Reinventing the dialysis process

Researchers in Germany are optimistic that a cryo-purification method of cleansing dialysate – the purified water used in dialysis – will pave the way for wearable, artificial kidneys

People who suffer from renal disease frequently have to undergo dialysis on a fixed, weekly schedule. For many patients, artificial washing of blood is a time-consuming, major burden. Hemodialysis often is hospital or medical centre-based and interferes deeply with the everyday lives of patients.

Also, to remove toxins from blood, large quantities of purified water – called dialysate – are required. Many patients undergo dialysis three times a week for four to five hours at a stretch. During treatment, harmful metabolites are removed from the blood in a filtering process that incorporates a semi-permeable membrane, the pores of which are so narrow that only toxins up to a certain size can fit through.

Small molecules such as water, electrolytes and uremic toxins – urea, uric acid and creatinine – transit the membrane into the dialysate, while large molecules such as proteins and blood cells are rejected. The blood is cleaned and recirculated about three times in an hour.

For each dialysis treatment, about 400 litres of dialysate are required. Hospitals and dialysis centres often use reverse osmosis systems – that consume lots of energy and are expensive – to prepare the purified water, which is then used only once, since no cost-effective method of reclaiming dialysate waste has been discovered.

Until now, that is. Researchers at the Fraunhofer Institute for Cell Therapy and Immunology in Germany are in the process of developing a cryo-purification method to cleanse dialysate, an approach that they believe will not only reduce costs, but which will pave the way for wearable, artificial kidneys.

“Dialysis water is precious,” says Dr Rainer Goldau, a scientist at the Department of Extracorporeal Immunomodulation at the Fraunhofer Institute in Rostock. “Although there are elaborate enzymatic techniques capable of cleaning dialysate, the filters and cartridges required for them are very expensive,” he says.

In his research, Goldau has focused on methods of cryo-purification based on freeze techniques used in the beverage and chemical industries. Through a process called upconcentration, he aims to reclaim from the dialysate all but the two to three litres of water the human body would usually eliminate in a day to get rid of toxins, and which patients can replace by drinking fluids.

“The remainder is cleared and fed back to dialysis,” he says. “In our experiments the volume of water that has to be discarded is less than 10 percent. This amount is required to filter the toxins. Thus, when it comes to upconcentration, our technique is almost as effective as the kidneys themselves,” he maintains.

Goldau says cryo-purification takes advantage of an ice crystal’s ability to exclude all previously dissolved contaminations, which are repelled to the surface when water freezes. “This permits separation of all the uremic toxins – metabolic waste products that the body needs to eliminate – from the dialysate,” he explains.

He says the procedure can be implemented within wash columns that are customary in the beverage or chemical industries. “For mobile dialysis, a small wash column is sufficient to produce 30 to 40 ml a minute of dialysate.

“To prepare fresh dialysate, only a small amount of energy is required. Electricity to power the process could arbitrarily be drawn from mains, a car battery or solar panels. A respective lab demonstrator with a chiller is being constructed and a patent application has been filed for the process,” he says.

Goldau says cryo-purification can be designed to be mobile. “Wearable hemodialysis would be feasible,” he says, explaining that blood could be extracted from the body via vascular access and returned after being washed in a vest worn by the patient, which incorporates a dialysis filter membrane and disposable cylinders containing up to four litres of dialysate.

“Every two or three hours the patient would have to connect the vest to a non-stationary base unit, which would flush the waste dialysate and refill the chambers with purified water within the same period it takes a healthy individual to visit the toilet,” he says.

Though development of the system is still in its early stages, Goldau believes that wearable, artificial kidneys could be on the market within five to seven years.