Papers by Keyword: Stress Shielding

Abstract: The current research presents a novel porous tibia implant design based on porous structure. The implant proximal portion was designed as a porous rhombic dodecahedron structure with 500 μm pore size. Finite element method (FEM) was used to assess the stem behavior under compressive loading compared to a solid stem model. CATIA V5R18 was used for modeling both rhombic dodecahedron and full solid models. Static structural analysis was carried out using ANSYS R18.1 to asses the implant designs. The results indicated enhanced clinical performance of tibial-knee implants compared to the solid titanium implant via increasing the maximum von-Mises stresses by 64% under the tibial tray in porous implant which reduce stress shielding. Also, the maximum shear stress developed in bone/implant interface was reduced by 68% combined with relieving the stress concentration under the stem tip to relieve patients' pain. Finally, porous implants provide cavities for bone ingrowth which improve implant fixation.

Abstract: Commercially pure titanium (cp Ti) is typically accepted as one of the best in vitro and in vivo bone replacement biomaterial, due to its excellent balance between biomechanical and biofunctional properties. In that context, the aim of this work is to prove the hypothesis of a simultaneous solution to certain specific limitations of cpTi, which can often compromise the reliability of implants: (i) stress-shielding phenomenon, and (ii) a deficient biointerface with bone, which reduces the osseointegration. Porous samples of cp Ti, grade IV, were obtained by space-holder technique (50 vol.% NH₄HCO₃, 800 MPa, at 1250 oC during 2h, under high vacuum), to produce a good balance between Young ́s Modulus and yield strength. Different types of porous samples were manufactured by considering different size particles ranges of NH₄HCO₃: 100-200μm, 250-355μm and 355-500μm. Afterwards, they were coated with a PEEK/45S5 bioactive glass composite by electrophoretic deposition, to be finally sintered at 350oC for 1h. The coatings homogeneity, infiltration efficiency, adhesion and cracking, were studied in order to establish correlations with processing conditions (time of deposition, applied voltage, composition, concentration and stability of the colloidal suspension). Detailed structural characterization of the coatings was performed (SEM and XRD), besides the contact angle and contact profilometry testing. Additional mechanical and chemical insights were achieved by evaluating both the tribo-mechanical (instrumented microindentation and micro-scratch testing) and electrochemical behaviors (potentiodynamic polarization and in vitro corrosion tests in SBF). All these results allowed us to determine the optimal balance of properties for a porous substrate (space holder of 250-355μm) with a coating obtained for 65 V, 2 min, 6 mm (distance between electrodes), 10 g/L bioactive glass and 20 g/l PEEK. The high adhesion estimated between the bioactive/biopolymer coatings and the porous titanium substrates (excellent infiltration) suggest that this new biocomposite is a good candidate for load-bearing applications.

Abstract: LC-DCP (limited contact—dynamic compression plate) is the preferred plate in internal fixation. A new LC-DCP fixed with the femur was designed. Its strength was investigated with finite element method during stair climbing. Also, stress shielding and strength of femur fixed with TC4 (Ti6Al4V) compression plate was analyzed for different load mode during stair climbing. Simulated results demonstrated that compression plate’s design was reasonable, and it was not obvious to eliminate femoral stress shielding through adding preload on the screws. Also the analytical methods of stress shielding for femur fracture, established in the work, can be widely applied to stress shielding analysis of other bone fracture.

Abstract: Porous titanium samples of cp Ti grade IV were obtained by space-holder technique (50%vol of NH₄HCO₃, 800 MPa, 1250 oC during 2h in high vacuum), producing a good balance between stiffness and mechanical strength. The samples were coated with chitosan/45S5 bioactive glass composite by electrophoretic deposition. Homogeneity, infiltration efficiency, and coatings integrity (cracking and adhesion) were evaluated in order to establish correlations with processing parameters. SEM, FTIR, and contact profilometry were performed for detailed characterization of the coatings; and micro-mechanical properties (P-h curves and scratch testing) were set-up as well. Optimum EPD parameters were 25V, 7 min and suspension containing 0.5 g/L chitosan and 1.5 g/L BG a titanium structure with pore sizes greater than 200 μm are required.

Abstract: This research investigates the stress distribution of the three types of implanted femurs using the finite element method analysis. The comparisons of the stress distribution between the implanted femursand the healthy femur were performed and the characteristics in the stress shielding of each casewere clarified. Since the load is transferred on the contact surface between the implant and the inner surface of the femur in the case of the total hip arthroplasty, the stress in the intertrochanteric zone (Gruen zone 7) become very small, and the phenomenon of the stress shielding is confirmed obviously. The stress distributions of the femurs afterthe resurfacing hiparthroplasty and the thrust plate prosthesis are about the same with that of the healthy femur, so, the possibility of the stress shielding is considered lower compared with the femur after the total hip arthroplasty. However, considering the stress concentration thatwill increase the risk of femoral fracture caused by the screws for the fixation of the implant in the thrust plate prosthesis, the resurfacing hiparthroplastymay beconcluded as the best method among these three types of implants to avoid stress shielding.

Abstract: To analyze the stress shielding in femoral fixation with TA3 Titanium compressioll plate by using the finite element method. Firstly, establish TA3 Titanium compressioll plate, screws and three-dimensional geometric model of the femur; and its mesh, and the establishment of the corresponding three-dimensional finite element model; the final definition of material properties, and load boundary conditions. During standing state, the strength of plate and screw has been analyzed by the finite element method, while the femoral stress shielding has been analyzed. Standing stress when compared to normal bone stock, TA3 Titanium compressioll plate and screws for femoral stress shielding effect is not obvious. Established in this paper plate on the femur stress shielding of the analytical method can be widely applied in other state analysis of stress shielding bone fracture.

Abstract: Biomechanical compatibility is one of the key targets for bone tissue engineering scaffolds. As the repair of hard tissue, the scaffold should be of similar strength and elasticity modulus with replaced bone to avoid stress shielding. This paper combines the finite element method and the computer simulation technology analyzing the stress influence of the porous β-TCP scaffold and the middle of femur in different internal architectures, and the simulation results show that scaffold implants at lower porosity conducive to the elimination of stress shielding. The aim of this paper is to provide the theory and design basis on the bone tissue engineering scaffolds.

Abstract: In order to understand an effect of crack-face bridging stress field of alumina ceramics on its fracture toughness, local residual stress distribution due to crack face grain bridging behind the crack tip was measured using synchrotron x-ray beam at SPring-8 in Japan. The SEPB (Single Edge Precracked Beam) specimens of two types of polycrystalline Al2O3 were used for stress measurement; one was pressureless sintered Al2O3 (AL1) and the other was hot-press sintered Al2O3 (TAL). Pop-in precracks were introduced by bridge-indentation method. Before residual stress mapping, the SEPB specimens were unloaded from a constant applied load to zero using four points bending device. Two-dimensional residual stress field was mapped by scanning a micro X-ray beam of 50×50 μm2 with the scanning interval of 12.5 or 25 μm. As a result, in the case of AL1 having conventional fracture toughness and strength, the compressive residual stresses due to crack-face bridging were only observed in the close vicinity of crack tip. On the other hand, in the case of TAL having higher fracture toughness and strength, the compressive residual stresses were widely distributed behind the crack tip. Larger compressive stress was locally generated along the crack path at interlocked grains. The compressive bridging stresses distributed behind the crack tip were found to enlarge with a decrease in the crack opening displacement against a constant applied stress intensity factor, Kapp. It was concluded that the difference in residual stress fields behind crack tip was attributed to the differences in its microstructure and microcrack propagation behavior, such as deflections and interlocked grains.

Abstract: A femoral Prosthesis Stem made from composite material is investigating to apply to real body. The purpose of this study is to propose a design method of novel composite stem. Finite element models of stem and femur have been developed by using CT images. Some design parameters of the stem have been described and the effect of mechanical properties on the femur has been also described and compared with a traditional metal stem. The evaluation procedure for the stem has been proposed and been applied to a composite stem. It is revealed that the stem made of composite is more effective than the traditional stem made of metal.

Abstract: It is often the case that the low fracture toughness of polycrystalline ceramics limit the load-bearing capabilities of components made from such materials. In an effort to improve the fracture toughness of a SiC-TiC composite material, a novel stress-shielding approach was adopted so as to reduce the effective mode I stress intensity around a crack tip within the composite body. To this end, a series of functionally graded materials were produced, with samples having a preselected spatial SiC-TiC composition variation. The spatial composition variation within each sample was set up according to one of several exponential mathematical functions. In this way the resultant spatial variation in thermal expansion coefficients was also controlled through the thickness of the material, and a particular stress and strain distribution could be tailored within the body. Samples with tailored near-surface compressive stress states showed a significant improvement in c KI , as measured by means of a flexure test, in comparison with stress-free samples of a homogeneous composition corresponding to the composition found at the test-point within the gradient materials.