**3. Biocompatibility and separation performance of the membrane in vitro**

The biocompatibility and separation performance of PES-based hemodialysis membranes in vitro are discussed. Protein adsorption on material surface is a common phenomenon during thrombogenic formation. Thus, the amount of protein adsorbed on the PES membrane is considered to be one of the important factors in evaluating the blood compatibility of the membrane. The adhesion of platelets to blood-contacting medical devices is a key event in thrombus formation on material surface. Thus, protein adsorption and platelet adhesion on PES membrane surface are studied. In addition, the clearance and

Polyethersulfone Hollow Fiber Membranes for Hemodialysis 73

character, surface free energy and topological structure, solution environment (e.g. pH, ionic strength), and protein characters (Leng et al., 2003; Okpalugo et al., 2004). The hydrophilic/hydrophobic character of membrane material plays a relatively important role in the interaction between protein and membrane. Since hydrophilic surface preferentially adsorbs water rather than solutes, many researchers have followed the idea of increasing the hydrophilicity of a membrane material with the goal of reducing protein fouling and/or protein adsorption (Mockel et al., 1999). Herein, the surfaces of the PES and some typical modified PES membranes (Copolymer of poly (acrylonitrile-co-acrylic acid), PAN-AA, modified PES membranes with the ratios of the copolymer to PES of 0/16, 0.4/16 and 0.6/16, respectively; and BSA grafted membranes following the copolymer/PES blended membranes) were studied in relation to the adsorption of BSA and FNG in vitro, data are

The adhesion of platelets to blood-contacting medical devices is a key event in thrombus formation on material surface. After the platelet adhesion and activation, a series of actions could produce the thrombins which led further coagulant. Therefore, in vitro platelet adhesion assay could reflect the blood compatibility of material surface. To study the platelet adhesion, the morphology of the adhering platelet and the amounts of platelet adhesion on the membrane surfaces are always investigated through scanning electron

Figure 6 shows the typical morphology of the platelets adhering to the PES and modified PES membranes. Herein, the membranes were modified by blending sulfonated PES and a terpolymer of poly (acrylonitrile-acrylic acid-N-vinyl pyrrolidinone) (P(AN-AA-VP)). To prepare the membranes, PES, SPES and P(AN-AA-VP) were dissolved in solvent NMP. The solution was vigorously stirred until clear homogeneous solution was obtained. The concentration of all the solute was 16 wt. %. In the experiment, different kinds of membranes were prepared by changing the ratios of PES, SPES and P(AN-AA-VP) in the casting solutions, and the ratios of PES, SPES and P(AN-AA-VP) were 16:0:0, 15:0:1, 14:0:2, 10:6:0,10:5:1, 10:4:2, respectively. After vacuum degassing, the casting solutions were prepared into membranes by spin-coating coupled with a liquid-liquid phase separation technique at room temperature. The obtained membranes were washed with distilled water thoroughly to remove the residual solvent, which were confirmed by UV scanning. All the prepared membranes were in a uniform thickness of about 60~70 μm, and the membranes were termed M-16-0-0, M-15-0-1, M-14-0-2, M-10-6-0, M-10-5-1, and M-10-4-2,

As shown in Figure 6, when compared the pictures in the same amplification multiple, it was observed that a large amount of platelets were adhered and aggregated on the PES membrane surface and the platelets formed circular or "pan-cake" shape, which suggested that the platelets were activated and already retracted the pseudopods. However, for the modified membranes, very sparse platelets were found; and the platelet expressed a

Figure 7 shows the amounts of the adhering platelets on the membranes from platelet-rich plasma. It could be observed that much lower number of the adhering platelets on the modified membranes compared with the PES membrane. Furthermore, the platelet

rounded morphology with nearly no pseudopodium and deformation.

shown in Fig. 5.

microscopy (SEM).

respectively.

**3.1.2.2 Platelet adhesion** 

the reduction ratio of small molecules (urea, creatinine, phosphate) during hemodialysis for the PES membrane in vitro are investigated.
