Probe spectrum measurements of Eu3+ ions as a relevant tool for monitoring in vitro hydroxyapatite formation in a new borate biomaterial

Abstract

CaB₂O₄ powders and ceramics were prepared by the conventional solid-state reaction. In vitro hydroxyapatite (HA) mineralization was investigated by soaking the samples in simulated body fluid (SBF) for various time periods. X-ray diffraction and structural refinements, scanning electron microscopy and X-ray energy-dispersive spectra measurements were applied to investigate apatite formation before and after immersion in SBF. HA can easily form flower-like nanostructures with nano-needles even when soaked in SBF for several hours. The in vitro bioactivity of CaB₂O₄ was attributed to easy formation of B–OH groups in the CaB₂O₄ structure when soaked in SBF solutions. In the process of mineralization, the luminescence evolution of Eu³⁺ ions, a well-known structural probe, was detected by photoluminescence spectra and photoluminescence decay curves. This suggested that the process of mineralization can be monitored by the luminescence intensity of Eu³⁺ ions in the mineralization products. The current study will open up a new and simple in vivo avenue for in situ monitoring of hydroxyapatite conversion using a fiber luminescence spectrometer.