Dr. William Fissell, an internist at the University of Michigan School of Medicine, in cooperation with the Cleveland Clinic’s Lerner Research Institute, is working to develop a superior filte. Dr. Fissell’s ultimate goal is to refine hemodialysis technology to allow for implantable renal replacement.
LiveScience reports:
The first step toward that goal, Fissell said, is improving the effectiveness of external artificial kidneys, or hemodialysis devices. Next would be to make an external device small enough for a patient to wear continuously. The final step would be a device that could be implanted, not unlike a pacemaker for the heart.
One of the keys to such a device, which Fissell and his colleagues, including Shuvo Roy, a biomedical engineer at the Cleveland Clinic’s Lerner Research Institute are developing, is a much more effective filter.
“We think that we have a platform technology that will revolutionize the way that renal replacement is delivered,” Fissell says.
Dialysis filters trap the good stuff (proteins and blood cells) and return it to the body while letting the bad stuff (toxins, excess fluids, and salt) through to be discarded.
The trick, Fissell says, is to refine the holes in the filter, which is a type of membrane. The holes need to be the right size, the right shape, and in the right pattern to let blood flow through the filter easily. They must be big enough to allow toxins to pass through the filter but not so big as to allow valuable proteins and blood cells to escape.
To trap the good stuff, current filters rely primarily on very small holes that are irregular in shape and are organized chaotically. Under a microscope they look like sponges.
But small holes means that blood must be forced through the filters with big, powerful pumps. And the chaotic patterns allow high-pressure-causing currents to form. These currents increase the pressure required to force blood through the filter.
A better membrane could be driven by a smaller, perhaps portable, pump. And an ideal membrane would work with normal blood pressure and so could be implanted into the body. The discarded toxins and other miscreants would be directed to bags attached to the patient.
Fissell’s team is building an easy-flow membrane by etching precise patterns into silicon wafers. Micromachine technologies let the scientists increase the number of pores in a given area (to 10,000 pores per square millimeter) and control their shape (a slit) and pattern (undulating rows) to reduce turbulence in the blood. The next version of the membrane will have 10 times as many pores, about 100,000 per square millimeter, further reducing the amount of pressure required to force blood through it.
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