The Self-Regulating Bioartificial Kidney, Part 1: Anatomy of the Device

With the growth of donor chains and other transplant opportunities, more patients with end stage renal disease (ESRD) are receiving transplants, experiencing new ways to live with their kidney failure and achieving better outcomes. In the future—thanks to a convergence of key breakthrough technologies and the research and work of, most notably, nephrologists William Fissell, MD, and David Humes, MD, and bioengineer and UCSF pharmacy professor Shuvo Roy, PhD—patients may gain even further access to kidney transplants through bioartificial kidneys.

The Kidney Project

Dr. Fissell, Dr. Humes and, later, Dr. Roy began work on a bioartificial kidney in the late 90s and early 2000s. The project languished for a period of time and was resurrected with such great energy in 2007 that in 2015 Fissell and Roy officially launched The Kidney Project. Its goal was “to create a small, surgically implanted and free-standing bioartificial kidney to treat ESRD.”

Although the Kidney Project and its technology are still at an early stage of development, the bioartificial kidney has recently been moving through porcine trials. It is possible that human trials could start in the near future, potentially leading to next steps and, ultimately, FDA approval. The timeframe for this is dependent on a number of events but, if all goes well, approval could occur within the early part of the next decade.

The bioartificial kidney

The bioartificial kidney is about the size of a soda can. It will sit in the abdomen, close to the bladder, where it will perform the filtration function of the glomerulus. It will also dispose of waste and direct nutrients back into the bloodstream.

The heart of the device is a stack of approximately 15 silicon microchips, coated with a biocompatible film that prevents the need for blood thinners. These microchips filter the incoming blood. On the inner side of these chips, a bioreactor of lab-grown kidney cells live and move nutrients back into the body. The heart circulates blood to the device similar to how it functions with natural organs.  In this case, the common iliac artery is connected to a tube that directs blood into the device. Another tube sends filtered blood into the common iliac vein. An additional silicone tube exits the device to move waste products to the bladder. While not yet confirmed, the device is expected to deliver GFR values of 20 to 30 mL/min.

One of the unique properties of the bioartificial kidney is that the microchip scaffolding serves as a barrier between the body’s immune system and the live cells in the device, so the risk of rejection is virtually eliminated.

The device is designed to last for years. If it fails, its filter or cells are reparable through minimally invasive surgery. Implantation will be similar to kidney transplant surgery; once available to the public, it can be completed by a trained surgical implant team at any hospital.

Fabric of the kidney: silicone, silicon and bioreactors

The device would not be feasible without the confluence of contemporary technology, including 3D printing, nanotechnology and laboratory cell advancements. 3D printing enabled production of the external tubing prototypes, and made modeling of the silicone interior possible. Silicone is the perfect material to provide the needed durability and flexibility for such a device, and 3D printing can produce the components with precision.

Nanotechnology supplies the precise tolerances needed in the silicon microchip filter stack. Each chip mimics glomeruli, and today’s manufacturing technology enables reliable replication of the seven nanometer slits that nephrons have for filtering blood components while keeping larger molecules out.

Growing suitable kidney cells in the lab was crucial to the device’s development. The “bio” in bioartificial is the product of years of research performed by Dr. Humes. His work in extracting and developing a specific kind of kidney cell found on the back end of cadaver nephrons for his (extracorporeal) Renal Assist Device set the stage for growing the human renal tubule cells used in the bioartificial kidney.

Upcoming post: The Self-Regulating Bioartificial Kidney, Part 2: Managing the Challenges