| Titanium alloy is the most commonly used material for internal fixation nowadays.However,if not remove the material timely,the stress shielding effects may lead to osteoporosis after a long period of time.Biodegradable polymer materials possess good biocompatibility.At the same time,it lacks strength and brings acidic products along with degradation,which can lead to sterile inflammation and affect the healing of bone repair.Magnesium alloy,which introduced into the orthopedic field in the last century,is a biodegradable material.But it was failed to promote to clinical use because of its fast degradation,hydrogen production and so on.Zinc alloy is a new material with sufficient strength,good histocompatibility and plasticity,the most important is that it can be degraded.Its relatively slow rate of degradation and biocompatibility make the material a hotspot.The research group adopted in this study is a patent for invention-a kind of human-degradable Zn alloy with highcorrosion resistance.The zinc alloy has good mechanical properties and good cytocompatibility.In addition,the material has good antibacterial properties,which can inhibit E.coli and Staphylococcus aureus.This study explored the efficacy,safety and degradation of zinc alloy for animal mandibular fracture model with internal fixation system of biodegradable zinc alloy.Objective The purpose of this study:1.To verify the efficacy of canine mandibular fracture model to study the zinc alloy applications.2.To observe the safety and efficacy of the new biodegradable zinc alloy internal fixation system for the treatment of canine mandibular fractures and the degradation of the zinc alloy internal fixation system in vivo.Methods In the first part of the study,we established the canine mandible fracture model.38 Beagle dogs were randomly divided into 3 groups,of which 12 were zinc alloy experimental group,12 were PLLA control group,12 were titanium alloy control group and 2 were blank control group.Except for the blank group,fracture line was made in the mandible for each side and treated by zinc alloy internal fixation system.In the second part of the study,to evaluate the safety,efficacy and biodegradable of the new biodegradable zinc alloy internal fixation system for the treatment of canine mandibular fractures.After the internal fixation model was established,follow-up observation was performed.X-ray,blood normal tests,blood biochemical tests and serum zinc for regular testing.The animals were euthanized at 1,3,6,9 and 12 months after operation.Micro-CT,SEM,undecalcified bone histomorphometry and three-point bending test of the mandible were performed.The organ of animals and the soft tissue surrounding the internal fixation were used for pathological sections.The mandibular fracture model of beagle dog was successfully established,and the zinc internal fixation alloy,titanium alloy and PLLA were implanted into the mandible of beagle dogs.The general condition of postoperative animals was good,with no implants failure during the whole observation time.The mandibular fractures in the experimental group were clinically healed.During the observation period,X-ray was taken,and the healing of fracture was observed in the mandible of zinc alloy,titanium alloy and PLLA group.Blood samples were taken at planned time points.Blood normal tests and blood biochemical tests of zinc alloy internal fixation group showed no significant difference compared with control group(P> 0.05),and there was no significant difference between each time point(P> 0.05).Serum zinc concentration slightly fluctuated within the normal range,no significant difference between the time points was observed.After animal euthanasia,clinical healing was generally observed in the fractures of the zinc alloy,titanium alloy and PLLA groups.Obvious particulate degradation products were observed on the surface of the zinc alloy,and there were more particles of degradation product over time.Micro-CT reconstruction of the mandibular fractures showed that the fracture healing of the internal fixation of the zinc alloy group was good.At one month,BV/TV,Tb.Th of zinc alloy were higher than those of PLLA and titanium alloy,and were significantly higher than those of PLLA(P <0.05).At 3 months,the difference between the three groups became smaller;at 6 months,there was no significant difference among the three groups.Micro-CT measurement of zinc implants volume showed that the volume of zinc alloy internal fixation system decreased significantly through time.The volume of titanium alloy did not change.Scanning electron microscopy showed that the surface morphology of biodegradable zinc alloy was almost uniform after the implantation without obvious serious local damage.VanGieson staining of hard tissue sections showed that the amount of new bone at the fracture site of the experimental group and the control group gradually increased over time at 1 and 3 months.Cortical bone of the zinc alloy and titanium alloy group is relatively thick and with high density.Cortical bone of PLLA group is relatively small and the distribution is Resultsmore dispersed.Mechanical experiments show that the maximum load of zinc alloy and titanium alloy are similar,and higher than PLLA at 3 months after surgery.At 6 months,the mechanical strength of the zinc alloy and PLLA group has increased and the mechanical strength of the titanium alloy did not change much.At 9 months,the loading capacity of the zinc alloy and PLLA groups was higher than that of the titanium alloy group.Histological examination showed that there were no obvious morphological changes and inflammatory cell infiltration in the heart,liver,kidney and gonads of the experimental group and two control groups.No accumulation of harmful substances in liver and kidney.No inflammatory cells were found in soft tissue around the zinc alloy plates.ConclusionBiodegradable zinc alloy internal fixation system provides a stable fixation for canine mandibular fracture model.It showed good mechanical properties in the healing process.The degradation rate of the biodegradable zinc alloy is relatively slow,the degradation is uniform,and there is no significant abnormal increase in zinc ion concentration in the blood.Biodegradable zinc alloy is non-toxic to the heart,liver,kidney and soft tissue around the implants,which showed good biocompatibility,As a novel biodegradable internal fixation material,the zinc alloy provides a new idea for fixation of maxillofacial fractures. |
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