Finding their range of comfort | EurekAlert! Science News

A Mason Engineering researcher has discovered that artificial microswimmers accumulate where their speed is reduced, an idea that may have an impact on improving the effectiveness of targeted cancer treatment.

Jeff Moran, assistant professor of mechanical engineering at the Volgenau School of Engineering, and colleagues from the University of Washington in Seattle studied semi-platinum / semi-automatic gold rods that “swim” in water use hydrogen peroxide as fuel. The more peroxide there is, the faster the swimming; without peroxide in fresh water, the rods will not swim.

In this work, they wanted to find out what happens when these artificial microswimmers are placed in a liquid reservoir containing a gradient of hydrogen peroxide – a lot of peroxide on one side, not much on the other side. other.

They found, predictably, that the microswimmers would swim faster in regions with high peroxide densities, said Moran, whose research was published in the new issue of Scientific Reports.

As others have seen, swimming direction changed at random in time as the swimmers explored their surroundings. In contrast, in the low-density areas, the rods slid down and accumulated in those areas over a few minutes.

The findings suggest a simple strategy to force microswimmers to accumulate passively in specific regions, an idea that could have useful, practical applications, he says.

Swimming at a microscopic scale is an ubiquitous phenomenon in biology, Moran says. “Many cells and microorganisms, such as bacteria, can automatically swim toward higher or lower concentrations of beneficial or damaging chemicals on the cell, individually.”

This behavior is called chemotaxis, and it is both common and important, he says. “For example, your immune cells use chemotaxis to find injury sites and swim towards them, so they can start tissue repair.”

Moran and colleagues, like others in the field, have long wondered whether artificial microswimmers can mimic cells by performing chemotaxis, swimming continuously toward higher chemical densities . Some had suggested that the platinum / gold rods, in particular, could swim independently towards peroxide-filled regions.

“We were skeptical about these applications because the rods do not live, so they do not have the sensory and response capabilities necessary for cells to activate this behavior,” he says.

“Instead, we found the opposite: the rods are built in the lowest density regions. This is the opposite of what would be expected from chemotaxis,” Moran says.

The researchers made computer simulations that predicted this and validated them with experiments, he says.

“We suggest a simple explanation for this behavior: Wherever they are, the rods move in different directions at random, examining what is around them. When they reach a low-fuel area. , they can’t study so strongly. In a sense, they get locked in their comfort zones, “Moran says.

“On the other hand, in the high-peroxide regions, they move at higher speeds and, because their direction is constantly changing, they will flee from those regions more often. Over time, the net result is that rods accumulate in low-density regions, “he says. “They have no information. They end up where mobility is lowest.”

Moran says this research is technically promising as it proposes a new strategy for causing chemicals to accumulate in a highly acidic area.

“As a result of their abnormal metabolic processes, cancer cells cause their surroundings to become acidic. These are the cells that need most drugs because they are known to have the An acidic environment promotes metastasis and drug resistance, so the cells in these regions are a major target of many cancer treatments. “

Moran and colleagues are now designing microswimmers that move slowly in acidic and fast-moving regions in neutral or basic regions. Through the approach they found here, they assume that acid-dependent swimmers collect and release their cargo favorably where their distances are. reduced, these are the most acidic and hypoxic regions of the eardrum, where the most troublesome cells reside.

There is much more research to be done, but “these rods may have the potential to deliver chemotherapy drugs to the cancer cells that need them most,” Moran says.

“To be clear, our study does not confirm that chemotaxis is impossible in artificial, time – consuming microswimmers; these specific microswimmers simply do not undergo chemotaxis.

“Instead, we have identified a very simple way to cause irregular microswimmers to accumulate and deliver drugs to the most troublesome cancer cells, which can affect the treatment of many cancers, as well as other diseases such as fibrosis. We are excited to see where this can go. ”

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