In vitro assessment of cellular responses to rod-shaped hydroxyapatite nanoparticles of varying lengths and surface areas

Rod-shaped hydroxyapatite nanoparticles of varying dimensions (≈ 60 ± 10, 120 ± 15, 240 ± 30 nm in length, labeled respectively as nHA60, nHA120 and nHA240) with specific surface areas (47.02, 23.33, 46.12 nm², respectively), were synthesized and their effects on cell viability, reactive oxygen species generation and cellular interaction with BEAS-2B, RAW264.7 and HepG2 were investigated. In vitro exposure of these cell lines to rod shape nHA particles within a range of 10-300 μg/ml for 24 h did not significantly alter cell viability studied by the WST-8 assay. A significant increase in reactive oxygen species (ROS) generation was however observed with the dihydrofluorescein diacetate (DFDA) assay after 4 h incubation with these nanoparticles. The lowest level of ROS generation was observed with nHA120 (with the smallest specific surface area); whereas nHA60 and nHA240 exhibited comparable ROS generation. Subsequently, the Alizarin Red-S (ARS) assay indicated a weaker association of calcium with cells compared to nHA60 and nHA240. The results thus suggest that high surface area may increase cell-particle interaction, which in turn influenced ROS generation. The combined results from all the cell lines thus indicated high biocompatibility of rod-shaped nHA.