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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Item Metadata only In situ design of a nanostructured ınterface between NiMo and CuO derived from metal-organic framework for enhanced hydrogen evolution in alkaline solutions(Amer Chemical Soc, 2024) 0000-0003-1164-1973; 0000-0002-2991-5488; N/A; 0000-0003-0832-0546; Yildirim, Ipek Deniz; Erdem, Emre; Department of Chemistry; N/A; N/A; N/A; Aydemir, Umut; Peighambardoust, Naeimeh Sadat; Chamani, Sanaz; Sadeghi, Ebrahim; Faculty Member; Researcher; Researcher; PhD Student; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; N/A; N/A; Graduate School of Sciences and Engineering; 58403; N/A; N/A; N/AHydrogen shows great promise as a carbon-neutral energy carrier that can significantly mitigate global energy challenges, offering a sustainable solution. Exploring catalysts that are highly efficient, cost-effective, and stable for the hydrogen evolution reaction (HER) holds crucial importance. For this, metal-organic framework (MOF) materials have demonstrated extensive applicability as either a heterogeneous catalyst or catalyst precursor. Herein, a nanostructured interface between NiMo/CuO@C derived from Cu-MOF was designed and developed on nickel foam (NF) as a competent HER electrocatalyst in alkaline media. The catalyst exhibited a low overpotential of 85 mV at 10 mA cm(-2) that rivals that of Pt/C (83 mV @ 10 mA cm(-2)). Moreover, the catalyst's durability was measured through chronopotentiometry at a constant current density of -30, -100, and -200 mA cm(-2) for 50 h each in 1.0 M KOH. Such enhanced electrocatalytic performance could be ascribed to the presence of highly conductive C and Cu species, the facilitated electron transfer between the components because of the nanostructured interface, and abundant active sites as a result of multiple oxidation states. The existence of an ionized oxygen vacancy (O-v) signal was confirmed in all heat-treated samples through electron paramagnetic resonance (EPR) analysis. This revelation sheds light on the entrapment of electrons in various environments, primarily associated with the underlying defect structures, particularly vacancies. These trapped electrons play a crucial role in augmenting electron conductivity, thereby contributing to an elevated HER performance.Item Metadata only Nanomechanical properties of Al-Tb marginal metallic glass(Elsevier Science Sa, 2023) 0000-0001-6753-9316; Okuyucu, Can; Ulucan, Tolga Han; Abboud, Mohammad; Motallebzadeh, Amir; Ozerinc, Sezer; Kalay, Ilkay; Kalay, Yunus Eren; N/A; Motallebzadeh, Amir; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/AAl-Rare Earth (RE) metallic glasses provide an effective model system to study the effect of nanocrystallites in an amorphous matrix on nanomechanical behavior. In this work, we achieved a series of Al-Tb metallic glasscrystalline composites with systematically varying crystalline content through annealing. The nanomechanical properties were characterized using micropillar compression tests and nanoindentation for as-quenched amorphous and annealed amorphous/nanocrystalline composite specimens. The promising hardness increases after annealing from 3.0 GPa to 4.6 GPa and elastic modulus increment from 68 GPa to 92 GPa were discussed in detail, considering the structural features of Al-RE marginal metallic glass formers. The increase in elastic modulus is associated with the nucleated fcc-Al nanocrystals that divide the amorphous matrix, leading to the branching of the shear bands. The correlation between the fcc-Al nanocrystals and the behavior of shear bands was discussed in detail.Item Metadata only Genetically encoded fluorescent probe for detection of heme-induced conformational changes in cytochrome C(MDPI, 2023) Genceroglu, Mehmet Yunus; Cavdar, Cansu; Manioglu, Selen; Bayraktar, Halil; N/A; Manioğlu, Selen; Master Student; Graduate School of Sciences and EngineeringCytochrome c (Cytc) is a key redox protein for energy metabolism and apoptosis in cells. The activation of Cytc is composed of several steps, including its transfer to the mitochondrial membrane, binding to cytochrome c heme lyase (CCHL) and covalent attachment to heme. The spectroscopic methods are often applied to study the structural changes of Cytc. However, they require the isolation of Cytc from cells and have limited availability under physiological conditions. Despite recent studies to elucidate the tightly regulated folding mechanism of Cytc, the role of these events and their association with different conformational states remain elusive. Here, we provide a genetically encoded fluorescence method that allows monitoring of the conformational changes of Cytc upon binding to heme and CCHL. Cerulean and Venus fluorescent proteins attached at the N and C terminals of Cytc can be used to determine its unfolded, intermediate, and native states by measuring FRET amplitude. We found that the noncovalent interaction of heme in the absence of CCHL induced a shift in the FRET signal, indicating the formation of a partially folded state. The higher concentration of heme and coexpression of CCHL gave rise to the recovery of Cytc native structure. We also found that Cytc was weakly associated with CCHL in the absence of heme. As a result, a FRET-based fluorescence approach was demonstrated to elucidate the mechanism of heme-induced Cytc conformational changes with spatiotemporal resolution and can be applied to study its interaction with small molecules and other protein partners in living cells.Item Metadata only MNO2 nanoflower integrated optoelectronic biointerfaces for photostimulation of neurons(Wiley, 2023) 0000-0003-0394-5790; 0000-0002-7669-9589; 0000-0003-3682-6042; 0000-0002-4355-7592; 0000-0001-9885-5653; 0009-0002-2549-3983; 0000-0001-7789-8152; Vanalakar, Sharadrao Anandrao; Department of Electrical and Electronics Engineering; N/A; N/A; N/A; N/A; N/A; N/A; Nizamoğlu, Sedat; Karatüm, Onuralp; Önal, Asım; Kaleli, Humeyra Nur; Hasanreisoğlu, Murat; Balamur, Rıdvan; Kaya, Lokman; Faculty Member; PhD Student; PhD Student; PhD Student; Faculty Member; PhD Student; Master Student; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Health Sciences; School of Medicine; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 130295; N/A; N/A; N/A; 182001; N/A; N/AOptoelectronic biointerfaces have gained significant interest for wireless and electrical control of neurons. Three-dimentional (3D) pseudocapacitive nanomaterials with large surface areas and interconnected porous structures have great potential for optoelectronic biointerfaces that can fulfill the requirement of high electrode-electrolyte capacitance to effectively transduce light into stimulating ionic currents. In this study, the integration of 3D manganese dioxide (MnO2) nanoflowers into flexible optoelectronic biointerfaces for safe and efficient photostimulation of neurons is demonstrated. MnO2 nanoflowers are grown via chemical bath deposition on the return electrode, which has a MnO2 seed layer deposited via cyclic voltammetry. They facilitate a high interfacial capacitance (larger than 10 mF cm(-2)) and photogenerated charge density (over 20 & mu;C cm(-2)) under low light intensity (1 mW mm(-2)). MnO2 nanoflowers induce safe capacitive currents with reversible Faradaic reactions and do not cause any toxicity on hippocampal neurons in vitro, making them a promising material for biointerfacing with electrogenic cells. Patch-clamp electrophysiology is recorded in the whole-cell configuration of hippocampal neurons, and the optoelectronic biointerfaces trigger repetitive and rapid firing of action potentials in response to light pulse trains. This study points out the potential of electrochemically-deposited 3D pseudocapacitive nanomaterials as a robust building block for optoelectronic control of neurons.Publication Metadata only Liquid metal microdroplet-initiated ultra-fast polymerization of a stimuli-responsive hydrogel composite(Wiley-V C H Verlag Gmbh, 2023) Zhang, Jianhua; Liao, Jiahe; Liu, Zemin; Zhang, Rongjing; Department of Mechanical Engineering; Department of Mechanical Engineering; Sitti, Metin; College of Engineering; School of MedicineRecent advances in composite hydrogels achieve material enhancement or specialized stimuli-responsive functionalities by pairing with a functional filler. Liquid metals (LM) offer a unique combination of chemical, electrical, and mechanical properties that show great potential in hydrogel composites. Polymerization of hydrogels with LM microdroplets as initiators is a particularly interesting phenomenon that remains in its early stage of development. In this work, an LM-hydrogel composite is introduced, in which LM microdroplets dispersed inside the hydrogel matrix have dual functions as a polymerization initiator for a polyacrylic acid-poly vinyl alcohol (PAA/PVA) network and, once polymerized, as passive inclusion to influence its material and stimuli-responsive characteristics. It is demonstrated that LM microdroplets enable ultra-fast polymerization in approximate to 1 min, compared to several hours by conventional polymerization techniques. The results show several mechanical enhancements to the PAA/PVA hydrogels with LM-initiated polymerization. It is found that LM ratios strongly influence stimuli-responsive behaviors in the hydrogels, including swelling and ionic bending, where higher LM ratios are found to enhance ionic actuation performance. The dual roles of LM in this composite are analyzed using the experimental characterization results. These LM-hydrogel composites, which are biocompatible, open up new opportunities in future soft robotics and biomedical applications. A composite hydrogel embedded with liquid metal (LM) microdroplets is introduced, where the LM microdroplets have dual roles of initiating ultra-fast polymerization and passive inclusion. The physical effects of LM on polymerization and stimuli-responsive behaviors are analyzed, including swelling and ionic actuation due to osmotic pressure differences. Their benefits to the LM-hydrogel functionalities, such as robot locomotion, are demonstrated.Publication Metadata only Nanodiamond-enhanced magnetic resonance imaging(Wiley-V C H Verlag Gmbh, 2023) Lazovic, Jelena; Goering, Eberhard; Wild, Anna-Maria; Schuetzenduebe, Peter; Shiva, Anitha; Loeffler, Jessica; Winter, Gordon; Department of Mechanical Engineering; Department of Mechanical Engineering; Sitti, Metin; College of Engineering; School of MedicineNanodiamonds (ND) hold great potential for diverse applications due to their biocompatibility, non-toxicity, and versatile functionalization. Direct visualization of ND by means of non-invasive imaging techniques will open new venues for labeling and tracking, offering unprecedented and unambiguous detection of labeled cells or nanodiamond-based drug carrier systems. The structural defects in diamonds, such as vacancies, can have paramagnetic properties and potentially act as contrast agents in magnetic resonance imaging (MRI). The smallest nanoscale diamond particles, detonation ND, are reported to effectively reduce longitudinal relaxation time T1 and provide signal enhancement in MRI. Using in vivo, chicken embryos, direct visualization of ND is demonstrated as a bright signal with high contrast to noise ratio. At 24 h following intravascular application marked signal enhancement is noticed in the liver and the kidneys, suggesting uptake by the phagocytic cells of the reticuloendothelial system (RES), and in vivo labeling of these cells. This is confirmed by visualization of nanodiamond-labeled macrophages as positive (bright) signal, in vitro. Macrophage cell labeling is not associated with significant increase in pro-inflammatory cytokines or marked cytotoxicity. These results indicate nanodiamond as a novel gadolinium-free contrast-enhancing agent with potential for cell labeling and tracking and over periods of time. The presence of paramagnetic centers in nanodiamonds drives effective reduction in longitudinal relaxation time (T1) and relaxation of neighboring water molecules, resulting in bright appearance on T1-weighted magnetic resonance images. , Using in vivo chicken embryos, it is confirmed nanodiamonds can provide high contrast to noise ratio for tracking and cell labeling over periods of time using magnetic resonance imaging (MRI).Publication Metadata only Machine learning-based shear optimal adhesive microstructures with experimental validation(Wiley-V C H Verlag Gmbh, 2023) Dayan, Cem Balda; Son, Donghoon; Aghakhani, Amirreza; Wu, Yingdan; Demir, Sinan Ozgun; Department of Mechanical Engineering; Department of Mechanical Engineering; Sitti, Metin; College of Engineering; School of MedicineBioinspired fibrillar structures are promising for a wide range of disruptive adhesive applications. Especially micro/nanofibrillar structures on gecko toes can have strong and controllable adhesion and shear on a wide range of surfaces with residual-free, repeatable, self-cleaning, and other unique features. Synthetic dry fibrillar adhesives inspired by such biological fibrils are optimized in different aspects to increase their performance. Previous fibril designs for shear optimization are limited by predefined standard shapes in a narrow range primarily based on human intuition, which restricts their maximum performance. This study combines the machine learning-based optimization and finite-element-method-based shear mechanics simulations to find shear-optimized fibril designs automatically. In addition, fabrication limitations are integrated into the simulations to have more experimentally relevant results. The computationally discovered shear-optimized structures are fabricated, experimentally validated, and compared with the simulations. The results show that the computed shear-optimized fibrils perform better than the predefined standard fibril designs. This design optimization method can be used in future real-world shear-based gripping or nonslip surface applications, such as robotic pick-and-place grippers, climbing robots, gloves, electronic devices, and medical and wearable devices. This study combines the machine learning-based optimization and finite-element-method-based shear mechanics simulations to find shear-optimized fibril designs automatically. The results show that the computed optimal fibrils perform better than the predefined standard fibril designs. This design optimization framework can be used in future nonslip surface applications in grippers, robots, gloves, and electronic, medical, and wearable devices.Publication Metadata only Magnetic putty as a reconfigurable, recyclable, and accessible soft robotic material(Wiley-V C H Verlag Gmbh, 2023) Li, Meng; Pal, Aniket; Byun, Junghwan; Gardi, Gaurav; Department of Mechanical Engineering; Department of Mechanical Engineering; Sitti, Metin; College of Engineering; School of MedicineMagnetically hard materials are widely used to build soft magnetic robots, providing large magnetic force/torque and macrodomain programmability. However, their high magnetic coercivity often presents practical challenges when attempting to reconfigure magnetization patterns, requiring a large magnetic field or heating. In this study, magnetic putty is introduced as a magnetically hard and soft material with large remanence and low coercivity. It is shown that the magnetization of magnetic putty can be easily reoriented with maximum magnitude using an external field that is only one-tenth of its coercivity. Additionally, magnetic putty is a malleable, autonomous self-healing material that can be recycled and repurposed. The authors anticipate magnetic putty could provide a versatile and accessible tool for various magnetic robotics applications for fast prototyping and explorations for research and educational purposes. Permanent magnetic particles embedded in a viscoelastic putty matrix result in a self-healing soft magnetic material with both high remanence and low coercivity, providing hard-magnetic performance without the need for inaccessible strong magnetic fields. Programmable and reconfigurable magnetization, frequency-dependent force output, and easy to shape and assemble, magnetic putty can be a versatile tool in research prototyping and inspire future explorations.Publication Metadata only Liquid metal actuators: a comparative analysis of surface tension controlled actuation(Wiley-V C H Verlag Gmbh, 2023) Liao, Jiahe; Majidi, Carmel; Department of Mechanical Engineering; Department of Mechanical Engineering; Sitti, Metin; College of Engineering; School of MedicineLiquid metals, with their unique combination of electrical and mechanical properties, offer great opportunities for actuation based on surface tension modulation. Thanks to the scaling laws of surface tension, which can be electrochemically controlled at low voltages, liquid metal actuators stand out from other soft actuators for their remarkable characteristics such as high contractile strain rates and higher work densities at smaller length scales. This review summarizes the principles of liquid metal actuators and discusses their performance as well as theoretical pathways toward higher performances. The objective is to provide a comparative analysis of the ongoing development of liquid metal actuators. The design principles of the liquid metal actuators are analyzed, including low-level elemental principles (kinematics and electrochemistry), mid-level structural principles (reversibility, integrity, and scalability), and high-level functionalities. A wide range of practical use cases of liquid metal actuators from robotic locomotion and object manipulation to logic and computation is reviewed. From an energy perspective, strategies are compared for coupling the liquid metal actuators with an energy source toward fully untethered robots. The review concludes by offering a roadmap of future research directions of liquid metal actuators. This review summarizes the operation and design principles of surface tension-controlled actuation by liquid metals and discusses their performance and functionalities. Theoretical pathways toward higher performances, thanks to the unique scaling law of surface tension, are analyzed and compared to other popular soft actuators. The review concludes by offering a roadmap for future research directions.Publication Metadata only Size-dependent locomotion ability of surface microrollers on physiologically relevant microtopographical surfaces(Wiley-V C H Verlag Gmbh, 2023) Bozuyuk, Ugur; Yildiz, Erdost; Han, Mertcan; Demir, Sinan Ozgun; Department of Mechanical Engineering; Department of Mechanical Engineering; Sitti, Metin; College of Engineering; School of MedicineControlled microrobotic navigation inside the body possesses significant potential for various biomedical engineering applications. Successful application requires considering imaging, control, and biocompatibility. Interaction with biological environments is also a crucial factor in ensuring safe application, but can also pose counterintuitive hydrodynamic barriers, limiting the use of microrobots. Surface rolling microrobots or surface microrollers is a robust microrobotic platform with significant potential for various applications; however, conventional spherical microrollers have limited locomotion ability over biological surfaces due to microtopography effects resulting from cell microtopography in the size range of 2-5 & mu;m. Here, the impact of the microtopography effect on spherical microrollers of different sizes (5, 10, 25, and 50 & mu;m) is investigated using computational fluid dynamics simulations and experiments. Simulations revealed that the microtopography effect becomes insignificant for increasing microroller sizes, such as 50 & mu;m. Moreover, it is demonstrated that 50 & mu;m microrollers exhibited smooth locomotion ability on in vitro cell layers and inside blood vessels of a chicken embryo model. These findings offer rational design principles for surface microrollers for their potential practical biomedical applications.