Effects of magnesium degradation products and hypoxia on angiogenesis and osteogenesis during fracture healing

Magnesium (Mg) based metals have been applied in orthopaedic and cardiovascular (as stent) applications due to (e.g.) their excellent biodegradability and tissue regeneration abilities. Endothelial cells (ECs) and mesenchymal stem cells (MSCs) represent two protagonists of angiogenesis and osteogenesis. The responding of angiogenesis and the EC-MSC communication to Mg degradation products and oxygen content are vital to vascular remodelling and later fracture regeneration. Firstly, human primary ECs were exposed to various concentrations of extracellular Mg degradation products under either hypoxia or normoxia. Furthermore, in order to understand the influences of Mg degradation and oxygen conditions on the ECs-MSCs communication, a non-contacting (or transwell system) and a contacting cell culture models were established. With these models, the various stages of fracture healing could be mimicked: angiogenesis, MSCs attraction / migration and tissue modelling. In the monoculture, cell metabolism and proliferation, as well as wound healing and tube formation assays (reflecting two different stages of angiogenesis: migration and tube formation) were studied. In coculture, cells proliferation and ratio were measured by deoxyribonucleic acid (DNA) content and flow cytometry, respectively. Additionally, MSCs migration was assessed by wound healing assay. Gene regulation in monoculture and different coculture were investigated by semi-quantitative real time polymerase chain reaction (qRT-PCR). Furthermore, several angiogenic factors, such as vascular endothelial growth factor A (VEGFA) were also quantified. These results suggest that Mg extracts did not interfere with angiogenesis under hypoxia. Furthermore, Mg, hypoxia, and heterotypic contact were beneficial to stromal ECs and MSCs, providing a suitable niche environment and highlighting the application of Mg in regenerative medicine.