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Simulation of Nonhomogeneous Bone
Published in Z. Yang, Finite Element Analysis for Biomedical Engineering Applications, 2019
The determination of the mechanical stresses in human bone is very important in both research and clinical practice because the understanding of the mechanical stresses in human bones benefits the design of prostheses and the evaluation of fracture risk. For example, after total hip replacement surgery, stresses in some regions of the remaining bone diminish because the implant carries a portion of the load, which is known as stress shielding. According to Wolff's law, the shielded bone remodels as a response to the changed mechanical environment, resulting in loss of bone mass through the resorption and consequent loosening of the prosthesis. To alleviate this problem, the stress distribution of the bone with the prosthesis should match that of the healthy bone as much as possible.
Biomaterials in Devices
Published in Heather N. Hayenga, Helim Aranda-Espinoza, Biomaterial Mechanics, 2017
Danieli C. Rodrigues, Izabelle M. Gindri, Sathyanarayanan Sridhar, Lucas Rodriguez, Shant Aghyarian
In terms of structural applications, the mechanical characteristics of the tissue to be replaced need to be taken into consideration in the selection of the appropriate class of biomaterials. This will ensure better distribution of loads at the tissue–material interface, minimizing stress shielding effects. Stress shielding is characterized by reduction in bone density (osteopenia) as a result of removal of normal stress from the bone by an implant [9]. For example, metals and bioinert ceramics are typically selected for hard tissue replacement while polymers are more suitable for soft tissue applications. Table 3.3 illustrates the modulus of elasticity and tensile strength of examples of soft and hard tissues commonly treated with the implantable materials described in Table 3.2.
Novel metallic bone fixation implants with reduced stiffness
Published in Fernando Moreira da Silva, Helena Bártolo, Paulo Bártolo, Rita Almendra, Filipa Roseta, Henrique Amorim Almeida, Ana Cristina Lemos, Challenges for Technology Innovation: An Agenda for the Future, 2017
Abdulsalam A. Al-Tamimi, P.J. Bártolo, C. Peach, P. Fernandes
After a fracture has healed bone fixation implants are no longer needed. However, in the majority of cases they are left inside the body with adverse consequences such as stress shielding effects, release of metallic ions, which can be toxic or even carcinogenic (Hofmann, 1992; Matusiewicz, 2014). Stress shielding is a consequence of stiffness differences between the implant and bone (Goshulak et al, 2016; Sumner, 2015; Chanlalit et al, 2012). Metallic implants have much higher elastic moduli than bone, e.g. Ti6Al4V has a modulus of around 110 GPa and CoCrMo has a modulus of around 210 GPa (Andani et al, 2014; Shibata et al, 2015). However, cortical bone has elastic moduli ranging from 3 to 30 GPa, while trabecular bone has lower elastic moduli ranging from 0.02 to 2 GPa (Shibata et al, 2015).
Study and numerical analysis of Von Mises stress of a new tumor-type distal femoral prosthesis comprising a peek composite reinforced with carbon fibers: finite element analysis
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Stainless steel, medical titanium alloys (Ti6Al4V), and cobalt-chromium-molybdenum alloys (CoCrMo) have been widely used in the manufacture of orthopedic implant prostheses for some time (Guo et al. 2019a; Guo et al. 2019b). However, these metal materials have some shortcomings (Guo et al. 2020). For example, the elastic modulus of the metal material and the bone do not match. The elastic modulus of human bones ranges from 3 to 20 GPa, while those of medical titanium alloys and medical stainless steel reach as high as 110 and 200 GPa, respectively. After the insertion of metal implants, the phenomenon of stress shielding occurs, which accelerates bone loss and increases the risk of secondary fractures. In addition, metal-based materials are extremely dense, and thus, can lead to fractures or wear after implantation. Moreover, metal implants produce toxic metal wear particles during use, causing inflammation in the surrounding tissues. Compared with the wear particles of metal materials, the wear particles of polymer materials are less toxic. Notably, during radiological examinations and radiotherapy, metal prostheses produce metal artifacts and exhibit radiation scattering.
Finite element study on the influence of pore size and structure on stress shielding effect of additive manufactured spinal cage
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Vijay Kumar Meena, Parveen Kalra, Ravindra Kumar Sinha
A considerable Young's modulus mismatch between the metal implant and the adjacent natural bone causes an irregular stress distribution at the bone-implant interface, resulting in a stress shielding effect (Alvarez and Nakajima 2009; Yan et al. 2015). Stress shielding increases the risk of fracture and implant loosening by causing bone tissue absorption around the metal implant (Huiskes et al. 1992). As a result, the ideal orthopedic implant material has Young's modulus that is similar to human bone tissue. The porous structures used in this study have this property similar to that of the natural human bone which is in the range of 0.5–20 GPa (Bonfield et al. 1998). Junchao et al. conducted a study on the compressive strength of titanium materials based on porosity and found that when porosity increases, the elasticity increases too (Junchao et al. 2016). The porous titanium alloy structures in this study can be identified with similar results that have the high elasticity to reduce the stress shielding effect.
Development of pore functionally graded Ti6Al4V scaffolds with biocompatible surface for bone repair
Published in Transactions of the IMF, 2019
E. Shahimoridi, S. M. Kalantari, A. Molaei
Although bioceramics and polymeric biomaterials have been characterised with weak mechanical behaviour and insufficient biocompatibility, titanium (Ti) and its alloys with high corrosion resistance, excellent mechanical properties, and remarkable biocompatibility have been widely utilised as promising implants in biomedical applications.1,2 Stress shielding is the main shortcoming of Ti and its alloys as bone replacements. Stress shielding occurs when part of the load is taken by implants and shielded from going to the bone. Based on Wolff's law, areas under lower load or stress will respond by decreasing the bone mass. Bone loss may lead to the loosening of failure of the implant. Minimising of damage to tissues adjacent to the implant has encouraged researchers to utilise porous structures as a solution for solving this problem.3,4