JOURNALOF MATERIALS SCIENCE: MATERIALS IN MEDICINE 14 (2003) 39±45 Wettable phosphorylcholine-containing polymers useful in blood ®ltration A. L. LEWIS, R. N. T. FREEMAN, R. P. REDMAN, L. A. TOLHURST, L. C. KIRKWOOD, D. M. GREY, T. A. VICK Biocompatibles Ltd., Chapman House, Farnham Business Park, Weydon Lane, Farnham, Surrey, GU9 8QL, UK E-mail: andrew_lewis@biocompatibles.co.uk The use of phosphorylcholine (PC)-containing polymers has long been acknowledged as a method to improve the haemocompatibility of blood contacting devices. Such polymers were investigated for coating leukocyte ®lters, as a means of preserving precious platelet numbers and function. It was demonstrated that by use of such coated ®lters, the platelet recovery could be signi®cantly increased by some 30%. This was however, balanced by a decrease in the leukocyte removal ef®ciency of the ®lter. More problematic however, was the poor critical wetting surface tension (CWST) of the ®lter (45 mNm  1 ). This was due to the surface expression of the hydrophobic groups of the polymer in air. In order to obtain a ®lter that could be immediately wetted by the blood and hence remove the need for any detrimental priming of the ®lter, the PC polymer was modi®ed in order to reduce its hydrophobic content. A series of new cross-linkable polymers was developed that contained other hydrophilic monomers, yet could ®lm-form to produce a coating stable to ¯uid contact. These materials demonstrated the required wetting characteristics (a CWST of > 78mNm  1 ), whilst retaining the excellent blood-contacting properties. # 2003 Kluwer Academic Publishers 1. Introduction The ®ltration of blood is necessary in order remove donor leukocytes and thus reduce the adverse effects they cause transfusion recipients [1,2]. Many types of ®ltration device have been developed from a range of materials. Most common are ®lters composed of a mat of nonwoven ®bers that separate the white cells from the other blood components on the basis of size. The ®lters are used only once and then disposed of, and are fabricated from materials such as polyethylene terephthalate ®bers which are far from compatible with the blood. Indeed, some of the ef®ciency of the ®lter can be attributed to the fact that granulocytes in particular recognize the ®bers as foreign and adhere to the surface [3]. The down side to this effect is that many other blood components become activated, in particular platelets, which are of great value to the transfusion patient. Hence, although ®ltration removes problematic leukocytes, the general condition of the blood is worsened and the level of platelets also reduced. Many approaches have been studied in order to improve the leukocyte depleting properties of ®lters whilst retaining maximal platelet recovery. One strategy has been simply to coat the ®lter ®bers with various polymer coatings in order to mask the thrombogenicity of the underlying substrate [4±6]. With this strategy in mind, one family of materials that has received a great deal of attention in recent years, and is indeed yielding many signi®cant clinical results in blood contacting applica- tions, is that based on PC-containing polymers [7]. Phosphorylcholine (PC) is the major phospholipid head- group found in the outer lea¯et of biomembranes. Biomimetic synthetic polymers that contain this head- group have been shown to be haemocompatible in nature in a variety of tests [8±10]. For instance, signi®cant reduction of platelet adhesion and activation has been demonstrated in vivo for PC-coated coronary stents [11]. Results such as these support the view that these materials may make ideal coatings for blood ®ltration materials, where platelet recovery and the general condition of the blood are of importance. Preliminary work using simple PC polymer coatings has supported this view, although issues concerning the immediate wettability of the coated ®lters was noted [12]. The work described here reports an extension of this initial investigation. 2. Materials and methods 2.1. Materials The monomer 2-methacryloyloxyethylphosphorylcho- line (MPC) was made and puri®ed by the method described previously [13]. Poly(ethylene glycol) metha- crylate (PEGMA, 550 Mw) was purchased from Inspec Ltd. (Bisomer 550) and all other monomers were purchased from the Aldrich Chemical Co. and used without further puri®cation. These included lauryl methacrylate (LMA), n-butyl methacrylate (BMA), 2- hydroxypropyl methacrylate (HPMA), 3-(trimethoxysi- lyl)propyl methacrylate and N,N'-dimethylacrylamide 0957±4530 # 2003 Kluwer Academic Publishers 39