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Öğe Design of poly(vinyl pyrrolidone) and poly(ethylene glycol) microneedle arrays for delivering glycosaminoglycan, chondroitin sulfate, and hyaluronic acid(Taylor and Francis Ltd., 2025) Choupani, Andisheh; Temuçin, Elif Şevval; Çiftçi Eda; Bakan, Feray; Çamiç, Büşra Tuğba; Özkoç, Güralp; Sezen, Meltem; Korkusuz, Petek; Korkusuz, Feza; Bediz, BekirOsteoarthritis (OA) is a prevalent joint disorder characterized by cartilage and bone degradation. Medical therapies like glucosaminoglycan (GAG), chondroitin sulfate (CS), and hyaluronic acid (HA) aim to preserve joint function and reduce inflammation but may cause side effects when administered orally or via injection. Microneedle arrays (MNAs) offer a localized drug delivery method that reduces side effects. Thus, this study aims to demonstrate the feasibility of delivering GAG, CS, and HA using microneedles in vitro. An optimal needle geometry is crucial for the successful application of MNA. To address this, here we employ a multi-objective optimization framework using the non-dominated sorting genetic algorithm II (NSGA-II) to determine the ideal MNA design, focusing on preventing needle failure. Then, a three-step fabrication approach is followed to fabricate the MNAs. First, the master (male) molds are fabricated from poly(methyl methacrylate) using mechanical micromachining based on optimized needle geometry. Second, a micro-molding with Polydimethylsiloxane (PDMS) is used for the fabrication of production (female) molds. In the last step, the MNAs were fabricated by microcasting the hydrogels using the production molds. Light microscopy (LIMI) confirms the accuracy of the MNAs manufactured, and in vitro skin insertion tests demonstrate failure-free needle insertion. Subsequently, we confirmed the biocompatibility of MNAs by evaluating their impact on the L929 fibroblast cell line, human chondrocytes, and osteoblasts. © 2024 Informa UK Limited, trading as Taylor & Francis Group.Öğe Effects of ov-poss nanoparticles on the vulcanization kinetics of natural rubber compounds(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2021) Uçtepe, Ebru; Yazıcı, Nazlı; Kodal, Mehmet; Karaağaç, Bağdagül; Özkoç, GüralpPolyhedral oligomeric silsesquioxanes (POSSs) are new-generation additives, which can provide improved properties of polymer matrices due to physical and/or chemical interactions between the polymer molecules and their reactive sites. In the case of rubber-based polymeric systems, POSSs are also able to accompany a vulcanization reaction. This study aimed to investigate the effect of octavinyl functionalized POSS (OV-POSS) on the sulphur vulcanization of a model natural rubber (NR) based compound. The reaction kinetics was studied using various kinetic approaches based on moving die rheometry and differential scanning calorimetry. Rheometric data was evaluated using a common non-linear cure kinetic model, called the Isayev and Deng Model. The Kissinger, Flynn-Wall-Ozawa and Crane Models were used to evaluate the thermal data for curing reactions. All the models were found to be able to analyze the vulcanization kinetics of OV-POSS containing NR-based rubber compounds as well as the effect of the OV-POSS incorporation.Öğe Enhanced crystallinity through melt annealing of thermoplastic polyurethanes(John wiley and sons inc, 2025) Akkoyun, Bahar Durak; Wis, Abdulmounem Alchekh; Yıldırım, Rümeysa; Makal, Ümit; Özkoç, Güralp; Kodal, MehmetThis study evaluated the influence of melt annealing on thermoplastic polyurethane (TPU) synthesized via reactive extrusion, aiming to enhance TPU melt crystallization behavior. The melt annealing process involved reprocessing the polymer in a twin-screw extruder, leveraging a novel approach to manipulating crystallization behavior by optimizing melt annealing conditions to activate microphase separation. Differential scanning calorimetry analysis indicated increased nucleation density and a shift in peak crystallization temperature to higher values during cooling. Phase morphology was examined using scanning electron microscopy, while gel permeation chromatography was utilized to assess molecular weight changes. X-ray diffraction provided insights into TPU microstructural modifications, and mechanical properties were evaluated via tensile tests. Fourier-transform infrared spectroscopy was employed to analyze annealing-induced changes in the hard segment structure and interpolymer bonding. The findings demonstrated that annealing enhances mechanical properties, promotes microphase separation, and increases the energy available for movement and realignment of hard segments, thereby improving TPU's thermal stability. Precise control of annealing temperature was critical to prevent adverse effects on polymer morphology or molecular weight reduction. Annealing at 210 degrees C yielded the highest degree of crystallinity, optimizing mechanical properties and thermal stability.Öğe Improving bonding strength of injection overmolded composites(John Wiley and Sons Inc, 2022) Akpınar, Serkan; Metin, Merve; Koçoğlu, Hürol; Kodal, Mehmet; Sezen, Meltem; Özkoç, Güralp; Altan, M. CengizThe overmolding of short fiber reinforced polymer compounds onto continuous fiber reinforced composite substrates provides design flexibility and the ability to tailor stiffness, strength, and damage tolerance for structural applications. In this work, a novel molding approach that enhances the bonding strength by mechanical interlocking is presented. The effectiveness of the proposed approach was validated by characterization of the bonding strength between a short glass fiber PP (SGFPP) composite overmolded onto a continuous glass fiber reinforced PP (CGFRPP) prepreg. Enhancement of the bonding strength was achieved by judiciously drilling tapered holes on the CGFRPP substrate before molding, which facilitated better interlocking with the injection molded SGFPP composite. The overmolding of preheated composites with tapered holes yielded up to 60% improvement in bonding strength. In general, having multiple holes helped improve bonding up to certain hole diameter. Similarly, preheating of the substrate over a short time improved the interfacial adhesion, while extended preheating resulted in a reduction of bonding quality. SEM analysis of the fracture surfaces after the tensile debonding test revealed that the SGFPP filled the holes on the substrate during overmolding. © 2022 Society of Plastics Engineers.Öğe Lab-scale twin-screw micro-compounders as a new rubber-mixing tool: ‘a comparison on EPDM/carbon black and EPDM/silica composites’(MDPI, 2021) Yazıcı, Nazlı; Kodal, Mehmet; Özkoç, GüralpThe research and development (R&D) in rubber formulation development require reproducible, repeatable, fast, accurate, and efficient sample preparation. The lab-scale formulation development is conventionally carried out using small-scale internal mixers and two-roll mills. However, high torque laboratory twin-screw micro-compounder, which have been serving the plastic industry for more than 30 years, can be used to formulate new rubber compounds for fast and accurate sample preparation that on top can contribute to the economics of R&D. In this study, we investigated the possibility of using lab-scale 15 mL high torque twin-screw micro-compounder as a tool for new rubber compound development. For this purpose, we formulated EPDM/carbon black and EPDM/silica recipes through conventional way using a Banbury mixer followed by a two-roll mill, and through the possible way using a lab-scale 15 mL twin-screw micro-compounder. We crosslinked both systems via hot press at a predefined temperature and time. The rheological and mechanical properties of the compounds were investigated. Moreover, the dispersion of carbon black and silica in the EPDM matrix was judged by DisperGrader and scanning electron microscope (SEM). The conventional way of sample preparation was compared with a possible sample preparation method based on materials’ parameters and ease of operation.Öğe A new approach for the reuse of scrap carbon fiber in high-added value continuous fiber reinforced composite structures(Elsevier Ltd, 2022) Koçoğlu, Hürol; Kodal, Mehmet; Altan, M. Cengiz; Özçelik, Babür; Özkoç, GüralpThis study proposes an innovative processing approach for high-added value hybrid fiber-reinforced composite structures by reusing scrap carbon fiber (CF). Thermoplastic prepregs were produced via wet-laid method using chopped polyamide 6.6 fibers as matrix and short scrap CFs as the reinforcing phase. These prepregs were then hot stacked with woven glass fabrics, forming a novel hybrid lightweight composite laminate. Silane treatment was used to improve the adhesion of glass fabric to the novel wet-laid scrap CF/PA6.6 prepregs. Tensile, flexural, dynamic-mechanical, and morphological properties of the composites were examined to characterize the effectiveness of the hybridization of short scrap CFs and glass fabric. The results showed that short scrap CF in the laminates increased the tensile strength up to 30 % and flexural strength up to 60 %. Moreover, silane surface modification of the glass fabric yielded a 140 % improvement in the flexural strength of scrap CF/PA6.6 prepreg-glass fabric hybrid laminates.Öğe A novel practical approach for monitoring the crosslink density of an ethylene propylene diene monomer compound: Complementary scanning acoustic microscopy and FIB-SEM-EDS analyses(SAGE, 2022) Yazıcı, Nazlı; Opar, Ekin; Kodal, Mehmet; Tanören, Bükem; Sezen, Meltem; Özkoç, GüralpTuning of the crosslink density (CLD) in the rubber compounds is very crucial for optimizing the physical and mechanical properties of the ultimate rubber products. Conventionally, CLD can be measured via rheological methods such as moving die rheometer (MDR), via mechanical tests such as temperature scanning stress relaxation analysis (TSSR), or via direct swelling experiments using Flory–Rehner approach. In the current study, two novel techniques, focused ion beam - scanning electron microscopy (FIB-SEM) processing, with simultaneous energy dispersive X-ray spectrometry (EDS) mapping analysis and scanning acoustic microscopy (SAM) were combined and correlated to conventional methods on a model recipe of ethylene propylene diene monomer (EPDM) compound having different sulphur contents. Depending on the applied technique, the increase in the crosslink density with sulphur content was found to be 1.7 fold for the Flory–Rehner approach and 1.2 fold for both TSSR and MDR. It is directly monitored from the FIB-SEM-EDS analysis that the sulphur distribution and agglomeration behavior increased in line with ZnO content, which is an indirect indication of the rise in crosslink density. The impedance maps of the crosslinked samples obtained through SAM analysis revealed that the impedance of the samples increased with the increasing sulphur content, which can be attributed to higher level of crosslink density. A quantified correlation was obtained between SAM images and the crosslink density of the samples. It was shown that SAM is a promising tool for practical and non-destructive analysis for determining the formation of crosslink density of the rubbers. © The Author(s) 2022.Öğe Reactive compatibilization of PLA/PBS bio-blends via a new generation of hybrid nanoparticles(John Wiley and Sons Ltd, 2022) Ullah, Muhammad Saeed; Yıldırım, Rümeysa; Kodal, Mehmet; Özkoç, GüralpPoly(butylene succinate) (PBS) is a worthy biodegradable thermoplastic polyester for blending along with other biopolymers, especially with poly (lactic acid) (PLA), to overcome its inadequacies in mechanical and thermal characteristics. Since binary blends of PLA and PBS showed that they are incompatible, compatibilization is required. In this work, multi-epoxide polyhedral oligomeric silsesquioxane (Glycidyl POSS) was added to PLA and PBS using the melt blending method to make them compatible. The blends were prepared at different weight ratios having different amounts of compatibilizer. SEM analysis showed that the Glycidyl POSS impacted the interfacial adhesion and other properties of PLA and PBS blends. Noticeable improvements in mechanical properties were revealed by tensile and impact test results. Tensile strength and Young's modulus were improved when epoxy-POSS was added up to 1 and 3 wt% into ternary blends, but further increasing POSS concentrations resulted in lower values. FTIR analysis showed a strong interaction between the epoxide group of POSS and the end groups of PBS or PLA. The thermal properties of samples were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The shifts in glass transition temperatures of the PLA phase towards lower values appeared in DSC, confirming the enhanced compatibility of PLA and PBS. Also, the reinforcing ability of the POSS inorganic core structure impacted the thermal stability of the blends.Öğe A review on polyhedral oligomeric silsesquioxanes as a new multipurpose nanohybrid additive for poly(lactic acid) and poly(lactic acid) hybrid composites(WILEY, 2022) Ullah, Muhammad Saeed; Yazıcı, Nazlı; Wis, Abdulmounem Alchekh; Özkoç, Güralp; Kodal, MehmetAbstract The production of petroleum-based polymers in huge amounts is perilous for our ecosystem and oil reserves. The use of biodegradable polymers instead of synthetic polymers for various commodity, engineering, and biomedical applications remains the overriding concern of the researchers in last decades. Although poly(lactic acid) (PLA) is considered to be the most befitting substitute for conventional petroleum-based products because of its superlative mechanical properties, material & processing cost, and non-toxicity, they have some consequential limitations for various applications because of their slow rate of crystallization, low thermal stability, high brittleness, and low toughness. To overwhelm these deficiencies during the last two decades, researchers have developed various techniques to tailor the properties of PLA, that is, blending with other polymers or using additives such as nanofillers. Among all the nanofillers, for example, carbon nanotubes and organoclays, polyhedral oligomeric silsesquioxanes (POSS) was found the most promising nanofiller because of its organic and inorganic nanostructure and fine dispersion into PLA matrix. This article reviews all the investigations relevant to POSS incorporation into PLA or blends of PLA with other polymers to compare the mechanical, morphological, and physical properties of the ameliorated composites and the neat PLA.
