Ag-doped CNT/HAP nanohybrids in a PLLA bone scaffold show significant antibacterial activity

Abstract

Bacterial infection is a major problem following bone implant surgery. Moreover, poly-l-lactic acid/carbon nanotube/hydroxyapatite (PLLA/CNT/HAP) bone scaffolds possess enhanced mechanical properties and show good bioactivity regarding bone defect regeneration. In this study, we synthesized silver (Ag)-doped CNT/HAP (CNT/Ag-HAP) nanohybrids via the partial replacing of calcium ions (Ca²⁺) in the HAP lattice with silver ions (Ag⁺) using an ion doping technique under hydrothermal conditions. Specifically, the doping process was induced using the special lattice structure of HAP and the abundant surface oxygenic functional groups of CNT, and involved the partial replacement of Ca²⁺ in the HAP lattice by doped Ag⁺ as well as the in situ synthesis of Ag-HAP nanoparticles on CNT in a hydrothermal environment. The resulting CNT/Ag-HAP nanohybrids were then introduced into a PLLA matrix via laser-based powder bed fusion (PBF-LB) to fabricate PLLA/CNT/Ag-HAP scaffolds that showed sustained antibacterial activity. We then found that Ag⁺, which possesses broad-spectrum antibacterial activity, endowed PLLA/CNT/Ag-HAP scaffolds with this activity, with an antibacterial effectiveness of 92.65%. This antibacterial effect is due to the powerful effect of Ag⁺ against bacterial structure and genetic material, as well as the physical destruction of bacterial structures due to the sharp edge structure of CNT. In addition, the scaffold possessed enhanced mechanical properties, showing tensile and compressive strengths of 8.49 MPa and 19.72 MPa, respectively. Finally, the scaffold also exhibited good bioactivity and cytocompatibility, including the ability to form apatite layers and to promote the adhesion and proliferation of human osteoblast-like cells (MG63 cells).

Graphic abstract