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Image courtesy of Leonardo
Submerged in surfaces
by Kimberly Krieger
Maryam Tabrizian would be the first to tell you her research barely scratches the surface of things, but don't accuse her of being superficial. Surfaces are her specialty. The biomedical engineering professor has projects on topics as diverse as coatings for damaged blood vessels to devising better ways to deliver medications. They have, however, a common theme: creating surfaces compatible with the human body.
We have miles and miles of surface area folded up within us. Spread out flat, a single person's skin would be about two square metres. If the same were done to the lungs, they would make a paper-thin sheet of 100 square metres. Our circulatory systems are more expansive still. Capillaries are often only one blood cell wide, but each of us possesses over 80,000 kilometres worth.
Every organ in our body has surfaces that meet blood or air or other tissue; surfaces that create an interface where one biological system communicates with another. When bioengineers like Tabrizian try to fool the body into accepting an artificial tissue or organ as the real thing, the surface of the replacement part is a crucial player in the deception. It's the part the body "sees." Ideally, the replacement would be exactly like the original. Often though, the real tissue is so complex and multi-functional that the bioengineered material can only approximate the most important features.
For example, take those 80,000 kilometres of capillaries, veins and arteries. Arteriosclerosis or other diseases can damage vital blood vessels beyond repair. But blood vessels are tricky to mimic since they have to be flexible and strong enough to withstand the pressure of blood pumping through them and they have to stay clear and open, with no kinks, scar tissue or clots. Previous researchers have used stainless steel stents to keep the blood vessel open, but Tabrizian has developed a nanocoating material that can coat damaged blood vessels to give them a smooth layer that prevents material from catching and clogging the flow. The material ó which goes by the moniker "self-assembled polyelectrolyte nano-coating" ó is not only compatible with blood, but can be a delivery system for medicines. The material is currently showing promise in animal clinical trials.
Blood vessels are the home of another of Tabrizian's projects, which aims to develop new ways to deliver medication and is funded by the Natural Sciences and Engineering Research Council. When drugs are taken orally as pills, they have to pass through the digestive system. It takes a sturdy molecule to survive the corrosive acid environment of the stomach and its digestive enzymes. In order to ensure some of the drug actually reaches its target, higher dosages have to be given than are really needed. Other medications are injected directly into the blood stream, but that has drawbacks as well. "Most drugs have toxic effects," Tabrizian says. "If we can give less drug over a longer period of time, we can reduce significantly the toxic effects while increasing the efficiency of the treatment." To do that, a slow-release system is needed.
Tabrizian's group is working with polysaccharide gels, also known as hydrogels. Hydrogels can be thought of as clumps of long molecules all tangled up like a ball of string that expand when wet, trapping water and other dissolved molecules such as medicines within them. Tiny balls of drug-containing hydrogels injected into the blood stream can slowly release the medication, allowing it to diffuse into the blood. This gradual drug delivery would allow constant amounts of the drug to be present in the body for long periods of time, which would reduce both the dosage necessary and the toxic side effects.
In addition to her research, Tabrizian is the director of the new International Centre of Biosensors and Biochips (ICBB). The centre, which currently has members from McGill, Laval University, Sherbrooke University, UniversitÈ de MontrÈal, and various hospitals, is funded primarily by the Fonds quÈbÈcois de la recherche sur la nature et les technologies (FQRNT). The ICBB is devoted to promoting the development of biosensors, diagnostic tools that can measure biological signals and report back to a doctor or scientist quickly and accurately. A biosensor could be used, for example, to monitor blood sugar levels in a diabetic, or detect dangerous chemical leaks in a laboratory.
Biosensors, hydrogels, artificial blood vessels and bones ó Tabrizian's research projects make the future of medicine sound almost mechanical. Maybe not quite like the Borg, those half-human, half-machine villains of Star Trek, but definitely the stuff of science fiction. How does Tabrizian view this merging of the mechanical and the human? "I think there are two drives: to dominate nature or to join nature, to become part of it. Early attempts to replace body parts were about domination, just replacing the part and forcing the body to accept it. Now, it's more to learn from nature, to work with nature. I think we will be more successful."