Blood filtration in a flash


A team of German researchers claim to have developed a new type of filter that clears blood faster than conventional methods by taking two steps at once.

BioMedNet, News, 26. August 2003


BMN260803 - Sepsis is a serious problem in hospitals worldwide, and the risk of infection is highest in intensive care units, where patients are most vulnerable. If sepsis occurs, blood has to be cleared of pathogens as fast as possible, a process that normally involves two steps.

First, plasma has to be separated from blood cells (erythrocytes, leukocytes and platelets). Only then can plasma be cleared of endotoxin, which may include fragments of bacteria such as pathogenic Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus, all capable of triggering inflammatory reactions.

The two-step clean-up procedure involves a large amount of apparatus and takes vital time. There is also an alternative method, where blood is passed over an endotoxin binding surface without separating plasma from blood cells. It is faster, but the endotoxin-binding constituents on the surface activate thrombocytes. Thus this method is not well accepted.

Now, claim German researchers, a method has been developed that takes the two steps in one, and should be well accepted. For this method, blood streams through a bundle of tiny hollow fibers, 360 micrometres in diameter. Everything takes place in that bundle. Plasma and endotoxin is separated from the blood cells in one step. "For this we use hollow fibers which have tiny pores all around, one to five micrometres in diameter," says Christian Oehr, chemist at Fraunhofer Institute for Interfacial Engineering and Biotechnology in Stuttgart.

The pores are big enough to allow plasma and endotoxin constitutents to pass through, but too small for blood cells. The fibers are composed of a common synthetic material used in several other types of filter. "The pores originate through the drying process, similar to the holes in Swiss cheese," Oehr explained. The pores turn each fiber into a filter.

For the second step, removing the endotoxin protein fragments from the plasma, Oehr and his colleagues coat the fiber with a layer of endotoxin binding molecules, including oligo-arginine, which acts as an anchor for toxin molecules. "Iteþs important that the fiber is not coated inside, because than it would cause plugging," said Oehr. In addition, thrombocytes would be activated again.

Early tests with artificial fluids and donated blood have proved successful. "Next, we start clinical trials," said Markus Storr, project manager at the company where the filter is being developed - Gambro in Hechingen, near Stuttgart. Storr will present the new filter to a broader audience at the European Society of Artificial Organs annual meeting, in Aachen, Germany, in September.

Besides clearing blood following sepsis, Storr predicts that the filter could also be used for dialysis. "Dialysis works through a simple size-dependent filter, which works because it lets past uremic toxins, which are small enough," he said. Storr and Oehr hope to use their new nanofilter to clear blood not just faster but also, in some cases, better. But, they warn, "First we have to take the hurdle of the clinical trials, then we will see."

BioMedNet, News, 26. August 2003

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