Morphological Characterization of the Polyflux 210H Hemodialysis Filter Pores

Abstract

Background. Morphological characterization of hemodialysis membranes is necessary to improve pore design. Aim. To delineate membrane pore structure of a high flux filter, Polyflux 210H. Methods. We used a Joel JSM-6010LV scanning electron microscope (SEM) and a SU6600 Hitachi field emission scanning electron microscope (FESEM) to characterize the pore and fiber morphology. The maximal diameters of selected uremic toxins were calculated using the macromolecular modeling Crystallographic Object-Oriented Toolkit (COOT) software. Results. The mean pore densities on the outermost and innermost surfaces of the membrane were 36.81% and 5.45%, respectively. The membrane exhibited a tortuous structure with poor connection between the inner and outer pores. The aperture's width in the inner surface ranged between 34 and 45 nm, which is 8.76-11.60 times larger than the estimated maximum diameter of β2-microglobulin (3.88 nm). Conclusion. The results suggest that the diameter size of inner pore apertures is not a limiting factor to middle molecules clearance, the extremely diminished density is. Increasing inner pore density and improving channel structure are strategies to improve clearance of middle molecules.

Figure 1

(a) Outer surface of a Polyflux capillary at 200x with measurements, (b) view of the cross section of a Polyflux capillary at 250x, (c) morphology of outside pore in contact with the dialysate at 800x, (d) morphology of outside pore in contact with the dialysate at 3000x, (e) morphology of outside pore in contact with the dialysate at 5000x, and (f) pores on the dialysate side of the Polyflux 210H capillary at 1000x with measurements.

Figure 2

(a) Morphology of the pores in contact with the blood at 15,000x. (b) Morphology of the pores in contact with the blood at 50,000x

Figure 3

(a) Dissected Polyflux capillary showing the morphologies of the outer and inner surfaces at 200x, (b) capillary wall thickness of Polyflux 210H at 1000x with measurements. (c) Cross section of Polyflux 210H illustrating the radial supporting structure that extends from the inner skin layer of the capillary to the outside surface. (d) Cross section of Polyflux 210H at 1000x illustrating the radial variation in compactness in the capillary's porosity.