Search results for: A. Aslihan Gokaltun

Authors: A. Aslihan Gokaltun, Ali Tuncel

Abstract:

The unique properties of capillary electrochromatography (CEC) such as high performance, high selectivity, low consumption of both reagents and analytes ensure this technique an attractive one for the separation of biomolecules including nucleosides and nucleotides, peptides, proteins, carbohydrates. Monoliths have become a well-established separation media for CEC in the format that can be compared to a single large 'particle' that does not include interparticular voids. Convective flow through the pores of monolith significantly accelerates the rate of mass transfer and enables a substantial increase in the speed of the separation. In this work, we propose a new approach for the preparation of cationic monolithic stationary phase for capillary electrochromatography. Instead of utilizing a charge bearing monomer during polymerization, the desired charge-bearing group is generated on the capillary monolith after polymerization by using the reactive moiety of the monolithic support via one-pot, simple reaction. Optimized monolithic column compensates the disadvantages of frequently used reversed phases, which are difficult for separation of polar solutes. Rapid separation and high column efficiencies are achieved for the separation of neutral analytes, nucleic acid bases and nucleosides in reversed phase mode. Capillary monolith showed satisfactory hydrodynamic permeability and mechanical stability with relative standard deviation (RSD) values below 2 %. A new promising, reactive support that has a 'ligand selection flexibility' due to its reactive functionality represent a new family of separation media for CEC.

Keywords: biomolecules, capillary electrochromatography, cationic monolith, neutral analytes

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Authors: A. Aslihan Gokaltun, Martin L. Yarmush, Ayse Asatekin, O. Berk Usta

Abstract:

In the last decade microfabrication processes including rapid prototyping techniques have advanced rapidly and achieved a fairly matured stage. These advances encouraged and enabled the use of microfluidic devices by a wider range of users with applications in biological separations, and cell and organoid cultures. Accordingly, a significant current challenge in the field is controlling biomolecular interactions at interfaces and the development of novel biomaterials to satisfy the unique needs of the biomedical applications. Poly(dimethylsiloxane) (PDMS) is by far the most preferred material in the fabrication of microfluidic devices. This can be attributed its favorable properties, including: (1) simple fabrication by replica molding, (2) good mechanical properties, (3) excellent optical transparency from 240 to 1100 nm, (4) biocompatibility and non-toxicity, and (5) high gas permeability. However, high hydrophobicity (water contact angle ~108°±7°) of PDMS often limits its applications where solutions containing biological samples are concerned. In our study, we created a simple, easy method for modifying the surface chemistry of PDMS microfluidic devices through the addition of surface-segregating additives during manufacture. In this method, a surface segregating copolymer is added to precursors for silicone and the desired device is manufactured following the usual methods. When the device surface is in contact with an aqueous solution, the copolymer self-organizes to expose its hydrophilic segments to the surface, making the surface of the silicone device more hydrophilic. This can lead to several improved performance criteria including lower fouling, lower non-specific adsorption, and better wettability. Specifically, this approach is expected to be useful for the manufacture of microfluidic devices. It is also likely to be useful for manufacturing silicone tubing and other materials, biomaterial applications, and surface coatings.

Keywords: microfluidics, non-specific protein adsorption, PDMS, PEG, copolymer

Procedia PDF Downloads 233

Authors: A. Aslihan Gokaltun, Martin L. Yarmush, Ayse Asatekin, O. Berk Usta

Abstract:

Poly(dimethylsiloxane) (PDMS) is one of the most widely used materials in the fabrication of microfluidic devices. It is easily patterned and can replicate features down to nanometers. Its flexibility, gas permeability that allows oxygenation, and low cost also drive its wide adoption. However, a major drawback of PDMS is its hydrophobicity and fast hydrophobic recovery after surface hydrophilization. This results in significant non-specific adsorption of proteins as well as small hydrophobic molecules such as therapeutic drugs limiting the utility of PDMS in biomedical microfluidic circuitry. While silicon, glass, and thermoplastics have been used, they come with problems of their own such as rigidity, high cost, and special tooling needs, which limit their use to a smaller user base. Many strategies to alleviate these common problems with PDMS are lack of general practical applicability, or have limited shelf lives in terms of the modifications they achieve. This restricts large scale implementation and adoption by industrial and research communities. Accordingly, we aim to tailor biocompatible PDMS surfaces by developing a simple and one step bulk modification approach with novel smart materials to reduce non-specific molecular adsorption and to stabilize long-term cell analysis with PDMS substrates. Smart polymers that blended with PDMS during device manufacture, spontaneously segregate to surfaces when in contact with aqueous solutions and create a < 1 nm layer that reduces non-specific adsorption of organic and biomolecules. Our methods are fully compatible with existing PDMS device manufacture protocols without any additional processing steps. We have demonstrated that our modified PDMS microfluidic system is effective at blocking the adsorption of proteins while retaining the viability of primary rat hepatocytes and preserving the biocompatibility, oxygen permeability, and transparency of the material. We expect this work will enable the development of fouling-resistant biomedical materials from microfluidics to hospital surfaces and tubing.

Keywords: cell culture, microfluidics, non-specific protein adsorption, PDMS, smart polymers

Procedia PDF Downloads 269

Authors: Aslihan Coban

Abstract:

As a result of the rapid development of information communication technology, especially the internet, consumers have become an active party in commerce and in law. Consequently, the protection of consumers in cross-border contracts has become increasingly important. This paper is confined to the international jurisdiction of courts over disputes arising from electronic consumer contracts according to the ‘5718 Turkish Act on Private International Law and Civil Procedure’ and the ‘1215/2012 Council Regulation On Jurisdiction and The Recognition and Enforcement Of Judgments In Civil and Commercial Matters’ (Hereafter ‘Brussels I Regulation’). The international jurisdiction of courts for consumer contracts is recognized under both acts above-mentioned; however, there exist some differences between the said legal regulations. Firstly, while there is a specific provision for electronic consumer contracts in Brussels I Regulation, there is no specific provision in the Turkish Act. Secondly, under the Turkish Act, habitual residence, domicile, and workplace of the other party who is not a consumer are all accepted as jurisdiction elements; while domicile is the only jurisdiction element in Brussels I Regulation. Thirdly, the ability to make jurisdiction agreements in disputes arising from electronic consumer contracts is a controversial issue under the Turkish Act while it is explicitly regulated under Brussels I Regulation that such jurisdiction agreements can be concluded by complying with certain conditions.

Keywords: Brussels I Regulation, electronic consumer contracts, jurisdiction, jurisdiction agreement

Procedia PDF Downloads 126

Authors: Aslihan Cetinbas Genc, Meral Unal

Abstract:

This study presents the structural and cytochemical alterations of stigma at the stages of pre-anthesis, anthesis and post-anthesis in Vibirnum tinus. Capitate stigma continues with a closed style. The receptive surface of stigma is composed of unicellular papillae which are short and flattened at pre-anthesis stage. The papillae in this stage have dense cytoplasm with small vacuoles and a centrally located nucleus. With the start of anthesis, the stigma widens, papillae lengthen and become cylindrical. At anthesis stage, vacuoles enlarge, and nucleus moves to the base of the cell. At post-anthesis stage, the boundaries of the papillae become less noticeable. As proved by Periodic Acid Schiff procedure, the cytoplasm of papillae is rich in insoluble polysaccharides at all stages of development but it becomes remarkable at post-anthesis, particularly at the sub-papillar area. Although there is no significant difference in the content of protein in all stages of the development, it is more abundant at post-anthesis stage, as in Coomassie Brillant Blue stained sections. The surface of papillae is covered by a cuticle which becomes thicker at post-anthesis, and it gives positive reaction with Sudan Black B and Auramine O. The cuticle is covered by a pellicle stained by Coomassie Brillant Blue, indicating dry type of stigma.

Keywords: develeopmental features, histochemistry, stigma, Vibirnum tinus

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Authors: Bhavini Patel, Aslihan Ugun-Klusek, Ellen Billet

Abstract:

The two main contributing factors to familial and idiopathic form of Parkinson’s disease (PD) are oxidative stress and altered proteolysis. Monoamine oxidase-A (MAO-A) plays a significant role in redox homeostasis by producing reactive oxygen species (ROS) via deamination of for example, dopamine. The ROS generated induces chemical modification of proteins resulting in altered biological function. The ubiquitin-proteasome system, which consists of three different types or proteolytic activity, namely “chymotrypsin-like” activity (CLA), “trypsin-like” activity (TLA) and “post acidic-like” activity (PLA), is responsible for the degradation of ubiquitinated proteins. Defects in UPS are known to be strongly correlated to PD. Herein, the effect of ROS generated by MAO-A on proteasome activity and the effects of proteasome inhibition on MAO-A protein levels in WT, mock and MAO-A overexpressed (MAO-A+) SHSY5Y neuroblastoma cell lines were investigated. The data in this study report increased proteolytic activity when MAO-A protein levels are significantly increased, in particular CLA and PLA. Additionally, 20S proteasome inhibition induced a decrease in MAO-A levels in WT and mock cells in comparison to MAO-A+ cells in which 20S proteasome inhibition induced increased MAO-A levels to be further increased at 48 hours of inhibition. This study supports the fact that MAO-A could be a potential pharmaceutical target for neuronal protection as data suggests that endogenous MAO-A levels may be essential for modulating cell death and survival.

Keywords: monoamine oxidase, neurodegeneration, Parkinson's disease, proteasome

Procedia PDF Downloads 98

Authors: Aslihan Caliskan

Abstract:

The term Mediterranean comes from the Latin “mediterraneus” (Medius, "middle" plus Terra, "land, earth"). For the ancient Romans, the Mediterranean was the center of the earth as they knew it. The desire to gain control of the Mediterranean has led to disputes between many nations throughout history, some of which continue to this day. The recent major natural gas discoveries in the Mediterranean have aggravated ongoing tensions in some neighboring countries. The sea border dispute between Turkey and Greece & Greek-Cypriot side is one of the most critical conflicts in the Mediterranean Sea region. This unresolved dispute has many implications for all countries involved, as well as for third parties that have direct or indirect interests in the region. The research question of this context is what are the implications of this controversial sea border problem on the maritime security of Turkey and its military spending. In this paper, the quantitative method is used. Records from the Turkish Defense Ministry, data from the Turkish naval forces have been obtained. In addition, literature research and the United Nations Convention on the Law of the Sea (UNCLOS) application cases were evaluated, and an incident analysis was carried out. This research shows that the sea border dispute issue has a significant impact on the Turkish military both in terms of the structures required to ensure maritime and border security, as well as rising military costs and its macroeconomic implications. The paper begins with a brief overview of relevant principles and methods applied for delimiting th esea borders. The paper continues with a brief description and a background of the sea border dispute between Turkey and Greece & Greek-Cypriot side in the light of the United Nations Convention on the Law of the Sea (UNCLOS). An analysis of the implications of the dispute on Turkey’s maritime security and its military spending is provided in the following chapters. The paper ends with concluding remarks of the author, including suggestions for the way forward.

Keywords: sea border security, mediterranean sea, greece-turkey dispute, limitation of sea, united nations convention on the law of the sea (UNCLOS)

Procedia PDF Downloads 148