JOURNALOF MATERIALS SCIENCE: MATERIALS IN MEDICINE 15 (2004) 877±883 Novel PEEK-WC membranes with low plasma protein af®nity related to surface free energy parameters L. DE BARTOLO*, A. GUGLIUZZA, S. MORELLI, B. CIRILLO, A. GORDANO, E. DRIOLI Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, c/o University of Calabria, via P. Bucci cubo 17/C, I-87030 Rende (CS), Italy E-mail: l.debartolo@itm.cnr.it There has been growing interest in innovative materials with speci®c physico-chemical properties that provide an improved blood/cell compatibility. In this paper we evaluated the performance of new membranes prepared from a modi®ed polyetheretherketone (PEEK-WC) contacting human plasma proteins. These membranes were prepared by using the phase inversion technique. Membrane wettability and af®nity to proteins were evaluated by means of contact angle experiments, roughness measurements, and quantitative UV analysis. The energy parameters of membrane surfaces were determined according to Good, van Oss and Chaudhury's theory. The extent of human albumin, ®brinogen and immunoglobulin G adsorption was related to quantitative expressions of the membrane surface hydrophilicity: the base parameter of surface free energy and the free energy of interfacial interaction. The performance of PEEK- WC membranes was compared to that of commercial membranes, which conventionally are used in biomedical applications. The experimental results showed a reduction of protein adsorption on PEEK-WC membranes with respect to other commercial membranes. The low protein af®nity of PEEK-WC membranes is due to the intrinsic physico-chemical characteristics of the polymeric material which makes these membranes interesting for potential use in biomedical applications. # 2004 Kluwer Academic Publishers Introduction Medical devices in contact with blood must completely avoid clot formation and immunoreactions [1, 2]. Several studies have shown that the biocompatibility of a material is linked to protein±surface interactions which constitute the ®rst phase of blood/tissue interactions [3,4]. Surface properties such as chemistry, topography and thermodynamics affect protein adhesion to poly- meric materials (i.e. membranes, sheets, etc.) [5]. Depending on the size, shape, overall charge, hydro- phobicity and internal stability of the molecule, proteins could adsorb on hydrophobic or hydrophilic substrata [6]. As a result, the interfacial properties of the polymer material are modi®ed by the physical adsorption of protein molecules with consequent changes in the extent of cell adhesion. Several studies have related the wettability properties of a material surface to protein adsorption and cell adhesion [7, 8]. With this in mind, different methods were used to characterize interfacial reactions. The contact angle is one of the most common methods used to provide information about the physico- chemical characteristics of material surface and proteins [9, 10]. Currently, the contact angle is often used as a physical parameter indicative only of surface wettability, but it allows more quantitative information concerning the energy parameters of a material surface to be obtained [11]. In this work, the contact angle is applied to characterize surface free energy parameters, the free energy of interfacial interactions of new modi®ed polyetheretherketone (PEEK-WC) membranes related to protein adsorption. Membranes were prepared from PEEK-WC, which exhibits chemical stability and excellent thermal and mechanical resistance similar to traditional PEEKs, which are used in medical implants. As opposed to PEEKs, PEEK-WC is soluble in various solvents owing to lack of crystallinity. This characteristic allows it to be used for preparing membranes by phase inversion, which proved to be a cheap and ¯exible method [12]. Previous studies have shown that this novel membrane is very promising for various applications [13]. The developed PEEK-WC membranes combine the advantageous properties of the polymer with those of permeability, selectivity and stability of the membranes. In this study the physico-chemical properties of *Author to whom all correspondence should be addressed. 0957±4530 # 2004 Kluwer Academic Publishers 877