Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 12Citation - Scopus: 12Biofouling-Resistant Ultrafiltration Membranes Via Codeposition of Dopamine and Cetyltrimethylammonium Bromide With Retained Size Selectivity and Water Flux(American Chemical Society, 2022) Cihanoğlu, Aydın; Schiffman, Jessica D.; Alsoy Altınkaya, SacideBiofouling is a serious problem in ultrafiltration (UF) membrane applications. Modifying the surface of membranes with low molecular weight, commercially available antibacterial chemistries is an excellent strategy to mitigate biofouling. Herein, we report a new strategy to impart antibacterial and anti-biofouling behavior without changing the support membrane’s size selectivity and pure water permeance (PWP). To this end, a strong antibacterial agent, cetyltrimethylammonium bromide (CTAB), was codeposited with dopamine onto commercial polyethersulfone (PES) UF membranes in the presence of nitrogen (N2) gas backflow. The PWP and pore size of the support membrane did not change with codeposition, confirming the benefit of N2 backflow in mitigating the solution intrusion phenomenon. X-ray photoelectron spectroscopy (XPS), surface ζ potentials, and contact angle measurements confirmed the successful codeposition of polydopamine (PDA) and CTAB onto the membrane. Among three different CTAB concentrations systematically investigated, the membrane functionalized with CTAB at the critical micelle concentration (CMC) provided the best anti-biofouling activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and retained its surface ζ potential after being stored in 1 M NaCl (pH = 6.8) for 3 months. Our results demonstrate the potential of using a facile, one-step approach to modify commercial UF membranes without compromising their pore size or flux, while simultaneously endowing antibacterial activity.Article Citation - WoS: 16Citation - Scopus: 15Ultrasound-Assisted Dopamine Polymerization: Rapid and Oxidizing Agent-Free Polydopamine Coatings on Membrane Surfaces(Royal Society of Chemistry, 2021) Cihanoğlu, Aydın; Schiffman, Jessica D.; Alsoy Altınkaya, SacideHerein, we report a controllable pathway to accelerate the polymerization kinetics of dopamine using ultrasound as a trigger. The use of ultrasound was demonstrated to dramatically accelerate the slow liquid phase reaction kinetics and increase the deposition rate of the polydopamine coating on the surface of polymeric membranes.Article Citation - WoS: 28Citation - Scopus: 29Development of a High-Flux Thin-Film Composite Nanofiltration Membrane With Sub-Nanometer Selectivity Using a Ph and Temperature-Responsive Pentablock Co-Polymer(American Chemical Society, 2019) Bar, Canbike; Çağlar, Nagahan; Uz, Metin; Mallapragada, Surya K.; Alsoy Altınkaya, SacideProducing block co-polymer-based nanofiltration (NF) membranes with sharp molecular weight cutoffs via an efficient method exhibiting persistent size-based separation quality is challenging. In this study, this challenge was addressed by reporting a facile approach to fabricate pentablock co-polymer (PBC)-based thin-film composite (TFC) NF membranes. The PBC, consisting of temperature-responsive Pluronic F127 (PEO-b-PPO-b-PEO) middle blocks and pH-responsive poly(N,N-(diethylamino)ethyl methacrylate) end blocks, were synthesized by atom-transfer radical polymerization. This polymer was then attached electrostatically to the surface of polysulfone/sulfonated polyether-sulfone support membranes fabricated using a non-solvent-induced phase separation technique. The conformational changes of the PBC chains in response to pH and temperature determined the, pure water flux and neutral solute (PEG 1000) rejection performance of TFC membranes. Permeability of the membranes increased from 13.0 +/- 0.63 to 15.9 +/- 0.06 L/m(2).h bar and from 6.7 +/- 0.00 to 13.9 +/- 0.07 L/m(2).h.bar by changing the solution pH from 4 to 8.5 and temperature from 4 to 25 degrees C, respectively. The pH- and temperature-responsive conformational changes did not affect the PEG 1000 rejection and membrane pore radius, which remained constant at similar to 89% and similar to 0.9 nm, respectively. This important finding was attributed to the high grafting density of co-polymer chains, resulting in spatial limitations among the grafted chains. The pore size of similar to 0.9 nm achieved with the proposed membrane design is the smallest size reported so far for membranes fabricated from block copolymers. TFC membranes demonstrated high stability and maintained their flux and rejection values under both static (storage in an acidic solution for up to 1 month) and dynamic (filtering PEG 1000 solution over 1 week) conditions. Pentablock copolymers enable a NF membrane with a sharp molecular weight cutoff suitable for size-selective separations. The membrane fabrication technique proposed in this study is a scalable and promising alternative that does not involve complex synthetic routes.Article Citation - WoS: 34Citation - Scopus: 35Development of High Flux Nanofiltration Membranes Through Single Bilayer Polyethyleneimine/Alginate Deposition(Elsevier Ltd., 2019) Tekinalp, Önder; Alsoy Altınkaya, SacideThe aim of this study is to prepare high flux, stable, antifouling nanofiltration membranes through single bilayer polyelectrolyte deposition. To this end, a tight ultrafiltration support membrane was prepared from a polysulfone/sulfonated polyethersulfone blend. Deposition of a polyethyleneimine and alginate pair on this support has reduced the molecular weight cut off from 6 kDa to below 1 kDa. The pure water permeability and polyethylene glycol 1000 rejection of the coated membrane were found to be 15.5 ± 0.3 L/m2·h·bar and 90 ± 0.6%, respectively, by setting the deposition pH for each layer to 8 and the ionic strengths to 0.5 M and 0 M. This membrane has exhibited significantly higher permeability than commercial membranes with the same molecular weight cut off, retaining 98% of the initial flux during 15 h filtration of bovine serum albumine. In addition, the membrane has been able to completely remove anionic dyes from aqueous solution by showing 99.9% retentions to Reactive red 141, Brilliant blue G and Congo red with a 2 bar transmembrane pressure. High flux and membrane stability in acidic and salty environments have been achieved when deposition conditions favor high adsorption levels for the first layer and strong ionic cross-linking between the carboxyl group on the alginate and the amine groups on the polyethyleneimineArticle Citation - WoS: 27Citation - Scopus: 37Nanofibrous Gelatine Scaffolds Integrated With Nerve Growth Factor-Loaded Alginate Microspheres for Brain Tissue Engineering(John Wiley and Sons Inc., 2018) Büyüköz, Melda; Erdal, Esra; Alsoy Altınkaya, SacideNeural regeneration research is designed in part to develop strategies for therapy after nerve damage due to injury or disease. In this study, a new gelatine-based biomimetic scaffold was fabricated for brain tissue engineering applications. A technique combining thermally induced phase separation and porogen leaching was used to create interconnected macropores and nanofibrous structure. To promote tissue regeneration processes, the scaffolds were integrated with nerve growth factor (NGF)-loaded alginate microspheres. The results showed that nanofibrous matrix could only be obtained when gelatine concentration was at least 7.5% (w/v). The scaffold with a modulus value (1.2 kPa) similar to that of brain tissue (0.5–1 kPa) was obtained by optimizing the heat treatment time, macropore size and gelatine concentration. The encapsulation efficiencies of NGF into 0.1% and 1% alginate microspheres were 85% and 100%, respectively. The release rate of NGF from the microspheres was controlled by the alginate concentration and the poly(L-lysine) coating. The immobilization of the microspheres in the scaffold reduced burst release and significantly extended the release period. The nanofibrous architecture and controlled release of NGF from the microspheres induced neurite extension of PC12 cells, demonstrating that the released NGF was in an active form. The results suggest that the scaffolds prepared in this study may have potential applications in brain tissue engineering due to topologic and mechanical properties similar to brain tissue and pore structure suitable for cell growth and differentiation.Article Citation - WoS: 40Citation - Scopus: 47Gelatin-Based 3d Conduits for Transdifferentiation of Mesenchymal Stem Cells Into Schwann Cell-Like Phenotypes(Elsevier Ltd., 2017) Uz, Metin; Büyüköz, Melda; Sharma, Anup D.; Sakaguchi, Donald S.; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.In this study, gelatin-based 3D conduits with three different microstructures (nanofibrous, macroporous and ladder-like) were fabricated for the first time via combined molding and thermally induced phase separation (TIPS) technique for peripheral nerve regeneration. The effects of conduit microstructure and mechanical properties on the transdifferentiation of bone marrow-derived mesenchymal stem cells (MSCs) into Schwann cell (SC) like phenotypes were examined to help facilitate neuroregeneration and understand material-cell interfaces. Results indicated that 3D macroporous and ladder-like structures enhanced MSC attachment, proliferation and spreading, creating interconnected cellular networks with large numbers of viable cells compared to nanofibrous and 2D-tissue culture plate counterparts. 3D-ladder-like conduit structure with complex modulus of ∼0.4 × 106 Pa and pore size of ∼150 μm provided the most favorable microenvironment for MSC transdifferentiation leading to ∼85% immunolabeling of all SC markers. On the other hand, the macroporous conduits with complex modulus of ∼4 × 106 Pa and pore size of ∼100 μm showed slightly lower (∼65% for p75, ∼75% for S100 and ∼85% for S100β markers) immunolabeling. Transdifferentiated MSCs within 3D-ladder-like conduits secreted significant amounts (∼2.5 pg/mL NGF and ∼0.7 pg/mL GDNF per cell) of neurotrophic factors, while MSCs in macroporous conduits released slightly lower (∼1.5 pg/mL NGF and 0.7 pg/mL GDNF per cell) levels. PC12 cells displayed enhanced neurite outgrowth in media conditioned by conduits with transdifferentiated MSCs. Overall, conduits with macroporous and ladder-like 3D structures are promising platforms in transdifferentiation of MSCs for neuroregeneration and should be further tested in vivo. Statement of Significance This manuscript focuses on the effect of microstructure and mechanical properties of gelatin-based 3D conduits on the transdifferentiation of mesenchymal stem cells to Schwann cell-like phenotypes. This work builds on our recently accepted manuscript in Acta Biomaterialia focused on multifunctional 2D films, and focuses on 3D microstructured conduits designed to overcome limitations of current strategies to facilitate peripheral nerve regeneration. The comparison between conduits fabricated with nanofibrous, macroporous and ladder-like microstructures showed that the ladder-like conduits showed the most favorable environment for MSC transdifferentiation to Schwann-cell like phenotypes, as seen by both immunolabeling as well as secretion of neurotrophic factors. This work demonstrates the importance of controlling the 3D microstructure to facilitate tissue engineering strategies involving stem cells that can serve as promising approaches for peripheral nerve regeneration.Article Citation - WoS: 65Citation - Scopus: 72Effect of Peg Grafting Density and Hydrodynamic Volume on Gold Nanoparticle-Cell Interactions: an Investigation on Cell Cycle, Apoptosis, and Dna Damage(American Chemical Society, 2016) Uz, Metin; Bulmuş, Volga; Alsoy Altınkaya, SacideIn this study, interactions of polyethylene glycol (PEG)-coated gold nanoparticles (AuNPs) with cells were investigated with particular focus on the relationship between the PEG layer properties (conformation, grafting density, and hydrodynamic volume) and cell cycle arrest, apoptosis, and DNA damage. Steric hindrance and PEG hydrodynamic volume controlled the protein adsorption, whereas the AuNP core size and PEG hydrodynamic volume were primary factors for cell uptake and viability. At all PEG grafting densities, the particles caused significant cell cycle arrest and DNA damage against CaCo2 and PC3 cells without apoptosis. However, at a particular PEG grafting density (∼0.65 chains/nm2), none of these severe damages were observed on 3T3 cells indicating discriminating behavior of the healthy (3T3) and cancer (PC3 and CaCo2) cells. It was concluded that the PEG grafting density and hydrodynamic volume, tuned with the PEG concentration and AuNP size, played an important role in particle-cell interactions.Article Citation - WoS: 29Citation - Scopus: 33Surface Modification of Polysulfone Based Hemodialysis Membranes With Layer by Layer Self Assembly of Polyethyleneimine/Alginate-heparin: a Simple Polyelectrolyte Blend Approach for Heparin Immobilization(Springer Verlag, 2013) Yaşar Mahlıçlı, Filiz; Alsoy Altınkaya, SacideThis study intends to improve blood compatibility of polysulfone (PSF) membranes by generating a nonthrombogenic surface through heparin immobilization. To achieve this task, the support membrane prepared from a blend of PSF and sulfonated polysulfone (SPSF) was modified with layer by layer (LBL) deposition of polyethyleneimine (PEI) and alginate (ALG) and heparin blended with ALG was immobilized only on the outermost surface of the LBL assembly. The results have shown that the adsorption of human plasma proteins and platelet activation on the LBL modified membranes decreased significantly compared with the unmodified PSF and PSF-SPSF blend membranes. Furthermore, blending ALG with a small amount of heparin remarkably prolonged the APTT values of heparin free PEI/ALG coated membranes. It is envisaged that the use of a blend of HEP and ALG only in the terminating layer of the LBL assembly can be an economical and alternative modification technique to create nonthrombogenic surfaces.Article Citation - WoS: 9Citation - Scopus: 11Modeling of Hemodialysis Operation(Springer Verlag, 2010) Abacı, Hasan Erbil; Alsoy Altınkaya, SacideIn this study, a theoretical model was developed to predict the solute concentrations in patients' blood and optimize the efficiency of the hemodialysis operation. The model takes into account simultaneous mass and momentum transfer on the blood side both in radial and axial directions. A key component of the model is the incorporation of the protein adsorption on the inner surface of the membrane. The validity of the model was confirmed with the experimental data available in the literature for two different types of hemodiafilter. To illustrate the importance of including the radial concentration gradients and protein adsorption kinetics in the model, the experimental data were predicted with and without consideration of these effects. The results have shown that assuming uniform concentration in the radial direction or neglecting protein adsorption on the inner surface of the membrane leads to higher error in predicting the experimental data. In addition, significant error can be introduced in the calculation of the dialysis time if protein adsorption is not considered. © 2010 Biomedical Engineering Society.Article Citation - WoS: 8Citation - Scopus: 8The Effects of Urease Immobilization on the Transport Characteristics and Protein Adsorption Capacity of Cellulose Acetate Based Hemodialysis Membranes(Springer Verlag, 2009) Yaşar Mahlıçlı, Filiz; Alsoy Altınkaya, SacideIn this study, cellulose acetate (CA) based hemodialysis membranes were prepared by a dry phase inversion method and the influences of urease immobilization on the clearing performance and protein adsorption capacity of the membranes were investigated. Permeation experiments have shown that modification of CA membranes with urease immobilization not only enhanced the transport rate of urea but also increased the permeation coefficients of uric acid and creatinine by changing the structure of the membrane. Furthermore, the protein adsorption capacity of the CA membranes decreased. On the other hand, the mechanical strength of the modified CA membrane did not change significantly compared with that of the unmodified one. A mathematical model was derived to determine the rate of mass transfer of urea through modified CA membranes. Model predictions along with the experimental data suggest that urease immobilization can be used as an alternative method in preparing CA based hemodialysis membranes with improved transport characteristics and biocompatibility through reduced protein adsorption capacities.