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Nanosponges Flow Through the Bloodstream to Absorb Toxins

While they're not robots, the UCSD team has developed so-called "nanosponges," which are capable of flowing about a mouse's bloodstream and absorbing lethal toxins.
The UCSD nanosponge features a polymer core, red blood cell covering, and is shown here absorbing toxins (small colored balls). Image: Zhang Research Lab

Medical nanobots that cruise through your bloodstream fighting disease are ever-present in science fiction, and now, thanks to work by engineers at UC San Diego, they seem a little less far-fetched. While they're not robots, the UCSD team has developed so-called "nanosponges," which are capable of flowing about a mouse's bloodstream and absorbing lethal toxins.

The research, published in Nature Nanotechnology, has pretty big implications for anti-viral therapies as well as combating antibiotic-resistant bacteria. It's important to note that the sponges aren't capable of an immune response like white blood cells; instead, they were shown to absorb lethal toxins that perforate cellular membranes, like those produced by MRSA and E. coli, as well as toxins produced by poisonous snakes and bees.

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That ability to absorb toxins still has beneficial effects, even if the nanosponges themselves won't fight off infection. For example, when studying MRSA infection in mice, those that were pre-inoculated with nanosponges before being exposed to lethal doses of alpha-haemolysin, a toxin produced by MRSA, 89 percent of mice survived. Even when mice were given nanosponges after the fact, 44 percent survived. For a bacterium as worrisome as MRSA, that's good news.

A video from UCSD describing how the nanosponges work.

"One of the first applications we are aiming for would be an anti-virulence treatment for MRSA. That's why we studied one of the most virulent toxins from MRSA in our experiments," said lead author "Jack" Che-Ming Hu in a release.

The difference in survival rates between pre- and post-exposure inoculation is important, because it means the nanosponges–at least in their current form, and tested in mice–aren't as effective in therapeutic treatment as they are when used as a sort of catch-all vaccine. (Perhaps it's due to a delay in how long it takes the nanosponges to spread through the bloodstream.)

But still, a 44 percent chance is better than dead, and the broad effectiveness of the sponges has huge benefits for medicine. For example, if the sponges were only effective against snake toxins, it could still go a long way towards benefiting patients who currently have to rely on finding specific antivenins.

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The nanosponges are about 85 nanometers in diameter, and are made of a polymer core that can be broken down by the body. To attract toxins and "cloak" them in the bloodstream, the UCSD team covers them in a skin of red blood cell membrane. (Because the nanosponges are so small, a single red blood cell membrane can coat thousands of the sponges.)

Transmission electron microscopy image of the nanosponge,
via Zhang Research Lab, UCSD

After absorbing toxins and preventing them from poking holes in mouse cells, the nanosponges were eventually absorbed by the liver and broken down. The researchers state that the half-life of the nanosponges is about 40 hours, and that the mouse livers didn't show any discernible damage from breaking down the nanosponges.

That 40 hour half-life is a good thing in one sense, as it's important to know that the tiny particles can be broken down easily by the body. But, considering the decrease in effectiveness between pre- and post-infection treatment, it also means that nanosponge vaccination, while a fascinating thought, isn't yet feasible.

That said, it's promising research. As is the usual caveat, what translates to mice doesn't necessarily translate to humans (we, for one, have a lot more blood to fill with nanosponges), but Hu and team say the next step is clinical trials.

It's also unclear how well the nanosponges could work in practice; while it's certainly feasible to think they could soak up all the venom from a snake bite, what happens with an infection like MRSA, which will continually produce new toxins? Perhaps regular treatment with nanosponges could keep a person healthy long enough for its own immune system to fight off the infection, but that's just speculation that the authors don't delve into. In any case, with the bacterial apocalypse ever on the horizon, it's promising to see a treatment that isn't simply a more powerful antibiotic.

@derektmead