With their recent work, including a study to be published recently in Langmuir, Eniola-Adefeso's team has shown that nanoparticle spheres face this problem in tiny arterioles and venulesone step up from capillariesall the way up to centimeter-sized arteries.
They discovered this with the help of plastic channels lined with the same cells that make up the interiors of blood vessels. Human blood, with added nano- or microspheres, ran through the channels, and the team observed whether or not the spheres migrated to the channel walls and bound themselves to the lining. The researchers present the first visual evidence that few nanospheres make it to the vessel wall in blood flow.
"Prior to the work that we have done, people were operating under the assumption that particles will interact with the blood vessel at some point," Eniola-Adefeso said.
While a relatively small fraction of nanospheres filter out to the blood vessel walls, many more stay in the bloodstream and travel all over the body. Increasing the nanoparticle dose gives poor returns; after the team added five times more nanospheres to the blood samples, the number of spheres that bonded with the blood vessel lining only doubled.
"If localized drug delivery is an important goal, then nanospheres will fail," she said.
But it's not all bad news. The red blood cells tended to push microspheres with diameters of two microns or more toward the wall. Whether the blood flowed evenly, as it does in arterioles and venules, or in pulses, as occurs in arteries, the larger microspheres were able to reach the vessel wall and bind to it. When the team added more microspheres to the flow, they saw a proportional increase in microspheres on the vessel wall.
While microspheres are too large to serve as drug carriers into cell or tissue space on their own, the team suggested that microspheres could ferry na
|Contact: Kate McAlpine|
University of Michigan