| Nanoparticles may someday come to the rescue of people exposed to chemical, biological or radiological hazards. Argonne researchers are in the early testing stages of a system that would cleanse the blood of contaminants using tiny magnetic particles and a portable, external magnetic separator. Current methods of cleaning the blood of radioactive and other hazardous materials are mainly limited to dialysis and filtration techniques, said Michael D. Kaminski of Argonne's Chemical Engineering Division. Kaminski is developing the new system with Axel J. Rosengart of the University of Chicago. Unfortunately, current medical procedures to detoxify human blood are restricted to only a few types of toxins, drastically limiting treatment options for exposed victims. Also, several important shortcomings exist with the currently available technology. Treatments can take several hours to complete, require the turnover and filtration of large volumes of blood, are rather inefficient at removing toxins and can be risky for the patient. For these reasons, current methods are mostly restricted to patients with kidney failure and certain types of drug overdoses. Alternative treatments exist, such antibodies and chelators - substances that combine with and neutralize toxins. These treatments can be used for specific kinds of toxins, but are not efficient. In addition, they can cause serious side effects, such as allergic reactions and organ failure. "The best that doctors can do for most biohazard exposure is supportive treatment," Kaminski said. "This new system will be designed to directly remove the toxic agents from the bloodstream — quickly and efficiently." The biohazard detoxification system envisioned by Kaminski and Rosengart will use biodegradable nanoparticles between 100 and 5,000 nanometers (one nanometer is one ten-millionth of a centimeter) in size — small enough to pass through tiny blood vessels and yet large enough to avoid being filtered from the bloodstream by the kidneys. The particles will contain a magnetic iron compound and will be coated with a type of polyethylene glycol, which prevents them from being attacked by white blood cells. The particles will contain a specific protein that binds to a specific toxic agent. The particles would be intravenously injected into the patient and circulate throughout the bloodstream, where the toxins would bind to the nanoparticle-antitoxin surfaces. To subsequently remove the nanoparticles and the attached toxins, a small dual-channel shunt (similar to exchange transfusion tubing) inserted into an arm or leg artery would circulate blood to and from an external magnetic separator. Within the separator, blood would flow through a branching array of tiny tubes, where strong magnets would immobilize the iron-based particles. Cleansed blood would continue to flow through the tubes and back into the body. Recent tests on rats showed the system's promise. The scientists used horseradish peroxidase, an enzyme commonly used in biology experiments, to simulate a toxin. The nanoparticles were made of magnetite, a highly magnetic mineral, encapsulated in polystyrene spheres. Various nanoparticle sizes and compositions were tested; the level of "toxin" in the rats' bloodstreams fell by 50 percent in a half-hour or less. "Although the immediate focus of the research centers on likely biological, chemical and radiological warfare toxins, the technology could be extended to other medical conditions," said Rosengart. The system may lend itself to drug and medication overdose emergencies, for example, or treatment of various chronic or acute illnesses. The foundation for this work was laid last year when Kaminski, Rosengart and their colleagues completed a small exploratory research project that led directly to this larger DARPA-funded research program. Future research will center on determining the optimum nanoparticle composition, finding types of receptors to bind to various toxins and developing a compact external separator that can be used by emergency responders. |