| BackgroundAnterior cruciate ligament(ACL)rupture is one of the most common joint injuries.Using interference screws to squeeze the transplanted ligament into the bone tunnel is a reliable fixation method commonly used in ACL reconstruction.Currently,the materials used to prepare interference screws mainly include metal,absorbable polymer,and bioceramic materials.Among them,metal interference screws have problems such as cutting ligament grafts and metal residues interfering with MRI imaging,and postoperative removal will cause a second surgical trauma.Although the absorbable polymer interference screw alleviates the defects of the metal nail,it is easy to break under high torque during implantation,and the excessive degradation rate after implantation leads to a mismatch with the tendon-bone healing rate.In contrast,bioceramic interference screws represented by zirconia have the advantages of excellent mechanical properties,good biocompatibility and stability,and do not need to be removed after surgery to avoid secondary surgical trauma.It has important scientific research value and broad clinical application prospects.However,ceramics’ unique brittle and hard machining characteristics restrict the design and preparation of complex screws in the research and development stage.The biological inertia of zirconia ceramics limits the stability of the tendon-bone-nail interface in the early stage of ACL reconstruction.Because of the above problems,this study intends to realize the optimal design and preparation of complex personalized shape ceramic interference screws by stereolithography SLA-3D printing technology.The screw parameters were optimized by screwing torque and axial tensile biomechanical test.ZrO2/PDA/RGD/Zn2+composite coating was assembled on the screw surface to improve the bioactivity of zirconia.Finally,ceramic 3D printing and coating technology were combined to prepare bio-modified zirconia interference screws.While maintaining the initial stability of ACL reconstruction with interference screws,it accelerated the interface osseointegration,promoted tendon-bone healing,and ensured the long-term stability of ACL reconstruction.ObjectiveThrough the design optimization of parameters such as thread tooth type,thread depth,top tooth width and driving structure shape,the fastening performance and retention ability of 3Dprinted zirconia interference screws is improved.To investigate the feasibility of preparing ZrO2/PDA/RGD/Zn2+ composite biological coating screw and its effect on osteoblast proliferation,adhesion and osteogenic differentiation.In order to prepare an interference screw with good initial stability,and can promote osseointegration.Methods1.The mechanical properties and X,Y and Z anisotropic size shrinkage of 3D printed zirconia standard specimens were characterized.Based on this,24 screw models with different thread profiles,thread depth,top tooth width and driving shape structural parameters were designed and compensated by Creo 5.0 software.Then,the dimensional accuracy and macroscopic and microscopic morphology of the screws were characterized by scanning electron microscopy.The biosafety of screws was determined by the CCK-8 method.2.According to ’People’s Republic of China Pharmaceutical Industry Standard YY/T05095,a screw-polyurethane foam model was established to detect the maximum screw-in torque and axial pull-out force of screws with different structural parameters.The biomechanical model of the interference screw squeezing the tibial ligament graft was established.The maximum insertion torque,ultimate load and stiffness of the screws with different structural parameters were tested.The screw model parameters with the best fastening performance and retention ability were finally optimized through the statistical analysis of the results by orthogonal experiment and range analysis.3.ZrO2/PDA/RGD/Zn2+composite bio-coated screws were prepared by layer-by-layer assembly.XPS and SEM detected the properties of the composite biological coating.The proliferation level of MC3T3-E1 cells was determined by the CCK-8 method.The number and morphology of MC3T3-E1 cells adhered to the material’s surface were observed by fluorescence staining and SEM.MC3T3-E1 cells were co-cultured with composite coating interface screws,and osteogenic differentiation potential was evaluated by alkaline phosphatase staining and determination of alkaline phosphatase activity.The level of cell mineralization was determined by alizarin red staining.Results1.The size shrinkage of 3D-printed zirconia parts was measured,and the size compensation parameters of interference screws were designed according to the anisotropic characteristics of sintering shrinkage of ceramic 3D printing.The zirconia interference screws of Φ 8 mm × 27.5 mm were successfully prepared by 3D printing.SEM observed the microstructure of the screw surface,the crystal was uniform,and the structure was complete.Geomagic control precision analysis,dimensional accuracy up to 0.064 mm;the CCK-8 method verified that the screw was safe and non-toxic.2.The results of the orthogonal experiment and variance analysis showed that the driving shape is the most critical factor affecting the screw torque,and the thread profile is the most important factor affecting the screw fixation strength.The mechanical properties of the regular hexagon drive screw with a serrated thread profile,thread depth of 0.8 mm and top tooth width of 0.4 mm are the best.3.ZrO2/PDA/RGD/Zn2+composite biological coating screws were prepared by layer-bylayer assembly and co-cultured with MC3T3-E1 cells.The results showed that ZrO2/PDA/RGD/Zn2+group promoted cell proliferation and adhesion compared with the ZrO2 group,and the difference was statistically significant.The ALP activity of the ZrO2/PDA/RGD/Zn2+group was 12.790 ± 1.135 mg/15 min/g prot,significantly higher than that of the ZrO2 group(P<0.01).The calcified nodules on the surface of the ZrO2/PDA/RGD/Zn2+group were significantly higher than those in other groups,which could promote the osteogenic differentiation and mineralization of MC3T3-E1 cells.PDA,RGD and Zn2+have synergistic effects.Compared with single or binary coatings,ZrO2/PDA/RGD/Zn2+ternary composite bio-coated screws always perform best in adhesion,proliferation and osteogenic differentiation.ConclusionsThe optimized serrated thread type,thread depth of 0.8 mm,and top tooth width of 0.4 mm of the hexagonal drive 3D printed zirconia interface screw has excellent mechanical properties,which is conducive to maintaining the initial stability of ACL reconstruction.At the same time,the prepared ZrO2/PDA/RGD/Zn2+composite biological coating can promote the osseointegration of the screw surface,accelerate the tendon-bone healing,and maintain the long-term stability of ACL reconstruction. |
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