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Polymers, Volume 3, Issue 2 (June 2011) – 20 articles , Pages 662-974

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432 KiB  
Communication
A Novel Self-Assembled Liposome-Based Polymeric Hydrogel for Cranio-Maxillofacial Applications: Preliminary Findings
by Victor Joo, Thiruganesh Ramasamy and Ziyad S. Haidar
Polymers 2011, 3(2), 967-974; https://doi.org/10.3390/polym3020967 - 14 Jun 2011
Cited by 14 | Viewed by 8209
Abstract
Soft nanogels are submicron-sized hydrophilic structures engineered from biocompatible polymers possessing the characteristics of nanoparticles as well as hydrogels, with a wide array of potential applications in biotechnology and biomedicine, namely, drug and protein delivery. In this work, nanogels were obtained using the [...] Read more.
Soft nanogels are submicron-sized hydrophilic structures engineered from biocompatible polymers possessing the characteristics of nanoparticles as well as hydrogels, with a wide array of potential applications in biotechnology and biomedicine, namely, drug and protein delivery. In this work, nanogels were obtained using the physical self-assembly technique or ‘layer-by-layer’ which is based on electrostatic interactions. Liposomal vesicles were coated with alternating layers of hyaluronic acid and chitosan yielding a more viscous hydrogel formulation that previously reported core-shell nanoparticulate suspension, via simply modifying the physico-chemical characteristics of the system. Structural features, size, surface charge, stability and swelling characteristics of the nanogel were studied using scanning electron microscopy and dynamic light scattering. With a specific cranio-maxillofacial application in mind, the hydrogel was loaded with recombinant human (rh) bone morphogenetic protein-7, also known as osteogenic protein-1 or rhOP-1 and release was monitored over an extended period of 60 days. This preliminary study reports promising results on the formulation of a novel core-shell polymeric nanogel. Full article
(This article belongs to the Special Issue Polymers for Oro-Dental and Cranio- Maxillo-Facial Applications)
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573 KiB  
Article
Effect of Moisture on the Orientation Birefringence of Cellulose Esters
by Mohd Edeerozey Abd Manaf, Manami Tsuji, Shogo Nobukawa and Masayuki Yamaguchi
Polymers 2011, 3(2), 955-966; https://doi.org/10.3390/polym3020955 - 14 Jun 2011
Cited by 37 | Viewed by 8994
Abstract
Orientation birefringence and its wavelength dispersion are studied for hot-drawn films of cellulose esters such as cellulose triacetate (CTA), cellulose diacetate (CDA), and cellulose acetate propionate (CAP) exposed to three different humidities of environments. Hot-drawn CTA films show negative birefringence that decreases with [...] Read more.
Orientation birefringence and its wavelength dispersion are studied for hot-drawn films of cellulose esters such as cellulose triacetate (CTA), cellulose diacetate (CDA), and cellulose acetate propionate (CAP) exposed to three different humidities of environments. Hot-drawn CTA films show negative birefringence that decreases with increasing wavelength. On the other hand, CDA and CAP films show positive birefringence that increases with increasing wavelength, i.e., the so-called extraordinary wavelength dispersion of birefringence. Upon exposure to high humidity environment, the orientation birefringence of CDA and CAP decreases. The decrease is prominent for the samples containing a large amount of water. CTA, however, shows an increase in magnitude of its negative orientation birefringence with increasing moisture content. The results can be explained by the increase of the polarizability anisotropy perpendicular to the stretching direction in the cellulose esters. It is found from ATR-FTIR measurements that hydrogen bonds are formed between carbonyl groups of cellulose esters and water molecules. Considering that orientation birefringence of cellulose esters is determined mainly by ester groups, the formation of hydrogen bonds contributes to the polarizability anisotropy, thus affecting the orientation birefringence. Full article
(This article belongs to the Collection Polysaccharides)
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813 KiB  
Article
Behavior of Na+-Polystyrene Sulfonate at the Interface with Single-Walled Carbon Nanotubes (SWNTs) and Its Implication to SWNT Suspension Stability
by Tabbetha Dobbins, Richard Chevious and Yuri Lvov
Polymers 2011, 3(2), 942-954; https://doi.org/10.3390/polym3020942 - 14 Jun 2011
Cited by 14 | Viewed by 10211
Abstract
The assembly of sodium polystyrene sulfonate (Na+-PSS) at the surface of single-walled carbon nanotubes (SWNTs) in pH 3 aqueous solution is described. Rather than forming linear or sheet-like chain morphologies over SWNT surfaces, Na+-PSS adopts a spherically collapsed conformation [...] Read more.
The assembly of sodium polystyrene sulfonate (Na+-PSS) at the surface of single-walled carbon nanotubes (SWNTs) in pH 3 aqueous solution is described. Rather than forming linear or sheet-like chain morphologies over SWNT surfaces, Na+-PSS adopts a spherically collapsed conformation believed to be the result of cation (either Na+ or H+) condensation onto the ionized polymer chain. It is well reported that cations (and also anions) adsorb preferentially onto single-walled and multi-walled carbon nanotube surfaces leading to an increased ion concentration in the near surface regions relative to the bulk solution. This work provides experimental evidence for preferentially absorbed cation condensation onto PSS anions until those cations are spaced at distances corresponding to the Bjerrum length ( B), as defined by the Manning theory of ion condensation, at the SWNT surface. The resulting electrostearic repulsions allow the SWNTs to remain suspended for days. Furthermore , coulombic repulsion among SWNT bundles after cation adsorption alone is not sufficient to form stable suspensions—but rather the stearic repulsions associated with spherically collapsed PSS at the nanotube surface is responsible for suspension stability. It is believed that the ultrasonic agitation drives cations into the small spaces between SWNT bundles and coulombic potential attracts the PSS to those regions. Full article
(This article belongs to the Special Issue Polyelectrolytes)
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629 KiB  
Communication
Physical and Chemical Characterization of Poly(hexamethylene biguanide) Hydrochloride
by Gustavo F. De Paula, Germano I. Netto and Luiz Henrique C. Mattoso
Polymers 2011, 3(2), 928-941; https://doi.org/10.3390/polym3020928 - 1 Jun 2011
Cited by 85 | Viewed by 19901
Abstract
We present the characterization of commercially available Poly(hexamethylene biguanide) hydrochloride (PHMB), a polymer with biocidal activity and several interesting properties that make this material suitable as a building block for supramolecular chemistry and “smart” materials. We studied polymer structure in water solution by [...] Read more.
We present the characterization of commercially available Poly(hexamethylene biguanide) hydrochloride (PHMB), a polymer with biocidal activity and several interesting properties that make this material suitable as a building block for supramolecular chemistry and “smart” materials. We studied polymer structure in water solution by dynamic light scattering, surface tension and capacitance spectroscopy. It shows typical surfactant behavior due to amphiphilic structure and low molecular weight. Spectroscopic (UV/Vis, FT-NIR) and thermal characterization (differential scanning calorimetry, DSC, and thermogravimetric analysis, TGA) were performed to give additional insight into the material structure in solution and solid state. These results can be the foundation for more detailed investigations on usefulness of PHMB in new complex materials and devices. Full article
(This article belongs to the Special Issue Water-Soluble Polymers)
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334 KiB  
Article
Using Light Scattering to Screen Polyelectrolytes (PEL) Performance in Flocculation
by Maria G. Rasteiro, Ineide Pinheiro, Fernando A. P. Garcia, Paulo Ferreira and David Hunkeler
Polymers 2011, 3(2), 915-927; https://doi.org/10.3390/polym3020915 - 27 May 2011
Cited by 19 | Viewed by 8288
Abstract
Flocculation of precipitated calcium carbonate (PCC) was monitored using light diffraction spectroscopy (LDS). Four cationic polyacrylamides of high molar mass and with different degrees of branching, all copolymers of acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (Q9), were tested. LDS supplied information about the [...] Read more.
Flocculation of precipitated calcium carbonate (PCC) was monitored using light diffraction spectroscopy (LDS). Four cationic polyacrylamides of high molar mass and with different degrees of branching, all copolymers of acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (Q9), were tested. LDS supplied information about the kinetic curves for flocs growth and also for the flocs structure evolution. Flocculation kinetics, flocs size and structure, flocs resistance and reflocculation capacity could be correlated with the degree of branching of the polyelectrolytes (PEL). Furthermore, PEL with different degrees of branching corresponded to different values for the intrinsic viscosity, indicating differences in the polymer conformation, which explained well the performance differences in flocculation. Full article
(This article belongs to the Special Issue Polyelectrolytes)
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423 KiB  
Review
Synthetic Polymer Scaffolds for Stem Cell Transplantation in Retinal Tissue Engineering
by Jing Yao, Sarah L. Tao and Michael J. Young
Polymers 2011, 3(2), 899-914; https://doi.org/10.3390/polym3020899 - 26 May 2011
Cited by 53 | Viewed by 9967
Abstract
Age-related macular degeneration and retinitis pigmentosa are two leading causes of irreversible blindness characterized by photoreceptor loss. Cell transplantation may be one of the most promising approaches of retinal repair. However, several problems hinder the success of retinal regeneration, including cell delivery and [...] Read more.
Age-related macular degeneration and retinitis pigmentosa are two leading causes of irreversible blindness characterized by photoreceptor loss. Cell transplantation may be one of the most promising approaches of retinal repair. However, several problems hinder the success of retinal regeneration, including cell delivery and survival, limited cell integration and incomplete cell differentiation. Recent studies show that polymer scaffolds can address these three problems. This article reviews the current literature on synthetic polymer scaffolds used for stem cell transplantation, especially retinal progenitor cells. The advantages and disadvantages of different polymer scaffolds, the role of different surface modifications on cell attachment and differentiation, and controlled drug delivery are discussed. The development of material and surface modification techniques is vital in making cell transplantation a clinical success. Full article
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364 KiB  
Review
Brillouin Scattering in Polymer Optical Fibers: Fundamental Properties and Potential Use in Sensors
by Yosuke Mizuno and Kentaro Nakamura
Polymers 2011, 3(2), 886-898; https://doi.org/10.3390/polym3020886 - 26 May 2011
Cited by 24 | Viewed by 9575
Abstract
We review the fundamental properties of Brillouin scattering in a perfluorinated graded-index polymer optical fiber (PFGI-POF) with 120 μm core diameter. The experiments were performed at 1.55 μm telecommunication wavelength. The Brillouin frequency shift (BFS) and the Brillouin bandwidth were 2.83 GHz and [...] Read more.
We review the fundamental properties of Brillouin scattering in a perfluorinated graded-index polymer optical fiber (PFGI-POF) with 120 μm core diameter. The experiments were performed at 1.55 μm telecommunication wavelength. The Brillouin frequency shift (BFS) and the Brillouin bandwidth were 2.83 GHz and 105 MHz, respectively. The Brillouin gain coefficient was calculated to be 3.09 × 10−11 m/W, which was comparable to that of fused silica fibers. The Brillouin threshold power of the 100 m POF was estimated to be as high as 24 W, which can be, for practical applications, reduced by using POFs with smaller cores. These properties were compared with those of silica-based graded-index multi-mode fibers. We also investigated the BFS dependences on strain and temperature. They showed negative dependences with coefficients of −121.8 MHz/% and −4.09 MHz/K, respectively, which are −0.2 and −3.5 times as large as those in silica fibers. These BFS dependences indicate that the Brillouin scattering in PFGI-POFs can be potentially applied to high-accuracy temperature sensing with reduced strain sensitivity. Full article
(This article belongs to the Special Issue Polymers for Optical Applications)
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568 KiB  
Communication
A Possibility for Construction of an Iodine Cleaning System Based on Doping for π-Conjugated Polymers
by Hiromasa Goto
Polymers 2011, 3(2), 875-885; https://doi.org/10.3390/polym3020875 - 16 May 2011
Cited by 21 | Viewed by 8572
Abstract
An iodine accumulation method using polyaniline (PANI) and a textile composite is proposed. PANI/pulp paper sheets prepared by a paper making technique are suitable for iodine adsorption, because of good processability. The PANI-based paper sheets can be applied for iodine cleanup as air [...] Read more.
An iodine accumulation method using polyaniline (PANI) and a textile composite is proposed. PANI/pulp paper sheets prepared by a paper making technique are suitable for iodine adsorption, because of good processability. The PANI-based paper sheets can be applied for iodine cleanup as air filters, water filters, and floorcloth. This concept may lead to a development of an iodine cleaning machine or iodine shield cloth based on π-conjugated polymer composites. In-situ vapor phase doping of iodine, observation of surface images, and IR measurements are carried out to examine iodine doping function for the PANI/pulp paper sheets. Full article
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714 KiB  
Article
Polarized Emission of Wholly Aromatic Bio-Based Copolyesters of a Liquid Crystalline Nature
by Kai Kan, Daisaku Kaneko and Tatsuo Kaneko
Polymers 2011, 3(2), 861-874; https://doi.org/10.3390/polym3020861 - 16 May 2011
Cited by 9 | Viewed by 8691
Abstract
A novel thermotropic liquid crystalline polymers poly{3-benzylidene amino-4-hydroxybenzoic acid (3,4-BAHBA)-co-trans-4-hydroxycinnamic acid (4HCA: trans-coumaric acid)} (Poly(3,4-BAHBA-co-4HCA)), was synthesized by the thermal polycondensation of 4HCA and 3,4-BAHBA, which was synthesized by a reaction of 3-amino-4-hydroxybenzoic acid (3,4-AHBA) with benzaldehyde. When [...] Read more.
A novel thermotropic liquid crystalline polymers poly{3-benzylidene amino-4-hydroxybenzoic acid (3,4-BAHBA)-co-trans-4-hydroxycinnamic acid (4HCA: trans-coumaric acid)} (Poly(3,4-BAHBA-co-4HCA)), was synthesized by the thermal polycondensation of 4HCA and 3,4-BAHBA, which was synthesized by a reaction of 3-amino-4-hydroxybenzoic acid (3,4-AHBA) with benzaldehyde. When the 4HCA compositions of Poly(3,4-BAHBA-co-4HCA)s were above 55 mol%, the copolymers showed a nematic, liquid crystalline phase. Differential scanning calorimetry (DSC) measurements of the copolymers showed a high glass transition temperature of more than 100 °C, sufficient for use in engineering plastics. Furthermore, the copolymers showed photoluminescence in an N-methylpyrrolidone (NMP) solution under ultraviolet (UV) light with a wavelength of 365 nm. Oriented film of Poly(3,4-BAHBA-co-4HCA) with a 4HCA composition of 75 mol% emitted polarized light, which was confirmed by fluorescent spectroscopy equipped with parallel and crossed polarizers. Full article
(This article belongs to the Special Issue Liquid Crystalline Polymers)
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397 KiB  
Article
Rotational Diffusion of Macromolecules and Nanoparticles Modeled as Non-Overlapping Bead Arrays in an Effective Medium
by Hengfu Wu, Umar Twahir, Alishia Davis, Ebenezer Duodo, Bahareh Kashani, Young Lee, Cindy Pena, Noni Whitley and Stuart A. Allison
Polymers 2011, 3(2), 846-860; https://doi.org/10.3390/polym3020846 - 13 May 2011
Viewed by 8554
Abstract
In this work, the retarding influence of a gel on the rotational motion of a macromolecule is investigated within the framework of the Effective Medium (EM) model. This is an extension of an earlier study that considered the effect of a gel on [...] Read more.
In this work, the retarding influence of a gel on the rotational motion of a macromolecule is investigated within the framework of the Effective Medium (EM) model. This is an extension of an earlier study that considered the effect of a gel on the translational motion of a macromolecule [Allison, S. et al. J. Phys. Chem. B 2008, 112, 5858-5866]. The macromolecule is modeled as an array of non-overlapping spherical beads with no restriction placed on their size or configuration. Specific applications include the rotational motion of right circular cylinders and wormlike chains modeled as strings of identical touching beads. The procedure is then used to examine the electric birefringence decay of a 622 base pair DNA fragment in an agarose gel. At low gel concentration (M ≤ 0.010 gm/mL), good agreement between theory and experiment is achieved if the persistence length of DNA is taken to be 65 nm and the gel fiber radius of agarose is taken to be 2.5 nm. At higher gel concentrations, the EM model substantially underestimates the rotational relaxation time of DNA and this can be attributed to the onset of direct interactions that become significant when the effective particle size becomes comparable to the mean gel fiber spacing. Full article
(This article belongs to the Special Issue Polymer Nanogels and Microgels)
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353 KiB  
Article
Mechanism Studies of LCP Synthesis
by Anne Buyle Padias and Henry K. Hall, Jr.
Polymers 2011, 3(2), 833-845; https://doi.org/10.3390/polym3020833 - 4 May 2011
Cited by 19 | Viewed by 13758
Abstract
The LCP (Liquid Crystal Polymer) known as Vectra is synthesized by acidolysis of 4-hydroxybenzoic acid with 6-hydroxy-2-naphthoic acid. The apparently simple acidolysis mechanism for LCP polycondensation is in fact a complex blend of mechanisms. Kinetics of model reactions and of actual polycondensations followed [...] Read more.
The LCP (Liquid Crystal Polymer) known as Vectra is synthesized by acidolysis of 4-hydroxybenzoic acid with 6-hydroxy-2-naphthoic acid. The apparently simple acidolysis mechanism for LCP polycondensation is in fact a complex blend of mechanisms. Kinetics of model reactions and of actual polycondensations followed second-order kinetics and their rate constants were comparable. In the latter stages, ketene loss leads to phenolic ends, while decarboxylation provides phenyl ester ends. Accordingly, the mechanism changes to phenolysis. A quinone methide intermediate may also intervene, as revealed by kinetics studies and MALDI-TOF spectroscopy. Tailor-made matrices and synthesis of alternating well-defined oligomers assisted our studies. Nucleophilic aromatic substitutions may play a role, and we speculate on possible chain polycondensation. Esterolysis may be a useful alternative to LCP synthesis. Complications caused by ketene loss can be averted by the use of methoxycarbonyloxy monomers. Full article
(This article belongs to the Special Issue Liquid Crystalline Polymers)
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628 KiB  
Article
Surface Modification of Poly(L-lactic acid) Nanofiber with Oligo(D-lactic acid) Bioactive-Peptide Conjugates for Peripheral Nerve Regeneration
by Sachiro Kakinoki, Sho Uchida, Tomo Ehashi, Akira Murakami and Tetsuji Yamaoka
Polymers 2011, 3(2), 820-832; https://doi.org/10.3390/polym3020820 - 27 Apr 2011
Cited by 30 | Viewed by 9854
Abstract
In some traumatic nerve injuries, autologous nerve grafting is the first choice for bridging the gap between the severed nerve ends. However, this therapeutic strategy has some disadvantages, including permanent loss of donor function and requirement of multiple surgeries. An attractive alternative to [...] Read more.
In some traumatic nerve injuries, autologous nerve grafting is the first choice for bridging the gap between the severed nerve ends. However, this therapeutic strategy has some disadvantages, including permanent loss of donor function and requirement of multiple surgeries. An attractive alternative to this therapeutic technique is the use of artificial nerve conduit. Poly (L-lactic acid) (PLLA) is widely used as a substrate for artificial nerve conduit because it is readily biodegradable, but it is not inherently biologically active. In this study, we developed a PLLA nanofibrous nerve conduit, modified with a conjugate of oligo (D-lactic acid) (ODLA) and the neurite outgrowth, thereby promoting peptide AG73 (RKRLQVQLSIRT) to improve nerve regeneration. PLA/ODLA-AG73 nanofibrous conduit was fabricated by electrospinning and then transplanted at the 10 mm gap of rat sciatic nerve. After six months, electrophysiological evaluation revealed that it achieved better functional reinnervation than silicone tube (used as a reference) or unmodified PLLA nanofibrous conduit. Full article
(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)
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359 KiB  
Article
Counterion Condensation and Effective Charge of PAMAM Dendrimers
by Ute Böhme, Anja Klenge, Brigitte Hänel and Ulrich Scheler
Polymers 2011, 3(2), 812-819; https://doi.org/10.3390/polym3020812 - 27 Apr 2011
Cited by 27 | Viewed by 8470
Abstract
PAMAM dendrimers are used as a model system to investigate the effects of counterion condensation and the effective charge for spherical polyelectrolytes. Because of their amino groups, PAMAM dendrimers are weak polyelectrolytes. Lowering the pH results in an increasing protonation of the amino [...] Read more.
PAMAM dendrimers are used as a model system to investigate the effects of counterion condensation and the effective charge for spherical polyelectrolytes. Because of their amino groups, PAMAM dendrimers are weak polyelectrolytes. Lowering the pH results in an increasing protonation of the amino groups which is monitored via the proton chemical shifts of the adjacent CH2 groups. The effective charge is determined from a combination of diffusion and electrophoresis NMR. The fraction of the charges, which are effective for the interaction with an external electric field or other charges, decreases with increasing generation (size) of the dendrimers. Full article
(This article belongs to the Special Issue Polyelectrolytes)
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607 KiB  
Review
Thermosensitive Self-Assembling Block Copolymers as Drug Delivery Systems
by Giulia Bonacucina, Marco Cespi, Giovanna Mencarelli, Gianfabio Giorgioni and Giovanni Filippo Palmieri
Polymers 2011, 3(2), 779-811; https://doi.org/10.3390/polym3020779 - 19 Apr 2011
Cited by 115 | Viewed by 18767
Abstract
Self-assembling block copolymers (poloxamers, PEG/PLA and PEG/PLGA diblock and triblock copolymers, PEG/polycaprolactone, polyether modified poly(Acrylic Acid)) with large solubility difference between hydrophilic and hydrophobic moieties have the property of forming temperature dependent micellar aggregates and, after a further temperature increase, of gellifying due [...] Read more.
Self-assembling block copolymers (poloxamers, PEG/PLA and PEG/PLGA diblock and triblock copolymers, PEG/polycaprolactone, polyether modified poly(Acrylic Acid)) with large solubility difference between hydrophilic and hydrophobic moieties have the property of forming temperature dependent micellar aggregates and, after a further temperature increase, of gellifying due to micelle aggregation or packing. This property enables drugs to be mixed in the sol state at room temperature then the solution can be injected into a target tissue, forming a gel depot in-situ at body temperature with the goal of providing drug release control. The presence of micellar structures that give rise to thermoreversible gels, characterized by low toxicity and mucomimetic properties, makes this delivery system capable of solubilizing water-insoluble or poorly soluble drugs and of protecting labile molecules such as proteins and peptide drugs. Full article
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530 KiB  
Article
Polyelectrolyte Complex Nanoparticles of Poly(ethyleneimine) and Poly(acrylic acid): Preparation and Applications
by Martin Müller, Bernd Keßler, Johanna Fröhlich, Sebastian Poeschla and Bernhard Torger
Polymers 2011, 3(2), 762-778; https://doi.org/10.3390/polym3020762 - 12 Apr 2011
Cited by 52 | Viewed by 12577
Abstract
In this contribution we outline polyelectrolyte (PEL) complex (PEC) nanoparticles, prepared by mixing solutions of the low cost PEL components poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAC). It was found, that the size and internal structure of PEI/PAC particles can be regulated by process, [...] Read more.
In this contribution we outline polyelectrolyte (PEL) complex (PEC) nanoparticles, prepared by mixing solutions of the low cost PEL components poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAC). It was found, that the size and internal structure of PEI/PAC particles can be regulated by process, media and structural parameters. Especially, mixing order, mixing ratio, PEL concentration, pH and molecular weight, were found to be sensible parameters to regulate the size (diameter) of spherical PEI/PAC nanoparticles, in the range between 80–1,000 nm, in a defined way. Finally, applications of dispersed PEI/PAC particles as additives for the paper making process, as well as for drug delivery, are outlined. PEI/PAC nanoparticles mixed directly on model cellulose film showed a higher adsorption level applying the mixing order 1. PAC 2. PEI compared to 1. PEI 2. PAC. Surface bound PEI/PAC nanoparticles were found to release a model drug compound and to stay immobilized due to the contact with the aqueous release medium. Full article
(This article belongs to the Special Issue Polyelectrolytes)
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633 KiB  
Review
Hydrogels for Cardiac Tissue Engineering
by Zhenqing Li and Jianjun Guan
Polymers 2011, 3(2), 740-761; https://doi.org/10.3390/polym3020740 - 9 Apr 2011
Cited by 161 | Viewed by 19834
Abstract
Cardiac tissue regeneration is an integrated process involving both cells and supporting matrix. Cardiomyocytes and stem cells are utilized to regenerate cardiac tissue. Hydrogels, because of their tissue-like properties, have been used as supporting matrices to deliver cells into infarcted cardiac muscle. Bioactive [...] Read more.
Cardiac tissue regeneration is an integrated process involving both cells and supporting matrix. Cardiomyocytes and stem cells are utilized to regenerate cardiac tissue. Hydrogels, because of their tissue-like properties, have been used as supporting matrices to deliver cells into infarcted cardiac muscle. Bioactive and biocompatible hydrogels mimicking biochemical and biomechanical microenvironments in native tissue are needed for successful cardiac tissue regeneration. These hydrogels not only retain cells in the infarcted area, but also provide support for restoring myocardial wall stress and cell survival and functioning. Many hydrogels, including natural polymer hydrogels, synthetic polymer hydrogels, and natural/synthetic hybrid hydrogels are employed for cardiac tissue engineering. In this review, types of hydrogels used for cardiac tissue engineering are briefly introduced. Their advantages and disadvantages are discussed. Furthermore, strategies for cardiac regeneration using hydrogels are reviewed. Full article
(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)
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1875 KiB  
Article
Multiblock Copolymers of Styrene and Butyl Acrylate via Polytrithiocarbonate-Mediated RAFT Polymerization
by Bastian Ebeling and Philipp Vana
Polymers 2011, 3(2), 719-739; https://doi.org/10.3390/polym3020719 - 31 Mar 2011
Cited by 23 | Viewed by 14101
Abstract
When linear polytrithiocarbonates as Reversible Addition-Fragmentation chain Transfer (RAFT) agents are employed in a radical polymerization, the resulting macromolecules consist of several homogeneous polymer blocks, interconnected by the functional groups of the respective RAFT agent. Via a second polymerization with another monomer, multiblock [...] Read more.
When linear polytrithiocarbonates as Reversible Addition-Fragmentation chain Transfer (RAFT) agents are employed in a radical polymerization, the resulting macromolecules consist of several homogeneous polymer blocks, interconnected by the functional groups of the respective RAFT agent. Via a second polymerization with another monomer, multiblock copolymers—polymers with alternating segments of both monomers—can be prepared. This strategy was examined mechanistically in detail based on subsequent RAFT polymerizations of styrene and butyl acrylate. Size-exclusion chromatography (SEC) of these polymers showed that the examined method yields low-disperse products. In some cases, resolved peaks for molecules with different numbers of blocks (polymer chains separated by the trithiocarbonate groups) could be observed. Cleavage of the polymers at the trithiocarbonate groups and SEC analysis of the products showed that the blocks in the middle of the polymers are longer than those at the ends and that the number of blocks corresponds to the number of functional groups in the initial RAFT agent. Furthermore, the produced multiblock copolymers were analyzed via differential scanning calorimetry (DSC). This work underlines that the examined methodology is very well suited for the synthesis of well-defined multiblock copolymers. Full article
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1939 KiB  
Article
Low Molecular Weight pDMAEMA-block-pHEMA Block-Copolymers Synthesized via RAFT-Polymerization: Potential Non-Viral Gene Delivery Agents?
by Olga Samsonova, Christian Pfeiffer, Markus Hellmund, Olivia M. Merkel and Thomas Kissel
Polymers 2011, 3(2), 693-718; https://doi.org/10.3390/polym3020693 - 28 Mar 2011
Cited by 69 | Viewed by 14610
Abstract
The aim of this study was to investigate non-viral pDNA carriers based on diblock-copolymers consisting of poly(2-(dimethyl amino)ethyl methacrylate) (pDMAEMA) and poly(2-hydroxyethyl methacrylate) (pHEMA). Specifically the block-lengths and molecular weights were varied to determine the minimal requirements for transfection. Such vectors should allow [...] Read more.
The aim of this study was to investigate non-viral pDNA carriers based on diblock-copolymers consisting of poly(2-(dimethyl amino)ethyl methacrylate) (pDMAEMA) and poly(2-hydroxyethyl methacrylate) (pHEMA). Specifically the block-lengths and molecular weights were varied to determine the minimal requirements for transfection. Such vectors should allow better transfection at acceptable toxicity levels and the entire diblock-copolymer should be suitable for renal clearance. For this purpose, a library of linear poly(2-(dimethyl amino)ethyl methacrylate-block-poly(2-hydroxyl methacrylate) (pDMAEMA-block-pHEMA) copolymers was synthesized via RAFT (reversible addition-fragmentation chain transfer) polymerization in a molecular weight (Mw) range of 17–35.7 kDa and analyzed using 1H and 13C NMR (nuclear magnetic resonance), ATR (attenuated total reflectance), GPC (gel permeation chromatography) and DSC (differential scanning calorimetry). Copolymers possessing short pDMAEMA-polycation chains were 1.4–9.7 times less toxic in vitro than polyethylenimine (PEI) 25 kDa, and complexed DNA into polyplexes of 100–170 nm, favorable for cellular uptake. The DNA-binding affinity and polyplex stability against competing polyanions was comparable with PEI 25 kDa. The zeta-potential of polyplexes of pDMAEMA-grafted copolymers remained positive (+15–30 mV). In comparison with earlier reported low molecular weight homo pDMAEMA vectors, these diblock-copolymers showed enhanced transfection efficacy under in vitro conditions due to their lower cytotoxicity, efficient cellular uptake and DNA packaging. The homo pDMAEMA115 (18.3 kDa) self-assembled with DNA into small positively charged polyplexes, but was not able to transfect cells. The grafting of 6 and 57 repeating units of pHEMA (0.8 and 7.4 kDa) to pDMAEMA115 increased the transfection efficacy significantly, implying a crucial impact of pHEMA on vector-cell interactions. The intracellular trafficking, in vivo transfection efficacy and kinetics of low molecular weight pDMAEMA-block-pHEMA are subject of ongoing studies. Full article
(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)
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955 KiB  
Article
Spectroscopic Investigation of Composite Polymeric and Monocrystalline Systems with Ionic Conductivity
by Darya V. Radziuk and Helmuth Möhwald
Polymers 2011, 3(2), 674-692; https://doi.org/10.3390/polym3020674 - 24 Mar 2011
Cited by 13 | Viewed by 8353
Abstract
The conductivity mechanism is studied in the LiCF3SO3-doped polyethylene oxide by monitoring the vibrations of sulfate groups and mobility of Li+ ion along the polymeric chain at different EO/Li molar ratios in the temperature range from 16 to [...] Read more.
The conductivity mechanism is studied in the LiCF3SO3-doped polyethylene oxide by monitoring the vibrations of sulfate groups and mobility of Li+ ion along the polymeric chain at different EO/Li molar ratios in the temperature range from 16 to 90 °С. At the high EO/Li ratio (i.e., 30), the intensity of bands increases and a triplet appears at 1,045 cm−1, indicating the presence of free anions, ionic pairs and aggregates. The existence of free ions in the polymeric electrolyte is also proven by the red shift of bands in Raman spectra and a band shift to the low frequency Infra-red region at 65 < T < 355 °С. Based on quantum mechanical modeling, (method MNDO/d), the energies (minimum and maximum) correspond to the most probable and stable positions of Li+ along the polymeric chain. At room temperature, Li+ ion overcomes the intermediate state (minimum energy) through non-operating transitions (maximum energy) due to permanent intrapolymeric rotations (rotation of C, H and O atoms around each other). In solid electrolyte (Li2SO4) the mobility of Li+ ions increases in the temperature range from 20 to 227 °С, yielding higher conductivity. The results of the present work can be practically applied to a wide range of compact electronic devices, which are based on polymeric or solid electrolytes. Full article
(This article belongs to the Special Issue New Polymer Synthesis Reactions)
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Routes to Nanoparticle-Polymer Superlattices
by Sara Mehdizadeh Taheri, Steffen Fischer and Stephan Förster
Polymers 2011, 3(2), 662-673; https://doi.org/10.3390/polym3020662 - 24 Mar 2011
Cited by 30 | Viewed by 11179
Abstract
Nanoparticles can self-assemble into highly ordered two- and three-dimensional superlattices. For many practical applications these assemblies need to be integrated into polymeric matrices to provide stability and function. By appropriate co-assembly of nanoparticles and polymers it has become possible to tailor the nanoparticle [...] Read more.
Nanoparticles can self-assemble into highly ordered two- and three-dimensional superlattices. For many practical applications these assemblies need to be integrated into polymeric matrices to provide stability and function. By appropriate co-assembly of nanoparticles and polymers it has become possible to tailor the nanoparticle superlattice structure via the length and stiffness of the polymer chains. The present article outlines and discusses established routes to nanoparticle-polymer superlattices. Recent progress has been remarkable so that the integration into functional devices has become the next challenge. Full article
(This article belongs to the Special Issue Nano-Structures of Block Copolymers)
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