Researcher:
Pekkan, Kerem

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Kerem

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Pekkan

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Pekkan, Kerem

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2013 - 2019342020 - 202318

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Now showing 1 - 10 of 53
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    The effect of strut protrusion on local shear stress and neointimal hyperplasia
    (Oxford University Press (OUP), 2019) Tenekecioglu, E.; Katagiri, Y.; Torii, R.; Onuma, Y.; Serruys, P. W.; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845
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    Infusion jet flow control in neonatal double lumen cannulae
    (Asme, 2020) Yıldız, Yahya; Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Mechanical Engineering; Rasooli, Reza; Jamil, Muhammad; Pekkan, Kerem; Researcher; Researcher; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; 161845
    Clinical success of extracorporeal membrane oxygenation (ECMO) depends on the proper venous cannulation. Venovenous (VV) ECMO is the preferred clinical intervention as it provides a single-site access by utilizing a VV double lumen cannula (VVDLC) with a higher level of mobilization and physical rehabilitation. Concurrent venous blood drainage and oxygenated blood infusion in the right atrium at the presence of the cannula makes the flow dynamics complex where potential mixing of venous and oxygenated blood can drastically decrease the overall performance of ECMO. There are no studies focusing on the neonatal and pediatric populations, in which the flow related effects are critical due to the small atrium size. In this study, fluid dynamics of infusion outflow jet for two commercially available neonatal VVDLC is analyzed using particle image velocimetry (PIV). Moreover, six new designs are proposed for the infusion channel geometry and compared. Important flow parameters such as flow turning angle (FTA), velocity decay, potential core, and turbulent intensity are investigated for the proposed models. The experiments showed that the outflow parameters of commercial cannulae such as FTA are strongly dependent on the operating Re number. This may result in a drastic efficiency reduction for cannula operating at off-design flow conditions. Moreover, the infusion outlet tip structure and jet internal guiding pathway (JIGP) was observed to greatly affect the outflow flow features. This is of paramount importance since the anatomical positioning of the cannula and the infusion outlet is strongly dependent on the outflow properties such as FTA.
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    Polymeric hollow fiber membrane oxygenators as artificial lungs: a review
    (Elsevier, 2022) Teber, Oğuz Orhun; Altınay, Ayşegül Derya; Mehrabani, Seyed Ali Naziri; Taşdemir, Reyhan Şengür; Zeytinci, Bihter; Genceli, Esra Ateş; Dilekgürgen, Ebru; Koyuncu, İsmail; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845
    The oxygenator is one of the most important components of respiratory support devices, which began as a heartlung machine for the treatment of heart diseases. Hollow fiber membranes have been widely used in oxygenators due to their outstanding performance in oxygen and carbon dioxide exchange with the blood. In this review, general information on the oxygenator historical evolutions is summarized. Then, the advantages and usage of hollow fiber membranes as oxygenators are explained. Modification strategies to prevent platelet adhesion, plasma leakage have been summarized. There has been some information given on design parameters for hollow fiber membrane oxygenators. In recent years, the rapid development of microchannel structures in oxygenators has been summarized. It is thought that this review will help the reader to find recent studies on the subject.
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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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    High-speed three-dimensional characterization of fluid flows induced by micro-objects in deep microchannels
    (2013) Chen, Chia-Yuan; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845
    Bio-inspired studies of micro-objects in microfluidics demand quantitative microflow visualization tools to evaluate their three-dimensional (3D) fluid dynamic performance. Experimental fluid dynamic measurements of bio-hybrid systems are employed when non-traditional small-scales, magnetohydrodynamic coupling and nonlinear material properties are involved. In this study a stereoscopic micro-Particle Image Velocimetry (mu PIV) system was developed to characterize instantaneous flow fields induced by (1) a micro-robot (280 x 200 x 150 mu m(3)) and (2) self-assembled magnetically actuated artificial cilia (similar to 50 mu m in diameter and 500 mu m in depth). A custom built micro jet flow microchannel was tested to provide the quantitative evidence of measurement accuracy with 14% error compared to theoretical solutions in the out-of-plane velocity component. Followed by these verification experiments, instantaneous in-plane spinning motion was analyzed in conjunction with translational movement and out-of-plane rotational movements of the micro-robot to obtain the induced 2D-3C (two-dimension, three-component) fluid velocity data. The second test case investigated the microscale vortical flow structures that were generated by self-assembled magnetically driven artificial cilia. The strength of this 3D micro vortex structure was computed based on the 3D flow measurements. In combination with the asymmetric cyclic motion of the magnetically actuated artificial cilia, it is expected that these structures can generate transverse flow efficiently in 3D, and thus provide a potential alternative for mixing in low Reynolds number flows, analogous to a micromixer. The acquired 3D microflow field, along with the validation tests, further extends the capability of using stereoscopic mu PIV technique to evaluate the performance of noninvasive microflow manipulators.
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    Novel fenestration designs for controlled venous flow shunting in failing fontans with systemic venous hypertension
    (Wiley, 2013) Albal, Priti G.; Menon, Prahlad G.; Kowalski, William; Undar, Akif; Turkoz, Riza; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845
    The Fontan procedure is employed as the final-stage palliation in single-ventricle congenital heart patients and results in diversion of venous blood directly to the pulmonary arteries. Fontan patients have been known to suffer from postoperative systemic venous hypertension, which in turn is associated with pleural effusions and protein losing enteropathy, leading to a decreased duration and quality of life. Despite the ongoing debate on its benefits, a circular fenestration hole (typically 4?mm) establishing a venous shunt to the common atrium is traditionally employed to relieve venous pressure in the Fontan conduit and improve early postoperative Fontan hemodynamics. However, these improvements come at the cost of reduced oxygen saturation due to excessive right-to-left shunting if the fenestration is permanent. The ideal selective fenestration would therefore limit or eliminate shunt flow at tolerable systemic venous pressures and allow increased flow at high pressures. The objective of this study is to introduce new fenestration designs that exhibit these desirable pressure-flow characteristics. Novel plus-shaped and S-shaped fenestration designs with leaflets are introduced as alternatives to the traditional circular fenestration, each having identical effective orifice areas at the fully open states. In vitro steady leakage flow tests were performed for physiological flow-driving pressures in order to obtain pressure-drop versus flow-rate characteristics. In addition, the leaflet opening kinematics of the plus-shaped fenestration was investigated computationally using finite element simulation. Fluid-structure interaction analysis was performed to determine leaflet displacements and pressure-flow characteristics at low pressures. Further, a lumped parameter model of the single-ventricle circuit was created to simulate pulsatile flow conditions For the plus-shaped fenestration, the flow rate was found to increase nonlinearly with increased driving systemic venous pressures at high physiological-pressure drops which did not cause the leaflets to fully open, and linearly for low driving pressures. These results indicate that leaflets of the plus-shaped fenestration design activated passively after a critical systemic venous pressure threshold. This feature is ideal for minimizing undesirable excessive venous shunting. A large variability in shunting flow rate may be obtained by changing the shape, thickness, size, and material of the fenestration to suit requirements of the patient, which can further limit shunt flow in a controlled manner.
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    Time-resolved OCT-mu PIV: a new microscopic PIV technique for noninvasive depth-resolved pulsatile flow profile acquisition (vol 54, 1426, 2013)
    (Springer, 2013) Chen, Chia-Yuan; Menon, Prahlad G.; Kowalski, William; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845
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    The impact of plaque type on strut embedment/protrusion and shear stress distribution in bioresorbable scaffold
    (Elsevier, 2019) Tenekecioglu, Erhan; Katagiri, Yuki; Torii, Ryo; Onuma, Yoshinobu; Van Geuns, Robert; Bourantas, Christos V.; Serruys, Patrick W.; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845
    Aims Scaffold design and plaque characteristics influence implantation outcomes and local flow dynamics in treated coronary segments. Our aim is to assess the impact of strut embedment/protrusion of bioresorbable scaffold on local shear stress distribution in different atherosclerotic plaque types. Methods and results Fifteen Absorb everolimus-eluting Bioresorbable Vascular Scaffolds were implanted in human epicardial coronary arteries. Optical coherence tomography (OCT) was performed post-scaffold implantation and strut embedment/protrusion were analysed using a dedicated software. OCT data were fused with angiography to reconstruct 3D coronary anatomy. Blood flow simulation was performed and wall shear stress (WSS) was estimated in each scaffolded surface and the relationship between strut embedment/protrusion and WSS was evaluated. There were 9083 struts analysed. Ninety-seven percent of the struts (n = 8840) were well-apposed and 243 (3%) were malapposed. At cross-section level (n = 1289), strut embedment was significantly increased in fibroatheromatous plaques (76 +/- 48 mu m) and decreased in fibrocalcific plaques (35 +/- 52 mu m). Compatible with strut embedment, WSS was significantly higher in lipid-rich fibroatheromatous plaques (1.50 +/- 0.81 Pa), whereas significantly decreased in fibrocalcified plaques (1.05 +/- 0.91 Pa). After categorization of WSS as low (<1.0 Pa) and normal/high WSS (>= 1.0 Pa), the percent of low WSS in the plaque subgroups were 30.1%, 31.1%, 25.4%, and 36.2% for non-diseased vessel wall, fibrous plaque, fibroatheromatous plaque, and fibrocalcific plaque, respectively (P-overall < 0.001). Conclusion The composition of the underlying plaque influences strut embedment which seems to have effect on WSS. The struts deeply embedded in lipid-rich fibroatheromas plaques resulted in higher WSS compared with the other plaque types.
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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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    Embryonic aortic arch material properties obtained by optical coherence tomography-guided micropipette aspiration
    (Elsevier Ltd, 2023) Çoban, Gürşan; Yap, Choon Hwai; Department of Mechanical Engineering; N/A; Department of Mechanical Engineering; Lashkarinia, Seyedeh Samaneh; Siddiqui, Hummaira Banu; Pekkan, Kerem; Researcher; PhD Student; Faculty Member; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 161845
    It is challenging to determine the in vivo material properties of a very soft, mesoscale arterial vesselsof size ∼ 80 to 120 μm diameter. This information is essential to understand the early embryonic cardiovascular development featuring rapidly evolving dynamic microstructure. Previous research efforts to describe the properties of the embryonic great vessels are very limited. Our objective is to measure the local material properties of pharyngeal aortic arch tissue of the chick-embryo during the early Hamburger-Hamilton (HH) stages, HH18 and HH24. Integrating the micropipette aspiration technique with optical coherence tomography (OCT) imaging, a clear vision of the aspirated arch geometry is achieved for an inner pipette radius of Rp = 25 μm. The aspiration of this region is performed through a calibrated negatively pressurized micro-pipette. A computational finite element model is developed to model the nonlinear behaviour of the arch structure by considering the geometry-dependent constraints. Numerical estimations of the nonlinear material parameters for aortic arch samples are presented. The exponential material nonlinearity parameter (a) of aortic arch tissue increases statistically significantly from a = 0.068 ± 0.013 at HH18 to a = 0.260 ± 0.014 at HH24 (p = 0.0286). As such, the aspirated tissue length decreases from 53 μm at HH18 to 34 μm at HH24. The calculated NeoHookean shear modulus increases from 51 Pa at HH18 to 93 Pa at HH24 which indicates a statistically significant stiffness increase. These changes are due to the dynamic changes of collagen and elastin content in the media layer of the vessel during development.