.

Key Points

The work showed for the first time that low-intensity polarized light can affect components within cells that drive their motility and change the orientation of cells within cultures.

Actin forms much of a cell's cytoskeleton. Cells primarily move through the generation and breakup of longer actin filaments from smaller, rod-like particles of the molecule, says Aristide Dogariu, Ph.D., professor of optics and photonics, University of Central Florida, Orlando, Fla., and senior author of the research.

Dr. Dogariu set out to see if the same process could be achieved using the force of light rather than biochemical signals.

While certain forms of light have been used as "tweezers" to grab and move cells in the lab, that process often results in damage to the cells. Dr. Dogariu chose to use a gentler form of light to test his hypothesis.

There is "a huge difference - six orders of magnitude in intensity," he says, between the power of the lasers he used and those currently used by dermatologists in their practices.

"The processes we are dealing with are not photochemical; we do not stimulate any chemical process with light, we just mechanically act on the components," Dr. Dogariu says. "It has the potential to really be nontoxic to the cells."

Working with the biomolecular science group of Kiminobu Sugaya, Ph.D., at the university, researchers tested the theory on a culture of neuronal progenitor stem cells. They stained the actin with a fluorescent material, exposed cells to both unpolarized and polarized illumination of the same intensity and at the same time, and observed the cells under microscopy.

"There was a directionalization of those fibers in cells exposed to specially prepared polarized light," Dr. Dogariu says.

The low-intensity light used in the experiment applies a kind of optical torque to the rod-like actin particles within the cells, and, much like a weathervane, "The rods tend to align along the direction of polarization," he says.

Broader effect

Researchers then pulled back to look at the broader effect of the polarized light on groups of cells, using a time-lapse video. Cells exposed to unpolarized light had no pattern of organization, but when exposed to polarized light, they clearly oriented into filaments along the axis of polarization.

Changing the direction of polarization also changed the direction of alignment of the cells, Dr. Dogariu said in the narrative to the video. The cells remained viable and functional after the experiment, with no suggestion that they had been damaged by it. That led Dr. Dogariu to judge the process as "noninvasive and gentle."

This first proof-of-concept demonstration acts only on the tissue surface, but Dr. Dogariu believes it likely will be possible to deliver the intervention deeper into tissue by tinkering with different wavelengths, light modulation and modes of delivery.

He says the polarization of light "probably can be manipulated easier than the light intensity. The light can be diffused, but the polarization can still be there."

For Dr. Dogariu, "The first application of this technology that comes to mind is tissue repair and wound healing. We don't know exactly the scalability of this, but probably, it would depend on the penetration.

"Once you solve that problem of depth, then it really doesn't matter how large the surface area is."

Work to date has been in tissue cultures, not animals, and Dr. Dogariu readily acknowledges that it will take significant time and research to realize any potential benefits from these findings in basic research. He is looking for clinical collaborators to help push the work in several different directions.

Joely Kaufman, M.D., director of geriatrics and anti-aging at the University of Miami, Fla., says this process of using polarized light seems similar to methodology that has been explored with low-level laser therapy and wound healing.

"In general, we know that almost any kind of light affects cells in culture, including increased cell activity, organization and metabolism," she says. "Translating these processes to the clinical setting has been the biggest obstacle."

Disclosure: Dr. Dogariu reports no relevant financial interests.