Deepening our understanding of bioactive glass crystallization using TEM and 3D nano-CT

•Crystallization of bulk Bioglass 45S5 has been imaged from nano- to microscale.•Combining ex situ and in situ techniques allows to follow the entire crystallization process.•Combeite crystallizes with a sphere-like morphology visualized by nano-CT.•Combeite spheres present a grain-like internal structure.•Crystallinity of powder and bulk samples have been correlated with the images.