There are three basic dialyzer designs: coil, parallel plate, and hollow fiber configurations.
Coil dialyzer: Coil dialyzers consist of a cellulose acetate membrane tightly wrapped around a plastic or metal coil and encased in a rigid plastic housing. The coil dialyzer was the first type of dialyzer sold commercially and mass produced. This design had serious performance limitations, which gradually restricted its use as better designs evolved. The coil design did not produce uniform dialysate flow distribution across the membrane. More efficient devices have replaced the coil design.
Parallel Plate Dialyzer: Sheets of membrane are mounted on plastic support screens, and then stacked in multiple layers ranging from 2 to 20 or more, like a sandwich. The blood flows through the sheets of the membrane. This design allows multiple parallel blood and dialysate flow channels with a lower resistance to flow. The physical size of the parallel plate dialyzers has been greatly reduced since their introduction. There have been major improvements which provide thinner blood and dialysate channels with uniform dimensions, minimal masking or blocking of membranes on the support, and minimal stretching or deformation of membranes across the supports.
Hollow Fiber Dialyzer: This is the most effective design for providing low-volume high-efficiency devices with low resistance to flow. The fibers in the device are termed the fiber bundle. The fibers are potted in polyurethane at each end of the fiber bundle in the tube sheet, which serves as the membrane support. The hollow-fiber artificial kidney (HFAK)/hollow fiber dialyzer is by far the most commonly used dialyzer. HFAKs are available in a wide variety of sizes and membranes.