Toxin dialysis is so 2017. The latest wrinkle in fluid filtering is nano-claws that can catch and hold onto bacteria swimming in your bloodstream, reports a team in Nature Communications. It bears mention that like your urine, your blood is not supposed to have any bacteria at all.
Ordinary dialysis helps people with impaired or no kidney function to clean the blood of toxins, solutes and excess water. Classic dialysis is not designed to remove germs. But when bacteria infect our blood, they can cause sepsis, an inflammation that affects the whole body and can lead to organ collapse and death.
The general strategy so far has been to dose the septic patient with antibiotics and hope for the best.
One snag with antibiotic treatment is that it’s generally target-specific. A given bacteria can only be treated by a certain antibiotic; a given antibiotic will only treat certain types of bacteria. Penicillin can treat many staph and strep cocci, for instance, but not all, and it can't treat urinary tract infection bacteria, for instance. That will require a cephalosporin.
So if you’re turning septic, before administering intravenous antibiotic to your suffering veins, the doctor has to identify the bacteria and select the appropriate medication. That can cause deadly delays.
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Or – your blood can be filtered somehow to capture the bacteria in their germy tracks – as the experts call it, “extra-corporeal blood-cleansing therapy”. Meshes and traps don’t care what bacteria get caught.
There have been any number of attempts to create blood-filtering systems that can effectively catch bacteria (or tumor cells), write the authors headed by Lizhi Liu of the Beijing-based Chinese Academy of Sciences: from filtration to three-dimensional nanotraps, from hard materials to softer ones.
But these techniques do not work well. The shearing force of the bloodstream causes the bacteria to fall off the filter, literally, and get flushed back into the body.
Jaws snap shut
The team found its inspiration in a rare rainforest denizen much beloved of impressionable children: the Venus flytrap.
In person, flytraps are delicate, tiny things that are really hard to cultivate in the bathroom. But in nature, the flytrap lurks unwearyingly until an insect lands on its paired, “toothed” leaf lobes. Triggered by the fly landing, the lobes snap shut, trapping the fly inside for the plant’s leisurely digestion.
Thus the team came up with its 3D nanoclaws. Technically, they made bendy nanoclaws out of flexible polycrystalline nanowires pre-grafted onto 3D carbon foam. When open, the nanowires are straight. When bacteria trigger the nanowires, they instantly bend and the trap closes.
A trap made with single-crystalline nanowires didn’t work so well. Rigid, stiff nano-claws didn’t work either because the bacteria fell off and were washed back into the bloodstream. The team reports that bacteria do not manage to escape their trap (“desorb”), even under conditions of natural rapid blood flow.
In short, the team of chemists proved that using bendable polycrystalline nanowires in bacteria traps improves the dialyzer’s capture efficiency.
It’s early days to conceive of technology for use in people, and what a bacteria-filtering lifestyle means is not clear. But as the team itself says, “The demonstration of efficient bacterial capture in normal saline and the human bloodstream, in a dialyzer filled by bendable polycrystalline nanowires/carbon foam, is clearly a major step toward the development of a nanotechnology platform that can meet evolving clinical and lifestyle needs.”