Bioglass and bioceramic composites processed by Spark Plasma Sintering (SPS): biological evaluation Versus SBF test

The biocompatibility of hydroxyapatite (HA), a lab-made bioglass (BGCaMIX) with high crystallization temperature and different HA/BGCaMIX composites, pro- duced by Spark Plasma Sintering (SPS), was tested with respect to murine osteocytes both by direct and indirect tests, in order to also investigate possible cytotoxic effects of the samples’ extracts. Previous investigations demon- strated that the samples’ bioactivity, evaluated in a simu- lated body fluid solution (SBF), increased with the increas- ing amount of BGCaMIX in the sample itself. Although none of the samples were cytotoxic, the findings of the bi- ological evaluation did not confirm those arising from the SBF assay. In particular, the results of direct tests did not show an enhanced “biological performance” of materials with higher glass content. This finding may be due to the high release of ions and particulate from the glass phase. On the contrary, the performance of the BGCaMIX alone is better for the indirect tests, based on filtered samples’ extracts. This work further demonstrates that, when con- sidering bioglasses and HA/bioglass composites, the re- sults of the SBF assays should be interpreted with great care, making sure that the results arising from direct con- tact tests are integrated with those arising from the indirect ones.