Introduction

2003). During these processes protein adsorption occurs rapidly, within seconds to minutes after the first blood contact. In addition to the aforementioned disadvantages of flux decline and change in selectivity, protein adsorption can trigger the cascading chemical reactions of clotting factors, which is followed by platelet adhesion and activation of the coagulation pathways, leading to thrombus formation (Dee et al. 2002).

It seems that proteins at the membrane surface stand at the center of membrane filtration processes, especially for the blood-contacting membranes. Proteins, not only model proteins of membrane fouling such as bovine serum albumin (BSA), but also a special protein type, enzymes, must be taken into account. Protein molecules should not be thought of as rigid structures. As we know, proteins are flexible chains that have been coiled, folded, and bent to assume a particular three-dimensional conformation. Changes in the microenvironment of proteins can alter the conformation of the molecules. Likewise, proteins experience structural alterations during interactions with solid surfaces, such as charged or noncharged membrane surfaces. As for protein fouling, protein denaturation and aggregation may result in radically different deposition compared to native proteins. Thus, keeping protein adsorption at a low level, thus allowing only little changes in its conformation, should be beneficial to membrane fouling.

Many approaches have been explored to build a friendly and biocompatible interface between protein and membrane. Among them, surface modifications to increase the hydrophilicity and to introduce steric hindrance and/or a biomimetic layer on the membranes have received considerable attention. Herein, we will review some recent progress in the field of protein resistance at PAN-based membrane surfaces, as effected by various surface modification methods.

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