Photo-click crosslinked hydrogel containing MgO2-loaded PLGA microsphere with concurrent magnesium and oxygen release for bone tissue engineering

Overcoming hypoxia and providing a proper microenvironment for osteogenic differentiation are the most critical challenges in bone tissue engineering (BTE). Hydrogels with the capability to release oxygen and magnesium ions are considered to be a promising approach for BTE. Here, MgO2-loaded polylactic-co-glycolic acid (PLGA) microspheres were prepared to improve oxygen release, magnesium release, and pH control. Then, PLGA/MgO2 microspheres-loaded thiolated alginate (AlgT)/gelatin methacryloyl (GelMA) photocrosslinkable hydrogel was prepared using click reaction, and the effect of different concentrations of AlgT on the physical and chemical properties of the hydrogel was investigated. The pore size decreased as AlgT concentration increased from 101.11 ± 26.04 to 74.48 ± 14.03 μm, and the swelling ratio, elastic modulus, and compressive strength were increased when AlgT concentration increased from 821.30 ± 30% to 950 ± 60%, 0.69–1.23 MPa and 1.293–2.81 MPa, respectively. Pore size, swelling ratio, elastic modulus, and compressive strength were 88.28 ± 20 μm, 522.82 ± 29%, 1.64 ± 0.04 MPa, and 4.044 ± 0.041 MPa for microsphere-loaded hydrogel, respectively. Besides, the level of released magnesium and oxygen during 14 days ranged from 13 to 22 mg/L and 7.7–8.2 mg/L, respectively. The MTT and live/dead assay results showed suitable cell viability and adhesion on the microsphere-loaded hydrogels. Also, the calcium content and alkaline phosphatase activity of human Adipose-derived mesenchymal stem cells (hAMSCs) cultured on samples were investigated. Moreover, hAMSCs indicated osteogenic differentiation after 21 days in culture, including the expression of significant alkaline phosphatase, osteocalcin, and osteopontin. This study's results indicate the prepared hydrogels' suitability for osteogenic differentiation and bone tissue engineering.