Synthesis of luminescent bioactive glasses containing erbium (Er3+) and terbium (Tb3+) for biomedical applications

Bioactive glasses are promising materials for tissue engineering applications. In this study, silicate-based 13-93 bioactive glasses containing erbium (Er3+) and terbium (Tb3+) (1, 3, 5 wt%) were synthesized to be used in bone tissue engineering applications, in the form of particle and nanofiber by sol-gel and electrospinning methods, respectively. The structural and morphological properties of the prepared bioactive glasses were examined by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) analyzes. In addition, the luminescence properties of bioactive glasses containing Er+3 and Tb+3 were investigated using photoluminescence (PL) spectroscopy. The ability of bioactive glasses to form hydroxyapatite in vitro was evaluated as a function of time in simulated body fluid (SBF). The cytotoxicity of the bioactive glasses synthesized within the scope of the study was tested in vitro by the MTT method using the MC3T3-E1 cell line. Gentamicin sulfate and amoxicillin trihydrate were loaded into the synthesized bioactive glasses and their release behavior in phosphate buffered saline (PBS) was investigated. The results showed that the additions of Er+3 and Tb+3 did not cause crystallization in bioactive glasses and mentioned rare earth element ions induced fluorescence properties. The median particle size and average diameter of the prepared glass powders and fibers were in the range of ~ 2.5-3.5 μm and 280-660 nm, respectively. Optimum concentration of the activator ions for the silicate-based 13-93 bioactive glasses were 1 wt% Er3+ and 5 wt% Tb3+. Additionally, presence of Er+3 and Tb+3 ions in the glass network, extended the florescence decay times and longer decay times were obtained as the dopant concentration was increased. The sol-gel derived bioactive glass particles exhibited stronger emission intensities whereas electrospun nanofibers showed extended decay times. It has been observed that hydroxyapatite deposited on the surface of the bare as well as the Er+3 and Tb+3 -containing 13-93 bioactive glasses which were kept in simulated body fluid for 7 days and the addition of the Er3+ and Tb3+ accelerated the HA formation. According to the findings of the in vitro cytotoxicity experiments after 72 hours of cell culture, Er3+ -containing bioactive glass powder- based scaffolds showed a cytotoxic effect at concentrations greater than 1%Er3+. On the other hand, no significant decrease in cell viability was observed in samples containing Tb3+ as the concentration was increased. Similarly, a decrease in cell viability was not observed in Er3+ and Tb3+ containing bioactive glass nanofiber-based samples Er3+ and Tb3+ as a function of rare earth element concentration. Gentamicin sulfate-loaded bioactive glass scaffolds prepared using powder and nanofibers containing Er3+ and Tb3+ showed burst release in PBS, however the release rate of amoxicillin trihydrate was lower under the same conditions. It was concluded that Er+3 and Tb+3 -containing luminescent 13-93 bioactive glasses, produced by sol-gel and electrospinning methods, can be utilized in bone tissue engineering applications.