Symmetric Membrane fibers
Symmetric membranes, which can be derived either from cellulose or entirely from synthetic polymers, have a homogeneous configuration throughout the membrane wall, with both the inner and outer layers usually containing similar pore sizes.
Asymmetric membranes
They synthetic polymers only, and have a thin innerselective layer and an outer thick support layer
Almost all membranes made of polysulfone (PSf) or polyethersulfone (PES) have this type of structure.
Diffusive resistance to small molecules due to the fiber wall being thick can be compensated by increasing porosity within the support layer.
Membranes made of polyethersulfone/PVP/polyamide (PEPA) contain three layers, with the outer layer providing mechanical stability
RIPPLED VERSUS STRAIGHT HOLLOW FIBERS
Rippled hollow fibers
Cellulose derived fibers are naturally wave like (Moire effect)
Synthetic fibers may be crimped to produce a rippled pattern that more evenly distributes the flow of dialysate.
Such a design prevents contact or excess packing among fibers and thus allows for better matching of blood and dialysate flows across all sections of the fiber bundle.
Cutting edge
After the membrane fibers are secured within the potting material
They are opened by cutting them in a manner that produces a smooth and flat surface
- preventing hemolysis
- blood clotting
- retention of residual blood
