Long-Term Culture of Stem Cells on Phosphate-Based Glass Microspheres: Synergistic Role of Chemical Formulation and 3D Architecture.

Phosphate-based glasses (PBGs) are biomaterials that degrade under physiological conditions and can be modified to release various ions depending on end applications. This study utilized slow-degrading (P45:45PO-16CaO-24MgO-11NaO-4FeO, mol %) and comparatively faster degrading (P40:40PO-16CaO-24MgO-20NaO, mol %) PBG microspheres with or without porosity, to evaluate the combined effect of chemical formulation and geometry on human mesenchymal stem cells (MSCs), a clinically relevant cell source for orthopedic applications. Scanning electron microscopy showed 2, 46, and 29% of P45 bulk (P45-B), P40 bulk (P40-B), and P40 porous (P40-P) microspheres, respectively, that had cracks or peeling off surfaces after 42 days of incubation in culture medium. Cytotoxicity assessment showed that glass debris released into the culture medium may interact with cells and affect their survival. Direct-contact cell experiments up to 42 days showed that P45-B microspheres did not sustain viable long-term cell cultures and did not facilitate extracellular matrix formation. On the other hand, P40-B microspheres enhanced alkaline phosphatase activity, calcium deposition, and collagen and osteocalcin production in MSCs. Introduction of porosity in P40 glass further enhanced these parameters and proliferation at later time points. The small pore windows (<5 μm wide) and interconnection (<10 μm wide) may have allowed limited cell penetration into the porous structures. P40-B and P40-P have potential for bone repair and reinforcement therapy based on their chemical formulation and porous geometry.