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    In silico analysis of elastomer-coated cerclage for reducing sternal cut-through in high-risk patients
    (NLM (Medline), 2021) Subasi, Omer; Oral, Atacan; Torabnia, Shams; Erdoğan, Deniz; Erdoğan, Mustafa Bilge; Lazoglu, Ismail
    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®) 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. Copyright
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    In silico evaluation of lattice designs for additively manufactured total hip implants
    (2022) Izri, Zineddine; Bijanzad, Armin; Torabnia, Shams; Lazoğlu, İsmail
    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.