Kidneys are responsible for removing harmful chemicals and impurities from our blood — the filter in the hot tub that is our body’s circulatory system. When kidneys fail, a condition known clinically as end stage kidney failure, a patient currently has two options: a kidney transplant, or dialysis.
Kidney transplants are challenging to obtain, due primarily to a massive shortage of living kidney donations. For every person who received a kidney transplant in 2016, five patients did not, and 4000 people died on the waiting list that year.
For those waiting for a transplant, dialysis is the only solution, but it is an imperfect one. Dialysis is a process in which blood is mechanically filtered to remove excess water, solutes and toxins from the blood, mimicking the job of a kidney. Compared to the real deal, it is far from a perfect replacement, as reported in a 2017 Wired feature:
Dialysis does a decent job cleansing blood of waste products, but it also filters out good stuff: salts, sugars, amino acids. Blame the polymer manufacturing process, which can’t replicate the 7-nanometer precision of nephrons — the kidney's natural filters.
Making dialysis membranes involves a process called extrusion, which yields a distribution of pore sizes — most are about 7nm but you also get some portion that are much smaller, some that are much larger, and everything in between. This is a problem because that means some of the bad stuff (like urea and excess salts) can sneak through and some of the good stuff (necessary blood sugars and amino acids) gets trapped.
Because of these realities, there has been a great deal of Internet buzz over a project out of the University of California, San Francisco named The Kidney Project. Lead by UCSF bioengineering professor Shuvo Roy and professor of medicine at Vanderbilt University William Fissell, it has the ultimate goal of creating an artificial kidney approved by the Food and Drug Administration that could be installed with a minimally invasive surgery and function for an indefinite amount of time.
The challenge, essentially, is to create a molecular-scale filter that the body can easily push blood through without the need for additional power, that does not cause the blood to clot, and that allows for the passage of "good stuff" while still blocking out the "bad stuff."
The solution the UCSF team has come up with involves two components: A nano-engineered silica filter to remove dissolved toxins, sugars, and salts, and a bioreactor containing live kidney cells that allow the body to resorb the sugar, salt, and water removed by the filter. A 2018 press release from the NIH's National Institute of Biomedical Imaging and Bioengineering describes the current conceptual design:
The experimental device is designed to accommodate up to a liter of blood per minute, filtering it through an array of silicon membranes. The filtered fluid contains toxins, water, electrolytes, and sugars. The fluid then undergoes a second stage of processing in a bioreactor of lab-grown cells of the type normally lining the tubules of the kidney. These cells reabsorb most of the sugars, salts, and water back into the bloodstream. The remainder becomes urine that is directed to the bladder and out of the body.
Advances in silicon nanotechnology spurred by electronics manufacturing gave the researchers the ability to manufacture silicon pores that consistently have the precise size and shape necessary to reduce stress on the blood cells and, as a result, clotting, Roy told Wired in 2017. On the cellular side, bioreactors that utilize living kidney cells have been tested successfully in animal studies since 1999.
The project, which aims to combine both of these elements into a single device, received a boost in 2015 when the researchers received a $6 million grant from the NIH, and the FDA included it an initiative aimed at fast-tracking the development, evaluation, and review of certain medical devices. The next steps will involve humans:
Clotting is the biggest concern, so they’ll surgically implant the device in each participant’s abdomen for a month to make sure that doesn’t happen. If that goes well they will do a follow-up study to make sure it actually filters blood in humans the way it’s supposed to. Only then can they combine the filter with the bioreactor portion of the device [...] to test the full capacity of the artificial kidney.
While some reports suggest that clinical trials began in 2017, Roy told us via e-mail that their hope was that clinical trials could begin later in 2018. He is optimistic about the prospect of bringing the device to market before the close of the decade, however. "We are hopeful that the first clinical trial will begin this year. If all goes well and funds are available, we could be on the market as early as 2020," he said.