Browsing by Author "Mallapragada, Surya K."

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Citation - WoS: 16
Citation - Scopus: 17
Crystallization of Poly(vinyl Alcohol) During Solvent Removal: Infrared Characterization and Mathematical Modeling
(John Wiley and Sons Inc., 2007-04) Wong, Sim-Siong; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Crystallization of semicrystalline polymer films during drying has a significant effect on the rate of solvent removal. Understanding and controlling the crystallization kinetics is important in controlling residual solvent levels and drying kinetics. The degree of crystallinity of the poly(vinyl alcohol) films during multicomponent drying was investigated using Fourier transform infrared spectroscopy (FTIR). The 1141 cm-1 band is sensitive to the degree of crystallinity of the polymer and the growth of intensity of this band was monitored as drying progressed. The results from the FTIR studies were comparable to the results obtained from differential scanning calorimetry. Studies were conducted to test the effect of initial solvent composition (water-methanol mixture), drying temperature, and polymer molecular weight on the rate of crystallization and the final crystallinity of the films. An increase in initial methanol composition increased the crystallization rate but did not affect the final degree of crystallinity. An increase in drying temperature and decrease in polymer molecular weight increased the rate of crystallization as well as the final degree of crystallinity. Based on the experimental data, rate constants for crystallization kinetics were extracted from our previously developed model based on free volume theory. The experimental data and the simulation results showed good agreement. The ability of the free volume theory to illustrate the crystallization behavior validated the model and improved its capability.
Citation - WoS: 25
Citation - Scopus: 27
Development 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, Sacide; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Producing 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.
Development of Functional Materials for Sirna Delivery and Neural Tissue Engineering
(AIChE, 2015) Uz, Metin; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The current nonviral siRNA delivery systems in the literature face many problems such as, cellular entry, endosomal escape and efficient siRNA release. Considering this motive, we developed gold nanoparticles (AuNPs) and temperature/pH responsive pentablock copolymer based siRNA delivery systems to address these problems. The temperature and pH responsive cationic and amphiphilic pentablock copolymers, which were consisted of the temperature responsive Pluronic F127 middle block constructed by PEO-PPO-PEO ((poly(ethyleneoxide)-block-poly(propyleneoxide)-block-poly(ethyleneoxide))) blocks contributing cellular entry through temperature responsive micellization and pH responsive cationic PDEAEM (poly(2-diethylaminoethyl methacrylate)) end blocks facilitating nucleic acid condensation and endosomal escape, were used for the first time in the development of polyplex and AuNP based multicomponent siRNA delivery systems (MCSs). The results indicated that systems managed to protect siRNA from external effects, maintain the system stability, facilitate cellular entry and enhance endosomal escape. It was noted that the transfection efficiency of the MCSs, which were boosted by the presence of cleavable disulfide bond, was ~15% higher than the commercial product RNAiMax while the efficacy of polyplexes alone were similar to the RNAiMax.
Citation - WoS: 44
Citation - Scopus: 46
Drying of Semicrystalline Polymers: Mathematical Modeling and Experimental Characterization of Poly(vinyl Alcohol) Films
(Elsevier Ltd., 2004-07) Wong, Sim-Siong; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
A mathematical model was developed to predict the drying mechanism of semicrystalline polymers involving multiple solvents. Since drying of semicrystalline polymers can be accompanied by changes in polymer degree of crystallinity, the model integrates crystallization kinetics and the Vrentas-Duda diffusion model to provide a better understanding of the mechanism. The model considers the effect of external conditions such as temperature, film shrinkage and diffusion and evaporation of multiple solvents during drying. Poly(vinyl alcohol) (PVA)/water/methanol was chosen as a test system. The drying kinetics of PVA films swollen in water and methanol were investigated using gravimetric techniques. The model predicts that higher temperatures, lower film thicknesses and lower methanol to water ratios increase the drying rate. The model predictions were compared with experimental data and showed good agreement.
Citation - WoS: 39
Citation - Scopus: 46
Gelatin-Based 3d Conduits for Transdifferentiation of Mesenchymal Stem Cells Into Schwann Cell-Like Phenotypes
(Elsevier Ltd., 2017-04) Uz, Metin; Büyüköz, Melda; Sharma, Anup D.; Sakaguchi, Donald S.; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
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.
Citation - WoS: 10
Citation - Scopus: 10
Multi-Zone Drying Schemes for Lowering the Residual Solvent Content During Multi-Component Drying of Semicrystalline Polymers
(Taylor and Francis Ltd., 2007-06) Wong, Sim-Siong; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The development of a glassy skin in multicomponent semicrystalline polymer systems limits the diffusion of solvents out of the system and increases residual solvent levels. Based on the results of a mathematical model that we had previously developed, we have proposed a multi-zone drying scheme aimed at lowering the residual solvent levels by taking into account the effect of interactions between the various solvents as predicted by the model. This article focuses on the application of this model to develop optimal drying schemes and to verify the effectiveness of these predictions using experimental techniques. The mathematical model developed previously to study the diffusion of multiple solvents and changes in the crystallinity of semicrystalline polymer systems during drying incorporates many features including Vrentas-Duda diffusion theory, solvent-induced crystallization kinetics, as well as glass transition effects and skinning of the film. The multi-zone drying system was developed by varying the drying temperature in each zone as well as changing the partial pressure of individual solvents during the drying process. The effectiveness of the multi-zone drying schemes predicted by the model was validated experimentally using thermogravimetric methods. The polymer-solvent system chosen was a poly(vinyl alcohol)-water-methanol system. Our experimental data suggested that the multi-zone drying schemes were superior to a single-zone drying system through direct comparison. Further examination of the mathematical model yielded individual solvent profiles and these data reaffirmed our conclusions that a multi-zone drying scheme has the ability to reduce the effect of solvent trapping and thus lower the overall residual solvent content.
Pentablok kopolimer bazlı yeni bir ince film kompozit nanofiltrasyon membranı geliştirilmesi
(2018) Mallapragada, Surya K.; Alsoy Altınkaya, Sacide; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Dıs uyarıcılara tepki veren membranlar, farklı uygulamalarda kirlenmenin önlenmesi ve seçiciligin düzenlenmesi için kullanılmaktadır. Ince film kompozit membranlar genellikle bir uyarıcıya tepki veren monomerin yüzeyde polimerizasyonu veya uyarıcıya tepki veren bir polimerin yüzeye kaplanması ile üretilmektedir. Dıs etkilere duyarlılık, polimerin pH, sıcaklık ve iyonik kuvvet gibi dıs ortamdaki degisiklikler sonucunda kütle transferi ve ara yüzey özelliklerindeki degisikliklerden kaynaklanmaktadır. Bu çalısmada orta blok olarak sıcaklıga duyarlı Pluronik F127 (PEO-b-PPO-b-PEO) ve uç bloklar olarak pH'a cevap veren poli(N, N- (dietilamino) etil metakrilat) (PDEAEM) içeren bir pentablok kopolimer (PBC) yeni bir ince film kompozit (TFC) nanofiltrasyon membranının gelistirilmesi için kullanılmıstır. Kompozit membranın destek katmanı, polisülfon/sülfonlanmıs polietersülfon karısımı ile çözücü olmayan faz ayrımı yöntemi ile hazırlanmıs, PBC elektrostatik etkilesim yoluyla destege tutturulmustur. Yüzeye tutunan PBC zincirlerinin konformasyonu, adsorpsiyon çalısmaları ve X ray photoelektron spektroskopisi (XPS) karakterizasyonu ile tespit edilmistir. PDEAEM blok uzunlugu, kopolimer konsantrasyonu ve adsorpsiyon süresinin adsorbe olan PBC miktarı üzerine olan etkileri arastırılmıstır. Incelenen üç kopolimer numunesi (15, 20 ve 25 kDa) arasında pH ve sıcaklıga karsı en fazla cevabı 25 kDa?lık polimer örnegi verdiginden daha sonraki çalısmalarda bu örnekle hazırlanmıs membranların seçicilik ve kirlenme potansiyelleri belirlenmistir. pH ve sıcaklıgın membranın yapısı ve seçiciligi üzerindeki etkileri, saf su akısı ölçümleri ile nötr bilesiklerin membranlar tarafından itilme düzeylerinden gözenek boyutundaki degisimin belirlenmesi ile incelenmistir. Diger taraftan membranların pH ve sıcaklık duyarlılıgının kirlenme potansiyeli üzerindeki etkileri model kirletici olarak seçilen sıgır serum albumini, aljinat ve E coli ?nin filtrasyonu sonucu akılardaki azalma düzeylerine göre degerlendirilmistir. Membranlar SEM, AFM, temas açısı, XPS ve zeta potansiyeli ölçümleri ile karakterize edilmistir. Bu çalısmada pH ve sıcaklıga duyarlı, yüksek akıya sahip, yeni bir ince film kompozit nanofiltrasyon membranı üretilebilecegi gösterilmistir.
Citation - WoS: 17
Citation - Scopus: 22
Responsive pentablock copolymers for siRNA delivery
(Royal Society of Chemistry, 2015) Uz, Metin; Mallapragada, Surya K.; Alsoy Altınkaya, Sacide; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
In this study, temperature and pH responsive cationic and amphiphilic pentablock copolymers, which consist of the temperature responsive triblock Pluronic F127 sandwiched between pH responsive PDEAEM (poly(2-diethylaminoethyl methacrylate)) end blocks, were used for the first time in the development of polyplex and gold nanoparticle (AuNP) based multicomponent siRNA delivery systems (MCSs). Copolymers in both systems protected siRNA from external effects, provided cell entry and endosomal escape. The thermoreversible micellization of the hydrophobic PPO block facilitated the cellular entry while the PDEAEM blocks enhanced the endosomal escape through protonated tertiary amine groups by pH buffering. The synergistic advantages of the different blocks showed an enhanced effect in the MCSs due to attachment and surface configuration reasons. The siRNA transfection efficiency of MCSs against luciferase expressing SKOV3 cells was 15% higher than both the polyplexes alone and the commercial siRNA transfection agent Lipofectamine RNAiMax at the same applied dose, without any toxicity. The results indicated that the multicomponent systems based on the responsive cationic pentablock copolymers and gold nanoparticles have promising potential as an efficient siRNA delivery vector for future applications.
Citation - WoS: 12
Citation - Scopus: 17
Stimuli Responsive Polymer-Based Strategies for Polynucleotide Delivery
(Cambridge University Press, 2017-08) Uz, Metin; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
In recent years, stimuli responsive polymer based gene delivery vehicle design for cancer treatment and treatment of other genetic disorders has received extensive attention. Early studies focusing on DNA delivery have been facilitated by functional polymers and this area has seen further growth spurred by recent gene silencing strategies developed for small RNA [i.e., small interfering RNA (siRNA) or micro RNA (miRNA)] delivery. DNA and small RNAs possess analogous properties; however, their explicit differences define the specific challenges associated with the delivery route and the design of functional materials to overcome distinct challenges. Apart from classical gene delivery, the recent advances in genome editing have revealed the necessity of new delivery devices for genome editing tools. A system involving CRISPR (clustered, regularly interspaced, short palindromic repeats) and an endonuclease CRISPR-associated protein 9 (Cas9) coupled with a short, single-guide RNA (sgRNA) has emerged as a promising tool for genome editing along with functional delivery systems. For all these nucleic acid based treatments, the internal or external physiochemical changes in the biological tissue/cells play a major role in the design of stimuli responsive delivery materials for both in vitro and in vivo applications. This review emphasizes the recent advances in the use of pH, temperature, and redox potential-responsive polymers overcoming hurdles for delivery of gene and gene editing tools for both in vitro and in vivo applications. Specifically the chapter focuses on recently proposed delivery strategies, types of delivery systems, and polymer synthesis/modification methods. The recent advances in CRISPR/Cas9-sgRNA technology and delivery are also described in a separate section. The review ends with current clinical trials, concluding remarks, and future perspectives.
Citation - WoS: 26
Citation - Scopus: 27
Understanding the Effect of Skin Formation on the Removal of Solvents From Semicrystalline Polymers
(John Wiley and Sons Inc., 2005-11) Wong, Sim-Siong; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The effect of glassy skin formation on the drying of semicrystalline polymers was investigated with a comprehensive mathematical model developed for multicomponent systems. Polymers with high glass-transition temperatures can become rubbery at room temperature under the influence of solvents. As the solvents are removed from the polymer, a glassy skin can form and continue to develop. The model takes into account the effects of diffusion-induced polymer crystallization as well as glassy-rubbery transitions on the overall solvent content and polymer crystallinity. A Vrentas-Duda free-volume-based diffusion scheme and crystallization kinetics were used in our model. The polymer-solvent system chosen was a poly(vinyl alcohol) (PVA)-water-methanol system. The drying kinetics of PVA films were obtained by gravimetric methods with swollen films with known water/methanol concentrations. The overall drying behaviors of the polymer system determined by our model and experimental methods were compared and found to match well.