A Review of Commercial Developments and Recent Laboratory Research of Dialyzers and Membranes for Hemodialysis Application

Abstract

Dialyzers have been commercially used for hemodialysis application since the 1950s, but progress in improving their efficiencies has never stopped over the decades. This article aims to provide an up-to-date review on the commercial developments and recent laboratory research of dialyzers for hemodialysis application and to discuss the technical aspects of dialyzer development, including hollow fiber membrane materials, dialyzer design, sterilization processes and flow simulation. The technical challenges of dialyzers are also highlighted in this review, which discusses the research areas that need to be prioritized to further improve the properties of dialyzers, such as flux, biocompatibility, flow distribution and urea clearance rate. We hope this review article can provide insights to researchers in developing/designing an ideal dialyzer that can bring the best hemodialysis treatment outcomes to kidney disease patients.

Keywords: blood; commercial dialyzer; dialysis; dialyzer design; hemodialysis; membrane.

Figure 1

(a) Number of research publications related to hemodialysis and dialyzers for the period of 1970–2020 (data from Scopus; assessed on 7 July 2021; search within: article title, abstract, keywords; search documents: “hemodialysis” or “haemodialysis” (for hemodialysis) and “dialyzer" or “dialyser” (for dialyzer)) and (b,c) number of research papers contributed by top 10 countries for hemodialysis- and dialyzer-related articles (inset: picture chart of country’s contribution in %).

Figure 2

The SEM images of Polyflux^® L dialyzer membrane, (a) membrane wall showing porous finger-like structure, (b) compact sponge-like layer and (c) thin dense layer [41].

Figure 3

The SEM images of Fresenius Helixone^® dialyzer made up of PSf membrane, (a) entire membrane structure, (b) partial cross-section showing skin layer of about 1 μm, (c) inner surface morphology (scale: 5 μm) and (d) outer surface morphology (scale: 2 μm) [26].

Figure 4

(a) SEM images of nanofibrous-based TFNC membranes with different concentrations of PVA coating solution, (i) 1 wt%, (ii) 1.5 wt%, (iii) 2.0 wt% and (iv) 2.5 wt%. (b) Relationship between pure water flux and BSA rejection of the nanofibrous-based TFNC membranes with the degree of cross-linking of the PVA hydrogel coating. (c) Sieving coefficients of best TFNC (i.e., PVA/PAN) membrane with conventional benchmark PSf membrane against several important markers. (d,e) Concentration of anaphylatoxins C3a and C5a for the samples with whole blood [82].

Figure 5

(a) Illustration of silicone nanopore membrane (SNM) fabricated using microelectromechanical system (MEMS) technology and SEM images of SNM, (b) image of membrane showing uniformly spaced array of slit pores, (c) image of the non-tortuous path of the pore and (d) close-up image of slit pore showing the smooth surface characteristic [85].

Figure 6

The microscopic images of (a) pristine PES, (b) PES/O-MWCNTs and (c) PES/PCA-g-MWCNT membranes [31].

Figure 7

(a) TEM image of synthesized Fe₃O₄/cGO and (b) SEM images of hollow fiber membranes modified by different Fe₃O₄/cGO loadings (note: M0—pristine membrane, M1—0.05% Fe₃O₄/cGO and M2—0.10% Fe₃O₄/cGO) [110].

Figure 8

(a) Location of blood port and dialysate port of a dialyzer (FX-class hemodialyzer, Fresenius) with “pinnacle structure” design [26]. (b) (i) The location of O-ring in the middle part of dialyzer and (ii) cross-section of 2.2-m² dialyzer (Fresenius Polysulfone^®) with housing made of PP [113].

Figure 9

SEM images of the cutting surfaces of two dialyzers, (a) smooth blood contacting surface and (b) rough blood contacting surface [118].

Figure 10

(a,b) Water contact angle and roughness of the inner (lumen) and outer surface of PSf membranes sterilized by different methods and (c) AFM images of outer surface of different fibers [119].

Figure 11

Selected images captured for the conditions of 25% Hct (left) and 40% Hct (right) in the blood compartment [113].

Figure 12

Contrastographic images of three different hemodialyzers, (a) P1—standard dialyzer, (b) P2—spacer yarn design dialyzer and (c) P3—Moirè structure [113].

Figure 13

Theoretical sieving curves for 4 different classes of membranes: (1) low flux (LF), (2) high flux (HF), (3) high cut-off (HCO) and (4) medium cut-off (MCO). The point in the curve where the sieving coefficient (SC) is 0.9 determines the molecular weight retention onset (MWRO) value, while the point where SC is 0.1 determines the molecular weight cut-off (MWCO) value. As the interval between MWCO and MWRO decreases, the profile of the curve becomes steeper, which leads to increased removal of large uremic toxins (e.g., β₂-m) but decreased albumin loss [24].