**1. Introduction**

64 Progress in Hemodialysis – From Emergent Biotechnology to Clinical Practice

Woodbury, D. (1956). Effect of acute hyponatremia on distribution of water and electrolytes

1956), pp. 281-286, ISSN 0002-9513

in various tissues of the rat. *The American Journal of Physiology.* Vol.185, No.2, (May

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

Polyethersulfone Hollow Fiber Membranes for Hemodialysis 67

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

Blending is the simplest and most widely used method to modify PES membranes both for flat-sheet and hollow fiber membranes, though sometimes the results might be not very well. By directly blending with hydrophilic polymers, such as polyvinylpyrrolidone (PVP) (Barzin et al., 2004; Mosqueda-Jimenez et al., 2006; Su BH, et al., 2008; Wang et al., 2009) and polyethyleneglycol (PEG) (Wang et al., 2006), PES membranes are easy to be modified; here PVP and PEG also are also used as pore-forming agents. The hydrophilicity of the membranes increased, the antifouling property and blood compatibility are also increased (Su BH, et al., 2008; Wang et al., 2006). However, the elution of the blended hydrophilic polymer is unavoidable. Thus, amphiphilic copolymers are synthesized recently and used for blending with PES to prepare membranes (Zhu et al.; 2008a, 2008b; Zhao et al., 2008; Peng et al., 2009). For hemodialysis membranes, the objective of blending is to improve the membrane hydrophilicity, biocompatibility, and other properties, such as protein

In our recent study (Su BH, et al., 2008), larger molecular weight PVP was used to blend with PES to prepare hollow fiber hemodialysis membrane, and the performance was evaluated in vitro and in vivo. The biocompatibility profiles of the membranes showed slight neutropenia and platelet adhesion at the initial stage of the hemodialysis. The clearance and the reduction ratio after the hemodialysis of small molecules (urea, creatinine,

Barzin et al. (Barzin et al., 2004) prepared two kinds of PES hollow fiber membranes for hemodialysis by blending two ratios of PES to PVP (PES/PVP = 18/3 and 18/6 by weight). It was observed that the water flux of the hollow fiber increased significantly when heattreated in water, while decreased when heat-treated in air. On the other hand, the molecular weight cutoff of the hollow fiber increased slightly when heat-treated in water, while decreased drastically when heat-treated in air. SEM images also showed that the surface morphology of the membranes was different before and after heat-treatment. The performance data of the hollow fiber heated in air at 150 C was found to be the most appropriate for hemodialysis application. It was also found that the hollow fiber membrane prepared from the blend ratio of PES/PVP = 18/3 showed slightly higher flux than that

phosphate) for the PES membrane were higher in vitro than that in vivo.

**2.1 Blending** 

antifouling property.

**2.1.1 Improve biocompatibility** 

surface to improve blood compatibility. However, not all the methods are suitable for the modification of PES hemodialysis membranes.

For hemodialysis membranes, safety and efficiency should be evaluated firstly in vitro before clinical application, and simulation solutions are used. Through the experiments in vitro, many results, which are useful for clinical applications, could be obtained, including protein adsorption, platelet adhesion, ultrafiltration (UF) coefficient, and solute clearances (such as for urea, creatinine, and phosphate, and so on). For high-flux hemodialysis membranes, the clearance of 2-microglobin should be investigated. When the membranes are applied for patients, the safety and efficiency are also very important.

In the present chapter, preparation and characterization of PES hemodialysis hollow fiber membranes are discussed firstly, and then the safety and efficiency in vitro and in vivo are discussed.
