Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Cryofixation Strategy for Fabrication of Robust Gelatin-Polyester Conductive Biocomposites(Taylor & Francis Inc, 2026) Koksal, Busra; Onder, Ahmet; Yildiz, Umit HakanThe development of mechanically robust and electroconductive biomaterials is critical for advancing tissue engineering strategies, particularly in neural, cardiac and musculoskeletal applications. Here, we report a polycaprolactone (PCL)-gelatin conductive polymer (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, PEDOT:PSS) biocomposite with tunable mechanical and electrical properties, fabricated via the cryofixation process relying on rapid reaction between isocyanate-terminated PCL, gelatin and PEDOT:PSS. Two isocyanate sources, hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) were employed to obtain reactive end-functionalized PCLHDI and PCLIPDI. The cryofixation (at -18 degrees C) of PCLHDI or PCLIPDI, gelatin and PEDOT:PSS was found to occur in unfrozen microdomains and enabled the resultant gel with an inherited network of ice, thereby increasing porosity. Electroconductivity was introduced via the incorporation of PEDOT:PSS, yielding conductive cryogels with porous morphology. The resulting scaffolds exhibited a Young's modulus of 637 Pa and electrical conductivity of 197 mu S/cm, alongside biocompatible nature of gelatin-based gels. This multifunctional platform offers significant promise for the engineering of electrically active tissues.Article Synthetic Memory: A Key Link Between Biocatalytically Synthesized Polyesters and Melt Electrowriting Performance(Taylor & Francis inc, 2025) Dinckal, Sanem; Yildiz, Umit HakanThe biocatalytic synthesis of polycaprolactone (PCL) and its copolymers has garnered significant attention due to their reduced toxicity and enhanced 3D processability compared to metal-catalyzed alternatives. The objective of this study is to employ biocatalysts-citric acid (CA), glycolic acid (GA) and salicylic acid (SAA)-and explore their catalytic effects on the synthesis of poly(epsilon-caprolactone) (PCL) and poly(epsilon-caprolactone)-b-poly(delta-valerolactone) (PCL-b-PVL) block copolymers. Additionally, we aimed to examine the link between synthetic memory of resultant PCL and PCL-b-PVL polymers and their melt electrowriting performance. Nuclear magnetic resonance analysis confirms successful synthesis of copolymers by monitoring signals of hydrogens at 2.30 ppm. Differential scanning calorimetry results reveal shifts in thermal properties of copolymers upon varying biocatalysts CA-, SAA- and GA-catalyzed copolymers exhibit Tm values between similar to 52 and 54 degrees C. Melt electrowriting (MEW) results demonstrate that catalyst selection plays significant role in fiber morphology and scaffold architecture, with GA- and CA-catalyzed copolymers exhibiting finer fibers (5-8 mu m), while SAA led to thicker fibers (similar to 12 mu m) and reduced spacing. Moreover, precipitation solvents MeOH and acetonitrile (ACN) affect fidelity, with ACN-prepared scaffolds exhibiting more uniform fiber diameters. Atomic force microscopy imaging of electrowritten scaffolds made of ACN- and MeOH-precipitated PCL-b-PVL both exhibit large (>15 mu m) and smaller (<10 mu m) spherulitic structure as major topological features. These findings confirm that the synthetic memory of polyesters-governed by catalyst choice and processing conditions-directly influences their printability, making them promising candidates for MEW-based biomedical scaffolds in tissue engineering, where fine fiber morphology and architectural fidelity are essential for cell attachment and tissue regeneration.Article Integration of Conductive Additives To Pla-Based Biodegradable Composite Films To Improve Their Electrical, Mechanical, and Physical Characteristics(Wiley, 2025) Rakea, Aisha Muthana; Tirkes, Suha; Yildiz, Umit Hakan; Tirkes, Seha; Tayfun, UmitIn this study, Oltu stone powder (OS) and Fe3O4/mica-based conductive pigment (CP) were compounded with polylactic acid (PLA) to develop bio-based conductive films. Four different concentrations of 1%, 10%, 20%, and 30% of powders were applied to determine their optimal concentration in the PLA matrix. The mechanical, thermomechanical, electrical conductivity, melt-flow, and morphological properties of composite films were reported using the tensile, hardness, and impact tests, dynamic mechanical analyses test, linear four-probe method, and atomic force microscopy (AFM), melt-flow index measurements, and scanning electron microscopy methodology, respectively. According to tensile test results, tensile strength and modulus characteristics of PLA decrease with additive integration. However, the elongation value of PLA declined as OS and CP loadings increased. The maximum tensile performance was attained for composites filled with 20% of both CP and OS. The unfilled PLA's Shore D value rose by including OS and CP. At the same loading levels, carbon-based OS produced comparatively higher hardness values than CP, which comprised iron oxide and alumina silicate. AFM analysis revealed that both CP and OS inclusions caused enhancements in surface roughness as their filling amounts increased. In summary, composite samples exhibiting a 20% loading ratio of both OS and CP showed significantly improved mechanical and thermomechanical performances compared to other composites. Composite films with 1% additives have the potential to be applied in electrostatic packing. Additionally, 3D-printed components can be fabricated using composites for applications where appropriate mechanical resistance and electrical conductivity specifications are required.Article Citation - WoS: 3Citation - Scopus: 3Performance Improvement of Carbon Fiber-Reinforced Abs Composites by Introducing Fullerene Nanoparticles(Wiley, 2025) Akar, Alinda Oyku; Yildiz, Umit Hakan; Tirkes, Seha; Tayfun, Umit; Hacivelioglu, FerdaRecently, polymer composites have been extensively researched in industrial fields such as electrical conductance, ohmic heating, electromagnetic shielding and electrostatic discharge, particularly in engineering polymers reinforced with carbonaceous additions. Herein, fullerene (C60) and short carbon fiber (CF) were incorporated with acrylonitrile-butadiene-styrene copolymer (ABS) using melt-compounding followed by an injection-molding process. Composite samples were produced with contents of 20 wt% of CF besides 0.1, 0.5 and 1.0 wt% of C60. Tensile, impact, hardness and wear tests, conductive atomic force microscopy, dynamic mechanical analysis, thermogravimetric analysis, melt flow index tests and scanning electron microscopy (SEM) were performed to characterize mechanical, electrical, thermomechanical, thermal, melt-flow and structural behaviors of ABS-based composites involving CF and C60. Based on the mechanical test findings obtained for the developed composites, comprising tensile and impact test results, C60 additions contributed to a significant rise in tensile strength and impact resistance of CF-reinforced ABS composites, with a 20% increase in tensile resistance being achieved by introduction C60 into the ABS/CF structure. C60 addition enhanced efficiency by 50% in terms of tensile modulus. Electrical conductivity measurements confirmed that C60 nanoparticles and CF exhibited a synergy. The optimum synergistic ratio of C60/CF was obtained as 0.5/20. The conductive path in the ABS/CF composite system was established by incorporating C60 with different loading amounts. SEM micrographs of composites demonstrated that C60 nanoparticles were dispersed homogeneously into the ABS matrix involving lower amounts of C60. (c) 2025 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.Article Free-Standing Three-Dimensional Graphene Scaffolds for Protease Functional Assay(Elsevier Science Sa, 2024) Ng, Zhi Kai; Yan, Evelias; Goyal, Garima; Gudlur, Sushanth; Kanagavel, Deepankumar; Yildiz, Umit Hakan; Teo, Edwin Hang TongThree-dimensional graphene scaffolds (3d-GS) of high porosity possessing good fluorescence quenching properties are potential candidates for the development of optical biosensors. Herein, we demonstrate the feasibility of utilising intact and free-standing 3d-GS for sensitive detection of proteases, a class of disease diagnosis bio-markers of significant interest. Recombinant OmpT was employed as a model protease for validating the pro-posed methodology. A short (15-residue) peptide sequence encoding a specific recognition site for OmpT was end-labelled with a fluorescent dye (5-FAM) whose fluorescence is quenched when the peptide is anchored to 3d-GS. However, in the presence of OmpT, the peptide is cleaved and released from 3d-GS, resulting in a sig-nificant recovery in fluorescence. The functional assay described herein involves a single step fabrication process of anchoring the peptide to 3d-GS. The integrity of the 3d-GS is hypothesised to overcome the concern of dynamic requenching associated with the typical homogeneous assays based on graphene, yielding a limit of detection (LOD) of similar to 140 nM, which is over an order higher than homogeneous assays performed using the same composition of graphene in powdered form. To the best of our knowledge, this is the first report on utilising free-standing 3d-GS for facile assaying of proteases.Conference Object Düşük Sükroz Derişimlerinin Görünür Bölge Spektroskopisi ve Yapay Sinir Aǧları ile Kestirimi(IEEE, 2017) Mezgil, Bahadir; Erdogan, Duygu; Alduran, Yesim; Yildiz, Umit Hakan; Yildiz, Ahu Arslan; Bastanlar, YahnLow sucrose concentrations in solutions is estimated by means of localized surface plasmon resonance of immobilized gold nanoparticles. The ultraviolet-visible spectra (UV-Vis) of samples with different sucrose concentrations were prepared and used to train artificial neural networks. In our study, MATLAB Neural Networks Toolbox was used and effect of different input sizes and network structures on the estimation accuracy is investigated. It is observed that using complete spectrum instead of peak point results in higher accuracy.