Browsing by Author "Elbuken, Çağlar"

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Open Access
Bioinspired hydrogel surfaces to augment corneal endothelial cell monolayer formation
(John Wiley & Sons, Inc., 2020-12-26) Elbuken, Çağlar
Corneal endothelial cells (CECs) have limited proliferation ability leading to corneal endothelium (CE) dysfunction and eventually vision loss when cell number decreases below a critical level. Although transplantation is the main treatment method, donor shortage problem is a major bottleneck. The transplantation of in vitro developed endothelial cells with desirable density is a promising idea. Designing cell substrates that mimic the native CE microenvironment is a substantial step to achieve this goal. In the presented study, we prepared polyacrylamide (PA) cell substrates that have a microfabricated topography inspired by the dimensions of CECs. Hydrogel surfaces were prepared via two different designs with small and large patterns. Small patterned hydrogels have physiologically relevant hexagon densities (∼2000 hexagons/mm2), whereas large patterned hydrogels have sparsely populated hexagons (∼400 hexagons/mm2). These substrates have similar elastic modulus of native Descemet's membrane (DM; ∼50 kPa) and were modified with Collagen IV (Col IV) to have biochemical content similar to native DM. The behavior of bovine corneal endothelial cells on these substrates was investigated and results show that cell proliferation on small patterned substrates was significantly (p ¼ 0.0004) higher than the large patterned substrates. Small patterned substrates enabled a more densely populated cell monolayer compared to other groups (p ¼ 0.001 vs. flat and p < 0.0001 vs. large patterned substrates). These results suggest that generating bioinspired surface topographies augments the formation of CE monolayers with the desired cell density, addressing the in vitro development of CE layers.
Open Access
Femtosecond laser fabrication of fiber based optofluidic platform for flow cytometry applications
(SPIE, 2017) Serhatlioglu, Murat; Elbuken, Çağlar; Ortac, Bülend; Solmaz, Mehmet E.
Miniaturized optofluidic platforms play an important role in bio-analysis, detection and diagnostic applications. The advantages of such miniaturized devices are extremely low sample requirement, low cost development and rapid analysis capabilities. Fused silica is advantageous for optofluidic systems due to properties such as being chemically inert, mechanically stable, and optically transparent to a wide spectrum of light. As a three dimensional manufacturing method, femtosecond laser scanning followed by chemical etching shows great potential to fabricate glass based optofluidic chips. In this study, we demonstrate fabrication of all-fiber based, optofluidic flow cytometer in fused silica glass by femtosecond laser machining. 3D particle focusing was achieved through a straightforward planar chip design with two separately fabricated fused silica glass slides thermally bonded together. Bioparticles in a fluid stream encounter with optical interrogation region specifically designed to allocate 405nm single mode fiber laser source and two multi-mode collection fibers for forward scattering (FSC) and side scattering (SSC) signals detection. Detected signal data collected with oscilloscope and post processed with MATLAB script file. We were able to count number of events over 4000events/sec, and achieve size distribution for 5.95μm monodisperse polystyrene beads using FSC and SSC signals. Our platform shows promise for optical and fluidic miniaturization of flow cytometry systems. © 2017 SPIE.
Open Access
Impedance-based viscoelastic flow cytometry
(WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Serhatlıoğlu, Murat; Asghari, Mohammad; Guler, M. T.; Elbuken, Çağlar
Elastic nature of the viscoelastic fluids induces lateral migration of particles into a single streamline and can be used by microfluidic based flow cytometry devices. In this study, we investigated focusing efficiency of polyethylene oxide based viscoelastic solutions at varying ionic concentration to demonstrate their use in impedimetric particle characterization systems. Rheological properties of the viscoelastic fluid and particle focusing performance are not affected by ionic concentration. We investigated the viscoelastic focusing dynamics using polystyrene (PS) beads and human red blood cells (RBCs) suspended in the viscoelastic fluid. Elasto‐inertial focusing of PS beads was achieved with the combination of inertial and viscoelastic effects. RBCs were aligned along the channel centerline in parachute shape which yielded consistent impedimetric signals. We compared our impedance‐based microfluidic flow cytometry results for RBCs and PS beads by analyzing particle transit time and peak amplitude at varying viscoelastic focusing conditions obtained at different flow rates. We showed that single orientation, single train focusing of nonspherical RBCs can be achieved with polyethylene oxide based viscoelastic solution that has been shown to be a good candidate as a carrier fluid for impedance cytometry.
Open Access
Invisible thin-film patterns with strong infrared emission as an optical security feature
(Wiley-VCH Verlag, 2018) Bakan, G.; Ayas S.; Serhatlioglu, M.; Elbuken, Çağlar; Dana, A.
Spectrally selective thermal emission is in high demand for thermophotovoltaics, radiative cooling, and infrared sensing applications. Spectral control of the emissivity is historically achieved by choosing the material with suitable infrared properties. The recent advancements in nanofabrication techniques that lead to enhanced light-matter interactions enable optical properties like infrared emissivity that are not naturally available. In this study, thermal emitters based on nanometer-thick dielectrics on field-enhancement surfaces as optical security features are proposed. Such a function is achieved by generating patterns by ultrathin dielectrics that are transparent in the visible and exhibit strong infrared absorption in the spectral range of thermal cameras. The invisible patterns are then revealed by thermal imaging. The field-enhancement surfaces enhance the emissivity of the patterns, in turn reduce the minimum temperature to detect the thermal emission down to ≈30 °C from >150 °C to exploit ubiquitous heat sources like the human body. The study provides a framework for the use of thermal emitters as optical security features and demonstrates applications on rigid and flexible substrates.
Open Access
Label-free sensing in microdroplet-based microfluidic systems
(MDPI Multidisciplinary Digital Publishing Institute, 2018) Kalantarifard, A.; Saateh, A.; Elbuken, Çağlar
Droplet microfluidic systems have evolved as fluidic platforms that use much less sample volume and provide high throughput for biochemical analysis compared to conventional microfluidic devices. The variety of droplet fluidic applications triggered several detection techniques to be applied for analysis of droplets. In this review, we focus on label-free droplet detection techniques that were adapted to various droplet microfluidic platforms. We provide a classification of most commonly used droplet platform technologies. Then we discuss the examples of various label-free droplet detection schemes implemented for these platforms. While providing the research landscape for label-free droplet detection methods, we aim to highlight the strengths and shortcomings of each droplet platform so that a more targeted approach can be taken by researchers when selecting a droplet platform and a detection scheme for any given application.
Open Access
Microfluidic measurement of erythrocyte sedimentation rate and monitoring of erytrocyte aggregation
(Chemical and Biological Microsystems Society, 2016) Isiksacan, Ziya; Elbuken, Çağlar
We developed a novel microfluidic opto-electro-mechanical system and performed ultrafast, cheap, and low-sample volume measurement of erythrocyte sedimentation rate (ESR) from erythrocyte aggregation (EA). We also showed EA dynamics in real-time during measurements.