Preliminary Study Of An Antibacterial And Absorbable Silk-based Material With Impressive Mechanical Properties And Biocompatibility

BackgroundFor now the use of internal fixation devices,especially metallic materials,is widespread to treat fracture and expected to increase in the future due to an aging population and improving medical care.Implant-associated infections and non-absorbing materials are two important reasons for a second surgical procedure to remove internal fixation devices after an orthopedic internal fixation surgery.It has been proved that silk fibroin as an absorbable biomaterial has impressive mechanical properties and biocompatibility.However,like all biomaterials,silk material may carry an elevated risk of implant-associated infections because of the formation of bacterial biofilms.Hence proposing a method to impart silk fibroin with antibacterial properties is becoming a hot research.ObjectiveThe objective of this study was to produce an antibacterial and absorbable fixation screw with impressive mechanical properties and biocompatibility by adding gentamicin to silk-based materials.In the present work,the antibacterial activity of gentamicin-loaded silk-based screws(GSS)was assessed in vitro.Furthermore,the properties of the silk-based screws containing gentamicin,such as the mechanical features,swelling properties,biocompatibility and degradation,were tested.The above research will provide the basis for clinical application in the future.MethodsSilk solutions were prepared from B.mori cocoons according to a previously reported procedure.Gentamicin sulfate was dissolved in 1,1,1,3 3 3-hexafluoro-2-propanol(HFIP),and solutions were prepared at four concentrations,which were used to dissolve vacuum-dried silk.The antibacterial activity was assessed against Staphylococcus aureus(S.aureus)and Escherichia coli(E.coli)in vitro by inhibition zone,plate cultivation and scanning electron microscopy(SEM).We also investigated the properties,such as the mechanical features,swelling properties,biocompatibility and degradation,of gentamicin-loaded silk-based screws.ResultsPure silk-based screws(PSS)promote obviously the growth of S.aureus since the bacteriostasis rates of PSS against S.aureus was-306.0±3.6%.At 1h the bacterio stasis rates of GSS with 16mg/g gentamicin against S.aureus and E.coli were both 100%.But for GSS with 8mg/g or 6mg/g gentamicin the time at which the bacteriostasis rate reached 100%was 12h.Only a few S.aureus and E.coli strains were observed on GSS by SEM.Furthermore,the morphologies of S.aureus on GSS were anomalous.After 4 weeks,no significant decrease was observed in the antimicrobial activity of GSS,which still possessed bacteriostasis rates of more than 90%against S.aureus and E.coli.In terms of mechanical properties,the GSS samples achieved a bending strength of 202.8± 7.8MPa,shear strength of 35.4±6.1MPa and Young’s modulus values of 8.5±0.7Gpa,which were no significant difference compared with PSS(p>0.05).There were no detrimental effects to cell proliferation or apoptosis in vitro resulting from the PSS and GSS.The experiments in vivo also indicated GSS and PSS didn’t result in significant inflammatory reaction and toxic effects.There were no detrimental effects to bone formation.Compared with PSS,the degradation rate of GSS in protease type XIV was faster and consistent with third-order(R2=0.99)polynomic trendlines.While GSS swells less and at a slower rate than PSS.ConclusionThe most suitable concentration of gentamicin is 16 mg/g,which endows GSS with rapid,high and durable antimicrobial activity.In the meantime,GSS still retains the remarkable mechanical properties and excellent biocompatibility.The rapid degradation of GSS is beneficial to a gradual transfer of the load-bearing burden to the developing tissue during fracture healing,which supports the restoration and maintenance of tissue function over the life of the patient.Our findings indicate that this antibacterial silk-based fixation material can overcome the limitations of metal and traditionally resorbable devices,with great potential for use in orthopedic implants to reduce the incidence of second surgical procedures for a given clinical application.