Use Of A 3D Printed PLGA/TCP Composite Scaffold Incorporating Magnesium Powder For Enhancement Of Bone Defect Repair In Rabbits

[Objective]Bone defects are a difficult orthopedic problem.For treatment of large bone defects,bone grafting remains the method of choice for the majority of surgeons,as it fills spaces and provides support to enhance biological bone repair.Magnesium containing bone materials have been widely used in clinical practice.The objectives of this study:1.To verify the repairing effect of bone defects with this biomaterial,a bioactive composite scaffold(Mg/PLGA/TCP)made of polylactide-co-gly-colide(PLGA)and tricalcium phosphate(TCP)as a basic carrier,incorporating magnesium powder(Mg).2.Try to use 3D printed porous scaffolds combined with guided bone regeneration technology to repair bone defects.[Methods]1.Scaffolds were fabricated as PLGA/TCP(control group,P/T)and PLGA/TCP incorporating magnesium(Mg/PLGA/TCP)using a low-temperature rapid-prototyping process.The scaffolds were scanned and reconstructed by Micro-CT.The microstructures were observed by scanning electron microscope,and the cytocompatibility and mechanical tests were carried out in vitro.2.A 15 mm bone defect model of the rabbit radius was established.There were 4 groups,including blank group,type Ⅰ collagen membrane group,P/T+I collagen membrane group and Mg/PLGA/TCP+I collagen membrane group with 12 rabbits in each group.The X-ray films were taken to evaluate the repair effect of bone defect area immediately after implantation and then at 2,4,8 and 12 weeks.3.A total of 24 New Zealand white rabbits were randomly divided into P/T and Mg/PLGA/TCP group,with 12 rabbits in each group and data of blank group was used from previous results.Radiographs of the operated radii were taken immediately after implantation and then at 2,4,8 and 12 weeks.New bone formation and remaining scaffold using Micro-CT and histological analysis were performed at 4,8,12 weeks after operation.[Results]1.PLGA/TCP scaffold is white and Mg/PLGA/TCP scaffold is black.The pore diameter and the porosity of the scaffold is 450 microns and above 85%,and the pore connectivity is greater than 97%.Porous scaffolds showed good compatibility in vitro.The young’s modulus of the scaffold incorporating magnesium group was significantly higher than that of the control group(P<0.01).2.In the 15 mm radius bone defect,two porous scaffolds were coated with type Ⅰ collagen membrane.From 4 weeks,bony ends of radii were gradually closed.3.After 4 to 12 weeks,the results of X ray observation and Lane Sandhu quantitative score showed that two composite scaffolds were better than the blank group(P<0.05),and the new bone in Mg/PLGA/TCP group was more than that in control group,although there was no statistical difference(P>0.05).After analysis by MicroView(GE corporation),at 4 weeks,the BV/TV in Mg/PLGA/TCP group was higher than that in control group(P<0.05).The BMD of Mg/PLGA/TCP group was higher than that of control group,though there was no statistical difference(P>0.05).At 8 weeks,the BV/TV and BMD in Mg/PLGA/TCP group were higher than those in control group(P<0.05).At 12 weeks,the BV/TV and BMD in Mg/PLGA/TCP group were lower than those in control group,but there was no statistical difference(P>0.05).From 4 to 12 weeks,the total volume percentage of residual scaffold in Mg/PLGA/TCP group was smaller than that in control group(P<0.05).The histological results showed that Mg/PLGA/TCP group had more mineralized bone(P<0.05)than control group at 4 weeks.The percentage of remaining scaffold area in Mg/PLGA/TCP group was significantly less than that of control group at the 8 and 12 weeks(P<0.05).Rat bone marrow mesenchymal stem cells(BMSCs)were implanted on the scaffolds.With live/dead staining 2 and 7 days after implantation,laser confocal 3D imaging showed that living cells and very few dead cells could be seen in both PLGA/TCP group and Mg/PLGA/TCP group.[Conclusion]1)A new type of composite Mg/PLGA/TCP porous scaffold was fabricated using low temperature rapid prototyping technology,which has high porosity,pore connectivity and good biocompatibility and biological activity.2)These findings verified that Mg/PLGA/TCP composite scaffold may be an orthopedic substitute material with good biocompatibility and potential clinical value.