Enhanced antibacterial activity and osteoinductivity of Ag-loaded strontium hydroxyapatite/chitosan porous scaffolds for bone tissue engineering

The properties of bone scaffolds, including biocompatibility, osteoinductivity and antibacterial activity, are of great importance for reconstruction of large bone defects and prevention of implant-associated infections. Herein, we develop an Ag-loaded strontium hydroxyapatite (SrHAP)/chitosan (CS) porous scaffold (Ag-SrHAP/CS) according to the following steps: (i) freeze-drying fabrication of a SrHAP/CS porous scaffold; and (ii) deposition of Ag nanoparticles on the above scaffold. In addition, HAP/CS and Ag HAP/CS porous scaffolds are prepared under the same conditions without doping Sr element. All the HAP/CS, Ag HAP/CS, SrHAP/CS and Ag SrHAP/CS porous scaffolds provide a friendly environment for the adhesion, spreading and proliferation of human bone marrow mesenchymal stem cells (hBMSCs). The three-dimensional (3D) interconnected macropores with a pore size of 100-400 mu m allow the spreading of hBMSCs throughout the whole scaffolds. Interestingly, the Sr ions and Ag ions released from the Ag SrHAP/CS porous scaffolds significantly enhance their osteoinductivity and antibacterial activity, respectively. The Sr element in the SrHAP/CS and Ag SrHAP/CS porous scaffolds increase the alkaline phosphatase (ALP) activity of hBMSCs, extracellular matrix (ECM) mineralization, and the expression levels of osteogenic-related genes BMP-2 and COL-1. Moreover, the Ag ions released from the Ag HAP/CS and Ag SrHAP/CS scaffolds can effectively inhibit the growth and attachment of Staphylococcus aureus (S. aureus, ATCC 25923). In conclusion, the Ag SrHAP/CS porous scaffold possesses excellent biocompatibility, osteoinductivity and antibacterial activity, so it has great potential for application in bone tissue engineering to repair bone defects and avoid infections.