Preparation Of Drug Loaded Mesoporous And Hollow Fe₃O₄ Nanoparticles And Its Antibacterial Effect Under An Alternating Magnetic Field

The bone defect caused by bone tuberculosis（TB）seriously affects patients’ability of activity and quality of life.At present,oral or intravenous administration of anti-TB drugs as well as surgical resection of the focus are the most common clinical treatments.But the former treatment will bring toxic side effects and the latter will induce bone defects.Based on this,this paper proposes a responsive drug delivery system for the treatment of bone tuberculosis by using the mesoporous hollow Fe₃O₄ nanoparticles（MHFPs）with drug loading capacity and magnetic response.After the implantation of the drug-loaded carrier,the antituberculous drug can be controllably released in the local lesions under the alternating magnetic field（AMF）.Thus the toxic side effects of the drug can be avoided and the problem of early bone defects induced by surgical resection can be solved by combining with bone repair materials.In this project,MHFPs were prepared as the drug carrier and magnetic Fe₃O₄nanoparticles loaded with hydrophobic drug rifampicin（MHFPs-RFP）were constructed.In order to achieve drug delivery and efficient utilization in cells and finally kill TB and cure bone tuberculosis,the bactericidal effect of MHFPs combined with AMF was studied.Later,the exploration was conducted on the bactericidal effect of MHFPs-RFP combined with AMF,which provided a theoretical basis for the treatment of bone damage after surgery and the prevention of recurrence of bone tuberculosis.The main research contents and results are as follows:（1）The MHFPs were prepared by one-step hydrothermal method.The maincomponents of the MHFPs were demonstrated to be Fe₃O₄ from the results of XRD and FT-IR.Scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and N₂ adsorption-desorption analysis proved its mesoporous and hollow structure.Finally,the good cytocompatibility of MHFPs was revealed by MTT assay.（2）In combination with AMF,the antibacterial effect of MHFPs on E.coli and S.aureus in vitro was investigated by colony forming methods,bacterial live/dead staining and biofilm crystal violet staining.Bacteria and bacterial biofilm didn’t show an obvious change when MHFPs or AMF was treated separately.However,the combination of MHFPs and AMF could effectively enhance the antibacterial and anti-biofilm properties of MHFPs and this enhancement performance increased with the increase of MHFPs’concentrations.（3）The antibacterial mechanism of the MHFPs in vitro was studied.By comparing the effects of normal heating mode in hot water and magnetothermal heating mode in AMF,the effects of MHFPs and commercial Fe₃O₄ nanoparticles（CFNPs）on bacteria,we proved that the antibacterial effect of MHFPs under the AMF was not only caused by the increase of macroscopic temperature,but also the temperature rise in the nanoscale vicinity of the particles.SEM and TEM for bacteria,the relative electric conductivity rate and the amount of nucleic acid release have showed that MHFPs could kill bacteria by enhancing the permeability of bacterial cell membrane of E.coli and S.aureus and even destroying the membrane integrity under the action of AMF.（4）Rifampin was successfully loaded into MHFPs to form MHFPs-RFP by decompression and spin evaporation.The FT-IR and TG results suggested that rifampin was successfully loaded and the loading rate was 33.92%.In combination with AMF,the antibacterial effect of MHFPs-RFP on E.coli and S.aureus in vitro was investigated.The colony forming method,bacterial live/dead staining and crystal violet staining were performed.The effect on bacteria and bacterial biofilm was limited when MHFPs-RFP or AMF was treated separately,but the combination of MHFPs-RFP and AMF could effectively enhance the antibacterial and anti-biofilm activities of MHFPs-RFP.Compared with MHFPs,the antibacterial and anti-biofilm performances of MHFPs-RFP were significantly improved.