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Polymers, Volume 4, Issue 3 (September 2012), Pages 1331-1626

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Research

Jump to: Review

Open AccessArticle Tailoring Crystallinity of Electrospun Plla Fibres by Control of Electrospinning Parameters
Polymers 2012, 4(3), 1331-1348; doi:10.3390/polym4031331
Received: 6 June 2012 / Accepted: 20 June 2012 / Published: 28 June 2012
Cited by 14 | PDF Full-text (1293 KB) | HTML Full-text | XML Full-text
Abstract
Poly(L-lactic acid) (PLLA) fibers were fabricated by electrospinning. The effects of various electrospinning process parameters on the thermal properties, especially the crystallinity of the electrospun fibers were investigated. Thermal analysis of the fibers revealed that they exhibited degree of crystallinity ranging from [...] Read more.
Poly(L-lactic acid) (PLLA) fibers were fabricated by electrospinning. The effects of various electrospinning process parameters on the thermal properties, especially the crystallinity of the electrospun fibers were investigated. Thermal analysis of the fibers revealed that they exhibited degree of crystallinity ranging from 23% to 46% while that for the as-received granules was approximately 37%, suggesting that the crystallinity of electrospun PLLA fibres can be controlled by optimizing the electrospinning process. This finding is very important because crystallinity affects polymer properties such as degradation, stiffness, yield stress, modulus and tensile strength, solubility, optical and electrical properties which will in turn affect the behavior of these materials when they are utilized in energy, environment, defense and security applications. The results presented in this paper show that the degree of crystallinity of the electrospun fibers decreased with increasing the polymer solution concentration. Furthermore, an optimum electrospinning voltage at which maximum degree of crystallinity can be obtained was observed. At voltages higher or lower than the optimum electrospinning voltage, the degree of crystallinity will decrease or increase, respectively. The effect of the needle tip to collector distance (NTCD) on the degree of crystallinity follows no predictable and consistent pattern. Full article
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Open AccessArticle A Systematic Study on the Self-Assembly Behaviour of Multi Component Fmoc-Amino Acid-Poly(oxazoline) Systems
Polymers 2012, 4(3), 1399-1415; doi:10.3390/polym4031399
Received: 9 May 2012 / Revised: 6 July 2012 / Accepted: 10 July 2012 / Published: 24 July 2012
Cited by 2 | PDF Full-text (1777 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report a systematic study of a modular approach to create multi-component supramolecular nanostructures that can be tailored to be both enzyme and temperature responsive. Using a straightforward synthetic approach we functionalised a thermal responsive polymer, poly(2-isopropyl-2-oxazoline), with fluorenylmethoxycarbonyl-amino acids that drive [...] Read more.
We report a systematic study of a modular approach to create multi-component supramolecular nanostructures that can be tailored to be both enzyme and temperature responsive. Using a straightforward synthetic approach we functionalised a thermal responsive polymer, poly(2-isopropyl-2-oxazoline), with fluorenylmethoxycarbonyl-amino acids that drive the self-assembly. Depending on the properties of appended amino acids, these polymers undergo substantial morphological changes in response to the catalytic action of alkaline phosphatase. Full article
(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)
Open AccessArticle Simulating Controlled Radical Polymerizations with mcPolymer—A Monte Carlo Approach
Polymers 2012, 4(3), 1416-1442; doi:10.3390/polym4031416
Received: 25 June 2012 / Revised: 17 July 2012 / Accepted: 18 July 2012 / Published: 30 July 2012
Cited by 8 | PDF Full-text (744 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Utilizing model calculations may lead to a better understanding of the complex kinetics of the controlled radical polymerization. We developed a universal simulation tool (mcPolymer), which is based on the widely used Monte Carlo simulation technique. This article focuses on the software [...] Read more.
Utilizing model calculations may lead to a better understanding of the complex kinetics of the controlled radical polymerization. We developed a universal simulation tool (mcPolymer), which is based on the widely used Monte Carlo simulation technique. This article focuses on the software architecture of the program, including its data management and optimization approaches. We were able to simulate polymer chains as individual objects, allowing us to gain more detailed microstructural information of the polymeric products. For all given examples of controlled radical polymerization (nitroxide mediated radical polymerization (NMRP) homo- and copolymerization, atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer polymerization (RAFT)), we present detailed performance analyses demonstrating the influence of the system size, concentrations of reactants, and the peculiarities of data. Different possibilities were exemplarily illustrated for finding an adequate balance between precision, memory consumption, and computation time of the simulation. Due to its flexible software architecture, the application of mcPolymer is not limited to the controlled radical polymerization, but can be adjusted in a straightforward manner to further polymerization models. Full article
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Open AccessArticle Novel Organic Sensitizers Containing 2,6-Difunctionalized Anthracene Unit for Dye Sensitized Solar Cells
Polymers 2012, 4(3), 1443-1461; doi:10.3390/polym4031443
Received: 29 June 2012 / Revised: 23 July 2012 / Accepted: 24 July 2012 / Published: 3 August 2012
Cited by 6 | PDF Full-text (780 KB) | HTML Full-text | XML Full-text
Abstract
A series of new organic dyes comprising different amines as electron donors, 2-(6-substituted-anthracen-2-yl)-thiophene as the π-conjugated bridge, and cyanoacrylic acid group as an electron acceptor and anchoring group, have been synthesized. There exists charge transfer transition from arylamine and anthracene to the [...] Read more.
A series of new organic dyes comprising different amines as electron donors, 2-(6-substituted-anthracen-2-yl)-thiophene as the π-conjugated bridge, and cyanoacrylic acid group as an electron acceptor and anchoring group, have been synthesized. There exists charge transfer transition from arylamine and anthracene to the acceptor in these compounds, as evidenced from the photophysical measurements and the computational results. Under one sun (AM 1.5) illumination, dye-sensitized solar cells (DSSCs) using these dyes as the sensitizers exhibited efficiencies ranging from 1.62% to 2.88%, surpassing that using 9,10-difunctionalized anthracene-based sensitizer. Full article
(This article belongs to the Special Issue Polymers for Fuel Cells & Solar Energy)
Open AccessArticle Microwave-Assisted Synthesis of Polyols from Rapeseed Oil and Properties of Flexible Polyurethane Foams
Polymers 2012, 4(3), 1462-1477; doi:10.3390/polym4031462
Received: 21 May 2012 / Revised: 18 July 2012 / Accepted: 24 July 2012 / Published: 10 August 2012
Cited by 9 | PDF Full-text (735 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The application of raw materials derived from renewable feedstock has given rise to growing interest recently, as it can be exploited for the production of bio-based materials from vegetable oils. Their availability, biodegradability and low prices have been taken into account. In [...] Read more.
The application of raw materials derived from renewable feedstock has given rise to growing interest recently, as it can be exploited for the production of bio-based materials from vegetable oils. Their availability, biodegradability and low prices have been taken into account. In this work, vegetable oil-based polyols as a prospective replacement for petroleum polyols were investigated. A two-stage method for polyol preparation by incomplete epoxidation of natural oils and subsequent complete oxirane ring opening under microwave irradiation is presented. The course of epoxidation and oxirane ring-opening process was determined analytically by an evaluation of iodine, epoxy and hydroxyl values. The samples of oils and their derivatives were also analyzed by FT-IR and characterized by size exclusion chromatography (SEC) in order to calculate their functionalities. Finally, polyols with two different hydroxyl values were obtained and used for the synthesis of flexible polyurethane (PUR) foams. The scope of this research includes the determination of the relationship between the rapeseed oil-based polyol content and the properties of the resulting materials. It was found that applying bio-based polyols in conjunction with petroleum-based polyols for PUR foams formulations resulted in materials with good mechanical properties and a higher number of cells with smaller dimensions. Full article
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Open AccessArticle Embedding of Hollow Polymer Microspheres with Hydrophilic Shell in Nafion Matrix as Proton and Water Micro-Reservoir
Polymers 2012, 4(3), 1499-1516; doi:10.3390/polym4031499
Received: 19 June 2012 / Revised: 1 August 2012 / Accepted: 10 August 2012 / Published: 20 August 2012
Cited by 2 | PDF Full-text (1621 KB) | HTML Full-text | XML Full-text
Abstract
Assimilating hydrophilic hollow polymer spheres (HPS) into Nafion matrix by a loading of 0.5 wt % led to a restructured hydrophilic channel, composed of the pendant sulfonic acid groups (–SO3H) and the imbedded hydrophilic hollow spheres. The tiny hydrophilic hollow [...] Read more.
Assimilating hydrophilic hollow polymer spheres (HPS) into Nafion matrix by a loading of 0.5 wt % led to a restructured hydrophilic channel, composed of the pendant sulfonic acid groups (–SO3H) and the imbedded hydrophilic hollow spheres. The tiny hydrophilic hollow chamber was critical to retaining moisture and facilitating proton transfer in the composite membranes. To obtain such a tiny cavity structure, the synthesis included selective generation of a hydrophilic polymer shell on silica microsphere template and the subsequent removal of the template by etching. The hydrophilic HPS (100–200 nm) possessed two different spherical shells, the styrenic network with pendant sulfonic acid groups and with methacrylic acid groups, respectively. By behaving as microreservoirs of water, the hydrophilic HPS promoted the Grotthus mechanism and, hence, enhanced proton transport efficiency through the inter-sphere path. In addition, the HPS with the –SO3H borne shell played a more effective role than those with the –CO2H borne shell in augmenting proton transport, in particular under low humidity or at medium temperatures. Single H2-PEMFC test at 70 °C using dry H2/O2 further verified the impactful role of hydrophilic HPS in sustaining higher proton flux as compared to pristine Nafion membrane. Full article
(This article belongs to the Special Issue Polymers for Fuel Cells & Solar Energy)
Open AccessArticle Polysaccharide-Based Hydrogels: The Key Role of Water in Affecting Mechanical Properties
Polymers 2012, 4(3), 1517-1534; doi:10.3390/polym4031517
Received: 20 July 2012 / Revised: 27 July 2012 / Accepted: 1 August 2012 / Published: 21 August 2012
Cited by 24 | PDF Full-text (805 KB) | HTML Full-text | XML Full-text
Abstract
Different hydrogels were prepared starting from natural or semi-synthetic polysaccharides (carboxymethylcellulose, hyaluronic acid and chitosan) which were cross-linked by the addition of a cross-linking agent chosen according to the chemical groups present along the polymer chains. The cross-linking reaction allows for the [...] Read more.
Different hydrogels were prepared starting from natural or semi-synthetic polysaccharides (carboxymethylcellulose, hyaluronic acid and chitosan) which were cross-linked by the addition of a cross-linking agent chosen according to the chemical groups present along the polymer chains. The cross-linking reaction allows for the formation of a three-dimensional network made of covalent bonds between the polymer chains, which is stable under physiological conditions. The presence of a substantial amount of water within the polysaccharide matrices makes such systems unique among hydrophilic gels. Water itself is responsible for some of their peculiar characteristics, one of which is their injectability which makes these hydrogels suitable for using as matrices for mini-invasive surgery and localized therapy. Full article
Open AccessArticle Physical Properties of Polypeptide Electrospun Nanofiber Cell Culture Scaffolds on a Wettable Substrate
Polymers 2012, 4(3), 1535-1553; doi:10.3390/polym4031535
Received: 20 April 2012 / Revised: 9 August 2012 / Accepted: 23 August 2012 / Published: 31 August 2012
Cited by 5 | PDF Full-text (1594 KB) | HTML Full-text | XML Full-text
Abstract
Physical properties of poly(L-ornithine) (PLO), a polycation, poly(L-glutamic acid4-co-L-tyrosine) (PLEY), a polyanion, and electrospun fibers made of these polymers have been determined and compared. The polymers adopted random coil-like conformations in aqueous feedstocks at neutral pH and in [...] Read more.
Physical properties of poly(L-ornithine) (PLO), a polycation, poly(L-glutamic acid4-co-L-tyrosine) (PLEY), a polyanion, and electrospun fibers made of these polymers have been determined and compared. The polymers adopted random coil-like conformations in aqueous feedstocks at neutral pH and in dehydrated cast films and fibers on glass, and the fibers comprised numerous counterions, according to spectral analysis. Adsorption of model proteins and serum proteins onto hydrated and crosslinked fibers depended on the electrical charge of the proteins and the fibers. The surface charge density of the fibers will be comparable to, but less than, the charge density on the outer leaflet of the plasma membrane of usual eukaryotic cells. The present analysis thus advances understanding of cell behavior on electrospun fiber scaffolds, a topic of considerable current interest. Full article
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Open AccessCommunication Selective Controlled/Living Photoradical Polymerization of Glycidyl Methacrylate, Using a Nitroxide Mediator in the Presence of a Photosensitive Triarylsulfonium Salt
Polymers 2012, 4(3), 1580-1589; doi:10.3390/polym4031580
Received: 23 July 2012 / Revised: 10 August 2012 / Accepted: 30 August 2012 / Published: 10 September 2012
Cited by 6 | PDF Full-text (144 KB) | HTML Full-text | XML Full-text
Abstract
The controlled/living photoradical polymerization of glycidyl methacrylate (GMA) was attained using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator and (2RS,2'RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate (tBuS). Whereas the polymerization in the absence of MTEMPO yielded a [...] Read more.
The controlled/living photoradical polymerization of glycidyl methacrylate (GMA) was attained using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator and (2RS,2'RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate (tBuS). Whereas the polymerization in the absence of MTEMPO yielded a gel-containing polymer, the MTEMPO-mediated polymerization produced poly(GMA) bonded at the vinyl site, and retained the oxirane ring structure. No occurrence of the cationic ring-opening photopolymerization of the oxirane ring even in the presence of the photosensitive onium salt indicated that tBuS served as the photoelectron transfer agent between MTEMPO in their excited states at the propagating chain end. The resulting polymers had comparatively narrow molecular weight distributions of Mw/Mn = 1.46–1.48. The living nature of the MTEMPO-mediated polymerization was confirmed on the basis of a linear increase in the conversion-molecular weight plots and gel permeation chromatography (GPC) analysis. Full article
Open AccessArticle Dye-sensitized Solar Cells with New One-Dimensional Halide-Bridged Cu(I)–Ni(II) Heterometal Coordination Polymers Containing Hexamethylene Dithiocarbamate Ligand
Polymers 2012, 4(3), 1613-1626; doi:10.3390/polym4031613
Received: 2 July 2012 / Revised: 5 September 2012 / Accepted: 10 September 2012 / Published: 20 September 2012
Cited by 9 | PDF Full-text (893 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
One-dimensional (1D) halide-bridged Cu(I)–Ni(II) heterometal coordination polymers containing a hexamethylene dithiocarbamate (Hm-dtc) ligand have been synthesized and crystallographically characterized. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the coordination polymers were estimated using UV-Vis-NIR and photoelectron spectroscopies, and it was revealed that these coordination polymers have appropriate HOMO levels for use as dye sensitizers. Direct-current electrical conductivity measurements and impedance measurements indicated that these 1D Cu(I)–Ni(II) heterometal coordination polymers were insulators (σ300K < 10−12 S cm−1). In addition, the coordination polymers were used as sensitizing materials in dye-sensitized solar cells (DSSCs). DSSCs with 1D Cu(I)–Ni(II) heterometal coordination polymers showed lower performances than those with 1D halide-bridged Cu(I)–Cu(II) mixed-valence coordination polymers. Full article
(This article belongs to the Special Issue Polymers for Fuel Cells & Solar Energy)

Review

Jump to: Research

Open AccessReview Polymer-Based Microfluidic Devices for Pharmacy, Biology and Tissue Engineering
Polymers 2012, 4(3), 1349-1398; doi:10.3390/polym4031349
Received: 2 March 2012 / Revised: 4 May 2012 / Accepted: 18 June 2012 / Published: 3 July 2012
Cited by 28 | PDF Full-text (735 KB) | HTML Full-text | XML Full-text
Abstract
This paper reviews microfluidic technologies with emphasis on applications in the fields of pharmacy, biology, and tissue engineering. Design and fabrication of microfluidic systems are discussed with respect to specific biological concerns, such as biocompatibility and cell viability. Recent applications and developments [...] Read more.
This paper reviews microfluidic technologies with emphasis on applications in the fields of pharmacy, biology, and tissue engineering. Design and fabrication of microfluidic systems are discussed with respect to specific biological concerns, such as biocompatibility and cell viability. Recent applications and developments on genetic analysis, cell culture, cell manipulation, biosensors, pathogen detection systems, diagnostic devices, high-throughput screening and biomaterial synthesis for tissue engineering are presented. The pros and cons of materials like polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polystyrene (PS), polycarbonate (PC), cyclic olefin copolymer (COC), glass, and silicon are discussed in terms of biocompatibility and fabrication aspects. Microfluidic devices are widely used in life sciences. Here, commercialization and research trends of microfluidics as new, easy to use, and cost-effective measurement tools at the cell/tissue level are critically reviewed. Full article
Open AccessReview Temperature-Responsive Polymer Modified Surface for Cell Sheet Engineering
Polymers 2012, 4(3), 1478-1498; doi:10.3390/polym4031478
Received: 23 April 2012 / Revised: 17 July 2012 / Accepted: 30 July 2012 / Published: 15 August 2012
Cited by 27 | PDF Full-text (1782 KB) | HTML Full-text | XML Full-text
Abstract
In the past two decades, as a novel approach for tissue engineering, cell sheet engineering has been proposed by our laboratory. Poly(N-isopropylacrylamide) (PIPAAm), which is a well-known temperature-responsive polymer, has been grafted on tissue culture polystyrene (TCPS) surfaces through an [...] Read more.
In the past two decades, as a novel approach for tissue engineering, cell sheet engineering has been proposed by our laboratory. Poly(N-isopropylacrylamide) (PIPAAm), which is a well-known temperature-responsive polymer, has been grafted on tissue culture polystyrene (TCPS) surfaces through an electron beam irradiated polymerization. At 37 °C, where the PIPAAm modified surface is hydrophobic, cells can adhere, spread on the surface and grow to confluence. By decreasing temperature to 20 °C, since the surface turns to hydrophilic, cells can detach themselves from the surface spontaneously and form an intact cell sheet with extracellular matrix. For obtaining a temperature-induced cell attachment and detachment, it is necessary to immobilize an ultra thin PIPAAm layer on the TCPS surfaces. This review focuses on the characteristics of PIAPAm modified surfaces exhibiting these intelligent properties. In addition, PIPAAm modified surfaces giving a rapid cell-sheet recovery has been further developed on the basis of the characteristic of the PIPAAm surface. The designs of temperature-responsive polymer layer have provided an enormous potential to fabricate clinically applicable regenerative medicine. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymers and Colloids)
Open AccessReview Microscale Strategies for Generating Cell-Encapsulating Hydrogels
Polymers 2012, 4(3), 1554-1579; doi:10.3390/polym4031554
Received: 4 May 2012 / Revised: 28 July 2012 / Accepted: 2 August 2012 / Published: 5 September 2012
Cited by 15 | PDF Full-text (3570 KB) | HTML Full-text | XML Full-text
Abstract
Hydrogels in which cells are encapsulated are of great potential interest for tissue engineering applications. These gels provide a structure inside which cells can spread and proliferate. Such structures benefit from controlled microarchitectures that can affect the behavior of the enclosed cells. [...] Read more.
Hydrogels in which cells are encapsulated are of great potential interest for tissue engineering applications. These gels provide a structure inside which cells can spread and proliferate. Such structures benefit from controlled microarchitectures that can affect the behavior of the enclosed cells. Microfabrication-based techniques are emerging as powerful approaches to generate such cell-encapsulating hydrogel structures. In this paper we introduce common hydrogels and their crosslinking methods and review the latest microscale approaches for generation of cell containing gel particles. We specifically focus on microfluidics-based methods and on techniques such as micromolding and electrospinning. Full article
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Open AccessReview Hydrogel-Based Platforms for the Regeneration of Osteochondral Tissue and Intervertebral Disc
Polymers 2012, 4(3), 1590-1612; doi:10.3390/polym4031590
Received: 16 April 2012 / Revised: 19 July 2012 / Accepted: 6 September 2012 / Published: 14 September 2012
Cited by 11 | PDF Full-text (699 KB) | HTML Full-text | XML Full-text
Abstract
Hydrogels currently represent a powerful solution to promote the regeneration of soft and hard tissues. Primarily, they assure efficient bio-molecular interactions with cells, also regulating their basic functions, guiding the spatially and temporally complex multi-cellular processes of tissue formation, and ultimately facilitating [...] Read more.
Hydrogels currently represent a powerful solution to promote the regeneration of soft and hard tissues. Primarily, they assure efficient bio-molecular interactions with cells, also regulating their basic functions, guiding the spatially and temporally complex multi-cellular processes of tissue formation, and ultimately facilitating the restoration of structure and function of damaged or dysfunctional tissues. In order to overcome basic drawbacks of traditional synthesized hydrogels, many recent strategies have been implemented to realize multi-component hydrogels based on natural and/or synthetic materials with tailored chemistries and different degradation kinetics. Here, a critical review of main strategies has been proposed based on the use of hydrogels-based devices for the regeneration of complex tissues, i.e., osteo-chondral tissues and intervertebral disc. Full article

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