A study on the characterisation and biostability of used and virgin dialysis membranes and biocompatibility of the composite biomaterials

In this study two composite systems consisted of polymers and ceramics respectively were investigated in terms of biocompatibility and biostability simultaneously. The selected polymers were polysulfone and cellulose acetate. Morphology, supramolecular and molecular structure, and mechanical properties of the virgin polymeric membranes used in hemodialysis and their variations after use were analyzed with respect to degradation and aging due to corrosion provoked by blood and by surrounding aggressive environment. The wall thicknesses and diameters of the polymeric hollow fibers were measured under a microscope. These measurements were entered to run mechanical tests. In virgin and used hollow fibers belonging to polysulfone and cellulose acetate, the morphology of the support structure and geometry of the pores together with fracture surfaces have been comparatively evaluated by SEM and AFM studies. Mechanical studies have revealed that ultimate tensile strength, strain to fracture and yield strength values have been reduced after blood-contact. These results coupled with fractographic evidences prove degradation and ductile to brittle transition after use. X-ray diffraction studies implied that internal, supramolecular structure of the hollow fibers altered in a way that the strong bonding of crystalline and amorphous regions into a composite structure giving rise to good mechanical properties has been impaired after use. The results were compared in an attempt to find out alternative methods to improve the quality of the membranes. On the other hand, alumina-zircon composites were investigated in parallel to the polymer studies. The alumina used had a purity of 99.7 % with 0.1 % Na2O by weight and dimensions of 7 mm diameter and 2 mm thickness. After sintering, the density of the alumina-zircon ranged from 3.2 to 3.6 g/cm3 respectively. Tissue reactions of test materials were performed using rats for 2 months duration. X-ray diffraction studies showed that alumina exists only in the form of corundum. As the amount of zircon increased, mullite formations became visible on the particle boundaries. Animal studies revealed that these ceramic composites do not have any adverse effect on the tissues investigated histologically. Herein it is postulated that composite systems consisting of basic polymers either, polysulfone or cellulose, and additives (ceramic) may improve the biostability and biocompatibility of the membranes used for hemodialysis or their respective degraded products as explained to different degrees after use, or may serve as new biomaterials. Hence, this study is partly aiming at improving the quality of membranes and formation of new biomaterials for biomedical applications. In future polymers mentioned such as cellulosic or synthetic ones reinforced with ceramics may create new benefits in the area of nephrology, whereas alumina-zircon reinforced by polymers may do the same in dentistry and orthopedics. Copyright (2001) The Australian Ceramic Society