| Medical diagnosis and treatment technology has improved in recent years,however,the treatment of chronic bone infection remains an arduous issue for orthopedic doctors.Chronic osteomyelitis is a common,potentially catastrophic,complication of trauma and orthopedic surgery.Its manifestations include multiple comorbidities,soft tissue defects,or the development of multiple drug resistance,and current treatment methods are unsatisfactory,with high recurrence rates and long treatment courses.Staphylococcus aureus is the organism most frequently implicated,accounting for 80%of human osteomyelitis.The efficacy of systemic antibiotic therapy is limited due to poor local permeability and insufficient blood supply at the site of infection,and side effects of long-term systemic drug use are common.Local antibiotic therapy can avoid systemic side effects,provide antibiotic directly at the site,and effectively clear bacterial infection.Antibiotic bone cement beads are the most popular non-biodegradable biomaterials for the treatment and prevention of bone infections.However,as a delivery vehicle,PMMA has some significant shortcomings,such as limited total amounts of antibiotics in the process of release,erratic drug release profile commonly characterized by a prominent initial burst release followed by a low,non therapeutic phase,and the potential to act as a foreign body and a seedbed for drug-resistant bacteria.As a result,it could not keep the long-term maintenance of effective antibiotic concentration for the treatment of chronic osteomyelitis,which is generally required for more than 3-4 weeks.Herein,researchers continue to seek an ideal local antibiotic delivery system,with the ability to maintain a high concentration of drug that remains within the safety range.In recent years,compound degradable materials that break down in a relatively short time so as not to act as a foreign body after elution of the antibiotic have been the subject of much interest.Biodegradable and resorbable materials mainly includes calcium sulfate,bioactive glass,calcium phosphates,collagen implants,demineralized bone matrix,and allograft bone.The inorganic composition of nano hydroxyapatite(n-HA)is very similar to that of natural bone tissue.Thus,it offers good biocompatibility and osteoconduction.Nevertheless,it does have drawbacks,such as unsatisfactory mechanical properties,brittleness,and fatigue failure.Therefore,in our study,we added polyurethane(PU)to n-HA to improve its mechanical properties for in vivo implantation.Due to its broad-spectrum antibacterial properties and good bone penetration,levofloxacin is effective against most sensitive bacterial bone and joint infections,has been reported to be useful for chronic osteomyelitis,and has good anti-staphylococcal activity and low toxicity.Mesoporous silica nanoparticles(MSNs)can offer a great capacity for carrying and adsorbing drugs,better control of drug loading and release,reduced drug toxicity and enhanced efficacy,excellent surface properties and porosity,and good biosafety,and are thus very suitable for bioactive material applications such as bone regeneration.Lev@MSNs/n-HA/PU is a novel biodegradable composite scaffold,our previous study confirmed that MSNs/n-HA/PU,loaded with 5 mg of levofloxacin,could inhibit the spread of the bacteria 12 weeks after implantation and promote bone repair.To evaluate its antibiotic release properties,antimicrobial activity,osteoconductivity and biomechanical properties more comprehensively,while continuing to use Lev@PMMA as a control in a chronic osteomyelitis rabbit model,further studies were designed and performed to offer more convincing evidence.This study consists of two parts.1.Study of the drug release characteristics of the novel composite scaffold in vitro.Objective Detect the release characteristics of antibiotics of new composite scaffolds Lev@MSNs/n-HA/PU in PBS to elucidate its antibacterial mechanism.Methods Levofloxacin-loaded mesoporous silica microspheres/nano-hydroxyapatite/polyurethane(Lev@MSNs/n-HA/PU)composite scaffolds were synthesized,immersed in PBS and refreshed at 1h,2h,6h,12h,and 24h,then the PBS solution was completely refreshed every 48 h until day 39.The drug concentration was determined by HPLC,using the bone cement with the same dose of antibiotics as control.Results In the 5 mg Lev@MSNs/n-HA/PU group,following rapid release over the first 24 hours,the release rate gradually declined,at 3 days,13 days and 30 days,second burst release was recorded.and the antibiotic released remained effective against Staphylococcus aureus for 39 days,longer than in the 1 mg Lev@MSNs/n-HA/PU and 5 mg Lev@PMMA groups,and the total amount of levofloxacin released was greater than from the 5 mg Lev@PMMA,which could serve as a solid foundation for further study in vivo.Conclusion Levofloxacin,released from 5 mg Lev@MSNs/n-HA/PU,a novel levofloxacin-loaded composite scaffold,following rapid release over the first 24 hours,the release rate gradually decline,which maintain at levels effective against S.aureus for 39 days,exhibited good release properties as revealed by in vitro elution,lay a theoretical basis for the treatment of chronic osteomyelitis in rabbits.2.Study of Lev@MSNs/n-HA/PU novel composite scaffolds in the treatment of chronic osteomyelitis of tibia in rabbits.Objective to further evaluate its efficiency in controlling infection and bone repairing in the chronic osteomyelitis model in rabbit,as well as to evaluate its biomechanical safety,explore its controlled release properties,biodegradation and compatibility,to provide experimental evidence for further clinical application.Methods The structural properties of the novel composite scaffolds Lev@MSNs/n-HA/PU were evaluated by SEM.A rabbit model of chronic osteomyelitis was established using the method described by Norden et al.45 animals were randomly divided into four groups,treated with 5 mg Lev@MSNs/n-HA/PU,1 mg Lev@MSNs/n-HA/PU,levofloxacin-loaded polymethyl methacrylate(5 mg Lev@PMMA,),or a blank as control after debridement.Animals were all sacrificed at 12 weeks posttreatment,Therapeutic efficacy was evaluated by general condition,venous blood analysis,and gross observation,X-ray,histology,SEM of implant-bone interface,microbiology,and biomechanical testing of the tibia.Results The loose and porous surface morphology of 5 mg MSNs/n-HA/PU were observed,the average porosity of the novel scaffolds was(54.46±5.68)%,and the pore size of the scaffolds are appropriate for bone tissue regeneration,mainly ranges from 200 ?m to 500 ?m.After 12 weeks of treatment,body weights had increased significantly,and body temperature had decreased significantly,compared with pretreatment in the 5 mg Lev@MSNs/n-HA/PU group,the WBC counts of the 5 mg Lev@MSNs/n-HA/PU group were decreased significantly compared with pretreatment or the blank control group,the bacterial counts in the 5 mg Lev@MSNs/n-HA/PU group decreased significantly compared with pretreatment as well as the control groups,which showed its effective bacteriostasis.Good bone repair and obvious degradation of the scaffold,without evidence of chronic osteomyelitis in X-ray,such as destruction of bone,was observed in the 5 mg Lev@MSNs/n-HA/PU group.Obvious PMMA occupation and no material degradation were seen in the PMMA group.Extensive destruction was found in the blank control group by gross pathology.However,the bone defects were completely repaired,and marked new bone growth on the surface and surrounding of 5 mg Lev@MSNs/n-HA/PU were seen,gap between materials and bone was observed in the control groups.SEM showed little new bone formation around the PMMA,and there was an obvious boundary between the material and bone tissue.A large amount of fibrous tissue,as well as a significant gap,were observed at the interface between the bone tissue and the 1 mg Lev@MSNs/n-HA/PU material.Nevertheless,bony connections and blurred boundaries were observed between 5 mg Lev@MSNs/n-HA/PU and peripheral bone tissue,and new bone formation was also observed on the surface of the material.Histology showed there was heavy new bone formation at the interface and along the voids of 5 mg Lev@MSNs/n-HA/PU,active bone resorption and bone formation around the peripheral interface were observed.Matured lamellar bone was formed in peripheral bone repair area.New bone trabeculaes were arranged orderly,with dense and continuous structure,and the speed and efficiency of new bone formation in 5 mg Lev@MSNs/n-HA/PU group outperformed the control group.Biomechanical testing showed the 5 mg Lev@MSNs/n-HA/PU group had the highest ultimate strength,and there was significant difference compared with that of blank control group as well as 1 mg Lev@MSNs/n-HA/PU group.Conclusion 5 mg Lev@MSNs/n-HA/PU was an effective treatment for chronic osteomyelitis in a rabbit model.Moreover,implants of 5 mg Lev@MSNs/n-HA/PU combined with radical surgical debridement could significantly control infection,did not result in local or systemic side effects,and exhibited good biocompatibility,osteoconductivity,and biomechanical properties.Herein,5 mg Lev@MSNs/n-HA/PU was shown to have great potential for the treatment of chronic bone infection. |
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