Researcher:
Torabnia, Shams

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PhD Student

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Shams

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Torabnia

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Torabnia, Shams

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2020 - 20224

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Researcher Of Publications: search.filters.isAuthorOfPublication.12eeb6a3-3b83-46b4-9d20-da1c6b6ec94c

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    In silico analysis of elastomer-coated cerclage for reducing sternal cut-through in high-risk patients
    (The American Society of Mechanical Engineers (ASME), 2021) Erdoğan, Mustafa Bilge; N/A; N/A; N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Subaşı, Ömer; Oral, Atacan; Torabnia, Shams; Erdoğan, Deniz; Lazoğlu, İsmail; PhD Student; PhD Student; PhD Student; Undergraduate Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; 179391
    Background: AISI 316 L stainless steel wire cerclage routinely used in sternotomy closure causes lateral cut-through damage and fracture, especially in cases of high-risk patients, which leads to postoperative complications. A biocompatible elastomer (Pellethane(R)) coating on the standard wire is proposed to mitigate the cut-through effect. Methods: Simplified peri-sternal and transsternal, sternum-cerclage contact models are created and statically analyzed in a finite element (FE) software to characterize the stress-reduction effect of the polymer coating for thicknesses between 0.5 and 1.125 mm. The performance of the polymer-coated cerclage in alleviating the detrimental cortical stresses is also compared to the standard steel cerclage in a full sternal closure FE model for the extreme cough loading scenario. Results: It was observed via the simplified contact simulations that the cortical stresses can be substantially decreased by increasing the coating thickness. The full closure coughing simulation on the human sternum further corroborated the simplified contact results. The stress reduction effect was found to be more prominent in the transsternal contacts in comparison to peri-sternal contacts. Conclusions: Bearing in mind the promising numerical simulation results, it is put forth that a standard steel wire coated with Pellethane will majorly address the cut-through complication.
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    In silico analysis of superelastic nitinol staples for trans-sternal closure
    (Elsevier, 2020) N/A; N/A; Department of Mechanical Engineering; Subaşı, Ömer; Torabnia, Shams; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391
    Background: Superelastic Nitinol staples, utilized routinely in foot surgeries, are proposed to be used for sternal closure application in this study. It is hypothesized that the shape memory induced superelasticity will allow multiple staples placed along the sternum to promote fast and safe recovery by maintaining constant clamping pressure at the sternotomy midline. Methods: Two different Nitinol staples of different alloying compositions, one representing the metal formed wire geometry and, the other, powder metallurgy manufactured rectangular geometry, are chosen from the literature. Austenite finish temperatures of both materials are confirmed to be appropriately below the body temperature for superelastic shape memory activation. The adopted finite element superelasticity model is first validated and, via design optimization of parametrized dimensions, the staple geometries for producing maximal clamping forces are identified. The performances of the optimized staples for full trans-sternal closure (seven staples for each) are then tested under lateral sternal loading in separate computational models. Results: The optimized metal formed staple exerts 70.2 N and the optimized powder metallurgy manufactured staple exerts 245 N clamping force, while keeping the maximum localized stresses under the yield threshold for 90 degrees leg bending. Testing the staple-sternum constructs under lateral sternal loading revealed that the former staple can be utilized for small-chested patients with lower expected physiological loading, while the latter staple can be used for high-risk patients, for which high magnitude valsalva maneuver is expected. Conclusion: Computational results prove that superelastic Nitinol staples are promising candidates as alternatives to routinely performed techniques for sternal closure.
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    In silico evaluation of lattice designs for additively manufactured total hip implants
    (Elsevier, 2022) Izri, Zineddine; Bijanzad, Armin; Department of Mechanical Engineering; N/A; Lazoğlu, İsmail; Torabnia, Shams; Faculty Member; PhD Student; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); College of Engineering; Graduate School of Sciences and Engineering; 179391
    Additive manufacturing restructures the fabrication of custom medical implants and transforms the design, topology optimization, and material selection perspectives in biomechanical applications. Additionally, it facilitated the design and fabrication of patient-oriented hip implants. Selection of proper lattice type is critical in additive manufacturing of hip implants. The lattice types reduce the implant mass and, due to higher stress distribution and deformations as compared to the rigid implants, it brings down the stress shielding issues. This study introduces a rigid shell structure and infill lattice hip implant.Additionally, the effect of various lattice unit cell thickness (0.2-1 mm) and elemental size (2.5-5 mm) while applying 2300 N axial force is explored numerically. A cubic structure with two rigid surfaces on the top and bottom is outlined to separate the effect of the hip implant cross-sectional area variations. The stress distribution and deformation characteristics are validated with the hip implant design. The Finite Element Analysis (FEA) demonstrated that the Weaire-Phelan lattice structure exhibits the least stress and deformation among the other types at various design parameters. Additionally, the same methodology is applied to three biocompatible hip implant materials as Ti-6Al-4V, TA15 (Ti-6Al-2Zr-1Mo-1V), and CoCr28Mo6. Finally, the effect of the unit cell thickness and size on the implant's mass reduction considering the lattice's safety factor is investigated for the mentioned materials. The selection of a Weaire-Phelan lattice with the optimized safety factor and mass reduction is represented considering all the results. The optimized parameters for Titanium-based alloys are approximately 3.5 mm unit cell size with 0.6 mm beam thickness. However, the CoCr Mo-based alloy requires a thicker beam size (about 0.8 mm) due to lower safety factors.
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    PublicationOpen Access
    Parametric analysis for the design of hip joint replacement simulators
    (Institute of Electrical and Electronics Engineers (IEEE), 2021) Mihçin, Şenay; Department of Mechanical Engineering; Lazoğlu, İsmail; Torabnia, Shams; Faculty Member; PhD Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; 179391; N/A
    The simulation of wear, between the components of artificial hip joint implants, is a complicated problem that does not have a robust analytical answer yet. Many studies have been conducted to predict the wear between the femur head and the acetabular cup, as the debris generated due to the wear might produce adverse effects after the surgery. Hip joint simulators provide a means to quantify the amount of wear in preclinical settings, as an in vitro method. However, this brings some other challenges in terms of bio-fidelity. The simulators use force and range of motion data as input and provide wear information as an output. For this reason, it is important to be able to simulate the realistic conditions, by the proper transmission of force and position controlling of the components. Many studies performed on wear simulators but none of them worked on the machine parameters such as power consumption and sensitivity to external inputs in detail. In this study, we perform a sensitivity analysis of the factors affecting the forces acting on the femur head. In silico simulations were performed by changing the values of acting force, friction coefficient, and radius of femur head to understand the effects of each parameter on the frictional moment of the joint. These analyses demonstrate the importance of using correct parameters while designing simulators, which accept flexible boundary conditions. The architecture of the hip simulator was also investigated for the first time. The results are expected to pave the way for improving the bio-fidelity of the simulators in the field of biomechanics.