Journal of the mechanical behavior of biomedical materials
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J Mech Behav Biomed Mater · Apr 2015
High compressive pre-strains reduce the bending fatigue life of nitinol wire.
Prior to implantation, Nitinol-based transcatheter endovascular devices are subject to a complex thermo-mechanical pre-strain associated with constraint onto a delivery catheter, device sterilization, and final deployment. Though such large thermo-mechanical excursions are known to impact the microstructural and mechanical properties of Nitinol, their effect on fatigue properties is still not well understood. The present study investigated the effects of large thermo-mechanical pre-strains on the fatigue of pseudoelastic Nitinol wire using fully reversed rotary bend fatigue (RBF) experiments. ⋯ Further, the mechanisms underlying fatigue were found to be similar; despite large differences in cycles to failure across strain amplitudes and pre-strain levels, cracks initiated from surface inclusions in nearly all wires. Compressive pre-strain-induced damage may accelerate such crack initiation, thereby reducing fatigue life. The results of the present study indicate that large compressive pre-strains are detrimental to the fatigue properties of Nitinol, and, taken together, the findings underscore the importance of accounting for thermo-mechanical history in the design and testing of wire-based percutaneous implants.
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J Mech Behav Biomed Mater · Mar 2015
ReviewBiomechanical properties of synthetic surgical meshes for pelvic prolapse repair.
Synthetic meshes are widely used for surgical repair of different kind of prolapses. In the light of the experience of abdominal wall repair, similar prostheses are currently used in the pelvic region, to restore physiological anatomy after organ prolapse into the vaginal wall, that represent a recurrent dysfunction. For this purpose, synthetic meshes are surgically positioned in contact with the anterior and/or posterior vaginal wall, to inferiorly support prolapsed organs. ⋯ Material and structural properties are key factors in determining mesh biochemical and mechanical compatibility in vivo. The most significant results on vaginal tissue and surgical meshes mechanical characterization are here reported and discussed. Moreover, computational models of the pelvic region, which could support the surgeon in the evaluation of mesh performances in physiological conditions, are recalled.
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J Mech Behav Biomed Mater · Mar 2015
Efficient and optimized identification of generalized Maxwell viscoelastic relaxation spectra.
Viscoelastic relaxation spectra are essential for predicting and interpreting the mechanical responses of materials and structures. For biological tissues, these spectra must usually be estimated from viscoelastic relaxation tests. ⋯ The algorithm was tested against trial data to characterize its robustness and identify its limitations and strengths. The algorithm was then applied to identify the viscoelastic response of reconstituted collagen, revealing an extensive distribution of viscoelastic time constants.
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J Mech Behav Biomed Mater · Feb 2015
Pore size and pore shape--but not mesh density--alter the mechanical strength of tissue ingrowth and host tissue response to synthetic mesh materials in a porcine model of ventral hernia repair.
Over 100 types of soft tissue repair materials are commercially available for hernia repair applications. These materials vary in characteristics such as mesh density, pore size, and pore shape. It is difficult to determine the impact of a single variable of interest due to other compounding variables in a particular design. Thus, the current study utilized prototype meshes designed to evaluate each of these mesh parameters individually. ⋯ Pore shape and pore size significantly altered the mechanical strength of tissue ingrowth and host-site integration in a porcine model of ventral hernia repair, while mesh density had no effect.
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J Mech Behav Biomed Mater · Feb 2015
Drilling in cortical bone: a finite element model and experimental investigations.
Bone drilling is an essential part of many orthopaedic surgery procedures, including those for internal fixation and for attaching prosthetics. Estimation and control of bone drilling forces are critical to prevent drill-bit breakthrough, excessive heat generation, and mechanical damage to the bone. An experimental and computational study of drilling in cortical bone has been conducted. ⋯ The model incorporates the dynamic characteristics involved in the process along with geometrical considerations. An elastic-plastic material model is used to predict the behaviour of cortical bone during drilling. The average critical thrust forces and torques obtained using FE analysis are found to be in good agreement with the experimental results.