Honorable Mention: Novaflux Outside-In Filtration (OIF)
Hollow fiber dialyzers/filters have always used intraluminal (IL) blood flow. Intra-fiber thrombus deposition limits filter life even with systemic anticoagulation. We propose that Outside In Filtration (OIF) in which blood flows on the outside of the fiber and dialysate flows in the IL space, may reduce or eliminate the anticoagulation required for all dialytic procedures and allow the long filter life required for CRRT and novel continuous/wearable therapies. Preliminary data shows that OIF has lower membrane clogging and is capable of extending filter life. In vitro data from testing with conventional filters using OIF flow demonstrate that OIF increases filter life to over 100 h vs ~24 h with standard filter flow with statistically equivalent clearance. With OIF, any thrombus formed have a minimal effect on blood flow, filter pressure, diffusive clearance, or filtrate flux due to dynamic 3D flow channels formed in the inter fiber (IF) space, thus overcoming obstacles to longer filter life.
Research points to two areas to refine the OIF technology, membrane and housing.
- Dialysis membranes are characterized by a smooth inner luminal active membrane skin layer. For OIF the active membrane layer is reversed with a thin tight smooth outer skin with a hydrated hydrophilic layer for hemocompatibility.
- If a conventional hemodialyzer is used for OIF, blood flows easily through the inter fiber space but a stagnant area forms at the blood inlet as the blood velocity and direction change upon entry into the fiber bundle. Stagnant areas can be eliminated with a new filter housing geometry that maintains a blood shear rate between 300-2500 sec-1 and a uniform velocity distribution in the inter fiber space. Novaflux is developing prototype housings with blood inlet design modifications to provide steady blood velocity and uniform flow distribution to prevent these complications.
OIF has the potential to reduce/eliminate anticoagulation for extracorporeal renal therapies, increase filter life for CRRT and reduce of small air emboli associated with priming thus enabling novel continuous/wearable renal technologies while lowering cost.
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