Synthesis, characterization, and in vitro apatite formation of strontium-doped sol-gel-derived bioactive glass nanoparticles for bone regeneration applications

Abstract

The morphology of bioactive glass nanoparticles has been reported to impact apatite-forming ability, biocompatibility, and cell functions. In this study, mesoporous bioactive glass nanoparticles (MBGNs) of mixed morphologies with nominal compositions (%mol) given by 74Si O2_(26−x)CaO_xSrO, (where x=0,1,3,and5) were prepared through a modified sol-gel method. The MBGNs were characterized by thermal gravimetric analysis (TGA), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption, X-ray diffraction (XRD), solid-state nuclear magnetic resonance (NMR), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). In particular, the effect of Sr concentration on the glass structure, surface morphology, particle size, microstructure, chemical durability, ion release, and in vitro mineralization on the MBGNs was studied. All compositions showed similar thermal degradation profiles irrespective of Sr concentrations. SEM observation showed a mixture of aggregated spherical- and rod-shaped particles in which particle sizes decreased with increasing Sr concentration. Textural analysis showed a decrease in specific surface area with increasing Sr concentration. NMR analysis revealed a reduction in glass network polymerization with increasing Sr concentration. NMR analysis showed hasty depletion of modifier cations from the MBGNs to the simulated body fluid (SBF), the effect more prominent in the pristine sample. We observed prompt surface modifications on MBGNs as a response to their interaction with SBF that led to interconversion of 29Si speciation in the order QCa,Sr1+QCa,Sr2→QH2→QH3. SEM, EDX, and XRD revealed the formation of crystalline hydroxyapatite (HA) on the MBGNs after three days of immersion in SBF. In vitro apatite-forming ability of MBGNs decreased with increasing Sr concentration. The MBGNs revealed promising potential properties for applications in orthopedics, dentistry, wound healing, and drug delivery systems.