Application of Membrane Distillation Technique to a New Artificial Kidney System

Hemodialysis (HD) based on both dialysis and ultrafiltration technique was first clinically performed on an acute renal failure patient 50 years ago. The technique has not been replaced ever since. In this study, we applied an industrially used membrane distillation (MD) technique as a new clinical separation technique. In MD, distilled vapor penetrates through a hydrophobic porous membrane by the driving force of vapor pressure difference, induced by a temperature difference between both sides of the membrane. In a blood purification system, the MD technique can remove some pure water from the extracorporeal blood of a patient and add some electrolytes. In this paper, we examined the water removal characteristics of MD in vitro and a canine ex vivo. In the in vitro study with a liquid-liquid system, reverse osmosis (RO) water of 10℃ and 37℃ was used as the "blood" and "penetrate" side fluids, respectively. During the experiment, a maximum of 45 mL water was collected from the "blood" to "penetrate" in 60 min at various flow conditions by using a 0.3 m^2 MD module which composed of polypropylene hollow fibers. In the in vitro study with a gas-liquid system, 6 to 80 L/min of the 10℃ cool air was used at the "penetrate" fluid side instead of the RO water on the outer side of the hollow fiber membrane. As a result, a maximum of 93.2 mL water was collected in 30 min because the cooled air had a lower heat capacity, which kept a larger temperature difference compared with the RO water in the MD module. For the ex vivo study, we verified the safety of the MD system and examined the collected amount of water removed from circulating blood in an anesthetized and bilaterally nephrectomized dog. The 4-hour experiment resulted in a body weight change from 11.4 kg to 11.0 kg and a 19.9% drop of blood volume. The MD technique is effective in removing excess water and could be a replacement therapy for patients with renal disease