Technical breakthroughs in the wearable artificial kidney (WAK)

Clin J Am Soc Nephrol. 2009 Sep;4(9):1441-8. doi: 10.2215/CJN.02790409. Epub 2009 Aug 20.


Background: The wearable artificial kidney (WAK) has been a holy grail in kidney failure for decades. Described herein are the breakthroughs that made possible the creation of the WAK V1.0 and its advanced versions V 1.1 and 1.2.

Design: The battery-powered WAK pump has a double channel pulsatile counter phase flow. This study clarifies the role of pulsatile blood and dialysate flow, a high-flux membrane with a larger surface area, and the optimization of the dialysate pH. Flows and clearances from the WAK pump were compared with conventional pumps and with gravity steady flow.

Results: Raising dialysate pH to 7.4 increased adsorption of ammonia. Clearances were higher with pulsatile flow as compared with steady flow. The light WAK pump, geometrically suitable for wearability, delivered the same clearances as larger and heavier pumps that cannot be battery operated. Beta(2) microglobulin (beta(2)M) was removed from human blood in vitro. Activated charcoal adsorbed most beta(2)M in the dialysate. The WAK V1.0 delivered an effective creatinine clearance of 18.5 +/- 3.2 ml/min and the WAK V1.1 27.0 +/- 4.0 ml/min in uremic pigs.

Conclusions: Half-cycle differences between blood and dialysate, alternating transmembrane pressures (TMP), higher amplitude pulsations, and a push-pull flow increased convective transport. This creates a yet undescribed type of hemodiafiltration. Further improvements were achieved with a larger surface area high-flux dialyzer and a higher dialysate pH. The data suggest that the WAK might be an efficient way of providing daily dialysis and optimizing end stage renal disease (ESRD) treatment.

Publication types

  • Comparative Study

MeSH terms

  • Ammonia / blood
  • Animals
  • Biomarkers / blood
  • Charcoal / chemistry
  • Creatinine / blood
  • Dialysis Solutions / chemistry
  • Disease Models, Animal
  • Electric Power Supplies
  • Equipment Design
  • Hemodiafiltration / instrumentation*
  • Humans
  • Hydrogen-Ion Concentration
  • Kidney Failure, Chronic / blood
  • Kidney Failure, Chronic / physiopathology
  • Kidney Failure, Chronic / therapy*
  • Kidneys, Artificial*
  • Materials Testing
  • Membranes, Artificial
  • Pressure
  • Pulsatile Flow
  • Swine
  • Time Factors
  • Uremia / blood
  • Uremia / physiopathology
  • Uremia / therapy*
  • beta 2-Microglobulin / blood


  • Biomarkers
  • Dialysis Solutions
  • Membranes, Artificial
  • beta 2-Microglobulin
  • Charcoal
  • Ammonia
  • Creatinine