Bismuth-carrying Nanotubes Show Great Promise for CT Scans

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Scientists at Rice University have managed to confine bismuth in a nanotube cage to tag and track stem cells for X-ray.

Bismuth is most probably known as an active element in a popular stomach-settling elixir and is also applied in cosmetics and medical applications. Rice chemist Lon Wilson and his peers are placing bismuth amalgams into single-walled carbon nanotubes with the intent of making a more efficient contrast agent for computed tomography (CT) scanners.

The work which was led by Wilson’s team and was in collaboration with the University of Houston, St. Luke's Episcopal Hospital, and the Texas Heart Institute are showcased in the Journal of Materials Chemistry B.

“This is not the first time bismuth has been tested for CT scans, and Wilson's lab has been experimenting for years with nanotube-based contrast agents for magnetic resonance imaging (MRI) scanners. But this is the first time anyone has combined bismuth with nanotubes to image individual cells,” said Wilson.

"At some point, we realized no one has ever tracked stem cells, or any other cells that we can find, by CTCT is much faster, cheaper and more convenient, and the instrumentation is much more widespread (than MRI). So we thought if we put bismuth inside the nanotubes and the nanotubes inside stem cells, we might be able to track them in vivo in real time,” he added.nanotubes stem cells

Recent experiments now verify their initial theory. In tests using pig bone marrow taken from mesenchymal stem cells, Wilson and lead author Eladio Rivera, a former postdoctoral researcher at Rice, discovered that the bismuth-filled nanotubes, which they refer to as Bi@US-tubes, generate CT images much brighter than those from regular iodine-centered contrast agents.

"Bismuth has been thought of before as a CT contrast agent, but putting it in nanotube capsules allows us to get them inside cells in high concentrations. That lets us take an X-ray image of the cell,” said Wilson.

The capsules are manufactured from a chemical process that cuts and purifies the nanotubes. When the tubes and bismuth chloride are blended in a compound; and after a period of time, they form Bi@US-tubes.

The nanotube capsules are between 20 and 80 nanometers in length and around 1.4 nanometers in diameter.

"They're small enough to diffuse into the cell, where they then aggregate into a clump about 300 nanometers in diameterWe think the surfactant used to suspend them in biological media is stripped off when they pass through the cell membrane. The nanotubes are lipophilic, so when they find each other in the cell they stick together,” said Wilson.
Wilson also claimed his team’s studies exhibited stem cells that readily took in Bi@US-tubes without compromising their basic function.

"The cells adjust over time to the incorporation of these chunks of carbon and then they go about their business," he said.

In addition, Wilson noted the prime benefits of Bi@US-tubes over their iodine-based counterparts.

"Bismuth is a heavy element, down near the bottom of the periodic table, and more effective at diffracting X-rays than almost anything else you could use," he said. Once the bismuth is encapsulated in the nanotubes, the agent can produce high contrast in very small concentrations. The nanotube surfaces can be modified to improve biocompatibility and their ability to target certain types of cells. They can also be modified for use with MRI, positron emission tomography and electron paramagnetic resonance imaging systems,” he said.

“The Rice lab is working to double the amount of bismuth in each nanotube. Bismuth ions appear to get into the nanotubes by capillary action, and we think we can improve on the process to at least double the contrast, maybe more. Then we would like to combine both bismuth and gadolinium into one nanotube to produce a bimodal contrast agent that can be tracked with both MRI and CT scanners."


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