Polyethersulfone Hollow Fiber Membranes for Hemodialysis

Polyethersulfone (PES) is one of the most important polymeric materials and is widely used in separation fields. PES and PES-based membranes show outstanding oxidative, thermal and hydrolytic stability as well as good mechanical and film-forming properties. PES membranes could endure many kinds of sterilized methods, including epoxy ethane gas, steam, and γ-ray. Furthermore, PES-based membranes show high permeability for low molecular weight proteins when used as hemodialysis membranes. Thus, PES membranes are also widely employed in biomedical fields such as artificial organs and medical devices used for blood purification, e.g., hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis and plasma collection (Zhao et al., 2001; Tullis, et al., 2002; Samtleben et al., 2003; Werner et al., 1995), especially in recent years. However, when contacting with blood, proteins will be rapidly adsorbed onto the surface of PES membrane and the adsorbed protein layer may lead to further undesirable results, such as platelet adhesion, aggregation and coagulation. As a consequence, the blood compatibility of PES membrane is not adequate, and injections of anti-coagulants are needed during its clinical application (Liu et al., 2009). The main disadvantage is related to the relatively hydrophobic character of PES membrane. And many studies have concluded that membrane fouling (as caused by protein adsorption) is directly related to hydrophobicity as reviewed by Van der Bruggen (Van der Bruggen, 2009) and Khulbe et al. (Khulbe et al., 2010), although the opposite has also been reported (Yu et al., 2008). Membrane fouling is mainly caused by adsorption of nonpolar solutes, hydrophobic particles or bacteria (Van der Bruggen, 2009; Koh et al., 2005). It is a serious problem in membrane filtration, resulting in a higher energy demand, shorter membrane lifetime, and unpredictable separation performance (Agenson & Urase, 2007). Thus, PES hollow fiber membranes used in hemodialysis are usually modified by hydrophilic polymers. For the modification of PES membranes, there are three approaches: (1) bulk modification of PES material, and then to prepare modified membrane; (2) surface modification of prepared PES membrane; and (3) blending, which can also be regarded as a surface modification. The modification procedures allow finding a compromise between the hydrophobicity and hydrophilicity, and localize the hydrophilic material specifically in the membrane pores, where they have a positive effect on flux and fouling reduction, and on the membrane