| Artificial cervical disc (ACD) replacement surgery provides a new method for the treatment ofcervical spondylosis. In order to overcome the poor anti-fatigue performance, complicated structureand postoperative complications, the typical shortcomings of the present ACDs, a new integratedartificial cervical disc prosthesis was designed and optimized numerically by finite element method(FEM) and experimentally with a bio-mimetic fatigue test fixture in present thesis.Initially, based on the CAD model of integrated ACD, the CAE software ANSYS was used toestablish the finite element models under the flexion, extension and lateral bending conditions, withthree kinds of bio-medical titanium alloys, β-type, TC4titanium alloy and pure titanium, as optionalmaterials. The overall finite element models comprised both C5-C6vertebral bodies and the ACDprosthesis, with the backend thickness of0.6mm,0.8mm,1.0mm and1.2mm as well as theherringbone, rhombic tooth fixation structure. The mechanical properties of β-type, TC4titanium alloyand pure titanium were measured and applied for the material parameters in the FEM model simulation.The simulated results indicated that all ACD prostheses presented the reasonable maximum Von Misesstress of below their own yielding strengths, except the pure titanium prosthesis with the backendthickness of0.6mm. Under the above mentioned three loading conditions, the maximum Von Misesstress of β-type titanium alloy prosthesis with backend thickness of0.8mm and herringbone toothstructure was383.264MPa, the activity of the C5-C6segments was2.506o,3.232o and1.194o,respectively. These activities under flexion and lateral bending were close to the50%of the normalcervical spine, while90%of the normal cervical spine under extension. By comparing the maximumVon Mises stress of the prosthesis and the activity of segments, the β-type titanium alloy prosthesiswith backend thickness of0.8mm and herringbone tooth structure was the best design.Considering the structure features of the integrated prosthesis, a fatigue test fixture was designednumerically using FEM for testing the fatigue behavior of the ACD prosthesis. Simulation resultsshowed that the fatigue test fixture for ACD prosthesis could represent the biomechanicalcharacteristics of the normal human cervical. By optimization of the test fixture, the stress levels of theACD prosthesis could be equivalent to the reality in the intervertebral region.According to the ANSYS/FE-SAFE simulated fatigue performances of the prostheses, the fatiguecycle life of the pure titanium prosthesis with backend thickness of0.8mm was21,320,000;furthermore, the fatigue life of the pure titanium prostheses with backend thickness beyond1.0mm, aswell as the β-type and the TC4titanium alloy prostheses with backend thickness beyond0.8mm were more than80million cycles, which met the design features very well. Moreover, the accumulatedfatigue damage always occurred near the inner of backend. The fatigue test results, with the help of thedesigned fatigue test fixture, revealed that the fatigue cycle life of the pure titanium prosthesis withbackend thickness of0.8mm was35,645,000. And no fatigue fracture occurred in pure titaniumprostheses with backend thickness of1.0mm after80million cycles, so did the β-type titanium alloyand TC4titanium alloy prostheses with backend thickness beyond0.8mm, which were coincide withthe fatigue simulation results.Finally, the fatigue fracture morphology was analyzed. The results indicated that the fatigue crackinitiation was found on the inner region of backend, and then propagated throughout the sectiontowards the outside of backend, consequently leading to the fatigue failure, which agreed well with thefatigue simulation results.In summary, the β-type titanium alloy ACD prosthesis with backend thickness of0.8mm couldgreatly restore segmental motion function and meet the needs of fatigue design requirements of thatthere was no fatigue failure in ACD prosthesis after80million loading cycles. |
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