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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 Molecularly imprinted nanoparticles with recognition properties towards diphtheria toxin for ELISA applications(Taylor and Francis Ltd., 2023) 0000-0003-4767-083X; Alkanlı, Süleyman Serdar; Yaşar, Merve; Güven, Celal; Kahraman, M. Vezir; Kayaman Apohan, Nilhan; Aktaş, Zerrin; Öncül, Mustafa Oral; Ünlü, Ayhan; Akçakaya, Handan; N/A; Yöntem, Fulya Dal; Teaching Faculty; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); School of Medicine; Koç University Hospital; 232576Plastic antibodies can be used for in vitro neutralization of biomacromolecules with different fragments due to their potential in separation, purification, chemical sensor, catalysis and drug production studies. These polymer nanoparticles with binding affinity and selectivity comparable to natural antibodies were prepared using functional monomer synthesis and copolymerization of acrylic monomers via miniemulsion polymerization. As a result, the in vitro cytotoxic effect from diphtheria toxin was reduced by MIPs. In vitro imaging experiments of polymer nanoparticles (plastic antibodies) were performed to examine the interaction of diphtheria toxin with actin filaments, and MIPs inhibited diphtheria toxin damage on actin filaments. The enzyme-linked immunosorbent assay (ELISA) was performed with plastic antibodies labeled with biotin, and it was determined that plastic antibodies could also be used for diagnostic purposes. We report that molecularly imprinted polymers (MIPs), which are biocompatible polymer nanoparticles, can capture and reduce the effect of diphtheria toxic and its fragment A.Publication Metadata only Objective-free ultrasensitive biosensing on large-area metamaterial surfaces in the near-IR(AMER CHEMICAL SOC, 2024) Department of Physics; Department of Physics; Ramazanoğlu, Serap Aksu; Öktem, Evren; College of Sciences; Graduate School of Sciences and EngineeringPlasmonic metamaterials have opened new avenues in medical diagnostics. However, the transfer of the technology to the markets has been delayed due to multiple challenges. The need of bulky optics for signal reading from nanostructures patterned on submillimeter area limits the miniaturization of the devices. The use of objective-free optics can solve this problem, which necessitates large area patterning of the nanostructures. In this work, we utilize laser interference lithography (LIL) to pattern nanodisc-shaped metamaterial absorber nanoantennas over a large area (4 cm(2)) within minutes. The introduction of a sacrificial layer during the fabrication process enables an inverted hole profile and a well-controlled liftoff, which ensures perfectly defined uniform nanopatterning almost with no defects. Furthermore, we use a macroscopic reflection probe for optical characterization in the near-IR, including the detection of the binding kinematics of immunologically relevant proteins. We show that the photonic quality of the plasmonic nanoantennas commensurates with electron-beam-lithography-fabricated ones over the whole area. The refractive index sensitivity of the LIL-fabricated metasurface is determined as 685 nm per refractive index unit, which demonstrates ultrasensitive detection. Moreover, the fabricated surfaces can be used multiple times for biosensing without losing their optical quality. The combination of rapid and large area nanofabrication with a simple optical reading not only simplifies the detection process but also makes the biosensors more environmentally friendly and cost-effective. Therefore, the improvements provided in this work will empower researchers and industries for accurate and real-time analysis of biological systems.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 Bulk MgB2 superconductor for levitation applications fabricated with boron processed by different routes(Elsevier Science Sa, 2023) Savaskan, B.; Ozturk, U. K.; Guner, S. B.; Abdioglu, M.; Bahadir, M. V.; Acar, S.; Ionescu, A. M.; Locovei, C.; Enculescu, M.; Badica, P.; Department of Chemistry; Department of Chemistry; Somer, Mehmet Suat; College of SciencesBulk MgB2 discs were prepared by an in situ route from mixtures of magnesium and boron powders. The boron powders were produced by two methods. The first one consisted of a self-propagating high tem-perature magnesiothermic synthesis (SHS) process followed by acid and fluorine cleaning and a heat treatment in inert atmosphere. This approach produced boron with purities between 86 % and 97 %, where the main impurity was Mg. Depending on the final heat treatment, these boron powders were amorphous or crystalline. In the second route, high purity nano powders (99 %) of boron were obtained by a diborane pyrolysis process. Bulks of MgB2 were characterized by structural, microstructural, and magnetic mea-surements. Critical current density, pinning force aspects and levitation force (including guiding force) details were assessed. Amorphous lower purity boron (86-97 %) obtained by the first processing route was found to promote the largest levitation forces of the MgB2 bulks and, among these samples, the best le-vitation results were recorded when using boron with a purity of 95-97 %. Use of a lower purity boron that decreases the cost of MgB2 promotes large scale production at industrial level of bulk MgB2 super-conducting magnets for levitation applications and enhances the applicability potential of MgB2 super-conductor. The relationship between levitation force and specific features of the samples such as pinning force details are discussed.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.Publication Metadata only Artificial-goosebump-driven microactuation(Nature Portfolio, 2024) Zhang, Mingchao; Pal, Aniket; Lyu, Xianglong; Wu, Yingdan; Department of Mechanical Engineering; Department of Mechanical Engineering; Sitti, Metin; College of Engineering; School of MedicineMicroactuators provide controllable driving forces for precise positioning, manipulation and operation at the microscale. Development of microactuators using active materials is often hampered by their fabrication complexity and limited motion at small scales. Here we report light-fuelled artificial goosebumps to actuate passive microstructures, inspired by the natural reaction of hair bristling (piloerection) on biological skin. We use light-responsive liquid crystal elastomers as the responsive artificial skin to move three-dimensionally printed passive polymer microstructures. When exposed to a programmable femtosecond laser, the liquid crystal elastomer skin generates localized artificial goosebumps, resulting in precise actuation of the surrounding microstructures. Such microactuation can tilt micro-mirrors for the controlled manipulation of light reflection and disassemble capillary-force-induced self-assembled microstructures globally and locally. We demonstrate the potential application of the proposed microactuation system for information storage. This methodology provides precise, localized and controllable manipulation of microstructures, opening new possibilities for the development of programmable micromachines. Light-induced artificial goosebumps on liquid crystal elastomer skin are used to precisely manipulate passive microstructures, achieving a localized and controllable system for programmable micromachines.