December 14, 2009 | 1
Biomedical breakthroughs rarely outdo nature itself—despite our ever-increasing knowledge of new materials and processes. So that’s why one group working on drug dispersal is looking, not to novel delivery systems, but rather to replicate the natural dynamics of blood cells.
By devising a flexible, biodegradable microparticle that looks and acts like a red blood cell, engineers have created a material that they think could be more effective at delivering drugs and imaging substances, they announced in a paper published online Monday in Proceedings of the National Academy of Sciences.
"While synthetic carriers have brought upon numerous advances in drug delivery, they fail to match the sophistication exhibited by innate biological entities," the researchers wrote.
Red blood cells, in particular, "represent a remarkably engineered biological entity," they noted. The flexible, disc-shaped red blood cells are able to pass through tiny capillaries narrower than the cells’ width, a coup that other stiffer, more spherical synthetic particles cannot pull off.
But getting a synthetic polymer (polystyrene) to take on these microscopic features was no small feat. "Changing the shape of a solid polystyrene microparticle into a [red blood cell]-shaped object…is quite challenging," the authors stated. But once they found the right combination of polymer (polylactic acid-co-glycolide) protein (hemoglobin and others) and polyelectrolyte layers, the team discovered that their synthetic discs could bend and unfold—and thus pass through smaller areas in the circulatory system—just like a red blood cell. Also like a natural red blood cell, these particles showed they could bind with and carry oxygen, especially when fortified with additional hemoglobin.
The authors reported that the material might be an excellent vehicle for time-release drugs and medical imaging agents. And now that they can make healthy-shaped blood cells, they also can begin experimenting with abnormal cells (like those found in people who have sickle-cell anemia or hereditary elliptocytosis) to better understand the physical properties of the diseases and work toward new therapies.
The California- and Michigan-based group (led by Nishit Doshi of the Department of Chemical Engineering at the University of California, Santa Barbara) is not the first to attempt fabricated blood components. Several biotech companies, including Dallas-based HemoBioTech, have been working for more than a decade to develop a safe whole-blood replacement that could help stock lagging supplies.
The new particles proved to have red blood cell size, shape, elasticity and oxygen capacity in the lab, but they have yet to be tested in vivo. If they prove safe and effective there, the researchers wrote, they "may open opportunities in drug delivery, medical imaging, and the establishment of improved disease models."
Image of synthetic red blood cells courtesy of Nishit Doshi