Research On Biomechanical Properties And Bio-tribology Of Cemented Hip Prosthesis Implants

Cemented hip arthroplasty is a widely used and mature surgery.Fixture failure is the major feature of THA postoperative revision.In this paper,the three majority objected failure factors of cemented hip arthroplasty,which were weight,osteoporosis and arthritis,was revealed and investigated to influencing cemented THA revision 37.31%,23.30% and 30.64%,respectively.The load affected by patients’ weight was acted upon the prosthesis which induced loosening and micro-cracks of stem-cement shear failure interface,resulting in material differences in early period.As a result of load increasing and the cement cumulative creep damage accelerating,the interface was loosened while stem was sunken.Cement was so thin just merely 1.2 ± 0.5mm that hardly preventing bone adaptive degradation at proximal medullary cavity of femur.Whilst,fretting mechanism of the loosen interface produced wear debris to stimulate osteoclast proliferation to accelerate bone dissolution.Spherical debris was prior to swallowed by Macrophages.Four points were defined and studied in this paper,such as viscoelasticity,interface debonding performance,dynamic mechanics and fretting wear.Firstly,it was found that the optimum program of hardness and compressive strength had 96.25 MPa,whose ratio of powder to liquid is 20g/12 ml with 30 s stirring time.The viscoelasticity characterizes of creep and stress relaxation were analyzed by pre-assembly embedded fiber bragg grating,whose results revealed the fact that stress made the contact interface of Ti6Al4 V metal and bone cement unstably and material energy consumption increased,which induced bone cement viscoelastic softening,whilst reformed macromolecule segment was forced to migrate for realize a new mechanical balance by tension stress,eventually.Secondly,the linear and nonlinear exponential model of the bond stress(τ)and the relative slip(s)for Ti6Al4 V bar-cement interface were established.It was achieved that the relationship of the average load and the displacement in the debonding failure stage and the splitting failure stage,the relationship evolution of bond stress and slippage was analyzed,thereby.The two internal stress peaks of Ti6Al4 V bar was found at 0.175 La position distanced from loading tip and 0.325 La position from free tip as well,respectively.They induced internal cracks damage of the cement mantle which has been confirmed by nondestructive testing.Thirdly,the dynamic mechanical test equipment of stem-cement components was designed,while the fiber bragg grating was assembled and collected stress and strain of stem and cement,respectively.It is found that the axial dislocation of stem-cement interface is round about 0.25 ± 0.05 nm.The hysteretic curve evolution of cement in dynamic energy consumption procession had gone through a linear shape to an oval shape and then to a twist shape.In another way,computational method of Prony series for bone cement viscoelastic material is designed and carried out the finite element dynamic simulation test of stem-cement components,and the test results were well verified.It was also found that fluctuating pattern of stress wave in cement mantle at the 45°±0.8°angle was guided from loading tip to free tip.Finally,it was showed by the Ft-D curve that the evolution of the dissipation energy of the contact material interface,as it was increased as cycles.Thermoplastic and micro torque damage was the main reasons for the damage of titanium alloy and bone interface.At the early stage of fretting wear test,the bovine serum has an influence of friction resistance and anti-wear on wear contact region,and the ability is decreased as load increased,then increased wear volume,eventually.The results showed the average dry friction coefficient was 0.123 and that was 0.157 in the bovine serum.Finally,concaves were formed in cement wear region,and convex plates and the ring-shaped concaves were formed on the opposite Ti6Al4 V surface.The six typical shapes of wear debris includes roundness,ellipsoid,strip,block,tear and flake.At last,fractal dimension of wear debris was analyzed by designed Matlab program,whose results revealed the nearly roundness shape owned the largest number of wear debris and obtained the fractal dimension is 0.3~0.6.