The dialyzer consists of a dialysis membrane and its supporting structure to replace the kidney. The dialysis membrane is the main part of the dialyzer, which separates the blood from the dialysate. During dialysis, blood and dialysate flow in opposite directions on both sides of the membrane, and water and solutes are exchanged through the semi-permeable membrane. The performance of the dialyzer determines the effect of the dialysis treatment and is an important reference factor for the development of hemodialysis programs.
The characteristics of the hemodialyzer are composed of two parts: design characteristics and working characteristics. Design features include the configuration of the dialyzer, the pre-charge of the blood chamber and the dialysate chamber, the type of membrane, and the biocompatibility. Working characteristics include the transfer rate of different solutes and water. There are several classification methods for dialyzers.
Dialyzers are divided into tube type, flat type, and hollow fiber type. At present, the commonly used dialyzers are hollow fiber type, and the flat-type and tube-type dialyzers used in the early days have been basically eliminated.
The hollow fibre dialyzer is composed of 8000-12000 hollow fibers, the fiber inner diameter is 200-300um, and the wall thickness is 2-30um. The hollow fibers are bundled into bundles and placed in the formed dialyzer casing, and the casing and the dialyzing membrane are sealed with polyurethane. The blood flows through the hollow fibers, and the dialysate flows in the opposite direction outside the fibers.
According to the membrane material, dialyzers can be divided into 4 categories:
1. Regenerated cellulose membrane dialyzer, including copper imitation membrane and copper ammonia membrane dialyzer. There are free hydroxyl groups on the surface of cellulose, which can react with blood components and has poor biocompatibility. After the Cupra treatment, the fiber surface is smoother and the biocompatibility is improved.
2. Acetate cellulose membrane dialyzer. The cellulose is acetylated before the film is formed, which improves the biocompatibility and performance of the film.
3. Replace the fiber membrane dialyzer. Blood imitation membrane is an alternative copper imitation membrane because its surface-free hydroxyl groups are covered by tertiary ammonia compounds, which have good biocompatibility.
4. Synthetic fiber membrane dialyzer. Materials for this dialyzer include polyacrylonitrile, polymethylmethacrylate, polysulfone, polycarbonate, polyethylene, and polyamide. They have a higher transport coefficient and ultrafiltration coefficient, better biocompatibility, but a higher price.
According to the ultrafiltration coefficient, there are two different dialyzer types:
1. Low ultrafiltration coefficient dialyzer. Ultrafiltration coefficient <15ml/(mmHg.h㎡), including copper imitation membrane, cuprammonium membrane, blood imitation membrane, and cellulose acetate membrane.
2. High-throughput and high-efficiency dialyzer. Ultrafiltration coefficient> 15 ml/(mmHg.h㎡), has a very high removal rate for medium molecular weight substances and can remove large molecular weight β2-microglobulin and other macromolecular substances. Typical high-efficiency hemodialyzers include polysulfone membrane series, PAN membrane, PMMA membrane, and cellulose acetate membrane dialyzer.