Dialyzer Membrane Materials
Dialyzers use either cellulose-based membranes (unmodified cellulose, modified cellulose like cellulose acetate) or synthetic polymer membranes (polysulfone, polyacrylonitrile, polyamide, polymethylmethacrylate, polycarbonate, polyarylethersulfone), with synthetic membranes being the preferred choice due to superior biocompatibility and reduced complement activation. 1
Primary Membrane Categories
Cellulose-Based Membranes
- Unmodified cellulose (e.g., cuprophane): Historically popular due to low cost but markedly activate complement and cause adverse blood interactions 1
- Modified cellulose (e.g., cellulose acetate, cellulose triacetate): Less complement activation than unmodified cellulose but still more than synthetic membranes 1
- Primarily hydrophilic in structure 1
Synthetic Polymer Membranes
The most commonly used synthetic materials include:
- Polysulfone: Strong adsorptive capacity for endotoxins and β2-microglobulin; used in high-flux dialyzers 1, 2
- Polyacrylonitrile (PAN): Demonstrated reduced incidence of carpal tunnel syndrome and bone cysts compared to cellulose membranes 1
- Polyamide: Capable of adsorbing endotoxins and β2-microglobulin 1
- Polymethylmethacrylate (PMMA): Shows strong adsorptive characteristics for larger molecules 1, 3
- Polycarbonate: Adsorbs β2-microglobulin through electrical charge mechanisms 1
- Polyarylethersulfone: Modern synthetic option with good biocompatibility 2, 4
Modern synthetic membranes possess mixed hydrophobic-hydrophilic structures 1
Clinical Superiority of Synthetic Membranes
Synthetic membranes are favored because they are more biocompatible, cause less complement activation, and can adsorb endotoxins and β2-microglobulin. 1
Key Advantages
- Reduced complement activation: Unmodified cellulose membranes markedly activate the alternate complement pathway, forming detrimental anaphylatoxins 1
- Better toxin removal: Synthetic membranes adsorb endotoxins through hydrophobic domains and β2-microglobulin through electrical charge distribution 1
- Improved long-term outcomes: High-flux synthetic polyacrylonitrile membranes reduce amyloid-associated carpal tunnel syndrome and cystic bone lesions 1
- Less granulocyte impairment: Cellulose membranes impair phagocytosis, adhesion, and reactive oxygen species formation 1
Important Caveat
Despite theoretical advantages, the evidence for mortality benefit remains mixed. The Cochrane Database found no definitive evidence of benefit when synthetic membranes were compared with cellulose or modified cellulose membranes regarding mortality and dialysis-related adverse effects 1. However, the long-term effects of intense complement activation remain largely unknown, supporting the prudent choice of synthetic membranes 1
Flux Classification
Both cellulose and synthetic membranes can be classified as:
- Low-flux: β2-microglobulin clearance <10 mL/min; Kuf 4-8 mL/h/mm Hg 1
- High-flux: β2-microglobulin clearance >20 mL/min; Kuf ≥14 mL/h/mm Hg 1
High-flux membranes (whether cellulose or synthetic) remove larger molecules like β2-microglobulin more effectively due to greater porosity, reducing the risk of β2-microglobulin amyloidosis 1
Cost Considerations
Unmodified cellulose dialyzers have lower cost, which could enable life-saving dialysis therapy in resource-limited settings where synthetic membranes would be cost-prohibitive 1. However, this is the only known advantage over synthetic membranes 1.