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Kidney Week

Abstract: FR-PO467

Outside-In Filtration Technology for Prolonged Filter Life

Session Information

Category: Dialysis

  • 701 Dialysis: Hemodialysis and Frequent Dialysis


  • Stamatialis, Dimitrios, University of Twente - Faculty of Science and Technology, Enschede, Netherlands
  • Kelly, Thomas D., MedCatalyst Consulting, LLC, Highland Park, Illinois, United States
  • Labib, Mohamed E., NovaFlux Inc., Princeton, New Jersey, United States

Maintaining circuit patency is a prerequisite for optimal treatment efficacy and is essential for continuous renal therapies. In currently marketed dialyzers, blood flows in the intra-luminal (IL) space where formation of thrombi inside the fibers leads to filter blockage. This effect limits set life in continuous acute therapies. NovaFlux is developing Outside-In (OI) hemodialyzers in which blood flows in the inter-fiber (IF) space and dialysate flows in the IL space.


In a simulated extracorporeal circuit we measured pressure drop and filter life using both bovine and donated human blood. Clearance of small and middle solutes were measured in the Outside-In and Inside-Out filter configurations using standard methods. Clotting of different zones of the filter was made by disecting the filter and estimating the number of clots in each zone.


In-vitro data using a conventional dialyzer in an OI configuration (blood outside fiber) reveals significantly lower membrane clogging and extended filter life. OI increases filter life to over 100 h vs ~24 h with standard filter flow with statistically equivalent clearance[i]. These advantages are due to new hydrodynamics where blood flows in 3-D interconnected flow channels created in the IF space.

When a conventional hemodialyzer is used in the OI configuration, we discovered that stagnant zones are created within the filter. Such zones can be eliminated with a modified filter housing that maintains an optimal blood shear rate and uniform velocity distribution. NovaFlux is developing prototype housings to overcome such limitations.

[i] Dukhin SS, Labib ME, et al. OI HF for prolonged operation. Jour Mem Sci, 464 (2014) 173–178.


Two key refinements are required for completing commercial OI dialyzers, namely: modified membrane and housing design. Current membranes are characterized by an asymmetrical membrane structure with a smooth tight inner luminal skin (active membrane layer). This membrane structure is reversed for OI so that the blood contacts a smooth active membrane layer on the outer surface of the fiber. We have made progress in developing a hemocompatible OI PES hollow fiber with an outer active hydrophilic membrane layer. OI dialyzers with these modifications should be able to be produced by current production equipment with relatively minor modifications, enabling longer set life and lower anticoagulation.