Self-Propelled Microrockets Use Water As Fuel
A new micromotor runs on stomach acid.
CREDIT: Wei Gao
The incredible journey through the human body depicted in the 1966 film "Fantastic Voyage" might soon be possible.
No, humans will not operate tiny submarines injected into patients. But researchers, led by Joseph Wang, a professor of engineering at the University of California, San Diego, have created self-propelled microrockets that use their surrounding environment as fuel.
In the development of self-propelled microrockets (or micromotors), fuel systems have long presented problems, since both have previously relied on cell-damaging hydrogen peroxide or cumbersome magnetic and electrical guiding systems. This new micromotor, on the other hand, is capable of exclusively using substances in its surrounding environment such as water for fuel, preventing any tissue damage that other fuel systems may have inflicted.
The team created two types of organically self-propelled micromotors, explained Wei Gao, a graduate student in Wang’s lab. One motor is made of biocompatible zinc that reacts with hydrochloric acid in the stomach and releases a stream of hydrogen gas bubbles to propel it forward. This style of propulsion has proven quite speedy —a rocket can move 100 times its length (.0004 inches) in one second.
But Gao is even more excited about the second motor type the team created: an aluminum-alloy motor that uses water as fuel. By splitting the water, this motor generates hydrogen bubbles to propel itself forward — a finding that could have broad applications.
"Seventy percent of the human body is water … so if water can be used to propel the micromotor, that would be a perfect choice of fuel," Gao told TechNewsDaily.
Gao said the water-fueled micromotors have received attention because of their potentially wide-ranging applications, from drug delivery to environmental cleanup.
One of the most exciting potential applications for the motors is drug delivery for cancer patients, Gao said. If the micromotor were modified to include antibodies on its surface, he added, it could function as a targeted drug-delivery system far superior to current techniques.
"Common nanoparticle-based drug delivery relies on diffusion, which has limited penetration depth into tumors," Gao said. "But in our case, we can use the micromotor … [to] carry the drug particles directly to the deep tumor tissues. It’s much more efficient."
But Gao and his team have some work ahead of them. Whereas the earlier, hydrogen-peroxide-fueled motors could survive for long periods of time, the current version of Gao’s micromotor has a lifetime of about seven minutes, which is not long enough for many medical procedures.
But Gao is optimistic that the lifespan of the microbots can be extended as the technology is refined. In fact, he and his team are collaborating with researchers at the University of California, San Diego to begin in vivo – or live animal – studies. "If it works well," Gao said.
"I think, in the near future, we can make this a reality."