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Nearly 400,000 people in the United States–and as many as two million worldwide–rely on dialysis machines to filter toxins from their blood because of chronic kidney failure.

Patients must be tethered to machines at least three times a week for three to five hours at a stretch. Even then, a dialysis machine is only about 13 percent as effective as a functional kidney, and the five-year survival rate of patients on dialysis is just 33 to 35 percent. To restore health, patients need a kidney transplant, and there just aren’t enough donor organs to go around. In August, there were 85,000 patients on the U.S. waiting list for a kidney in the U.S., while only 17,000 kidney transplants took place last year.

A collaborative, multidisciplinary group of labs is working to create the first implantable artificial kidney. The prototype, revealed last week, is compact, no larger than a soup can. It not only filters toxins out of the bloodstream but also uses human kidney cells to perform other vital functions, such as regulating blood pressure and producing vitamin D.

“Dialysis is not only time-consuming, but it’s also debilitating. Many patients don’t feel good, because it’s not doing all the functions of a normal, healthy kidney,” says bioengineer Shuvo Roy, whose lab at the University of California, San Francisco produced the new device and is already testing it in animals. “The kidney doesn’t just filter toxins. It also has metabolic functions and hormonal functions, and dialysis doesn’t capture these abilities.”

Making an artificial kidney small enough to fit inside the body is, however, a big challenge. A healthy kidney filters 90 liters of water each day. Current dialysis machines are the size of a small refrigerator, and require substantial pressure to pump enough water through the machine’s porous membranes to allow contaminants to be filtered out of the blood.

The new implant is a fusion of multiple lines of research, and takes advantage of two recent advances in the field. University of Michigan nephrologist David Humes has shown that human kidney cells could be used in a room-sized filtration machine to greatly improve the health of patients whose kidneys have stopped functioning. Meanwhile, Roy and William Fissell, a nephrologist at the Cleveland Clinic, have produced a nano-pore silicon membrane that–with its dense and precise pore-structure–could help miniaturize dialysis machines.

The prototype is a two-part system: half consists of a toxin-removing filter, in which thousands of silicon membranes are stacked together. Their nano-pores are so dense, and so precisely shaped, that they can filter very precisely using only the force of the body’s own blood pressure. Blood flows in through this filter, where the toxins, sugars, water, and salts are removed as a filtered solution.

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Credit: William Fissell, The Cleveland Clinic.

Tagged: Biomedicine, dialysis, donor organs, implantable devices

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