Mineralized extracellular matrix composite scaffold incorporated with salvianolic acid A enhances bone marrow mesenchymal stem cell osteogenesis and promotes calvarial bone regeneration

Natural products, especially phenolic components isolated from Traditional Chinese Medicine (TCM), were reported to exhibit significant osteogenic potential in treating bone defects. However, low bioavailability, short half-life, and high clearance rate in the body hindered their practical applications in many cases. To develop delivery technologies for a bioactive phenolic acid from Salvia miltiorrhiza (Danshen), salvianolic acid A (SAA), a sustained release system based on biocompatible extracellular matrix (ECM) meticulously modified with a Hydroxyapatite (HAP) mineralized coating was established. The SAA construction of such delivery system not only addressed the low bioavailability of TCM formulation for SAA by local sustained release of this molecule, but also remarkably promoted its bone healing outcomes by synergizing with calcium and phosphate ion release during SAA release period. This approach collectively had a synergistic effect of osteogenesis with SAA, thereby significantly enhanced the efficacy of SAA in promoting bone formation. The in vitro experimental results indicated that the SAA@MECM exhibited good biocompatibility and significantly enhances angiogenesis and osteogenic differentiation. By day 14, compared to the MECM group, the gene expression levels of Col-I, ALP, Runx-2, and OCN in the SAA-H group increased by 1.8, 1.5, 1.5, and 2.0 times, respectively. This demonstrates the potential role of SAA in promoting the activity and differentiation of osteoblasts, highlighting its potential applications in bone tissue engineering. Leveraging such favorable feature of this system, SAA-loaded MECM demonstrated extraordinary bone healing capability in a rat calvarial defect model by showing successful bridging of the defects and large amount of new bone formation. Histological analysis further confirmed its outstanding osteogenic potential, while the dense distribution of micro vessels in the newly formed bone revealed the scaffold's remarkable potential in enhancing vascularization. This study might offer an innovative delivery strategy for enhancing the efficacy of natural phenolic acids through biomaterials.