Research On Microwave-Triggered Drug Delivery System With Thermal Synergistic Effect For Treating Osteomyelitis And Ununited Bone Defects

Methicillin resistant Staphylococcus aureus（MRSA）infected chronic osteomyelitis is a deep bone tissue infection,which carries a serious risk of systemic infection and severe morbidity from amputation.In clinical,antibiotic therapy and debridement are common treatments for chronic osteomyelitis.However,Chronic osteomyelitis has poor local revascularization and a low rate of antimicrobial penetration into bone tissue,necessitating the use of high doses of antibiotics to achieve antibacterial effects.Yet,using high doses of antibiotics is also accompanied by toxic side effects that tend to be dose-dependent and an increasing risk of drug resistance.Debridement creates a certain degree of bone defects,and bone regeneration is not favored at the lesion of osteomyelitis.Therefore,in this study,black phosphorus nanosheets were used as substrates to prepare a microwave sensitizer（Fe₃O₄@APNs）with excellent microwave thermal effects by surface modification.For the treatment of chronic osteomyelitis with recurrent infections and difficulties repairing bones,a core-shell drug delivery system（PMP/PVA）was created with Fe₃O₄@APNs-porous scaffold（PMP）served as the core layer and Fe₃O₄@APNs-drug loaded hydrogel（PVA）served as the shell layer,and its antibacterial and osteogenic activities were verified by microwave thermal properties,antibacterial assays in vitro,cell assays in vitro,and chronic osteomyelitis assays in vivo.This paper was mainly divided into the following five sections:1.Preparation and microwave thermal properties of ferric oxide incorporation into phytic acid dodecasodium modified black phosphorus nanosheets（Fe₃O₄@APNs）This chapter sought to construct a black phosphorus nanosheet-based microwave sensitizer and provided it high antioxidant capabilities in addition to superior microwave thermal performance.BPNs with small size and thin thickness are less stable and prone to oxidative degradation layer-by-layer.The liquid phase exfoliation method was employed to create modified black phosphorus nanosheets of phytic acid dodecasodium（APNs）,which has a superior antioxidant property.APNs are non-metallic dielectric materials that are hybridized with metallic magnetic material Fe₃O₄ to obtain microwave sensitizer（Fe₃O₄@APNs）.Under microwave irradiation（2.45 GHz,10 w/cm²）,the surface of 10:1 Fe₃O₄@APNs showed enhanced dielectric loss due to increased interfacial defects,resulting in more excellent microwave thermal effects（53.5℃,5 min）.In conclusion,10:1 Fe₃O₄@APNs had good antioxidant and microwave thermal properties.2.Preparation,antibacterial and osteoblast responsive properties in vitro of Fe₃O₄@APNs-magnesium phosphate porous scaffolds（PMP）This chapter aimed to construct a bone cement scaffold with specific antibacterial capacity paired with good osteogenic activity to solve the issue of ununited bone defects formed after debridement in chronic osteomyelitis.Magnesium phosphate cement scaffold（MPC）is a degradable scaffold for bone repair.Combined Fe₃O₄@APNs with MPC to form a composite bone cement scaffold（PMP）,endowing it with microwave thermal properties and osteogenic properties,generating a dual impact of microwave thermal antibacterial and osteogenesis.Compared with MPC and 0.5%PMP,1%PMP（1 wt%Fe₃O₄@APNs）exhibited a significant microwave thermal effect.Antibacterial assays in vitro showed that 1%PMP could inhibit the activities of MRSA（90.03±0.97%）and E.coli（93.03±2.00%）under microwave irradiation;cell assays in vitro displayed that the presence of black phosphorus nanosheets further promoted the cellular response（adhesion,proliferation and osteogenic differentiation）of BMSC.Therefore,1%PMP possessed both excellent osteogenic activity and certain antibacterial properties.3.Preparation,antibacterial and osteoblast responsive properties in vitro of Fe₃O₄@APNs-drug loaded hydrogels（PVA）The traditional sustained-release drug delivery system’s poor penetration,drug resistance,and toxic side effects in treating chronic osteomyelitis can be addressed.This chapter designed a controlled-drug delivery system with microwave responsive drug release.A solvent-volatilization technique was employed to create VAN-PLGA sustained-release microspheres.The Fe₃O₄@APNs-drug loaded hydrogels（PVA）were prepared by a sol-gel method,endowing it with dual antibacterial properties for microwave hyperthermia and chemotherapy.In vitro drug release behavior showed that drug release reached 51.69±1.00%of MV group in 7 d（Ctrl group:29.62±20.16%）.Antibacterial assays in vitro exhibited that microwave combined with PVA showed excellent antibacterial properties with antibacterial rates of 98.4±0.6%and91.4±0.7%against MRSA and E.coli.Cell assays in vitro showed osteogenic differentiation of BMSC due to black phosphorus nanosheets.Therefore,PVA had both excellent antibacterial properties and a certain osteogenic activity.4.Preparation,antibacterial and osteoblast responsive properties in vitro of core-shell drug delivery system（PMP/PVA）For the treatment of chronic osteomyelitis with ununitable bone defect,a core-shell drug delivery system（PMP/PVA）was prepared by sol-gel method with 1%PMP as the nuclear layer and PVA as the shell layer.Under microwave irradiation,the shell layer PVA exerted dual antibacterial activity of microwave thermal effect and antibiotics;Subsequently,the nuclear layer PMP exerted dual effects of antibacterial and osteogenic by releasing Ca and Mg ions to promote osteogenic differentiation.Antibacterial assays in vitro showed that PMP/PVA exhibited excellent antibacterial activity（MRSA:99.98±0.02%,E.coli:99.43±0.73%）and the antibacterial effect was superior to PVA and PMP;Cell assays in vitro showed that PMP/PVA might more effectively encourage BMSC osteogenic development since it was non-cytotoxic to BMSC,better than PMP.Therefore,PMP/PVA had better antibacterial and osteogenic differentiation properties than PMP and PVA.5.An animal study of the PMP/PVA for chronic osteomyelitis treatmentThe antibacterial properties and bone regeneration properties of PMP/PVA were further investigated by constructing a rabbit model of chronic osteomyelitis.X-ray imaging,micro-CT imaging results showed that PMP/PVA group’s bone healing was better without a major periosteal reaction,while the other groups’bone implant sites had some degree of dead bone and bone defects after 12 w.Microbiological evaluation results displayed that there was no obvious bacterial infection in the bone marrow cavity of PMP/PVA group.Histological evaluation exhibited that there was no significant inflammatory reaction and infection at the bone implant site in PMP/PVA group.Therefore,PMP/PVA system exhibited multiple antibacterial effects with osteogenic activity under microwave irradiation and could effectively treat chronic osteomyelitis accompanied by bone defects.In summary,the designed microwave sensitizer Fe₃O₄@APNs,exhibiting excellent microwave thermal effects through dielectric and magnetic losses.And the core-shell drug delivery system PMP/PVA showed outstanding antibacterial activity through microwave responsive drug release coupled with microwave thermal effect.At the same time,microwave thermal effect can promote acceleration of blood microcirculation,and the release of synergistic calcium and magnesium ions can further promote osteoblast response and new bone regeneration.PMP/PVA holds great promise for the treatment of chronic osteomyelitis with ununited bone defects by MV irradiation.