Facile synthesis of zeolitic imidazolate framework coated glass microspheres

In this study we report a facile one-step, room temperature synthetic methodology for fabricating ZIF-8-coated phosphate-based glass (PBG) microspheres. ZIF-8 was grown in situ onto solid (non-porous) and porous P40 glass microspheres (composition 20Na₂O-24MgO-16CaO-40P₂O₅, average diameter 153-172 µm), confirmed by PXRD and SEM analyses, with reaction times of one hour sufficient for coating onto solid P40 microspheres. An extended reaction time of 4.5 hours resulted in more homogeneous ZIF-8 coverage on the porous P40 microspheres. The ZIF-8 layer reduced microsphere degradation in water and slowed ion release from the microspheres, demonstrating a sacrificial protective coating effect of the ZIF-8. The ZIF-8 layer also enabled Zn²⁺ release (6.9-13.6 ppm over 7 days) and demonstrated improved methylene blue loading capacity, showing promise for pH-responsive drug delivery. This adaptable synthetic method to produce P40-based MOF composites highlights the potential synergistic benefits of combining PBG microspheres (bioactivity, tuneable degradation rates) and MOFs (high surface areas and porosity), offering an underexplored strategy to new MOF@PBG composites for drug delivery, antibacterial coatings and bone repair.