Chitosan microcarriers deposited with Mg2+-doped phase-transited lysozyme: osteogenesis, pro-angiogenesis and anti-inflammatory for promoting bone regeneration

Microcarriers, as injectable cell carriers, provide a new strategy for bone defect repair due to their advantages of large specific surface area, flexible and controllable size, and injectability. Magnesium ion (Mg2+) is important trace element and has been demonstrated to improve bone tissue regeneration. The development of bone tissue engineering microcarriers that can sustainably control Mg2+ release could show significant impacts on bone regeneration. Herein, chitosan (CS) microcarriers deposited with Mg2+-doped phase-transited lysozyme (PTL) were fabricated for accelerating bone regeneration. The results prove that Mg2+-doped PTL was successfully self-assembled onto CS microcarriers through hydrogen bonds and electrostatic interactions. The introduction of Mg2+-doped PTL in CS microcarriers increased zeta potential of the materials. The microcarriers exhibited a spherical and interconnected porous structure with sizes of 300–400 μm and pore sizes of 35–40 μm. Due to the PTL deposition, the microcarriers displayed controlled release of Mg2+. Moreover, they showed good degradation ability. In vitro, the composite microcarriers supported cell attachment and improved proliferation and osteogenic differentiation of stem cells, attributed to the combined effects of PTL and Mg2+. Furthermore, they stimulated cell migration and tube formation of HUVECs, and induced LPS-activated macrophages polarized to the anti-inflammatory M2 phenotype. In vivo, the microcarriers accelerated bone regeneration, enhanced angiogenesis, and reduced inflammation in a rat model of right medial femoral malleolus defects. In summary, the results demonstrate that the prepared composite microcarriers have potential to be used as a new type of microcarrier for bone tissue engineering applications.