Development of an in vitro bone model to study bone-macrophage communication

Bone-immune crosstalk is poorly understood due to a lack of human-relevant in vitro models. This thesis aims to fabricate an in vitro bone model with features enabling the study of communication between bone cells and macrophages. Previous research has shown that polyHIPEs (polymerised emulsions) are suitable porous scaffolds for cell culture. A 3D arrangement is crucial for cell communication, and inadequate polyHIPEs’ pore features can limit this. Therefore, this research studies how pore interconnectivity affects cell growth and infiltration. Results indicated that polyHIPEs with enhanced interconnectivity, despite similar pore size ranges, improved infiltration and osteogenic differentiation of Y201 mesenchymal stromal cells (MSCs) compared to previously published polyHIPE formulations. The research subsequently investigated the feasibility of the most interconnected polyHIPE for co-culture models. When seeded with Y201-MSCs, polyHIPEs effectively supported the invasion of breast cancer cells. Macrophages were added to the co-culture to study their participation. Results showed that pro-inflammatory macrophages (M1) inhibited cancer cell migration, while anti-inflammatory (M2) did not. M2-like macrophage behaviour aligns with clinical and other experimental studies. Finally, to assess their potential for use in dynamic environments, polyHIPEs were integrated into a microfluidic device, which was also used to observe monocyte behaviour under fluid flow. Studies exist on macrophage behaviour on 3D scaffolds or in microfluidic devices; however, here we combined both to create a more physiologically relevant model. Results showed that while there was no significant difference in monocyte recruitment toward Y201 MSC-seeded scaffolds between static and dynamic conditions, a synergistic effect of Y201-MSCs and the monocyte chemoattractant protein-1 (MCP-1) was demonstrated on monocyte recruitment. Also, the fluid flow itself could shift macrophages towards a pro-inflammatory phenotype, confirming findings observed in other studies. Overall, results confirm that these polyHIPEs are promising for creating in vitro bone models to study complex cellular interactions in the bone microenvironment.