Nanorobots to fight cancer, diagnose disease
Scientists design drug-delivery systems, diagnostic tests around nanoparticles
More than 40 years ago, the film Fantastic Voyage took moviegoers on a journey that was pure science fiction — a submarine and its crew were shrunk to the size of a cell and injected into the bloodstream of a dying scientist.
The mission was to navigate their way to his brain, where they would blast apart a soon-to-be-fatal blood clot and save his life.
While the premise of the movie was, well, fantastic, the notion of sending impossibly tiny fixers into the human body to cure what ails us is no longer just the stuff of imagination.
Around the world, billions of dollars are being poured into the burgeoning field of nanomedicine, the science of using molecular-scale technology to diagnose, treat and prevent disease.
At the heart of this technology is the nanoparticle, a speck of matter around which scientists are designing drug-delivery systems, quicker and more precise diagnostic tests and the building blocks for regenerating lost or damaged organs and limbs.
Technically, a nanoparticle is 100 nanometres or less, with one nanometre equal to one-billionth of a metre. To put that into perspective, think of particles so minuscule that a red blood cell that can only be seen through a microscope would dwarf them in size by at least 80 times. Or consider a human hair: its width is tens of thousands of times larger than a nanoparticle, as is the period at the end of this sentence.
Although the idea of injecting, let alone making, anything so incredibly diminutive may be difficult to wrap one's head around, scientists say we only have to look to our own bodies to grasp the concept.
|Medical research driven by nanotechnology|
|Body part regrowth: United States military researchers have used "nanoscaffolding" to regrow a lost fingertip, including the nail, bone and tissue. Their goal is to regrow entire limbs and organs.|
|New blood vessels: Mayo Clinic researchers are using nanorods to grow new blood vessels in the lab, with the hope of treating cardiovascular disease.|
|Anti-plaque stents: At Laval University in Quebec, researchers are coating metal stents, used to prop open coronary arteries, with a nanometres-thick polymer to stop plaque reforming.|
|Bandages that replace stitches: The Massachusetts Institute of Technology-Harvard is designing bandages covered with nano-scale fibres resembling a gecko's foot pad that could replace sutures and surgical staples.|
|Better replacement teeth and joints: Dental implants with nano-sized surface features to make them fuse better with the jawbone while resisting infection are in the research pipeline, as are longer-lasting nano-surfaced replacement hip and knee joints.|
|Source: Canadian Press|
Thomas Webster, an associate professor of engineering at Brown University in Providence, R.I., says that to peer at the intricacies of various tissues, such as bone or skin, through a super-powered microscope is to enter the nano world at a glance.
"What we're finding out is that nanomaterials make up our tissues," says Webster, editor-in-chief of the International Journal of Nanomedicine, who points as an example to enzymes and proteins that power the functions that give us life.
"So we are walking nano things. We are assembled from nanomaterials."
While nanomedicine is still in its infancy, its principles have already started being put into practice.
Some drugs and devices have been approved for treating humans. One is a skin patch that incorporates infection-fighting silver oxide nanoparticles to promote faster wound healing. Another is a pin for mending fractures. It's made from microscopic bits of synthetic materials that mimic those found naturally in bone.
Liposomes — ultra-tiny sacs made from fats, or lipids, which transport drugs, vaccines and enzymes to targeted cells in the body — have been around for some time.
And when it comes to diagnosis, many Canadians may have been using nanotechnology without even realizing it. Some home pregnancy kits employ gold nanoparticles on their test sticks. It's the particles that change colour in response to a hormone present in the urine of pregnant women.
But if nanomedicine's current applications are relatively few in number, that won't be the case for long, say scientists, who predict an explosion of advances in nano-based drug delivery, diagnostics and tissue regeneration over the next decade.
No matter what nanomedicine ends up looking like in the future, scientists bent on expanding its boundaries are realizing they need to take a step back and consider the possible downsides of the new technology.
Nanoparticles could infiltrate and accumulate in organs like the liver and kidneys, where they could conceivably do unforeseen damage.
One recent study found that nanoparticles of titanium dioxide, a white pigment widely used in paints, cosmetics and sunscreens, were able to migrate through the nose to the brains of mice, where they destroyed neurons.
"Toxicity is incredibly important for us to understand when we're making these materials or when we're using them," says Webster, whose own research includes designing nanomaterials for such orthopedic applications as joint replacements and limb prosthetics.
"We need to figure out what are the toxicity limits for all nanomaterials that we're currently investigating. I think the scientific community is just beginning to do that now."
Lori Sheremeta, a research associate in the Health Law Institute at the University of Alberta in Edmonton, agrees a much better understanding is needed about how nanomaterials break down in the body.
"This is no different than in the past," she told The Canadian Press, pointing to silicone breast implants as an example.
"We've put these things in people and we learned over time that actually the silicone breaks down and we don't understand the whole biological implications. And maybe we should have studied that more."
Colour-coded cancer diagnosis
The possibilities, however, offer so much hope.
Warren Chan, a biomedical engineer at the University of Toronto, is experimenting with particles known as quantum dots, with the goal of improving cancer diagnosis.
Smaller than a virus at under 100 nanometres in size, quantum dots emit light when their electrons are excited. The theory is that if a cancer-seeking protein is attached to the dots and they are injected into the body, they will accumulate in a tumour and give off different colours when exposed to light.
"So, for example, if you have breast cancer at stage zero, which is pretty healthy, you might have three blues, six greens, five reds," corresponding to various proteins in the cancer cells, explains Chan, who has successfully tested the system in lab mice.
A different colour profile from the lit-up dots — say 10 blue, one red and one green — would instantly show that the cancer has spread.
"So by looking at the colour combinations, you would be able to identify the stage of the disease."
Chan's lab is also researching how quantum dots might be used to deliver chemotherapy directly to cancer cells, without harming healthy cells along the way.
Improving cancer treatment is a major goal of nanomedicine researchers around the globe, including internationally renowned biomedical engineer Robert Langer of the Massachusetts Institute of Technology.
In one project, Langer and colleagues created nanoparticles designed to evade destruction by the immune system while they home in on prostate cancer cells. Once inside malignant cells, these tiny parcels release their payload of anti-cancer drug and destroy the tumour from within.
"We're doing a lot of different things," says Langer, whose team has tested the targeted nanoparticles for human prostate cancer in lab mice and hopes to soon move into clinical trials.
Armies of medical nanorobots
Just how far can nanomedicine go?
Some visionaries predict that medicine will someday have a lot in common with the concept behind Fantastic Voyage. They see armies of infinitesimally minute machines moving throughout the body to repair and rejuvenate aging or damaged tissues.
As the theory goes, these medical nanorobots, kitted out with onboard computerized sensors and job-specific biomedical tools, would go about zapping tumours, cleaning up scar tissue and nibbling away at plaque-encrusted arteries to prevent heart attack and stroke.
Robert Freitas, who has written extensively on nanomedicine and its future applications, has conceived the notion of a "respirocyte," a mechanical cousin of the red blood cell. According to Freitas, the respirocyte would be designed to supply the body with massive quantities of oxygen, thereby imbuing a person with superhuman endurance that would make uber-cyclist Lance Armstrong look like a weakling by comparison.
For most mainstream researchers, the idea of nanorobots "knocking out the nasties" inside the body is still the stuff of Star Trek, suggests Neil Branda, a professor of organic materials at Simon Fraser University in B.C. and a founding director of the Nanomed Canada Research Network.
"You say they're conceptual. I say they're delusional," scoffs Branda. "I'm not convinced that they're ever going to be around."
But even if such nano-devices were actually created some day, it would be their function that would matter, not their appearance. They're not going to look like a robot or an other ultra-miniaturized version of machines that exist on a macroscopic scale in our everyday world, he says.
"If you come into our lab, you're not going to see a little micron toaster popping up nano pieces of toast."