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Methods for the detection of positive or negative charges on the surface of biomaterials/membranes and inside a membrane are important for the characterisation of such materials. We tested different dyes and optimized staining procedures. Under standardized conditions negatively charged membranes were stained with cationic triarylmethane compounds such as crystal violet and positively charged membranes with the anionic anthraquinone dye anthralan blue B. There was no staining of uncharged cellulose membranes. The applicability of these methods was demonstrated on membranes coated to varying degrees with charged compounds such as heparin, these changes in charge being detectible quantitatively by photometry. The distribution of charges inside a membrane was detected by optical sectioning across the stained (FITC labelled poly-L-lysine) membrane using confocal laser scanning microscopy (LSM). LSM offers a completely new application possibility in biomaterial and biocompatibility research.

Seven different types of dialysers were investigated in five dialysis centres in four countries with respect to behaviour of white blood cells and the complement system. The results of this controlled crossover study demonstrated significant differences in the dialysers. Those containing cuprammonium cellulose (G10-3N and G120M) showed the greatest changes in white blood cell count, including monocytes and neutrophils, as well as the greatest complement activation. With regard to lymphocytes the subpopulation of low-mobility cells, which were predominantly the B-cells, showed the greatest mobility with dialysers containing cuprammonium cellulose. The PAN copolymer- and PMMA-containing dialysers Filtral and T 150 clearly caused the least changes in white blood cells and complement factors. Dialysers containing cellulose acetate and polysulphone membranes (Duo-Flux ™ Artificial Kidney, CD 4000, and F 60) produced only a moderate decrease of WBC, monocyte, neutrophil, and lymphocyte counts, and this result corresponded to a relatively small change in complement factors.