The Development And Experimental Study Of Artificial Cervical Disc Based On 3D Printing Technology

Introduction:Cervical spondylosis can cause difficulty in holding and walking,which often brings great inconvenience to people’s daily life and work.At present,there are about 10%of the people in our country suffering from cervical spondylosis,and the age of onset is young.It has become a social problem which cannot be ignored.Intervertebral disc degeneration is the most important reason of cervical spondylosis.With aging,the intervertebral disc begins to degenerate gradually,resulting in the rupture of the outer fibrous.The protruded nucleus pulposus cause nerve compression which can lead neurological symptoms.Anterior cervical discectomy and fusion(ACDF)has been considered as a standard surgical procedure for treating cervical spondylosis for a long time.ACDF excised the diseased intervertebral disc to relieve its nerve compression,and implanted autogenous bone,allograft or artificial bone to fuse the adjacent motion segments to treat cervical spondylosis.The clinical practice in recent years have found ACDF on cervical spondylosis is satisfactory,but the problem of adjacent segments degeneration(ASD)as well as fusion failure,graft dislocation happened,which left room for ACDF operation for further improvement.In recent ten years,artificial cervical disc replacement(ACDR),which can restore physiological function of cervical spine,has become a new trend treatment method for cervical spondylosis.The advantage of ACDR is not only to achieve sufficient decompression effect,relieve symptoms of cervical spondylosis,but also retain the physiological function of cervical spine,which could avoid the degeneration and acceleration caused by compensatory overactivity after ACDF.It has been 15 years since the development of ACDR in China,and there are differences of race,region and other characteristics of cervical artificial disc prosthesis.Prosthesis are in accordance with the design of the west race cervical structures,not entirely suitable for Chinese patients,sometimes will seriously affect the replacement effect.In addition,long-term complications such as ASD,prosthesis displacement,subsidence,heterotopic ossification and other clinical complications also occurred after ACDR.These complications may be related to factors such as prosthesis design,size and mechanical mismatch.In this situation,the research and development of the artificial cervical intervertebral disc which can suit for the anatomical and biomechanical characteristics of the cervical endplate is very important and urgent.3D printing technology,also known as additive manufacturing technology,is a technology based on digital model files,which uses plastic or powdered metal and other adhesive materials to build objects through layering and stacking.Because 3D printing is accurate,complex and individualized,it is in line with the direction of individualized treatment in orthopedics,and is in the forefront of the application of orthopedics.The appearance of 3D print personalized metal prosthesis has made up for the poor matching of artificial prosthesis,and has become an important direction in the field of 3D printing in orthopedics.The metal 3D printing prosthesis can form a similar pore structure to the surface or interior of the plant,besides providing rapid and complex molding.In the ACDR operation,the size and shape of the prosthesis plays an important role in ensuring the success of the operation.Therefore,the best matching of the artificial cervical disc material and the size and shape of the artificial cervical disc can be achieved by using the precise structure and the complex molding advantage of the 3D printing technology.Based on the above problems,we design an artificial cervical endplate according to the anatomic characteristics of disc,and use metal 3D printing technology preparation with novel artificial cervical intervertebral disc endplate porous structure,mechanical testing,analysis of its impact on cervical spine biomechanics,and to evaluate the compatibility of humman osteoblast,in order to better meet the clinical needs of patients.Methods:Using CT data to design a new artificial cervical disc.The biomechanical effects of artificial cervical disc on cervical spine were observed by finite element(FE)analysis,including cervical spine motion(ROM),intradiscal pressure,facet joint pressure and prosthetic bone interface stress.Using electron beam melting(EBM)to 3D print of Ti6Al4V and CoCrMo alloy;test the young’s modulus of porous samples;artificial disc compression performance test was done according to ASTM F2346-05(2011)standard,the range of testing load 0-10000N;fatigue performance test was done according to ASTM F2346-05(2011)standard,select600N to do the fatigue strength of two kinds of materials for the study of artificial cervical disc fatigue test load.The experimental specimens are human cadaver cervical spine.According to the order of test,they are divided into complete group,new artificial cervical disc group,Prestige LP artificial cervical disc group and Cage internal fixation group.The Motion capture system was used to measure the ROM of each segment of the cervical spine,and the Tekscan joint pressure test system was used to measure the pressure of the facet joints.Hydroxyapatite nanoparticles were prepared by hydrothermal method;using X ray diffraction(XRD),energy dispersive spectrometer(EDS)and transmission electron microscopy(TEM)to characterization;using immunofluorescent staining examine the adhesion of osteoblasts;using CCK-8 kit observe cell activity;using flow cytometry detect cell apoptosis.Results:The ball groove joint design of the new prosthesis is same with Prestige LP prosthesis,but extended endplate area,with the dome roof endplate,with three stable teeth.C3-C7FE model was successfully established.The new disc group and Prestige LP group have similar cervical ROM,and cervical ROM were retained compared with the normal group.intradiscal pressure of C4-C5,C6-C7 in the new disc group and Prestige LP group had no difference with the normal group.There is no difference in the facet contact force among groups.Peak stress were distributed in the anchoring tooth in two groups.The stress distribution in new disc group was more uniform than that of Prestige LP group.The new artificial cervical disc endplate with porous structure using 3D printing technology was prepared successfully.Elastic modulus and porosity of porous structure was the opposite trend,the value is 0.4-20 GPa.Compression experiment results of the two discs in the range of experimental tests(0-10000N)showed not failure.Fatigue test results of 10~7 times at 600N load showed not failure.There was no significant difference among three groups in ROM of C5-C6,and each direction of ROM significantly reduced in the Cage fixation group.facet joint pressure in extension,left lateral bending and right rotation was significantly lower in the Cage fixation group.Porous Ti6A4V and CoCrMo alloy coatings were prepared successfully by nano HAP.Porous Ti6Al4V alloy,HAP Ti6Al4V alloy,porous CoCrMo alloy,HAP CoCrMo alloy showed osteoblast adhesion and growth.Coating group showed better actin microfilament bundles extension compared with non-coated group.Coating group showed higher cell survival rate than non-coated group.Osteoblast apoptosis had no significant difference among different groups.Conclusions:C3-C7 FE model was established based on the CT data.The FE results of the new artificial cervical disc and Prestige LP artificial disc showed both of them can reduce the risk of ASD,and the new artificial cervical disc had more advantages in reducing subsidence risk than Prestige LP artificial disc.Using EBM 3D printing technology,a new cervical intervertebral disc with porous and dome shaped endplate was successfully made,which reduced the elastic modulus of Ti6Al4V and CoCrMo alloy,and meet the requirements of compression resistance and fatigue resistance.In vitro biomechanics,the new cervical disc replacement is similar to Prestige LP artificial disc replacement,which can maintain normal cervical spine biomechanics.Compared with ACDF,the activity of the segment was retained after ACDR,and the pressure of the facet joint was the same as that of the normal cervical spine.The pure phase hydroxyapatite nanorods can be successfully prepared by hydrothermal method.In situ deposition method can effectively deposit the nano HAP coating on the surface of 3D printing Ti6Al4V and CoCrMo alloys.3D printing alloy and nano HAP coating alloy did not promote the apoptosis of human osteoblasts,and there was no statistical difference among them.In addition,HAP coating could promote the adhesion and proliferation of osteoblasts.Nano HAP coating porous alloys have potential application value in orthopedics.