**5. Conclusions**

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. Furthermore, PES-based membranes show high permeability for low molecular weight proteins when used as hemodialysis membranes. However, the blood compatibility of the PES membrane is not adequate, and injections of anti-coagulants are needed during its clinical application.

Thus, all the PES membranes used for hemodialysis are not the pristine PES membranes, and most widely used modification method for hemodialysis PES membranes is blending. Poly (vinyl pyrrolidone) (PVP) is the most widely used for the modification of PES membranes by blending, and PVP also acts used as a hydrophilic additive and a membrane forming agent. Surface-coating and grafting methods can also be used for the modification of PES hollow fiber membranes. All the modifications are based on the premise that the materials used in the modification give inherently more hydrophilicity and adsorb less protein than the underlying substrate.

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. The adhesion of platelets to blood-contacting medical devices is a key event in thrombus formation on material surface. The clearances and the reduction ratios of small molecules (urea, creatinine, phosphate) for the PES membrane after the hemodialysis in vitro were larger than those in vivo. Animal experiments and clinical experiments indicated that the PES-based high-flux hemodialysis membrane had good blood compatibility, and could effectively remove "middle" molecular solute as 2-microglobulin.

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The blood compatibility and performance in hemodialyzation were compared with two conventional high-flux membranes, polysulfone (PSF) and polyamide (PA) membranes. The PES and PSF membranes showed similar blood compatibility and solute clearance, and the blood compatibility for PES and PSF might be better than the PA membrane.

In conclusion, PES-based hollow fiber membranes have good blood compatibility and solute clearance, and the PES hollow fiber membrane hemodialyzer might be a good commercial product in the future.
