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OBJECTIVE@#To study and establish the preliminary linear and modified models for the interface shear mechanics performance between implant and bone cement and to explore its damage significance.@*METHOD@#The loosening research between artificial hip joint prosthesis stem and bone cement interface performance can be evaluated by the push-in test. Based on the debonding performance test, the analytical expressions of the average load and displacement from the debonding failure and splitting failure process were deduced and determined. The correlations of the expressions of the average load-displacement and statistical experimental data were analyzed.@*RESULTS@#It demonstrated that the interface debonding failure mechanical model could be characterized as interface bond strength mechanical performance. Based on analysis of models and experimental data by the three statistical analysis methods, the results indicated the modified model could be better represented by the interfacial debonding strength properties. The bond stress τ and relative sliding s distribution along the embedment regional were coupling affected by both pressure arch effect and shear lag effect in bone cement. Two stress peaks of implant have been found at the distance from 0.175La loading tip to 0.325La free tip, which also verified the early loosening clinical reports for the proximal and latter region. As the bone cement arch effect, the bond stress peak tend to move to the free tip when the debonding failure would be changed into the splitting failure, which presents a preliminary study on the mechanism of early debonding failure for the stem-cement interface.@*CONCLUSIONS@#Functional models of the stem-bone cement interfacial debonding failure are developed to analyze the relevant mechanism. The different locational titanium alloy stress, and the interfacial bond stress and the relative slides are evaluated to acquire a guide of the different positions of interfacial damage. The coupling effect which is original from the pressure arch and the interfacial shear hysteresis cumulative effect has influence on the interfacial debonding and damage process.
Subject(s)
Bone Cements , Chemistry , Hip Prosthesis , Materials Testing , Models, Statistical , Shear Strength , Titanium , ChemistryABSTRACT
Objective To investigate the influence of acetabular morphology on contact mechanics of the human hip joint. Methods One anatomical finite element (FE) model of natural hip joint and three simplified FE models with different acetabular geometry were established to study the contact mechanics of hip joint under gait loads. Results (1) Contact predicted by the anatomical model was mainly distributed in the acetabular medial-superior area, from anterior to posterior, with the peak contact pressure occurred in the anterior-superior area; (2) Compared with the anatomical model, the rotational ellipsoid produced similar contact behavior, while the sphere and the rotational conchoids predicted that contact was distributed in the medial-lateral direction; (3) The rotational ellipsoid predicted the largest contact area and the lowest peak contact pressure and Von-Mises stress; (4) The sphere and rotational conchoids had similar contact mechanical behavior. Conclusions Compared with the sphere and rotational conchoids, the rotational ellipsoid could be more preferable to represent the anatomical morphology of the acetabulum and its contact mechanics.
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Objective To cross-link the porous biological ceramics and PVA hydrogel to form a double layer construction between the artificial cartilage and hard joint, and to analyze its morphologies and mechanical properties. Methods With hydroxyl apatite (HA) as the substrate, the porous hydroxyl apatite biological ceramics with different porosities were prepared by using NH4HCO3 crystal grains as the pore-formed material. The poly vinyl alcohol (PVA) and epoxypropane were used as the primary material and cross-linking agent, respectively. The PVA hydrogel with double layer construction was cross-linked and prepared on the porous biological ceramics surface. The fracture appearances of the test specimen section were characterized. The performances of anti tensile strength and anti-shear strength for PVA hydrogel were analyzed. Results The cross-linked PVA hydrogel could permeate in the biological ceramics substrate, and the union between ceramic substrate and PVA hydrogel performed well. With the porosity of the porous biological ceramics increasing, the tension load and shear load of the PVA hydrogel samples both increased, and with the average porosity of 70%, the samples’ biggest tension load and shear load were 153.61 N and 64.46 N, respectively. But the corresponding tensile strength and shear strength both decreased and with the average porsity of 70%, the samples’ biggest tensile strength and shear strength were 2.12 MPa and 1.13 MPa, respectively. The failure mode of both tension and shear tests for PVA hydrogel samples was due to the crack propagation, and the fracture morphologies showed that obvious cracks and internal defects appeared on the fracture surface, while the source of the crack and the direction of the crack propagation could be observed. Conclusions Considering the compression strength of porous biological ceramics, the permeation effect on the porous biological ceramic substrate with the average porosity of 50% is moderate to be used, which ensures the appropriate shear and tensile strength of PVA hydrogel samples and the compression strength of porous biological ceramic.
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Objective To study the deformation and stress distribution of femur after total hip arthroplasty (THA) and its influence on the vibration mode and natural frequency of femur. Method Two finite element models of natural femur and femur after THA were developed on the basis of computed tomography (CT) scans from a normal young man to investigate the biomechanical behavior of the subjectunder gait condition and make the modal analysis. Results (1) After THA, obvious stress concentration was obtained around the prosthesis neck, and the stress shielding was observed; (2) The peak stress of femur model after THA increased to 4.36 times of the original one; (3) The natural frequency for constrained mode was much higher than that of free mode; (4) With the increase of vibration mode, the differences in natural frequency between two models became larger; (5) Bending and twisting were the main vibration mode of femur, and there were no significant changes in vibration mode before and after THA. Conclusions The prosthesis could change the mechanical and structural properties of the original femur. In order to avoid prosthesis loosening derived from sympathetic vibration, the vibration property of femur must be taken into consideration in the design of prosthesis.