Natural diatomite particles: Size-, dose- and shape- dependent cytotoxicity and reinforcing effect on injectable bone cement

Natural diatomite (DT) is the ancient deposit of diatom skeleton with many regular pores of 50-200 nm and also an abundant source of biogenic silica. Although silica is considered biologically safe and there is an increasing interest of using natural diatomite for biomedical applications, the toxicity information about natural diatomite is still missing. Here, cytotoxicity of natural diatomite on osteoblasts and fibroblasts were compared to hydroxyapatite and the relationships between cytotoxicity and diatomite sizes, dose, geometry or impurity were systematically investigated. Cell adhesion and interaction with diatomite particles were also fluorescently observed. The results clearly suggested a size-, dose- and shape-dependent cytotoxicity of natural diatomite. Disk-shaped diatomite particles with average size of 30 μm in diameter revealed the least toxicity, while the diatomite particles with irregular shapes and sizes less than 10 μm were remarkably toxic. Diatomite particles with proper sizes were then selected to investigate the reinforcing effect on injectable calcium phosphate bone cement. Results showed that diatomite significantly improved the compressive strength of bone cement but did not alter the injectability of the cement. This work provided important biocompatibility information of natural diatomite and demonstrated the feasibility of using selected diatomite as bone implant material.