16.08.2005 New opportunities for cleansing blood

Extracorporeal blood cleansing techniques are a vital treatment method in modern medicine. This becomes all the more apparent given that every year there are approx. 150 million dialysis patients worldwide with chronic or acute renal failure and around 200,000 people in Germany alone who contract potentially fatal blood poisoning (septicaemia). To combat this, new treatments known as apheresis have been developed alongside conventional kidney dialysis techniques. These treatments can remove specific toxins from the blood. Together with Hechingen-based Gambro Dialysatoren GmbH and the Institute for Interfacial Engineering (IGVT) at the Univer-sity of Stuttgart, researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB are working on developing innovative hollow fibre mem-branes for blood cleansing. This new medical technology aims to filter toxins out of the blood without changing the patient's blood count.

Up till now, one common problem with blood cleansing was that the sensitive blood cells had to be separated from the blood plasma in a mechanically complex and therefore expensive two-stage process before the actual filtering process could begin. The objective of the scientists involved in this development was to create a membrane structure that integrates both steps. In a development project lasting three years, the team succeeded in using a dry low-pressure plasma gas phase technique to modify the surface of a hollow fibre membrane so that the plasma can be sepa-rated in a single process step without an upstream plasma filter and toxins can be specifically filtered out. "What's revolutionary about this development is that not the entire surface of the filter membrane is modified, but rather that the modification is regioselective," explains project manager Dr. Michael Müller from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB. According to Müller, this is the only way of ensuring the hollow fibre membrane developed by Gambro especially for this application is compatible with blood. "Surfaces that absorb toxins are often not suitable for use with blood." As a result, traditional medtech methods for apheresis generally require blood cells and plasma to be separated and treated independently. "This conundrum is resolved by ensuring the areas of the membrane in contact with the blood cells remain compatible with blood. The surface is only functionalised in areas where the blood plasma flows," says Müller.

To this end, the Fraunhofer Institute for Interfacial Engineering and Biotech-nology IGB developed a dry-working plasmachemical treatment method which ensures that only the surface of the external wall of the hollow fibre and the internal surface of the membrane pores are functionalised. However, the surface properties of the lumen, the internal canal of the hollow fibre, remain unchanged. When the blood flows through the porous hollow fibres in the filtration process, only the plasma penetrates the finer pores. The larger, sensitive blood cells remain in the blood-compatible lumen, meaning the cells and plasma follow different routes. Adhesion molecules remove toxins from the plasma at the surface areas functionalised by the special gas phase process. The detoxified plasma and blood cells from the lumen are reunited at the end of every fibre. An essential part of this invention is the low-pressure plasma technology from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB to modify the chemical properties of the membrane surface. This technology utilises a further key benefit of this technique, namely the possibility of functionalising large surfaces within a short time using environmentally friendly procedures.

The innovative blood washing system successfully passed the majority of tests in the lab phase. "The next step is to integrate the lab operation into an existing production line," says Müller. Everything from membrane manufacture and the inte-gration of low-pressure plasma treatment right through to the finished module has to run automatically at a defined speed. After chemical processing, the ultra-thin capillary membranes are brought together in a plastic filter module with a diameter of approx. five centimetres that can hold up to 3,000 fibres arranged in parallel. The next stage is to perform clinical tests involving the new apheresis technique.

Medtech research and development work is always lengthy and expensive and it generally takes around ten years to get from the initial idea to an approved product. However, Dr. Müller believes the market potential for the new blood washing technique is very positive. The range of potential applications for the innovative modified hollow fibre membrane is immense. The new filtration process could go beyond treating blood poisoning and be used for cases of drug poisoning, leukaemia and other immunological diseases. In essence, says Müller, close cooperation bet-ween research, industry and hospitals in medtech development work is indispen-sable. "Although we have developed the modified hollow fibres, clinicians require the finished module integrated into a usable device before they can actually use the innovation." Cooperation such as that between the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, Gambro Dialysatoren GmbH and a medical institute is typical of the STERN region and ideal for Dr. Müller: "We benefit from optimal synergies in this region. There are no difficulties when it comes to locating the required expertise in all fields and pathways are kept short."

The external diameter of the hollow synthetic fibre is 0,4 mm. © Gambro Dialysatoren GmbH

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