**2.1 Blending**

66 Progress in Hemodialysis – From Emergent Biotechnology to Clinical Practice

surface to improve blood compatibility. However, not all the methods are suitable for the

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

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

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

PES hollow fiber

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

Take-up unit

Coagulation bath Solvent exchange bath

are applied for patients, the safety and efficiency are also very important.

PES spinning

dope

Pump Filter

modification of PES hemodialysis membranes.

Bore fluid

Pump Filter

Spinneret

Fig. 1. PES hollow fiber spinning line

based on the methods and the modification objective.

discussed.

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 antifouling property.
