Basic And Translational Research On Biodegradable Magnesium Based Implants For The Prevention And Treatment Of Bone And Joint Infection

Background: With the progress of orthopedic medical technology,joint replacement,internal fixation of fracture,the reconstruction of ligaments & tendons and other implant related surgery has become an important method of reconstruction of movement function.However,the implant associated infection and other bone & joint infection remains disastrous complication for patients.How to reduce the morbidity of implant associated infection became an important issue in orthopedic medical field.The present study focused on the research on development new biomaterial that could be resistance of infection,which has become a new strategy for prevention and treatment of implant related infections.Magnesium and its alloy is a new type biodegradable implant material which has great potential for clinical application.And our previous research found that its alkaline degradation produce a strong anti-infection effect to orthopedic common pathogenic bacteria,suggesting that our further antibacterial modification of magnesium-based material(such as alloying modification and coating modification)is expected to enhance its resistance to infection,better bioactivity and optimized biological suitability,and thus make it become a new type of implants for prevention and treatment of implant related infections and bone & joint infection such as osteomyelitis.Objective: 1.We aimed to use a variety of physical & chemical technology and biological methods to explore different ways of antibacterial modification to strengthen the antibacterial property and bioactivity of Mg-based metal implant material:(1)functional alloying modification(2)functional coating surface modification.2.We aimed to systematically evaluate microstructures,mechanical properties,corrosion behavior,and ion release of different modified Mg-based alloys in vitro.Then the biocompatibility,antibacterial activity and osteoinductive activity of them were also studied in vitro and in vivo.3.We aimed to discover how Mg-based alloys achieve their antibacterial properties and what effects,if any,this has on biofilm performance,virulence,and drug resistance.We investigated these effects at the genetic level(including of the expression of biofilm-associated,virulence,and antibiotic-resistance genes).4.We aimed to further improve the antibacterial performance of Mg-based implants and optimize biocompatibility and biological activity of them thus to adapt to the actual demand in the clinical treatment.Methods & Results: 1.Peri-prosthetic infection remains a challenging clinical complication.We investigated the antibacterial properties of pure magnesium(Mg,99.9%)in vitro and in an in vivo rat model of implant-related infection.Mg was highly effective against methicillin-resistant Staphylococcus aureus-induced osteomyelitis and improved new peri-implant bone formation.Bacterial ica A and agr RNAIII transcription levels were also assessed to characterize the mechanism underlying the antibacterial properties of the Mg implant.2.We prepared biodegradable magnesium(Mg)–copper(Cu)alloys with different amounts of copper(0.05,0.1,and 0.25 wt.%)and assessed their potential for the treatment of methicillin-resistant Staphylococcus aureus(MRSA)-induced osteomyelitis.We evaluated the alloys’ microstructures,mechanical properties,corrosion behavior,and ion release in vitro,and biocompatibility and antibacterial activity in vitro and in vivo.The antibacterial activity of the Mg-Cu alloys in vitro was demonstrated by microbiological counting,confocal laser scanning microscopic observation of bacterial viability,field-emission scanning electron microscopic observation of biofilm formation,and polymerase chain reaction analysis of the expression of biofilm-associated,virulence,and antibiotic-resistance genes.In addition,imaging examination,microbiological cultures,and histopathology consistently showed the antibacterial activity of Mg-Cu alloys in vivo.Of those tested,the alloy containing 0.25 wt.% Cu exhibited an excellent biocompatibility,without local/systemic side effects and no obvious Cu2+ or Mg2+ ion-complex deposition in organs or tissues,indicating that this alloy possesses a suitable magnesium/copper ratio and proper corrosion rate.Together our results indicate that the Mg-Cu alloy containing 0.25 wt.% Cu has great potential for use as an implant biomaterial in the treatment of orthopedic infections.3.Different amounts of silver added to biodegradable Mg-Nd-Zn-Zr alloy to get access to implants infection problem.We assessed its treatment effect of methicillin-resistant Staphylococcus aureus(MRSA)-induced osteomyelitis.The mechanical properties and corrosion behaviors were also evaluated.Cytotoxicity test revealed none of the alloys induced toxicity to Balb/c mouse embryo fibroblasts(3T3 cells).Together our results indicate that Mg-Nd-Zn-Zr-1.1Ag alloy has great potential for use as orthopedic implant biomaterial in treatment of implant associated infections.4.We report on the fabrication of gentamicin-loaded Poly(lactic-co-glycolic acid)(PLGA)coating on porous magnesium scaffold(Gent-PLGA-Mg)for use as a type of controlled antibiotic delivery system bone scaffolds to achieve the sustained release of antibiotics in the local sites of bone defects.The drug loaded PLGA coating of Mg scaffold enable higher drug loading efficiency(28-33%)than non-coating gentamicin loaded Mg scaffold(Gent-Mg)(2-3%).Gent-PLGA-Mg exhibited sustained drug release for more than 14 days,and this controlled release of gentamicin significantly inhibited bacterial adhesion and prevented biofilm formation by S.aureus(ATCC25923)and S.epidermidis(ATCC35984).Biocompatibility tests with human bone marrow stromal cells(h BMSCs)indicated that PLGA-Mg had better biocompatibility than Mg.Therefore,Gent-PLGA-Mg is potential to be used as a controlled drug delivery system bone scaffolds to prevent and/or treat orthopedic peri-implant infections.5.Implant-associated infection remains a difficult medical problem in orthopaedic surgery.Therefore,the development of multifunctional bone implants for treating infection and regenerating lost bone tissue,which may be a result of infection,is important.In the present study,we report on the fabrication of Enoxacin-loaded Poly(lactic-co-glycolic acid)(PLGA)coating on porous magnesium scaffold(Enox-PLGA-Mg)which combine the favorable properties of magnesium,the antibacterial property and the effect of inhibition of osteoclastic bone resorption of Enoxacin.The drug loaded PLGA coating of Mg scaffold enable higher drug loading efficiency(52-56%)than non-coating Enoxacin loaded Mg scaffold(Enox-Mg)(4-5%).Enox-PLGA-Mg exhibited sustained drug release for more than 14 days,and this controlled release of Enoxacin significantly inhibited bacterial adhesion and prevented biofilm formation by S.epidermidis(ATCC35984)and S.aureus(ATCC25923).Biocompatibility tests with Balb/c mouse embryo fibroblasts(Balb/c 3T3 cells)indicated that PLGA-Mg had better biocompatibility than Mg.Finally,we also demonstrated that Enox-PLGA-Mg extract potently inhibited osteoclast formation in vitro.Therefore,Enox-PLGA-Mg is potential to be used as a multifunctional controlled drug delivery system bone scaffolds to prevent and/or treat orthopedic peri-implant infections.Conclusion: 1.Alkaline environment produced by degradation of pure magnesium can significantly inhibit bacterial biofilm formation,and shows a certain osteogenesis induction activity,suggesting that it has potential prevent implant related infections.But pure magnesium antibacterial function only depends on alkaline environment,its antibacterial performance is affected by the degradation rate,which needs to be further modified.2.Mg0.25 Cu alloy exhibit ideal antibacterial property and good bio-safety,can effective treatment and prevention of rabbit tibia osteomyelitis and inhibit bacterial biofilm formation by downregulated the expression of bacterial virulence,drug resistance and biofilm formation related genes.We believe it can be used as alternative antibiotics chain of beads or bone cement,but its degradation rate is too fast to be used as bone defect repair material.3 Mg-Nd-Zn-Zr-1.1Ag alloy can effectively inhibit bacteria proliferation and biofilm formation in vitro,while maintaining a good mechanical property.It can also control the development of osteomyelitis,and the degradation rate is slow in the body.So it has a great potential as a kind of osteomyelitis related bone defect repair materials.4.Two drug loaded coatings(Gent-PLGA-Mg and Enox-PLGA-Mg)on the surface of the porous magnesium delayed the degradation of the Mg implant,improved its biocompatibility,and achieved a high drug load efficiency and stable drug release property,so as to achieve the ideal antibacterial effect.It has potential as antimicrobial coatings for Mg implants.5.In this present study,we introduced several antibacterial modification methods of Mg-based metal implant,put forward some different kinds of the Mg implants application forms for the prevention and treatment of orthopaedic infectious diseases.We also provided preliminary theoretical foundation for its translational products to clinical device.