Researcher:
Pişkin, Şenol

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Şenol

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Pişkin

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Pişkin, Şenol

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2015 - 20198

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Now showing 1 - 8 of 8
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    Noninvasive in vivo determination of residual strains and stresses
    (ASME, 2015) N/A; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; Donmazov, Samir; Pişkin, Şenol; Pekkan, Kerem; PhD Student; Researcher; Faculty Member; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; 148702; 161845
    Vascular growth and remodeling during embryonic development are associated with blood flow and pressure induced stress distribution, in which residual strains and stresses play a central role. Residual strains are typically measured by performing in vitro tests on the excised vascular tissue. In this paper, we investigated the possibility of estimating residual strains and stresses using physiological pressure-radius data obtained through in vivo noninvasive measurement techniques, such as optical coherence tomography or ultrasound modalities. This analytical approach first tested with in vitro results using experimental data sets for three different arteries such as rabbit carotid artery, rabbit thoracic artery, and human carotid artery based on Fung's pseudostrain energy function and Delfino's exponential strain energy function (SEF). We also examined residual strains and stresses in the human swine iliac artery using the in vivo experimental ultrasound data sets corresponding to the systolic-to-diastolic region only. This allowed computation of the in vivo residual stress information for loading and unloading states separately. Residual strain parameters as well as the material parameters were successfully computed with high accuracy, where the relative errors are introduced in the range of 0-7.5%. Corresponding residual stress distributions demonstrated global errors all in acceptable ranges. A slight discrepancy was observed in the computed reduced axial force. Results of computations performed based on in vivo experimental data obtained from loading and unloading states of the artery exhibited alterations in material properties and residual strain parameters as well. Emerging noninvasive measurement techniques combined with the present analytical approach can be used to estimate residual strains and stresses in vascular tissues as a precursor for growth estimates. This approach is also validated with a finite element model of a general two-layered artery, where the material remodeling states and residual strain generation are investigated.
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    Effect of modified blalock-taussig shunt anastomosis angle and pulmonary artery diameter on pulmonary flow
    (Turkish Society of Cardiology, 2018) Arnaz, Ahmet; Yalçınbas, Yusuf; Sarioglu, Tayyar; Department of Mechanical Engineering; Department of Mechanical Engineering; N/A; Pişkin, Şenol; Pekkan, Kerem; Oğuz, Gökçe Nur; Researcher; Faculty Member; PhD Student; Department of Mechanical Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; 148702; 161845; N/A
    Objective: This study aimed to identify the best graft-to-pulmonary artery (PA) anastomosis angle measuring pulmonary blood flow, wall shear stress (WSS), and shunt flow. Methods: A tetralogy of Fallot with pulmonary atresia computer model was used to study three different modified Blalock-Taussig shunt (mBTS) anastomosis angle configurations with three different PA diameter configurations. Velocity and WSS were analyzed, and the flow rates at the right PA (RPA) and left PA (LPA) were calculated. Results: A 4-mm and 8-mm diameter of RPA and LPA, respectively with vertical shunt angle produces the highest total flow. In the RPA larger diameter than the LPA configutations, the left-leaning shunt produces the lowest total PA flow whereas in the LPA larger diameter than the RPA configuratios, the right-leaning shunt produces the lowest total PA flow. Therefore, the shunt anastomosis should not be leaned through the narrow side of PA to reach best flow. As the flow inside the shunt increased, WSS also increased due to enhanced velocity gradients. Conclusion: The anastomosis angle between the conduit and PA affects the flow to PA. Vertical anastomosis configurations increase the total PA flow; thus, these configurations are preferable than the leaned configurations.
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    Increased energy loss due to twist and offset buckling of the total cavopulmonary connection
    (ASME, 2017) Arnaz, Ahmet; N/A; Department of Molecular Biology and Genetics; N/A; N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Oğuz, Gökçe Nur; Pişkin, Şenol; Ermek, Erhan; Donmazov, Samir; Altekin, Naz; Pekkan, Kerem; PhD Student; Researcher; Other; PhD Student; Undergraduate Student; Faculty Member; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; 148702; N/A; N/A; N/A; 161845
    The hemodynamic energy loss through the surgically implanted conduits determines the postoperative cardiac output and exercise capacity following the palliative repair of single-ventricle congenital heart defects. In this study, the hemodynamics of severely deformed surgical pathways due to torsional deformation and anastomosis offset are investigated. We designed a mock-up total cavopulmonary connection (TCPC) circuit to replicate the mechanically failed inferior vena cava (IVC) anastomosis morphologies under physiological venous pressure (9, 12, 15 mmHg), in vitro, employing the commonly used conduit materials: Polytetrafluoroethylene (PTFE), Dacron, and porcine pericardium. The sensitivity of hemodynamic performance to torsional deformation for three different twist angles (0 deg, 30 deg, and 60 deg) and three different caval offsets (0 diameter (D), 0.5D, and 1D) are digitized in three dimensions and employed in computational fluid dynamic (CFD) simulations to determine the corresponding hydrodynamic efficiency levels. A total of 81 deformed conduit configurations are analyzed; the pressure drop values increased from 80 to 1070% with respect to the ideal uniform diameter IVC conduit flow. The investigated surgical materials resulted in significant variations in terms of flow separation and energy loss. For example, the porcine pericardium resulted in a pressure drop that was eight times greater than the Dacron conduit. Likewise, PTFE conduit resulted in a pressure drop that was three times greater than the Dacron conduit under the same venous pressure loading. If anastomosis twist and/or caval offset cannot be avoided intraoperatively due to the anatomy of the patient, alternative conduit materials with high structural stiffness and less influence on hemodynamics can be considered.
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    Role of flow preference in decision making regarding the use of Blalock-Taussig shunt Reply
    (Turkish Soc Cardiology, 2018) Arnaz, Ahmet; Department of Mechanical Engineering; Pişkin, Şenol; Researcher; Department of Mechanical Engineering; College of Engineering; 148702
    N/A
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    Biomechanical restoration potential of pentagalloyl glucose after arterial extracellular matrix degeneration
    (Mdpi, 2019) Patnaik, Sourav S.; Pillalamarri, Narasimha Rao; Romero, Gabriela; Escobar, G. Patricia; Sprague, Eugene; Finol, Ender A.; Department of Mechanical Engineering; Pişkin, Şenol; Researcher; Department of Mechanical Engineering; College of Engineering; 148702
    The objective of this study was to quantify pentagalloyl glucose (PGG) mediated biomechanical restoration of degenerated extracellular matrix (ECM). Planar biaxial tensile testing was performed for native (N), enzyme-treated (collagenase and elastase) (E), and PGG (P) treated porcine abdominal aorta specimens (n = 6 per group). An Ogden material model was fitted to the stress-strain data and finite element computational analyses of simulated native aorta and aneurysmal abdominal aorta were performed. The maximum tensile stress of the N group was higher than that in both E and P groups for both circumferential (43.78 +/- 14.18 kPa vs. 10.03 +/- 2.68 kPa vs. 13.85 +/- 3.02 kPa; p = 0.0226) and longitudinal directions (33.89 +/- 8.98 kPa vs. 9.04 +/- 2.68 kPa vs. 14.69 +/- 5.88 kPa; p = 0.0441). Tensile moduli in the circumferential direction was found to be in descending order as N > P > E (195.6 +/- 58.72 kPa > 81.8 +/- 22.76 kPa > 46.51 +/- 15.04 kPa; p = 0.0314), whereas no significant differences were found in the longitudinal direction (p = 0.1607). PGG binds to the hydrophobic core of arterial tissues and the crosslinking of ECM fibers is one of the possible explanations for the recovery of biomechanical properties observed in this study. PGG is a beneficial polyphenol that can be potentially translated to clinical practice for preventing rupture of the aneurysmal arterial wall.
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    Computational pre-surgical planning of arterial patch reconstruction: parametric limits and in vitro validation
    (Springer, 2018) Salihoglu, Ece; Yerebakan, Can; Department of Mechanical Engineering; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; N/A; Lashkarinia, Seyedeh Samaneh; Pişkin, Şenol; Pekkan, Kerem; Bozkaya, Tijen Alkan; Researcher; Researcher; Faculty Member; Doctor; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; Koç University Hospital; N/A; 148702; 161845; 143793
    Surgical treatment of congenital heart disease (CHD) involves complex vascular reconstructions utilizing artificial and native surgical materials. A successful surgical reconstruction achieves an optimal hemodynamic profile through the graft in spite of the complex post-operative vessel growth pattern and the altered pressure loading. This paper proposes a new in silico patient-specific pre-surgical planning framework for patch reconstruction and investigates its computational feasibility. The proposed protocol is applied to the patch repair of main pulmonary artery (MPA) stenosis in the Tetralogy of Fallot CHD template. The effects of stenosis grade, the three-dimensional (3D) shape of the surgical incision and material properties of the artificial patch are investigated. The release of residual stresses due to the surgical incision and the extra opening of the incision gap for patch implantation are simulated through a quasi-static finite-element vascular model with shell elements. Implantation of different unloaded patch shapes is simulated. The patched PA configuration is pressurized to the physiological post-operative blood pressure levels of 25 and 45 mmHg and the consequent post-operative stress distributions and patched artery shapes are computed. Stress-strain data obtained in-house, through the biaxial tensile tests for the mechanical properties of common surgical patch materials, Dacron, Polytetrafluoroethylene, human pericardium and porcine xenopericardium, are employed to represent the mechanical behavior of the patch material. Finite-element model is experimentally validated through the actual patch surgery reconstructions performed on the 3D printed anatomical stenosis replicas. The post-operative recovery of the initially narrowed lumen area and post-optortuosity are quantified for all modeled cases. A computational fluid dynamics solver is used to evaluate post-operative pressure drop through the patch-reconstructed outflow tract. According to our findings, the shorter incisions made at the throat result in relatively low local peak stress values compared to other patch design alternatives. Longer cut and double patch cases are the most effective in repairing the initial stenosis level. After the patch insertion, the pressure drop in the artery due to blood flow decreases from 9.8 to 1.35 mm Hg in the conventional surgical configuration. These results are in line with the clinical experience where a pressure gradient at or above 50 mm Hg through the MPA can be an indication to intervene. The main strength of the proposed pre-surgical planning framework is its capability to predict the intraoperative and post-operative 3D vascular shape changes due to intramural pressure, cut length and configuration, for both artificial and native patch materials.
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    Tetralogy of fallot surgical repair: shunt configurations, ductus arteriosus and the circle of willis
    (Springer, 2017) Unal, Gozde; Arnaz, Ahmet; Sarioglu, Tayyar; Department of Mechanical Engineering; Department of Mechanical Engineering; Pişkin, Şenol; Pekkan, Kerem; Researcher; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; 148702; 161845
    In this study, hemodynamic performance of three novel shunt configurations that are considered for the surgical repair of tetralogy of Fallot (TOF) disease are investigated in detail. Clinical experience suggests that the shunt location, connecting angle, and its diameter can influence the post-operative physiology and the neurodevelopment of the neonatal patient. An experimentally validated second order computational fluid dynamics (CFD) solver and a parametric neonatal diseased great artery model that incorporates the ductus arteriosus (DA) and the full patient-specific circle of Willis (CoW) are employed. Standard truncated resistance CFD boundary conditions are compared with the full cerebral arterial system, which resulted 21, -13, and 37% difference in flow rate at the brachiocephalic, left carotid, and subclavian arteries, respectively. Flow splits at the aortic arch and cerebral arteries are calculated and found to change with shunt configuration significantly for TOF disease. The central direct shunt (direct shunt) has pulmonary flow 5% higher than central oblique shunt (oblique shunt) and 23% higher than modified Blalock Taussig shunt (RPA shunt) while the DA is closed. Maximum wall shear stress (WSS) in the direct shunt configuration is 9 and 60% higher than that of the oblique and RPA shunts, respectively. Patent DA, significantly eliminated the pulmonary flow control function of the shunt repair. These results suggests that, due to the higher flow rates at the pulmonary arteries, the direct shunt, rather than the central oblique, or right pulmonary artery shunts could be preferred by the surgeon. This extended model introduced new hemodynamic performance indices for the cerebral circulation that can correlate with the post-operative neurodevelopment quality of the patient.
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    PublicationOpen Access
    Role of flow preference in decision making regarding the use of Blalock-Taussig shunt reply
    (Turkish Society of Cardiology, 2018) Arnaz, Ahmet; Department of Mechanical Engineering; Pişkin, Şenol; Researcher; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; 148702