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Publication Open Access 3D bioprinted organ?on?chips(Wiley, 2022) Mustafaoğlu, Nur; Zhang, Yu Shrike; Department of Mechanical Engineering; N/A; N/A; Dabbagh, Sajjad Rahmani; Sarabi, Misagh Rezapour; Birtek, Mehmet Tuğrul; Taşoğlu, Savaş; Faculty Member; Department of Mechanical Engineering; KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Koç Üniversitesi İş Bankası Yapay Zeka Uygulama ve Araştırma Merkezi (KUIS AI)/ Koç University İş Bank Artificial Intelligence Center (KUIS AI); College of Engineering; Graduate School of Social Sciences and Humanities; Graduate School of Sciences and Engineering; N/A; N/A; N/A; 291971Organ-on-a-chip (OOC) platforms recapitulate human in vivo-like conditions more realistically compared to many animal models and conventional two-dimensional cell cultures. OOC setups benefit from continuous perfusion of cell cultures through microfluidic channels, which promotes cell viability and activities. Moreover, microfluidic chips allow the integration of biosensors for real-time monitoring and analysis of cell interactions and responses to administered drugs. Three-dimensional (3D) bioprinting enables the fabrication of multicell OOC platforms with sophisticated 3D structures that more closely mimic human tissues. 3D-bioprinted OOC platforms are promising tools for understanding the functions of organs, disruptive influences of diseases on organ functionality, and screening the efficacy as well as toxicity of drugs on organs. Here, common 3D bioprinting techniques, advantages, and limitations of each method are reviewed. Additionally, recent advances, applications, and potentials of 3D-bioprinted OOC platforms for emulating various human organs are presented. Last, current challenges and future perspectives of OOC platforms are discussed.Publication Open Access 3D printed personalized magnetic micromachines from patient blood-derived biomaterials(American Association for the Advancement of Science (AAAS), 2021) Ceylan, Hakan; Doğan, Nihal Olcay; Yaşa, İmmihan Ceren; Department of Mechanical Engineering; Sitti, Metin; Musaoğlu, Miraç Nur; Kulalı, Zeynep Umut; Faculty Member; Department of Mechanical Engineering; College of Engineering; School of Medicine; 297104; N/A; N/AWhile recent wireless micromachines have shown increasing potential for medical use, their potential safety risks concerning biocompatibility need to be mitigated. They are typically constructed from materials that are not intrinsically compatible with physiological environments. Here, we propose a personalized approach by using patient blood-derivable biomaterials as the main construction fabric of wireless medical micromachines to alleviate safety risks from biocompatibility. We demonstrate 3D printed multiresponsive microswimmers and microrollers made from magnetic nanocomposites of blood plasma, serum albumin protein, and platelet lysate. These micro-machines respond to time-variant magnetic fields for torque-driven steerable motion and exhibit multiple cycles of pH-responsive two-way shape memory behavior for controlled cargo delivery and release applications. Their proteinaceous fabrics enable enzymatic degradability with proteinases, thereby lowering risks of long-term toxicity. The personalized micromachine fabrication strategy we conceptualize here can affect various future medical robots and devices made of autologous biomaterials to improve biocompatibility and smart functionality.Publication Open Access 3D-printed contact lenses: challenges towards translation and commercialization(Future Medicine, 2022) Yetişen, Ali K.; Department of Mechanical Engineering; Taşoğlu, Savaş; Özdalgıç, Berin; Faculty Member; PhD Student; Department of Mechanical Engineering; KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; Graduate School of Sciences and Engineering; 291971; 323683NAPublication Open Access 3D-printed microneedles in biomedical applications(Elsevier, 2021) Rahbarghazi, Reza; Yetişen, Ali Kemal; N/A; Department of Mechanical Engineering; Dabbagh, Sajjad Rahmani; Sarabi, Misagh Rezapour; Sokullu, Emel; Taşoğlu, Savaş; Faculty Member; Faculty Member; Department of Mechanical Engineering; KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Social Sciences and Humanities; Graduate School of Sciences and Engineering; School of Medicine; College of Engineering; N/A; N/A; 163024; 291971Conventional needle technologies can be advanced with emerging nano- and micro-fabrication methods to fabricate microneedles. Nano-/micro-fabricated microneedles seek to mitigate penetration pain and tissue damage, as well as providing accurately controlled robust channels for administrating bioagents and collecting body fluids. Here, design and 3D printing strategies of microneedles are discussed with emerging applications in biomedical devices and healthcare technologies. 3D printing offers customization, cost-efficiency, a rapid turnaround time between design iterations, and enhanced accessibility. Increasing the printing resolution, the accuracy of the features, and the accessibility of low-cost raw printing materials have empowered 3D printing to be utilized for the fabrication of microneedle platforms. The development of 3D-printed microneedles has enabled the evolution of pain-free controlled release drug delivery systems, devices for extracting fluids from the cutaneous tissue, biosignal acquisition, and point-of-care diagnostic devices in personalized medicine.Publication Open Access A comparative analysis of austenite-to-martensite and austenite-to-bainite phase transformation kinetics in steels(Taylor _ Francis, 2013) Holzweissig, M.J.; Lambers, H.-G.; Maier, H.J.; Department of Mechanical Engineering; Uslu, Mehmet Can; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 23433This paper presents a comparison of the macroscopic transformation strain evolution as a function of the bainite and martensite phase fractions in steels. Specifically, the evolution of anisotropic strain with phase fraction follows a linear trend for the martensitic transformation due to continuous stress-induced variant selection. In the case of bainitic transformation, the anisotropic strain evolves non-linearly owing to diffusion, minimizing the distortion around the bainitic sheaves and further promoting stress-induced variant selection at the early stages of the bainitic phase transformation. However, this effectiveness is reduced when the bainitic sheaves start constricting the growth of each other.Publication Open Access A critical approach to the biocompatibility testing of NiTi orthodontic archwires(Vibgyor Online Publishers, 2016) Şahbazoğlu, D.; Toker, S. M.; Saher, D.; Department of Mechanical Engineering; Canadinç, Demircan; Gümüş, Berkay; Uzer, Benay; Yıldırım, Cansu; Polat-Altıntaş, Sevgi; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433; N/A; N/A; N/A; N/AThe biocompatibility of Nickel-Titanium (NiTi) archwires was investigated by simulating actual contact state of archwires around brackets, which enabled incorporation of realistic mechanical conditions into ex situ experiments. Specifically, archwires (undeformed, and bound to brackets on acrylic dental molds) were statically immersed in artificial saliva (AS) for 31 days. Following the immersion, the archwires and the immersion solutions were analyzed with the aid of variouselectron-optical techniques, and it was observed that carbon-rich corrosion products formed on both archwire sets upon immersion. The corrosion products preferentially formed at the archwire–bracket contact zones, which is promoted by the high energy of these regions and the micro-cracks brought about by stress assisted corrosion. Moreover, it is suggested that these corrosion products prevented significant Ni or Ti ion release by blocking the micro-cracks, which, otherwise, would have led to enhanced ion release during immersion. The current findings demonstrate the need for incorporating both realistic chemical and mechanical conditions into the ex situ biocompatibility experiments of orthodontic archwires, including the archwire-bracket contact.
Publication Metadata only A finite-volume front-tracking method for computations of multiphase flows in complex geometries(Frontiers, 2005) N/A; Department of Mechanical Engineering; Muradoğlu, Metin; Faculty Member; Department of Mechanical Engineering; College of Engineering; 46561A finite-volume/front-tracking (FV/FT) method is developed for computations of multiphase flows in complex geometries. The front-tracking methodology is combined with a dual time-stepping based FV method. The interface between phases is represented by connected Lagrangian marker points. An efficient algorithm is developed to keep track of the marker points in curvilinear grids. The method is implemented to solve two-dimensional (plane or axisymmetric) dispersed multiphase flows and is validated for the motion of buoyancy-driven drops in a periodically constricted tube with cases where drop breakup occurs.Publication Metadata only A finite-volume/front-tracking method for computations of multiphase flows in complex geometries(Springer, 2006) N/A; Department of Mechanical Engineering; N/A; N/A; Muradoğlu, Metin; Olgaç, Ufuk; Kayaalp, Arif Doruk; Faculty Member; Master Student; Master Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 46561; N/A; N/AA finite-volume/front-tracking (FV/FT) method is developed for computations of multiphase flows in complex geometries. The front-tracking methodology is combined with a dual time-stepping based FV method. The interface between phases is represented by connected Lagrangian marker points. An efficient algorithm is developed to keep track of the marker points in curvilinear grids. The method is implemented to solve two-dimensional (plane or axisymmetric) dispersed multiphase flows and is validated for the motion of buoyancy-driven drops in a periodically constricted tube with cases where drop breakup occurs.Publication Metadata only A new characterization approach to study the mechanical behavior of silicon nanowires(Springer, 2021) Esfahani, Mohammad Nasr; Taşdemir, Zuhal; Wollschlaeger, Nicole; Li, XueFei; Li, Taotao; Leblebici, Yusuf; N/A; N/A; Department of Mechanical Engineering; Zarepakzad, Sina; Yılmaz, Mustafa Akın; Alaca, Burhanettin Erdem; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; N/A; N/A; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 115108This work proposes a new approach to characterize the mechanical properties of nanowires based on a combination of nanomechanical measurements and models. Silicon nanowires with a critical dimension of 90 nm and a length of 8 mu m obtained through a monolithic process are characterized through in-situ three-point bending tests. A nonlinear nanomechanical model is developed to evaluate the mechanical behavior of nanowires. In this model, the intrinsic stress and surface parameters are examined based on Raman spectroscopy measurements and molecular dynamics simulations, respectively. This work demonstrates a new approach to measure the mechanical properties of Si nanowires by considering the surface effect and intrinsic stresses. The presented technique can be used to address the existing discrepancies between numerical estimations and experimental measurements on the modulus of elasticity of silicon nanowires.Publication Open Access A new consistent hybrid algorithm for solution of the PDF equations of turbulent reactive flow(American Institute of Physics (AIP) Publishing, 2013) Department of Mechanical Engineering; Sheikhsarmast, Reza Mokhtarpoor; Inmas, Shabrina Virta; Muradoğlu, Metin; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 46561This paper presents a newly developed consistent hybrid finite-volume (FV)/particle algorithm for solution of joint PDF (JPDF) model equation of turbulent reacting flows. In this approach, the open source FV package of OpenFOAM is employed to solve the Favre-averaged mean mass and momentum equations using pressure-based PISO algorithm while a particle-based Monte Carlo algorithm is used to solve the fluctuating velocity-turbulence frequency-compositions JPDF transport equation. In the earlier hybrid method [2, 3], a density-based FV algorithm was used to solve the mean flow equations but it has been found to be too dissipative and yet not very robust for incompressible or nearly incompressible flows mainly due to stiffness of the compressible flow equations in the low Mach number limit. In the this work, the density-based FV algorithm is first replaced with a pressure-based PISO algorithm to tackle this problem and then applied for simulation of the Sydney swirl stabilized bluff-body flame SM1. All the equations solved by the FV and particle algorithms are directly derived from the modeled JPDF transport equation so the present method is completely consistent at the level of governing equations. The position and velocity correction algorithms [3] are used to enforce full constancy at the numerical solution level. The results are found to be in a good agreement with the available experimental data and the recent computational results of De Meester et al. [1].