Evaluation of lysozyme adsorptive behaviour of pHEMA-based affinity membranes related to the surface energy and its components to be used in chromatographic fields

We have studied the influence of the surface energy and its components of two different dye-ligand immobilised poly(hydroxyethylmethacrylate) (pHEMA) membranes to the adsorption of a protein "lysozyme" from aqueous solutions. For this purpose, macroporous pHEMA membranes were prepared by UV-initiated photo-polymerisation. Two different affinity dye-ligands (i.e. Reactive Brown-10 (RB-10) and Reactive Green-5 (RG-5)) were immobilised onto pHEMA membranes. The adsorption of lysozyme on the affinity membranes was carried out from solutions in the concentration range 0.05-3.00 mg/ml. The measurements of the contact angle for water, glycerol, formamide, diiodomethane (DIM), ethylene glycol and dimethylsulphoxide (DMSO) on plain, both RB-10 and RG-5 immobilised and their lysozyme covered counterpart pHEMA membranes were made. In accordance to the Young equation, the smaller the surface tension of the test liquid, the smaller becomes the contact angle measured on the membrane samples surfaces. The highest contact angles were obtained with water, whereas DMSO gave the lowest contact angles for all the tested membranes. The surface energy parameters of the investigated membranes were calculated from the measured contact angle values, using the mostly used three methods (i.e. the harmonic mean by Wu, the geometric mean by Fowkes and acid-base by van Oss). The adsorption of lysozyme significantly changed both the contact angles and component of surface free energy. It was found that the immobilisation of both dye-ligand increased the lysozyme adsorption capacity of the affinity membranes most significant, although there is not very large difference of surface energy between plain and both dye-ligand immobilised pHEMA membranes. (C) 2004 Elsevier B.V. All rights reserved.