Journal of the mechanical behavior of biomedical materials
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J Mech Behav Biomed Mater · Feb 2012
Titanium and zirconium based alloys modified by intensive plastic deformation and nitrogen ion implantation for biocompatible implants.
Titanium and zirconium alloys are considered to be promising materials for orthopaedics because of their biocompatibility with tissues. Their main drawbacks for application as implants have generally been considered to be insufficient levels of mechanical and tribological properties. In this research the influence of equal channel angular pressing and nitrogen ion implantation on the structure and properties of Ti and Zr alloys has been investigated to ensure the optimum combination of the bulk material and surface layer properties. The data obtained showed that equal channel angular pressing and nitrogen ion implantation can be efficiently used to improve bulk and surface properties of Ti and Zr based implants.
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J Mech Behav Biomed Mater · Nov 2011
Thiel-fixation preserves the non-linear load-deformation characteristic of spinal motion segments, but increases their flexibility.
Human cadaveric specimens are recommended as the best option for in-vitro tests. However, fresh human spine specimens are often difficult to obtain. Further problems are the potential risk of infection and they can only be used over a limited test period. ⋯ In conclusion, the results still suggest a preference for fresh cadaveric spine specimens for quantitative biomechanical in-vitro testing, because they provide the best physiological conditions. However, for preliminary tests, which may only be used for orientation, embalmed specimens using the Thiel fixation method might serve as an alternative. Compared to formalin-fixated specimens which become approximately 5 times stiffer and completely lose their non-linear load-deformation-characteristic, as found in a previous study; the Thiel fixation maintains the non-linear load-deformation-characteristic but increases the range of motion.
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J Mech Behav Biomed Mater · Nov 2011
Mechanical characterization and numerical simulation of polyether-ether-ketone (PEEK) cranial implants.
Cranial implants have experienced a significant evolution in the last decade in different aspects such as materials, method of fixation, and the structure. In addition, patient-specific cranial implants have recently been started to be developed. To achieve this objective, efficient mechanical characterization and numerical modeling of the implant are required to guarantee its functionality on each patient as well as to facilitate further developments. ⋯ The two numerical models were compared. The homogenized model gave results that were very close to those obtained with the detailed model, while reducing the number of degrees of freedom by 90%, and therefore the overall computational burden. The results showed that the models are able to reproduce experimental results conducted on actual implants, offering a valid alternative to be used in the design of customized cranial implants with a scaffold structure.
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J Mech Behav Biomed Mater · Nov 2011
Computation of axonal elongation in head trauma finite element simulation.
In the case of head trauma, elongation of axons is thought to result in brain damage and to lead to Diffuse Axonal Injuries (DAI). Mechanical parameters have been previously proposed as DAI metric. Typically, brain injury parameters are expressed in terms of pressure, shearing stresses or invariants of the strain tensor. ⋯ The feasibility of integrating axon fiber direction information within a dedicated post-processor is also established in the context of the computation of axonal elongation. The accuracy obtained when estimating level and location of the computed axonal elongation indicates that coupling classical isotropic finite element simulation with axonal structural anisotropy is an efficient strategy. Using this method, tensile elongation of the axons can be directly invoked as a mechanism for Diffuse Axonal Injury.
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J Mech Behav Biomed Mater · Oct 2011
Axial creep loading and unloaded recovery of the human intervertebral disc and the effect of degeneration.
The intervertebral disc maintains a balance between externally applied loads and internal osmotic pressure. Fluid flow plays a key role in this process, causing fluctuations in disc hydration and height. The objectives of this study were to quantify and model the axial creep and recovery responses of nondegenerate and degenerate human lumbar discs. ⋯ The fast response was correlated with degeneration, suggesting larger changes in the NP with degeneration compared to the AF. However, the fast response comprised only 10%-15% of the total equilibrium displacement, with the AF-dominated slow response comprising 40%-70%. Finally, the physiological loads and deformations and their associated long equilibrium times confirm that diurnal loading does not represent "equilibrium" in the disc, but that over time the disc is in steady-state.