EPR studies of defects in pure sol-gel matrices and their influence on cytotoxicity of the material

Sol-gel based biomaterials may be used for various applications, including biomedical ones. In this respect it is important to investigate the influence of sol-gel matrices on biological systems in order to establish their cytotoxic activity. The results of EPR studies of sol-gels are described in this work. They demonstrate that various defects are present in sol-gel matrices: surface defects, peroxycentres or hydrogen-related centres. These defects arise spontaneously during the gelation, being responsible for cytotoxicity of sol-gels. It was found that the ratio of the number of solvent moles to the number of precursor moles (the molar ratio R) is one of the factors determining the level of cytotoxicity. More defects were present in samples prepared with a lower molar ratio R. A higher concentration of defects was detected in freshly prepared samples, as compared to samples aged for a longer time.