Polymers

2529 KiB

Open AccessArticle

Strong Screening Effect of Polyhedral Oligomeric Silsesquioxanes (POSS) Nanoparticles on Hydrogen Bonded Polymer Blends

by Chin-Wei Chiou, Yung-Chih Lin, Lei Wang, Chiharu Hirano, Yoshinori Suzuki, Teruaki Hayakawa and Shiao-Wei Kuo

Polymers 2014, 6(3), 926-948; https://doi.org/10.3390/polym6030926 - 21 Mar 2014

Cited by 29 | Viewed by 11362

Abstract

In this study we used anionic living polymerization to prepare two different homopolymers: a poly(methyl methacrylate) (PMMA) and a PMMA derivative presenting polyhedral oligomeric silsesquioxane (PMA-POSS) units as its side chains. We then employed differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, [...] Read more.

In this study we used anionic living polymerization to prepare two different homopolymers: a poly(methyl methacrylate) (PMMA) and a PMMA derivative presenting polyhedral oligomeric silsesquioxane (PMA-POSS) units as its side chains. We then employed differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD) to investigate the miscibility and specific interactions of PMMA and PMA-POSS with three hydrogen bonding donor compounds: poly(vinyl phenol) (PVPh), phenolic resin, and bisphenol A (BPA). DSC revealed that all of the PVPh/PMMA, phenolic/PMMA, and BPA/PMMA blends exhibited a single glass transition temperature, characteristic of miscible systems; FTIR spectroscopic analyses revealed that such miscibility resulted from hydrogen bonding interactions between the C=O groups of PMMA and the OH groups of these three hydrogen bonding donor compounds. In contrast, all of the PVPh/PMA-POSS, phenolic/PMA-POSS, and BPA/PMA-POSS blends were immiscible: DSC revealed two glass transition temperatures arising from strong screening effects (FTIR spectroscopy) and high degrees of aggregation (WAXD) of the POSS nanoparticles. We propose that the value of the intramolecular screening effect (γ) should be very close to 1 for all PMA-POSS blend systems when POSS nanoparticles appear as the side chains of PMMA, such that the OH groups of the hydrogen bonding donor compounds cannot interact with the C=O groups of PMA-POSS. Full article

(This article belongs to the Special Issue Polymer Blends)

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1274 KiB

Open AccessArticle

Voltage Effect in Holograms of Polyvinyl Alcohol with FeCl₃

by Arturo Olivares-Pérez, Mary Paz Hernández-Garay, Santa Toxqui-López, Israel Fuentes-Tapia and Manuel Jorge Ordóez-Padilla

Polymers 2014, 6(3), 899-925; https://doi.org/10.3390/polym6030899 - 21 Mar 2014

Cited by 2 | Viewed by 8546

Abstract

We show experimentally that the metallic salt, FeCl₃, at different concentrations, provides photosensitivity and conductivity characteristics with poly(vinyl alcohol) material. The holographic recording in this photosensitive material was made in real time. The effect of applied voltage on holographic diffraction gratings [...] Read more.

We show experimentally that the metallic salt, FeCl₃, at different concentrations, provides photosensitivity and conductivity characteristics with poly(vinyl alcohol) material. The holographic recording in this photosensitive material was made in real time. The effect of applied voltage on holographic diffraction gratings in the recording process and the changes in their diffraction efficiency, depending on their composition, are shown. In addition, we describe the photo-mechanism, physicochemical processes, and water condensations involved in changes of the formation of images due to applied voltage. The results suggest that polymers doped with metallic salts may have potential as inexpensive photosensitive materials that are easy to work under normal laboratory condition. Full article

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264 KiB

Open AccessArticle

Preparation of Poly(acrylic acid) Hydrogel by Radiation Crosslinking and Its Application for Mucoadhesives

by Young-Chang Nho, Jong-Seok Park and Youn-Mook Lim

Polymers 2014, 6(3), 890-898; https://doi.org/10.3390/polym6030890 - 19 Mar 2014

Cited by 78 | Viewed by 12361

Abstract

A mucoadhesive drug delivery system can improve the effectiveness of a drug by maintaining the drug concentration and allowing targeting and localization of the drug at a specific site. Acrylic-based hydrogels have been used extensively as a mucoadhesive system owing to their flexibility [...] Read more.

A mucoadhesive drug delivery system can improve the effectiveness of a drug by maintaining the drug concentration and allowing targeting and localization of the drug at a specific site. Acrylic-based hydrogels have been used extensively as a mucoadhesive system owing to their flexibility and excellent bioadhesion. In this experiment, poly(acrylic acid) was selected to prepare the bioadhesive hydrogel adhering to mucosal surfaces using a radiation process. Poly(acrylic acid) was dissolved in water to a prepare poly(acrylic acid) solution, and the solution was then irradiated by an electron beam at up to 75 kGy to make hydrogels. Their physical properties, such as gel percent, swelling percent and adhesive strength to mucosal surfaces, were investigated. Triamcinolone acetonide was used as a model drug. The dried poly(acrylic acid) film was dipped in a 0.1 wt% triamcinolone acetonide solution in ethanol, and then dried at 25 °C. The release of triamcinolone acetonide was determined at different time intervals, and UV (Ultraviolet)-Vis spectroscopy was used to determine the released concentration of triamcinolone acetonide at 238 nm. It was shown that poly(acrylic acid)-based drug carriers were successfully prepared for use in a bioadhesive drug delivery system. Full article

(This article belongs to the Special Issue Polymers for Drug Delivery)

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970 KiB

Open AccessArticle

Behavior of FRP Bars-Reinforced Concrete Slabs under Temperature and Sustained Load Effects

by Hizia Bellakehal, Ali Zaidi, Radhouane Masmoudi and Mohamed Bouhicha

Polymers 2014, 6(3), 873-889; https://doi.org/10.3390/polym6030873 - 18 Mar 2014

Cited by 24 | Viewed by 7456

Abstract

The large temperature variation has a harmful effect on concrete structures reinforced with fiber reinforced polymer (FRP) bars. This is due to the significant difference between transverse coefficient of thermal expansion of these bars and that of the hardened concrete. This difference generates [...] Read more.

The large temperature variation has a harmful effect on concrete structures reinforced with fiber reinforced polymer (FRP) bars. This is due to the significant difference between transverse coefficient of thermal expansion of these bars and that of the hardened concrete. This difference generates a radial pressure at the FRP bar/concrete interface, and may cause splitting cracks within concrete. This paper presents results of an experimental and analytical study carried out on FRP-reinforced concrete slabs subjected, simultaneously, to thermal and mechanical loads. The analytical model based on the theory of linear elasticity consists to evaluate combined effects of thermal and mechanical loads on the transverse expansion of FRP bars. Parameters studied in this investigation are the concrete cover thickness, FRP bar diameter, and the temperature variation. The thermal cycles were varied from −30 to +60 °C. Comparisons between analytical and experimental results show that transverse strains predicted from the proposed model are in good correlation with experimental results. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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879 KiB

Open AccessArticle

Living Radical Polymerization via Organic Superbase Catalysis

by Lin Lei, Miho Tanishima, Atsushi Goto and Hironori Kaji

Polymers 2014, 6(3), 860-872; https://doi.org/10.3390/polym6030860 - 17 Mar 2014

Cited by 34 | Viewed by 8653

Abstract

Organic superbases reacted with alkyl iodides (R–I) to reversibly generate the corresponding alkyl radicals (R^•). Via this reaction, organic superbases were utilized as new and highly efficient organic catalysts in living radical polymerization. The superbase catalysts included guanidines, aminophosphines [...] Read more.

Organic superbases reacted with alkyl iodides (R–I) to reversibly generate the corresponding alkyl radicals (R^•). Via this reaction, organic superbases were utilized as new and highly efficient organic catalysts in living radical polymerization. The superbase catalysts included guanidines, aminophosphines and phosphazenes. Low-polydispersity polymers (M_w/M_n = 1.1–1.4) were obtained up to high conversions (e.g., 80%) in reasonably short times (3–12 h) at mild temperatures (60–80 °C) for methyl methacrylate, styrene and several functional methacrylates. The high polymerization rate and good monomer versatility are attractive features of these superbase catalysts. Full article

(This article belongs to the Special Issue Controlled/Living Radical Polymerization)

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976 KiB

Open AccessArticle

Thermo-Responsive and Biocompatible Diblock Copolymers Prepared via Reversible Addition-Fragmentation Chain Transfer (RAFT) Radical Polymerization

by Kenichi Fukuda, Ryusuke Enomoto, Kazuhiko Ishihara, Yotaro Morishima and Shin-ichi Yusa

Polymers 2014, 6(3), 846-859; https://doi.org/10.3390/polym6030846 - 17 Mar 2014

Cited by 11 | Viewed by 7083

Abstract

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-b-poly(N,N-diethyl acrylamide) (PMPC_m-PDEA_n) was synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. Below, the critical aggregation temperature (CAT) the diblock copolymer dissolved in water as a unimer with a hydrodynamic [...] Read more.

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-b-poly(N,N-diethyl acrylamide) (PMPC_m-PDEA_n) was synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. Below, the critical aggregation temperature (CAT) the diblock copolymer dissolved in water as a unimer with a hydrodynamic radius (R_h) of ca. 5 nm. Above the CAT the diblock copolymers formed polymer micelles composed of a PDEA core and biocompatible PMPC shells, due to hydrophobic self-aggregation of the thermo-responsive PDEA block. A fluorescence probe study showed that small hydrophobic small guest molecules could be incorporated into the core of the polymer micelle above the CAT. The incorporated guest molecules were released from the core into the bulk aqueous phase when the temperature decreased to values below the CAT because of micelle dissociation. Full article

(This article belongs to the Special Issue Controlled/Living Radical Polymerization)

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5676 KiB

Open AccessArticle

Morphologies and Thermal Variability of Patterned Polymer Films with Poly(styrene-co-maleic anhydride)

by Pieter Samyn and Gustaaf Schoukens

Polymers 2014, 6(3), 820-845; https://doi.org/10.3390/polym6030820 - 14 Mar 2014

Cited by 7 | Viewed by 8647

Abstract

Patterned films of poly(styrene-co-maleic anhydride) copolymers were deposited by dip-coating from acetone solutions. A qualitative study of the film morphologies shows the formation of polymer spheres with smaller diameters at higher amounts of maleic anhydride (MA), and long-fibrous features at higher [...] Read more.

Patterned films of poly(styrene-co-maleic anhydride) copolymers were deposited by dip-coating from acetone solutions. A qualitative study of the film morphologies shows the formation of polymer spheres with smaller diameters at higher amounts of maleic anhydride (MA), and long-fibrous features at higher molecular weights. Upon heating, the films progressively re-assemble with short- and long-fibrous structures as a function of heating time and temperature. In parallel, the film morphologies are quantified by image processing and filtering techniques. The differential scanning calorimetry confirms the higher glass transition temperatures with increasing amount of MA. The analysis with Raman spectroscopy shows interactions between the molecules in solution and effects of ring-opening (hydrolysis) and ring-closure (formation of MA) during drying of the films. The water contact angles on the patterned films are within the hydrophilic range. They mainly correlate with the amount of MA moieties calculated from spectroscopy, while the roughness parameters have a minor effect. The variations in film patterns illustrate the self-assemble ability of the copolymers and confirm a heterogeneous molecular structure, as previously assumed. Full article

(This article belongs to the Special Issue Non-Equilibrium Blockcopolymer Self-Assembly)

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454 KiB

Open AccessReview

Drugs and Polymers for Delivery Systems in OA Joints: Clinical Needs and Opportunities

by Maarten Janssen, George Mihov, Tim Welting, Jens Thies and Pieter Emans

Polymers 2014, 6(3), 799-819; https://doi.org/10.3390/polym6030799 - 13 Mar 2014

Cited by 41 | Viewed by 16136

Abstract

Osteoarthritis (OA) is a big burden of disease worldwide and one of the most common causes of disability in the adult population. Currently applied therapies consist of physical therapy, oral medication, intra-articular injections, and surgical interventions, with the main goal being to reduce [...] Read more.

Osteoarthritis (OA) is a big burden of disease worldwide and one of the most common causes of disability in the adult population. Currently applied therapies consist of physical therapy, oral medication, intra-articular injections, and surgical interventions, with the main goal being to reduce pain and improve function and quality of life. Intra-articular (IA) administration of drugs has potential benefits in OA treatment because it minimizes systemic bioavailability and side effects associated with oral administration of drugs without compromising the therapeutic effect in the joint. However, IA drug residence time is short and there is a clinical need for a vehicle that is able to provide a sustained release long enough for IA therapy to fulfill its promise. This review summarizes the use of different polymeric systems and the incorporated drugs for IA drug delivery in the osteoarthritic joint with a primary focus on clinical needs and opportunities. Full article

(This article belongs to the Special Issue Polymers for Drug Delivery)

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3073 KiB

Open AccessReview

Molecular Modeling of PEGylated Peptides, Dendrimers, and Single-Walled Carbon Nanotubes for Biomedical Applications

by Hwankyu Lee

Polymers 2014, 6(3), 776-798; https://doi.org/10.3390/polym6030776 - 12 Mar 2014

Cited by 36 | Viewed by 10990

Abstract

Polyethylene glycol (PEG) has been conjugated to many drugs or drug carriers to increase their solubility and circulating lifetime, and reduce toxicity. This has motivated many experimental studies to understand the effect of PEGylation on delivery efficiency. To complement the experimental findings and [...] Read more.

Polyethylene glycol (PEG) has been conjugated to many drugs or drug carriers to increase their solubility and circulating lifetime, and reduce toxicity. This has motivated many experimental studies to understand the effect of PEGylation on delivery efficiency. To complement the experimental findings and uncover the mechanism that cannot be captured by experiments, all-atom and coarse-grained molecular dynamics (MD) simulations have been performed. This has become possible, due to recent advances in simulation methodologies and computational power. Simulations of PEGylated peptides show that PEG chains wrap antimicrobial peptides and weaken their binding interactions with lipid bilayers. PEGylation also influences the helical stability and tertiary structure of coiled-coil peptides. PEGylated dendrimers and single-walled carbon nanotubes (SWNTs) were simulated, showing that the PEG size and grafting density significantly modulate the conformation and structure of the PEGylated complex, the interparticle aggregation, and the interaction with lipid bilayers. In particular, simulations predicted the structural transition between the dense core and dense shell of PEGylated dendrimers, the phase behavior of self-assembled complexes of lipids, PEGylated lipids, and SWNTs, which all favorably compared with experiments. Overall, these new findings indicate that simulations can now predict the experimentally observed structure and dynamics, as well as provide atomic-scale insights into the interactions of PEGylated complexes with other molecules. Full article

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2011 KiB

Open AccessReview

Local Delivery of Antiproliferative Agents via Stents

by Hyuck Joon Kwon and Sangsoo Park

Polymers 2014, 6(3), 755-775; https://doi.org/10.3390/polym6030755 - 12 Mar 2014

Cited by 19 | Viewed by 9040

Abstract

A stent is a medical device for serving as an internal scaffold to maintain or increase the lumen of a body conduit. Stent placement has become a primary treatment option in coronary artery disease for more than the last two decades. The stenting [...] Read more.

A stent is a medical device for serving as an internal scaffold to maintain or increase the lumen of a body conduit. Stent placement has become a primary treatment option in coronary artery disease for more than the last two decades. The stenting is also currently used for relieving the symptoms of narrowed lumen of nonvascular organs, such as esophagus, trachea and bronchi, small and large intestines, biliary, and urinary tract. Local delivery of active pharmaceutical agents via the stents can not only enhance healing of certain diseases, but it can also help decrease the potential risk of the stenting procedure to the surrounding tissue. In this review, we focus on reviewing a variety of drug-impregnated stents and local drug delivery systems using the stents. Full article

(This article belongs to the Special Issue Polymers for Drug Delivery)

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1304 KiB

Open AccessReview

Start a Research on Biopolymer Polyhydroxyalkanoate (PHA): A Review

by Giin-Yu Amy Tan, Chia-Lung Chen, Ling Li, Liya Ge, Lin Wang, Indah Mutiara Ningtyas Razaad, Yanhong Li, Lei Zhao, Yu Mo and Jing-Yuan Wang

Polymers 2014, 6(3), 706-754; https://doi.org/10.3390/polym6030706 - 12 Mar 2014

Cited by 369 | Viewed by 48939

Abstract

With the impending fossil fuel crisis, the search for and development of alternative chemical/material substitutes is pivotal in reducing mankind’s dependency on fossil resources. One of the potential substitute candidates is polyhydroxyalkanoate (PHA). PHA is a carbon-neutral and valuable polymer that could be [...] Read more.

With the impending fossil fuel crisis, the search for and development of alternative chemical/material substitutes is pivotal in reducing mankind’s dependency on fossil resources. One of the potential substitute candidates is polyhydroxyalkanoate (PHA). PHA is a carbon-neutral and valuable polymer that could be produced from many renewable carbon sources by microorganisms, making it a sustainable and environmental-friendly material. At present, PHA is not cost competitive compared to fossil-derived products. Encouraging and intensifying research work on PHA is anticipated to enhance its economic viability in the future. The development of various biomolecular and chemical techniques for PHA analysis has led to the identification of many PHA-producing microbial strains, some of which are deposited in culture collections. Research work on PHA could be rapidly initiated with these ready-to-use techniques and microbial strains. This review aims to facilitate the start-up of PHA research by providing a summary of commercially available PHA-accumulating microbial cultures, PHA biosynthetic pathways, and methods for PHA detection, extraction and analysis. Full article

(This article belongs to the Special Issue Polymers from Biomass)

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2309 KiB

Open AccessArticle

All Green Composites from Fully Renewable Biopolymers: Chitosan-Starch Reinforced with Keratin from Feathers

by Cynthia G. Flores-Hernández, Arturo Colín-Cruz, Carlos Velasco-Santos, Víctor M. Castaño, José L. Rivera-Armenta, Armando Almendarez-Camarillo, Perla E. García-Casillas and Ana L. Martínez-Hernández

Polymers 2014, 6(3), 686-705; https://doi.org/10.3390/polym6030686 - 11 Mar 2014

Cited by 80 | Viewed by 14130

Abstract

The performance as reinforcement of a fibrillar protein such as feather keratin fiber over a biopolymeric matrix composed of polysaccharides was evaluated in this paper. Three different kinds of keratin reinforcement were used: short and long biofibers and rachis particles. These were added [...] Read more.

The performance as reinforcement of a fibrillar protein such as feather keratin fiber over a biopolymeric matrix composed of polysaccharides was evaluated in this paper. Three different kinds of keratin reinforcement were used: short and long biofibers and rachis particles. These were added separately at 5, 10, 15 and 20 wt% to the chitosan-starch matrix and the composites were processed by a casting/solvent evaporation method. The morphological characteristics, mechanical and thermal properties of the matrix and composites were studied by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis. The thermal results indicated that the addition of keratin enhanced the thermal stability of the composites compared to pure matrix. This was corroborated with dynamic mechanical analysis as the results revealed that the storage modulus of the composites increased with respect to the pure matrix. The morphology, evaluated by scanning electron microscopy, indicated a uniform dispersion of keratin in the chitosan-starch matrix as a result of good compatibility between these biopolymers, also corroborated by FTIR. These results demonstrate that chicken feathers can be useful to obtain novel keratin reinforcements and develop new green composites providing better properties, than the original biopolymer matrix. Full article

(This article belongs to the Collection Polysaccharides)

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768 KiB

Open AccessArticle

Flexural Behavior of RC Members Using Externally Bonded Aluminum-Glass Fiber Composite Beams

by Ki-Nam Hong, Chang-Geun Cho, Swoo-Heon Lee and Yeonho Park

Polymers 2014, 6(3), 667-685; https://doi.org/10.3390/polym6030667 - 10 Mar 2014

Cited by 6 | Viewed by 8522

Abstract

This study concerns improvement of flexural stiffness/strength of concrete members reinforced with externally bonded, aluminum-glass fiber composite (AGC) beams. An experimental program, consisting of seven reinforced concrete slabs and seven reinforced concrete beams strengthened in flexure with AGC beams, was initiated under four-point [...] Read more.

This study concerns improvement of flexural stiffness/strength of concrete members reinforced with externally bonded, aluminum-glass fiber composite (AGC) beams. An experimental program, consisting of seven reinforced concrete slabs and seven reinforced concrete beams strengthened in flexure with AGC beams, was initiated under four-point bending in order to evaluate three parameters: the cross-sectional shape of the AGC beam, the glass fiber fabric array, and the installation of fasteners. The load-deflection response, strain distribution along the longitudinal axis of the beam, and associated failure modes of the tested specimens were recorded. It was observed that the AGC beam led to an increase of the initial cracking load, yielding load of the tension steels and peak load. On the other hand, the ductility of some specimens strengthened was reduced by more than 50%. The A-type AGC beam was more efficient in slab specimens than in beam specimens and the B-type was more suitable for beam specimens than for slabs. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)

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1326 KiB

Open AccessArticle

Structure and Frictional Properties of Colloid Gel

by Masayuki Tokita

Polymers 2014, 6(3), 651-666; https://doi.org/10.3390/polym6030651 - 06 Mar 2014

Cited by 5 | Viewed by 7342

Abstract

Polymer gels are known to be opaque when the preparation conditions, such as the reaction temperature and the composition, are changed. The increase of the opaqueness of the gel suggests strongly the change of network structure. Here, we are going to review the [...] Read more.

Polymer gels are known to be opaque when the preparation conditions, such as the reaction temperature and the composition, are changed. The increase of the opaqueness of the gel suggests strongly the change of network structure. Here, we are going to review the recent studies on the structure and the frictional study of the opaque poly(acrylamide) gel. The results indicate that the opaque poly(acrylamide) gel consists of the fractal aggregate of the colloidal particles of sub-micrometer in size. The density of the colloid particle is calculated from the structural parameters and is found to be of the order of about 1 g/cm³. The results indicate that the main chain component and the cross-linker is densely cross-linked into the particle. The frictional property of poly(acrylamide) gel is analyzed in terms of the structural parameters of the gel. It is found that the frictional property of the opaque gel is well explained in terms of the structural parameters of the opaque gel. Full article

(This article belongs to the Special Issue Polymer Colloids)

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705 KiB

Open AccessArticle

Endocytosis Pathways of the Folate Tethered Star-Shaped PEG-PCL Micelles in Cancer Cell Lines

by Yu-Lun Li, Nguyen Van Cuong and Ming-Fa Hsieh

Polymers 2014, 6(3), 634-650; https://doi.org/10.3390/polym6030634 - 06 Mar 2014

Cited by 25 | Viewed by 7898

Abstract

This study reports on the cellular uptake of folate tethered micelles using a branched skeleton of poly(ethylene glycol) and poly(ε-caprolactone). The chemical structures of the copolymers were characterized by proton nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. Doxorubicin (DOX) was utilized [...] Read more.

This study reports on the cellular uptake of folate tethered micelles using a branched skeleton of poly(ethylene glycol) and poly(ε-caprolactone). The chemical structures of the copolymers were characterized by proton nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. Doxorubicin (DOX) was utilized as an anticancer drug. The highest drug loading efficiencies of DOX in the folate decorated micelle (DMCF) and folate-free micelle (DMC) were found to be 88.5% and 88.2%, respectively, depending on the segment length of the poly(ε-caprolactone) in the copolymers. A comparison of fluorescent microscopic images of the endocytosis pathway in two cell lines, human breast cancer cells (MCF-7) and human oral cavity carcinoma cells (KB), revealed that the micelles were engulfed by KB and MCF-7 cells following in vitro incubation for one hour. Flow cytometric analysis revealed that free folic acid can inhibit the uptake of DOX by 48%–57% and 26%–39% in KB cells and MCF-7 cells, respectively. These results prove that KB cells are relatively sensitive to folate-tethered micelles. Upon administering methyl-β-cyclodextrin, an inhibitor of the caveolae-mediated endocytosis pathway, the uptake of DOX by KB cells was reduced by 69% and that by MCF-7 cells was reduced by 56%. This finding suggests that DMCF enters cells via multiple pathways, thus implying that the folate receptor is not the only target of tumor therapeutics. Full article

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1464 KiB

Open AccessArticle

RC Beams Strengthened with Mechanically Fastened Composites: Experimental Results and Numerical Modeling

by Enzo Martinelli, Annalisa Napoli, Bruno Nunziata and Roberto Realfonzo

Polymers 2014, 6(3), 613-633; https://doi.org/10.3390/polym6030613 - 05 Mar 2014

Cited by 13 | Viewed by 7240

Abstract

The use of mechanically-fastened fiber-reinforced polymer (MF-FRP) systems has recently emerged as a competitive solution for the flexural strengthening of reinforced concrete (RC) beams and slabs. An overview of the experimental research has proven the effectiveness and the potentiality of the MF-FRP technique [...] Read more.

The use of mechanically-fastened fiber-reinforced polymer (MF-FRP) systems has recently emerged as a competitive solution for the flexural strengthening of reinforced concrete (RC) beams and slabs. An overview of the experimental research has proven the effectiveness and the potentiality of the MF-FRP technique which is particularly suitable for emergency repairs or when the speed of installation and immediacy of use are imperative. A finite-element (FE) model has been recently developed by the authors with the aim to simulate the behavior of RC beams strengthened in bending by MF-FRP laminates; such a model has also been validated by using a wide experimental database collected from the literature. By following the previous study, the FE model and the assembled database are considered herein with the aim of better exploring the influence of some specific aspects on the structural response of MF-FRP strengthened members, such as the bearing stress-slip relationship assumed for the FRP-concrete interface, the stress-strain law considered for reinforcing steel rebars and the cracking process in RC members resulting in the well-known tension stiffening effect. The considerations drawn from this study will be useful to researchers for the calibration of criteria and design rules for strengthening RC beams through MF-FRP laminates. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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728 KiB

Open AccessArticle

Injection Compression Molding of Replica Molds for Nanoimprint Lithography

by Keisuke Nagato

Polymers 2014, 6(3), 604-612; https://doi.org/10.3390/polym6030604 - 05 Mar 2014

Cited by 16 | Viewed by 10251

Abstract

As a breakthrough in the cost and durability of molds for nanoimprint lithography (NIL), replica molds are fabricated by injection compression molding (ICM). ICM is commonly used for optical disks such as DVDs or Blu-ray disks and is also a practical fabrication method [...] Read more.

As a breakthrough in the cost and durability of molds for nanoimprint lithography (NIL), replica molds are fabricated by injection compression molding (ICM). ICM is commonly used for optical disks such as DVDs or Blu-ray disks and is also a practical fabrication method for nanostructures. In this paper, I successfully demonstrated the fabrication of cycloolefin polymer replica molds with structures smaller than 60 nm by ICM. Furthermore, ultraviolet (UV)-NIL using these replica molds was demonstrated. UV-cured resist was replicated over an area of 60 mm diameter. The degree of replication by UV-NIL in the first usage of each replica mold had good repeatability. Because ICM is a high-throughput, low-cost process, the replica mold can be disposed of after a certain time for UV-NIL. This method leads to a high-integrity UV-NIL process of patterned media because multiple large-area replica molds can be fabricated simultaneously. Full article

(This article belongs to the Special Issue Patterning and Photosensitive Polymers)

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Polymers, Volume 6, Issue 3 (March 2014) – 17 articles , Pages 604-948

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