Publications with Fulltext

Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6

Browse

Filters

2018 - 201912020 - 20224

Advanced Search

Filter by

Settings

Department: search.filters.department.Department of Mechanical EngineeringQuartile: search.filters.quartile.Q4

Search Results

Now showing 1 - 5 of 5
  • Thumbnail Image
    PublicationOpen Access
    Estimation of pulsatile energy dissipation in intersecting pipe junctions using inflow pulsatility indices
    (American Institute of Physics (AIP) Publishing, 2021) Dur, Onur; Department of Mechanical Engineering; Pekkan, Kerem; Rasooli, Reza; Faculty Member; Researcher; Department of Mechanical Engineering; Graduate School of Health Sciences; College of Engineering; 161845; N/A
    This study aims to characterize the effect of inflow pulsatility on the hydrodynamic power loss inside intersecting double-inlet, double-outlet pipe intersection (DIPI) with cross-flow mixing. An extensive set of computational fluid dynamics (CFD) simulations was performed in order to identify the individual effects of flow pulsatility parameters, i.e., amplitude, frequency, and relative phase shift between the inflow waveform oscillations, on power loss. An experimentally validated second order accurate solver is employed in this study. To predict the pulsatile flow performance of any given arbitrary inflow waveforms, we proposed three easy-to-calculate pulsatility indices. The frequency-coupled quasi-steady flow theory is incorporated to identify the functional form of pulsatile power loss as a function of these indices. Our results indicated that the power loss within the inflow branch sections, lumped outflow-junction section, and the whole conduit correlates strongly with the pulsatility of each inflow waveform, the total inflow pulsatility, and inflow frequency content, respectively. The complete CFD simulation matrix provided a unified analytical expression that predicts pulsatile power loss inside a one-degree offset DIPI geometry. The predictive accuracy of this expression is evaluated in comparison to the CFD evaluation of arbitrary multi-harmonic inflow waveforms. These results have important implications on hydrodynamic pipe networks that employ complex junctions as well as in the patient-to-patient comparison of surgically created vascular connections. Coupling the present analytical pulsatile power loss expression with non-dimensional steady power loss formulation provided a valuable predictive tool to estimate the pulsatile energy dissipation for any arbitrary junction geometry with minimum use of the costly CFD computations.
  • Thumbnail Image
    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
  • Thumbnail Image
    PublicationOpen Access
    Patient-specific hemodynamics of new coronary artery bypass configurations
    (Springer, 2020) Pişkin, Senol; Tenekecioğlu, Erhan; Karagöz, Haldun; N/A; Department of Mechanical Engineering; Rezaeimoghaddam, Mohammad; Oğuz, Gökçe Nur; Lashkarinia, Seyedeh Samaneh; Pekkan, Kerem; Ateş, Mehmet Şanser; Bozkaya, Tijen Alkan; Researcher; Faculty Member; Doctor; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; Koç University Hospital; N/A; N/A; N/A; 161845; N/A; N/A
    Purpose: this study aims to quantify the patient-specific hemodynamics of complex conduit routing configurations of coronary artery bypass grafting (CABG) operation which are specifically suitable for off-pump surgeries. Coronary perfusion efficacy and local hemodynamics of multiple left internal mammary artery (LIMA) with sequential and end-to-side anastomosis are investigated. Using a full anatomical model comprised of aortic arch and coronary artery branches the optimum perfusion configuration in multi-vessel coronary artery stenosis is desired. Methodology: two clinically relevant CABG configurations are created using a virtual surgical planning tool where for each configuration set, the stenosis level, anastomosis distance and angle were varied. A non-Newtonian computational fluid dynamics solver in OpenFOAM incorporated with resistance boundary conditions representing the coronary perfusion physiology was developed. The numerical accuracy is verified and results agreed well with a validated commercial cardiovascular flow solver and experiments. For segmental performance analysis, new coronary perfusion indices to quantify deviation from the healthy scenario were introduced. Results: the first simulation configuration set;-a CABG targeting two stenos sites on the left anterior descending artery (LAD), the LIMA graft was capable of 31 mL/min blood supply for all the parametric cases and uphold the healthy LAD perfusion in agreement with the clinical experience. In the second end-to-side anastomosed graft configuration set;-the radial artery graft anastomosed to LIMA, a maximum of 64 mL/min flow rate in LIMA was observed. However, except LAD, the obtuse marginal (OM) and second marginal artery (m2) suffered poor perfusion. In the first set, average wall shear stress (WSS) were in the range of 4 to 35 dyns/cm(2)for in LAD. Nevertheless, for second configuration sets the WSS values were higher as the LIMA could not supply enough blood to OM and m2. Conclusion: the virtual surgical configurations have the potential to improve the quality of operation by providing quantitative surgical insight. The degree of stenosis is a critical factor in terms of coronary perfusion and WSS. The sequential anastomosis can be done safely if the anastomosis angle is less than 90 degrees regardless of degree of stenosis. The smaller proposed perfusion index value,O(0.04 - 0) x 10(2), enable us to quantify the post-op hemodynamic performance by comparing with the ideal healthy physiological flow.
  • Thumbnail Image
    PublicationOpen Access
    Deagglomeration of nanoparticle clusters in a "cavitation on chip" device
    (American Institute of Physics (AIP) Publishing, 2020) Gevari, M.T.; Niazi, S.; Şendur, K.; Mengüç, M. P.; Ghorbani, M.; Koşar, A.; Department of Mechanical Engineering; Karimzadehkhouei, Mehrdad; Researcher; Department of Mechanical Engineering; Graduate School of Sciences and Engineering
    Due to the potential of significant energy release in cavitating flows, early cavitation inception and intensification of cavitating flows are of great importance. To use this potential, we investigated the deagglomeration of nanoparticle clusters with the implementation of hydrodynamic cavitation in a microfluidic device. For this purpose, a microfluidic device with a micro-orifice geometry was designed and fabricated using standard microfabrication processes. The system was tested with distilled water in the assembled experimental setup. The flow patterns were characterized using the cavitation number and inlet pressure. Titania nanoparticles were utilized to prepare nanoparticle suspensions. The suspensions were heated to allow agglomeration of nanoparticles. The system was operated with the new working fluid (nanoparticle clusters) at different inlet pressures. After characterizing flow patterns, the flow patterns were compared with those of pure water. The deagglomeration effects of hydrodynamic cavitation on nanoparticle clusters showed the possibility to apply this method for the stabilization of nanoparticles, which paves way to the implementation of nanoparticle suspensions to thermal fluid systems for increased energy efficiency as well as to drug delivery. Our results also indicate that the presence of nanoparticles in the working fluid enhanced cavitation intensity due to the increase in the number of heterogeneous nucleation sites.
  • Thumbnail Image
    PublicationOpen Access
    3D engineered neural co-culture model and neurovascular effects of marine fungi-derived citreohybridonol
    (American Institute of Physics (AIP) Publishing, 2022) Polat, İrem; Özkaya, Ferhat Can; El-Neketi, Mona; Ebrahim, Weaam; Şengül, Gülgün; Department of Mechanical Engineering; Sokullu, Emel; Sarabi, Misagh Rezapour; Taşoğlu, Savaş; Faculty Member; Faculty Member; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Koç Üniversitesi İş Bankası Yapay Zeka Uygulama ve Araştırma Merkezi (KUIS AI)/ Koç University İş Bank Artificial Intelligence Center (KUIS AI); KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); School of Medicine; Graduate School of Sciences and Engineering; College of Engineering; 163024; N/A; 291971
    Marine-based biomolecules are emerging metabolites that have gained attention for developing novel biomaterials, drugs, and pharmaceutical in vitro platforms. Here, we developed a 3D engineered neural co-culture model via a 3D prototyped sliding frame-platform for multi-step UV lithography and investigated the neurovascular potential of citreohybridonol in neuroblastoma treatment. Citreohybridonol was isolated from a sponge-derived fungus Penicillium atrovenetum. The model was characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy analysis. Human umbilical cord vein endothelial cells (HUVECs) and neuroblastoma (SH-SY5Y) cell lines were encapsulated in gelatin methacrylate (GelMA) with and without citreohybridonol. The effect of citreohybridonol on the proliferation capacity of cells was assessed via cell viability and immunostaining assays. GelMA and 3D culture characterization indicated that the cells were successfully encapsulated as axenic and mixed with/without citreohybridonol. The cytotoxic test confirmed that the 3D microenvironment was non-toxic for cultural experiments, and it showed the inhibitory effects of citreohybridonol on SH-SY5Y cells and induced the proliferation of HUVECs. Finally, immunohistochemical staining demonstrated that citreohybridonol suppressed SH-SY5Y cells and induced vascularization of HUVECs in mixed 3D cell culture.