Guided Tissue Engineering Approaches In Repair Long Bone Defects Through Distraction Osteogenesis

ObiectiveBone defects in weight bearing long bones resulted from trauma,bone infections and tumour resections are challenges for orthopaedic surgeons.External and internal fixations in conjunction with autologus bone grafting or synthetic biomaterials are commonly used,but the pitfalls are lengthy treatment,slow to consolidate and remodel,infections and re-fractures.Distraction osteogenesis(DO) technology has been developed to treat bone defects and deformities with outstanding clinical outcomes,but the DO treatment is sometimes associated with complications such as slow bone consolidation.Methods of promoting bone consolidation during DO treatment have been studied,such as using ultrasound,grow factors and stem cells,but these treatments require expensive molecules or additional procedures. One of the cost effective approach may be using platelet-rich plasma to promote bone consolidation during DO,which is yet to be tested.Taken the advantages of the rapid bone formation and vascularization associated with DO,and the new developments in bioengineering sciences,this project aims to investigate whether by combining the use of biomaterials and DO techniques,will greatly reduce the time needed for the treatment of long bone defects.We will investigate if the combined treatment with biomaterials and DO will reduce the treatment time vs.Controls(single treatments)in a rabbit model of tibial lengthening;Methods:An rabbit tibial bone defect/lengthening model will be established for this study firstly.New Zealand White rabbits(male,20-24 weeks,body weight 3.0-3.5 kg) will be anaesthetized by intramuscular injection of SuMingXing and Midazolam. Osteotomy will be made by handsaw in the left tibia in the rabbit,and a 0.5 cm or 1.0 cm length of the tibial shaft will be removed below the tibiofibular junctionthrough a second osteotomy,the tibia will then be fixed with Orthfix M100 unilateral lengthener with 4 pins(2.5cm self-tapping pins),the treatments below will follow:Group 1 (N=10).The 0.5-cm defect gap will be immediately reduced,with the tibia shortened for 0.5-cm and the wound will be closed.Lengthening will start 7 days after the osteotomy surgery,at a rate of 1.0 mm/day,in two steps,for 10 days.Once the lengthening(0.5cm)is achieved,the regenerate is allowed to consolidate for further 20 days.The animals will be terminated at day 37 following initial surgery. Group 2(N=10).In this group,1.0 cm bone defect will be created during the osteotomy surgery.The 1.0-cm defect gap will be immediately filled with 1.0 cm restorable porous HA/TCP cylindrical block(EBI OsteoStim,Millenium Biologix Inc, Canada)and the bone will be stabilized by the Orthfix M100 unilateral fixator and wound closed.The animals will be terminated at day 37 following initial surgery. Group 3(N=10).The 0.5-cm defect gap will be immediately filled with 0.5 cm restorable porous HA/TCP cylindrical block(EBI OsteoStim,Millenium Biologix Inc, Canada)and held in position with the Orthfix M100 unilateral lengthener. Lengthening will start 7 days after the osteotomy surgery,at a rate of 1.0 mm/day,in two steps,for 5days.Once the lengthening(0.5 cm)is achieved,the regenerate will be allowed to consolidate for further 25 days.The animals will be terminated at day 37 following initial surgery.Group 4(N=10).The 0.5-cm defect gap will be immediately filled with 0.5 cm restorable porous HA/TCP cylindrical block(EBI OsteoStim,Millenium Biologix Inc,Canada)soaked with 75 ug rhBMP-2(Provided by Wyeth,USA),and held in position with the Orthfix M100 unilateral lengthener. Lengthening will start 7 days after the osteotomy surgery,at a rate of 1.0 mm/day,in two steps,for 5 days.Once the lengthening(0.5cm)is achieved,the regenerate will be allowed to consolidate for further 20 days.The animals will be terminated at day 37 following initial surgery.Radiographic examination:Serial radiographs will be taken at the day of surgery,5 days,10 days during lengthening,end of lengthening,10 days and 20 days (termination point)post-lengthening,Serial radiographs of each group are compared.Peripheral micro computed tomography(Micro CT):To assess the volumetric density of the regenerate,the excised bone specimens are scanned using a Micro CT GE Health care explore locus with MicroView v2.1 software ABA,The mean volumetric bone mineral densities(BMD)of the regenerates from per sample are calculated and compared.Mechanical testing:Mechanical testing will be performed on samples after the Micro CT examination in Moses Mushipe's laboratory(co-applicant).Torsion tests will be performed on a MTS 858 Mini BionixRll at room temperature(22℃).The rotation angle was applied at a rate of 4.5deg/sec and the torque and angular displacement was measured by the in-built devices and recorded.The biomechanical properties of specimens were determined by the maximum torque,torsional stiffness, and the maximum angular displacement required to failure.Histological examination:After the Micro CT examination and mechanical testing, the samples are cut at 7μm sections and stained with routine hematoxylin and eosin (HE)and Alcian blue/Sirius red.Alcian blue/Sirius red staining,following de-paraffin, re-hydration,nuclear staining with Weigert's hematoxylin,sections are stained with Alcian blue and Sirius red.All histological sections will be examined and compared.Results:Radiographic examination:The radiographic signs of cortical continuity was completely continuation in the group D and groupC in the 37day,meanwhileboth Group A and Group B are partially united.From the17 day,the bone density in the group D and group C were greater than Group A and B,and the bone density in the group D was greatest.Moreover,Bone generation was greater in the group C and D than in the group A and B.The maturity and consolidation of the callus in the group C and D were greater than those in the group A and B.Micro-CT Images and Data:Micro-CT images of the distraction gap tissues demonstrated promoted bone formation in the Group C and D compared to the Group A and B.The newly formed bone was much more evenly distributed across the entire distraction gap in Group C and D compared to Group A and B.The mean volumetric TMC,TMD BMC,BMD,BV/TV Calib.Tb.Th.3D,Calib.Tb.Sp.3D,Mean Thickness (mm),Std Dev Thickness(mm)in the group C and D are greater than in the group A and B.Mechanical Testing Results:Maximum Torque(N-m)and Torsion stiffness(N-m/deg)are significantly higher in the Group C and D,compared to Group A and B.Maximum Torque(N-m)and Torsion stiffness(N-m/deg)in the group Dare significantly greater than in the group C.Histology Results:The regenerate of group C and D was more mature in the group C and D and The regenerate of Group D was the most mature in the four groupsConclusion:In the rabbit model of tibial lengthening,the combined treatment with biomaterials and distraction osteogenesis technique can reduce the treatment time and promote bone consolidation vs.Controls(single treatments).BMP can farther boost the bone formation and reduce the treatment time.