3 Ways to Build an Artificial Kidney
Photo: Stephen Brashear
The Wearable Artificial Kidney showed promising results in a recent clinical trial.
June 26, 2016
Three research groups taking very different approaches to building an artificial kidney all have the same goal: giving people with kidney failure an escape from today’s dialysis routine. Because dialysis keeps people alive, but it’s also pretty terrible.
A typical patient goes to a clinic three times each week to be hooked up to a dialysis machine, then lies there for three or four hours while blood cycles out of the body, through the machine, and back in again. The machine does the job that the kidneys can no longer do, filtering out toxic waste products that have built up in the blood since the last session, maintaining the balance of electrolytes, and removing excess water.
Losing time and mobility is a major downside of today’s dialysis process. Also, most patients have to carefully restrict their diet and fluid intake, and often experience extreme fatigue after treatment and other side effects including low blood pressure, nausea, and muscle cramps.
So what’s the alternative?
The team behind the wearable artificial kidney (WAK) believes the answer is a device that looks rather like a bulky utility belt. In a recent clinical trial, patients wore the WAK for 24 hours of continuous treatment. The results,published this month in the journal JCI Insight, were mixed. Technical problems halted the study early, but the inventors say those problems can be overcome, and stress that the device provided both effective treatment and better quality of life for the research subjects.
In typical dialysis machines, blood flows into a small tube called the dialyzer, where waste particles in the blood pass through a membrane into a solution called the dialysate, which carries away the waste. Fresh dialysate continuously flows into the dialyzer.
On the WAK belt, which weighs 5 kilograms, a small two-channel pump propels the patient’s blood and the dialysate through separate tubes into a small dialyzer, where the standard filtering process occurs. But in the WAK, the dialysate flows back to cartridges where the toxins are absorbed, so the solution can be cycled through again and again.
In the 24-hour test, the battery-powered wearable device cleared toxins from the blood as effectively as a traditional dialysis machine. The researchers note that studies of traditional dialysis have demonstrated better results for patients with longer treatment times, and suggest that the WAK’s constant filtering may benefit patients.
What’s more, the trial subjects’ experience suggests that the WAK can improve quality of life for dialysis patients. The subjects in the study could walk around during treatment, eat and drink whatever they wanted (because they didn’t have to worry about maintaining the correct balance of fluids and electrolytes between dialysis sessions), and sleep.
The technical problems encountered were not insignificant: In the trial’s seven participants, the researchers encountered kinked tubes, an erratic pump, and batteries and absorbent cartridges that needed replacing. Most importantly, they ran into trouble with carbon dioxide bubbles in the dialysate circuit, and gas bubbles can be deadly if they reach the heart or brain. The WAK included both gas bubble alarms and degassing vents, but the incidents made it clear that the device needs a redesign to reduce the production of gas and improve its venting.
The WAK will have to operate flawlessly to fulfill the researchers’ ultimate goal: “For treatment with the WAK to be self-administered independently by patients and caregivers in the home environment.”
2) The Cyborg Kidney
In the implantable “bioartificial kidney,” mechanical and biological parts would work in concert to mimic the natural organ.
Researchers from the University of California at San Francisco and Vanderbilt University have been forging ahead with The Kidney Project since 2010, and got a major boost last year when the U.S. National Institutes of Health gave them a $6 million grant to push on toward clinical trials. The researchers hope to start those human trials in late 2017.
The bioartificial kidney, which is about the size of a coffee cup, contains two main components: a filtering unit that uses a silicon membrane with nanopores to clear waste particles from the blood; and an innovative bioreactor unit that holds living kidney cells inside. The bioreactor performs the various metabolic and endocrine roles of a functioning kidney.
The cells inside the bioreactor cartridge come from donated kidneys that weren’t suitable for transplant. The cells grow on a synthetic scaffold with nanopores that allow small molecules through, but keep out immune system cells that patrol the body, looking for foreign invaders. This protective barrier prevents an immune reaction that would destroy the kidney cells, the researchers have shown.
Researchers haven’t yet tested an entire prototype of their cyborg kidney, but trials of the individual units have yielded promising results. In one study, described in a 2014 paper, they tested the bioreactor on patients in the ICU with life-threatening acute kidney injuries. Half the patients had their blood cycled through a dialyzer, while the other half’s blood went through both a dialyzer and an external bioreactor unit. The control group’s survival rate (measured 180 days later) was 39 percent, while the bioreactor group’s rate was 67 percent.
The Kidney Project is actively soliciting funding to reach its goal: A commercial device that offers “a cure rather than a treatment.”
3) The Dark Horse Kidney
The third contender is a young startup currently being nurtured at IndieBio, a San Francisco accelerator for biotech companies. Qidni Labs is building a fully implantable artificial kidney that uses a nano-filtration system to mimic the organ’s function, and drains waste products into the bladder.
At this point, company founder Morteza Ahmadi will divulge only the basics about his hardware and his plans. But Qidni is making progress, he says: The company will begin testing its lab prototype in pigs at the end of this month.
Ahmadi began working on miniaturized dialysis systems in 2010, while he was earning his PhD in systems engineering at the University of Waterloo, in Ontario, Canada. Like the researchers behind The Kidney Project, he also set out to make ultrathin membranes out of crystalline silicon that would serve as the filter between the blood and the dialysate.
Thanks to manufacturing techniques perfected in the semiconductor industry, such silicon membranes can be mass produced with pore sizes ranging from 5 to 20 nanometers, which means they’re big enough to allow waste particles to pass through, but too small for blood cells.
In a 2013 paper that Ahmadi published with several colleagues to describe his filtering device (pictured above), the researchers noted that this ultrathin crystalline silicon is challenging to work with because it’s prone to fracture. Also, as silicon can provoke an immune reaction, the membrane has to be coated with a biocompatible material.
Ahmadi won’t say how his design team solved these problems, or how the fully implantable device would be powered. But he does say that the device will continuously filter the patient’s blood for years without requiring maintenance or cleaning. And if the device can do that job, he can achieve his goal: “The idea is to free patients from dialysis machines forever,” he says.