**2. Preparation and modification of polyethersulfone hollow fiber membranes**

Fig. 1. PES hollow fiber spinning line

PES hollow fiber membranes for hemodialysis are usually spun by dry-wet spinning technique based on liquid-liquid phase separation method, see Figure 1. The cross-section view of the PES hollow fiber membrane is shown in Figure 2. After post-treatment, PES hollow fiber hemodialyzer is prepared by using polyurethane resin as the potting material. However, the blood compatibility of the PES membrane is not adequate, and injections of anticoagulants are needed during hemodialysis. Thus, all the PES membranes used for hemodialysis are not the pristine PES membranes. As a hydrophilic additive and a membrane forming agent, poly (vinyl pyrrolidone) (PVP) is most widely used for the modification of PES membranes by blending. Many other methods can also be used for modifying PES membranes. The aim of the modification is to improve the biocompatibility and protein antifouling property of the membranes, thus different sections are separated based on the methods and the modification objective.

Fig. 2. SEM images of PES hollow fiber membrane (From reference, Su et al., 2008)
