Polymers

743 KiB

Open AccessReview

Recombinant Spider Silks—Biopolymers with Potential for Future Applications

by Martin Humenik, Andrew M. Smith and Thomas Scheibel

Polymers 2011, 3(1), 640-661; https://doi.org/10.3390/polym3010640 - 17 Mar 2011

Cited by 74 | Viewed by 21810

Nature has evolved a range of materials that compete with man-made materials in physical properties; one of these is spider silk. Silk is a fibrous material that exhibits extremely high strength and toughness with regard to its low density. In this review we [...] Read more.

Nature has evolved a range of materials that compete with man-made materials in physical properties; one of these is spider silk. Silk is a fibrous material that exhibits extremely high strength and toughness with regard to its low density. In this review we discuss the molecular structure of spider silk and how this understanding has allowed the development of recombinant silk proteins that mimic the properties of natural spider silks. Additionally, we will explore the material morphologies and the applications of these proteins. Finally, we will look at attempts to combine the silk structure with chemical polymers and how the structure of silk has inspired the engineering of novel polymers. Full article

(This article belongs to the Special Issue Bioinspired Polymers)

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682 KiB

Open AccessArticle

Reusable Polymer-Supported Terpyridine Palladium Complex for Suzuki-Miyaura, Mizoroki-Heck, Sonogashira, and Tsuji-Trost Reaction in Water

by Toshimasa Suzuka, Kosuke Kimura and Takuya Nagamine

Polymers 2011, 3(1), 621-639; https://doi.org/10.3390/polym3010621 - 14 Mar 2011

Cited by 35 | Viewed by 10309

Abstract

A novel heterogeneous transition-metal catalyst comprising a polymer-supported terpyridine palladium(II) complex was prepared and found to promote the Suzuki-Miyaura, Mizoroki-Heck, Sonogashira, and Tsuji-Trost, reactions in water under aerobic conditions with a high to excellent yield. The catalyst was recovered by simple filtration and [...] Read more.

A novel heterogeneous transition-metal catalyst comprising a polymer-supported terpyridine palladium(II) complex was prepared and found to promote the Suzuki-Miyaura, Mizoroki-Heck, Sonogashira, and Tsuji-Trost, reactions in water under aerobic conditions with a high to excellent yield. The catalyst was recovered by simple filtration and directly reused several times without loss of catalytic activity. Full article

(This article belongs to the Special Issue New Polymer Synthesis Reactions)

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Graphical abstract

906 KiB

Open AccessArticle

Modulating Biofunctional starPEG Heparin Hydrogels by Varying Size and Ratio of the Constituents

by Petra Birgit Welzel, Silvana Prokoph, Andrea Zieris, Milauscha Grimmer, Stefan Zschoche, Uwe Freudenberg and Carsten Werner

Polymers 2011, 3(1), 602-620; https://doi.org/10.3390/polym3010602 - 14 Mar 2011

Cited by 69 | Viewed by 14027

Abstract

Heparin and four-armed, end-functionalized polyethylene glycol (starPEG) were recently combined in sets of covalently linked biohybrid hydrogel networks capable of directing various therapeutically relevant cell types. To extend the variability and applicability of this novel biomaterials platform, the influence of size and molar [...] Read more.

Heparin and four-armed, end-functionalized polyethylene glycol (starPEG) were recently combined in sets of covalently linked biohybrid hydrogel networks capable of directing various therapeutically relevant cell types. To extend the variability and applicability of this novel biomaterials platform, the influence of size and molar ratio of the two building blocks on the hydrogel properties was investigated in the present study. Heparin and starPEG were converted in various molar ratios and in different molecular weights to tune swelling, stiffness and pore size of the obtained polymer networks. Hydrogels with a range of elastic moduli could be generated by controlling either the crosslinking density or the chain length of the starPEG, whereas altering the molecular mass of heparin did not significantly affect hydrogel strength. The concentration of heparin in the swollen gels was found to be nearly invariant at varying crosslinking degrees for any given set of building blocks but adjustable by the size of the building blocks. Since heparin is the base for all biofunctionalization schemes of the gels these findings lay the ground for an even more versatile customization of this powerful new class of biomaterials. Full article

(This article belongs to the Collection Polysaccharides)

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Graphical abstract

484 KiB

Open AccessArticle

Phase Diagrams of the Aqueous Two-Phase Systems of Poly(ethylene glycol)/Sodium Polyacrylate/Salts

by Hans-Olof Johansson, Eloi Feitosa and Adalberto Pessoa Junior

Polymers 2011, 3(1), 587-601; https://doi.org/10.3390/polym3010587 - 09 Mar 2011

Cited by 61 | Viewed by 13852

Abstract

Aqueous two-phase systems consisting of polyethylene glycol (PEG), sodium polyacrylate (NaPAA), and a salt have been studied. The effects of the polymer size, salt type (NaCl, Na₂SO₄, sodium adipate and sodium azelate) and salt concentrations on the position of [...] Read more.

Aqueous two-phase systems consisting of polyethylene glycol (PEG), sodium polyacrylate (NaPAA), and a salt have been studied. The effects of the polymer size, salt type (NaCl, Na₂SO₄, sodium adipate and sodium azelate) and salt concentrations on the position of the binodal curve were investigated. The investigated PEG molecules had a molar mass of 2,000 to 8,000 g/mol, while that of NaPAA was 8,000 g/mol. Experimental phase diagrams, and tie lines and calculated phase diagrams, based on Flory-Huggins theory of polymer solutions are presented. Due to strong enthalpic and entropic balancing forces, the hydrophobicity of the added salt has a strong influence on the position of the binodal, which could be reproduced by model calculations. Full article

(This article belongs to the Special Issue Polyelectrolytes)

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1063 KiB

Open AccessArticle

PLGA-Based Microparticles for the Sustained Release of BMP-2

by Giles T. S. Kirby, Lisa J. White, Cheryl V. Rahman, Helen C. Cox, Omar Qutachi, Felicity R. A. J. Rose, Dietmar W. Hutmacher, Kevin M. Shakesheff and Maria A. Woodruff

Polymers 2011, 3(1), 571-586; https://doi.org/10.3390/polym3010571 - 01 Mar 2011

Cited by 58 | Viewed by 15693

Abstract

The development of growth factor delivery strategies to circumvent the burst release phenomenon prevalent in most current systems has driven research towards encapsulating molecules in resorbable polymer matrices. For these polymer release techniques to be efficacious in a clinical setting, several key points [...] Read more.

The development of growth factor delivery strategies to circumvent the burst release phenomenon prevalent in most current systems has driven research towards encapsulating molecules in resorbable polymer matrices. For these polymer release techniques to be efficacious in a clinical setting, several key points need to be addressed. This present study has investigated the encapsulation of the growth factor, BMP-2 within PLGA/PLGA-PEG-PLGA microparticles. Morphology, size distribution, encapsulation efficiency and release kinetics were investigated and we have demonstrated a sustained release of bioactive BMP-2. Furthermore, biocompatibility of the PLGA microparticles was established and released BMP-2 was shown to promote the differentiation of MC3T3-E1 cells towards the osteogenic lineage to a greater extent than osteogenic supplements (as early as day 10 in culture), as determined using alkaline phosphatase and alizarin red assays. This study showcases a potential BMP-2 delivery system which may now be translated into more complex delivery systems, such as 3D, mechanically robust scaffolds for bone tissue regeneration applications. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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513 KiB

Open AccessArticle

Synthesis and Characterization of Poly(3-hexylthiophene)-b-Polystyrene for Photovoltaic Application

by Zhijie Gu, Ying Tan, Kousuke Tsuchiya, Takeshi Shimomura and Kenji Ogino

Polymers 2011, 3(1), 558-570; https://doi.org/10.3390/polym3010558 - 01 Mar 2011

Cited by 40 | Viewed by 10050

Abstract

Poly(3-hexylthiophene)-block-polystyrene (P3HT-b-PS) was synthesized by Suzuki coupling reaction between P3HT and PS, prepared by Grignard metathesis polymerization and atom transfer radical polymerization (ATRP), respectively. The formation of block copolymer was confirmed by gel permeation chromatography (GPC) and NMR. Differential [...] Read more.

Poly(3-hexylthiophene)-block-polystyrene (P3HT-b-PS) was synthesized by Suzuki coupling reaction between P3HT and PS, prepared by Grignard metathesis polymerization and atom transfer radical polymerization (ATRP), respectively. The formation of block copolymer was confirmed by gel permeation chromatography (GPC) and NMR. Differential scanning calorimetry (DSC) thermogram of block copolymers showed glass transition of PS block and melting/crystallization of P3HT block, suggesting a microphase separated structure, which was also confirmed by atomic force microscopy (AFM) images and UV-vis absorption spectra. The annealing effect on the morphology of the composite films consisting of P3HT-b-PS and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) was investigated. Photovoltaic cells fabricated using P3HT-b-PS and PCBM were evaluated. Full article

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476 KiB

Open AccessArticle

The Challenge of Synthesizing Oligomers for Molecular Wires

by Roar Søndergaard and Frederik C. Krebs

Polymers 2011, 3(1), 545-557; https://doi.org/10.3390/polym3010545 - 28 Feb 2011

Cited by 5 | Viewed by 6985

Abstract

Controlling the size of the oligomer and introducing functional groups at the ends of the oligomer that allow it to react with separate electrodes are critical issues when preparing materials for molecular wires. We demonstrate a general synthetic approach to oligophenylenevinylene (OPV) derivative [...] Read more.

Controlling the size of the oligomer and introducing functional groups at the ends of the oligomer that allow it to react with separate electrodes are critical issues when preparing materials for molecular wires. We demonstrate a general synthetic approach to oligophenylenevinylene (OPV) derivative molecules with a molecular length up to 9–10 nm which allow for the introduction of aromatic thioacetate functionality in fully conjugated oligomer systems. Oligomers containing 3–15 phenyl units were synthesized by step wise Horner-Wadsworth-Emmons (HWE) reactions of a bifunctional OPV-monomer, which demonstrated good control of the size of the OPVs. Workup after each reaction step ensures a high purity of the final products. End group functionalization was introduced as a last step. Full article

(This article belongs to the Special Issue Single Molecular Wire)

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571 KiB

Open AccessArticle

A 3D Electroactive Polypyrrole-Collagen Fibrous Scaffold for Tissue Engineering

by Soh-Zeom Yow, Tze Han Lim, Evelyn K. F. Yim, Chwee Teck Lim and Kam W. Leong

Polymers 2011, 3(1), 527-544; https://doi.org/10.3390/polym3010527 - 28 Feb 2011

Cited by 55 | Viewed by 11164

Abstract

Fibers that can provide topographical, biochemical and electrical cues would be attractive for directing the differentiation of stem cells into electro-responsive cells such as neuronal or muscular cells. Here we report on the fabrication of polypyrrole-incorporated collagen-based fibers via interfacial polyelectrolyte complexation (IPC). [...] Read more.

Fibers that can provide topographical, biochemical and electrical cues would be attractive for directing the differentiation of stem cells into electro-responsive cells such as neuronal or muscular cells. Here we report on the fabrication of polypyrrole-incorporated collagen-based fibers via interfacial polyelectrolyte complexation (IPC). The mean ultimate tensile strength of the fibers is 304.0 ± 61.0 MPa and the Young’s Modulus is 10.4 ± 4.3 GPa. Human bone marrow-derived mesenchymal stem cells (hMSCs) are cultured on the fibers in a proliferating medium and stimulated with an external electrical pulse generator for 5 and 10 days. The effects of polypyrrole in the fiber system can be observed, with hMSCs adopting a neuronal-like morphology at day 10, and through the upregulation of neural markers, such as noggin, MAP2, neurofilament, β tubulin III and nestin. This study demonstrates the potential of this fiber system as an attractive 3D scaffold for tissue engineering, where collagen is present on the fiber surface for cellular adhesion, and polypyrrole is encapsulated within the fiber for enhanced electrical communication in cell-substrate and cell-cell interactions. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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Graphical abstract

226 KiB

Open AccessReview

Biopolymers for Hard and Soft Engineered Tissues: Application in Odontoiatric and Plastic Surgery Field

by Eriberto Bressan, Vittorio Favero, Chiara Gardin, Letizia Ferroni, Laura Iacobellis, Lorenzo Favero, Vincenzo Vindigni, Mario Berengo, Stefano Sivolella and Barbara Zavan

Polymers 2011, 3(1), 509-526; https://doi.org/10.3390/polym3010509 - 28 Feb 2011

Cited by 43 | Viewed by 10675

Abstract

The goal of modern dentistry and plastic surgery is to restore the patient to normal function, health and aesthetics, regardless of the disease or injury to the stomatognathic and cutaneous system respectively. In recent years tissue engineering and regenerative medicine have yielded many [...] Read more.

The goal of modern dentistry and plastic surgery is to restore the patient to normal function, health and aesthetics, regardless of the disease or injury to the stomatognathic and cutaneous system respectively. In recent years tissue engineering and regenerative medicine have yielded many novel tissue replacements and implementation strategies. Scientific advances in biomaterials, stem cell isolation, growth and differentiation factors and biomimetic environments have created unique opportunities to fabricate tissues in the laboratory. Repairing of bone and skin is likely to become of clinical interest when three dimensional tissue reconstructive procedures and the appropriate supporting biomimetic materials are correctly assembled. In the present review, we provide an overview of the most promising biopolymers that may find clinical application in dento-maxillo-facial and plastic surgery. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

967 KiB

Open AccessArticle

Cellulose Chemistry Meets Click Chemistry: Syntheses and Properties of Cellulose-Based Glycoclusters with High Structural Homogeneity

by Kaori Negishi, Yoichi Mashiko, Erika Yamashita, Atsushi Otsuka and Teruaki Hasegawa

Polymers 2011, 3(1), 489-508; https://doi.org/10.3390/polym3010489 - 24 Feb 2011

Cited by 30 | Viewed by 10321

Abstract

b-1,4-Glucans having oligosaccharide appendages (O-/N-linked b-maltoside and O-/N-linked b-lactoside) at 6C positions of all repeating units can be readily prepared from cellulose through a two step strategy composed of: (1) regio-selective and quantitative bromination/azidation to afford [...] Read more.

b-1,4-Glucans having oligosaccharide appendages (O-/N-linked b-maltoside and O-/N-linked b-lactoside) at 6C positions of all repeating units can be readily prepared from cellulose through a two step strategy composed of: (1) regio-selective and quantitative bromination/azidation to afford 6-azido-6-deoxycellulose; and (2) the subsequent Cu⁺-catalyzed coupling with oligosaccharides having terminal alkyne. The resultant cellulose derivatives showed improved water solubility in comparison to native cellulose; they, however, bound to carbohydrate-binding proteins in a rather non-specific manner. Molecular dynamics calculations revealed that these properties are attributable to rigid sheet-like structures of the cellulose derivatives and the subsequent exposure of their hydrophobic moieties to solvents. Full article

(This article belongs to the Collection Polysaccharides)

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1081 KiB

Open AccessReview

Bioinspired Poly(2-oxazoline)s

by Richard Hoogenboom and Helmut Schlaad

Polymers 2011, 3(1), 467-488; https://doi.org/10.3390/polym3010467 - 11 Feb 2011

Cited by 129 | Viewed by 14886

Abstract

Poly(2-oxazoline)s are regarded as pseudopeptides, thus bioinspired polymers, due to their structural relationship to polypeptides. Materials and solution properties can be tuned by varying the side-chain (hydrophilic-hydrophobic, chiral, bioorganic, etc.), opening the way to advanced stimulus-responsive materials and complex colloidal structures. The [...] Read more.

Poly(2-oxazoline)s are regarded as pseudopeptides, thus bioinspired polymers, due to their structural relationship to polypeptides. Materials and solution properties can be tuned by varying the side-chain (hydrophilic-hydrophobic, chiral, bioorganic, etc.), opening the way to advanced stimulus-responsive materials and complex colloidal structures. The bioinspired “smart” solution and aggregation behavior of poly(2-oxazoline)s in aqueous environments are discussed in this review. Full article

(This article belongs to the Special Issue Bioinspired Polymers)

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Graphical abstract

795 KiB

Open AccessArticle

Electrically Conductive Epoxy Adhesives

by Erol Sancaktar and Lan Bai

Polymers 2011, 3(1), 427-466; https://doi.org/10.3390/polym3010427 - 10 Feb 2011

Cited by 72 | Viewed by 22469

Abstract

Conductive adhesives are widely used in electronic packaging applications such as die attachment and solderless interconnections, component repair, display interconnections, and heat dissipation. The effects of film thickness as functions of filler volume fraction, conductive filler size, shape, as well as uncured adhesive [...] Read more.

Conductive adhesives are widely used in electronic packaging applications such as die attachment and solderless interconnections, component repair, display interconnections, and heat dissipation. The effects of film thickness as functions of filler volume fraction, conductive filler size, shape, as well as uncured adhesive matrix viscosity on the electrical conduction behavior of epoxy-based adhesives are presented in this work. For this purpose, epoxy-based adhesives were prepared using conductive fillers of different size, shape, and types, including Ni powder, flakes, and filaments, Ag powder, and Cu powder. The filaments were 20 μm in diameter, and 160 or 260 μm in length. HCl and H₃PO₄ acid solutions were used to etch and remove the surface oxide layers from the fillers. The plane resistance of filled adhesive films was measured using the four-point method. In all cases of conductive filler addition, the planar resistivity levels for the composite adhesive films increased when the film thickness was reduced. The shape of resistivity-thickness curves was negative exponential decaying type and was modeled using a mathematical relation. The relationships between the conductive film resistivities and the filler volume fractions were also derived mathematically based on the experimental data. Thus, the effects of surface treatment of filler particles, the type, size, shape of fillers, and the uncured epoxy viscosity could be included empirically by using these mathematical relations based on the experimental data. By utilizing the relations we proposed to model thickness-dependent and volume fraction-dependent conduction behaviors separately, we were able to describe the combined and coupled volume fraction-film thickness relationship mathematically based on our experimental data. Full article

(This article belongs to the Special Issue Conductive Polymers)

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Graphical abstract

855 KiB

Open AccessReview

Electrospun Nanofibrous Materials for Neural Tissue Engineering

by Yee-Shuan Lee and Treena Livingston Arinzeh

Polymers 2011, 3(1), 413-426; https://doi.org/10.3390/polym3010413 - 09 Feb 2011

Cited by 119 | Viewed by 14910

Abstract

The use of biomaterials processed by the electrospinning technique has gained considerable interest for neural tissue engineering applications. The tissue engineering strategy is to facilitate the regrowth of nerves by combining an appropriate cell type with the electrospun scaffold. Electrospinning can generate fibrous [...] Read more.

The use of biomaterials processed by the electrospinning technique has gained considerable interest for neural tissue engineering applications. The tissue engineering strategy is to facilitate the regrowth of nerves by combining an appropriate cell type with the electrospun scaffold. Electrospinning can generate fibrous meshes having fiber diameter dimensions at the nanoscale and these fibers can be nonwoven or oriented to facilitate neurite extension via contact guidance. This article reviews studies evaluating the effect of the scaffold’s architectural features such as fiber diameter and orientation on neural cell function and neurite extension. Electrospun meshes made of natural polymers, proteins and compositions having electrical activity in order to enhance neural cell function are also discussed. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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607 KiB

Open AccessLetter

A Pendulum-Like Motion of Nanofiber Gel Actuator Synchronized with External Periodic pH Oscillation

by Hiroki Nakagawa, Yusuke Hara, Shingo Maeda and Shuji Hasimoto

Polymers 2011, 3(1), 405-412; https://doi.org/10.3390/polym3010405 - 08 Feb 2011

Cited by 34 | Viewed by 9003

Abstract

In this study, we succeeded in manufacturing a novel nanofiber hydrogel actuator that caused a bending and stretching motion synchronized with external pH oscillation, based on a bromate/sulfite/ferrocyanide reaction. The novel nanofiber gel actuator was composed of electrospun nanofibers synthesized by copolymerizing acrylic [...] Read more.

In this study, we succeeded in manufacturing a novel nanofiber hydrogel actuator that caused a bending and stretching motion synchronized with external pH oscillation, based on a bromate/sulfite/ferrocyanide reaction. The novel nanofiber gel actuator was composed of electrospun nanofibers synthesized by copolymerizing acrylic acid and hydrophobic butyl methacrylate as a solubility control site. By changing the electrospinning flow rate, the nanofiber gel actuator introduced an anisotropic internal structure into the gel. Therefore, the unsymmetrical motion of the nanofiber actuator was generated. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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646 KiB

Open AccessArticle

The Effect of Polyterpenol Thin Film Surfaces on Bacterial Viability and Adhesion

by Kateryna Bazaka, Mohan V. Jacob, Vi Khanh Truong, Russell J. Crawford and Elena P. Ivanova

Polymers 2011, 3(1), 388-404; https://doi.org/10.3390/polym3010388 - 28 Jan 2011

Cited by 52 | Viewed by 9948

Abstract

The nanometer scale surface topography of a solid substrate is known to influence the extent of bacterial attachment and their subsequent proliferation to form biofilms. As an extension of our previous work on the development of a novel organic polymer coating for the [...] Read more.

The nanometer scale surface topography of a solid substrate is known to influence the extent of bacterial attachment and their subsequent proliferation to form biofilms. As an extension of our previous work on the development of a novel organic polymer coating for the prevention of growth of medically significant bacteria on three-dimensional solid surfaces, this study examines the effect of surface coating on the adhesion and proliferation tendencies of Staphylococcus aureus and compares to those previously investigated tendencies of Pseudomonas aeruginosa on similar coatings. Radio frequency plasma enhanced chemical vapor deposition was used to coat the surface of the substrate with thin film of terpinen-4-ol, a constituent of tea-tree oil known to inhibit the growth of a broad range of bacteria. The presence of the coating decreased the substrate surface roughness from approximately 2.1 nm to 0.4 nm. Similar to P. aeruginosa, S. aureus presented notably different patterns of attachment in response to the presence of the surface film, where the amount of attachment, extracellular polymeric substance production, and cell proliferation on the coated surface was found to be greatly reduced compared to that obtained on the unmodified surface. This work suggests that the antimicrobial and antifouling coating used in this study could be effectively integrated into medical and other clinically relevant devices to prevent bacterial growth and to minimize bacteria-associated adverse host responses. Full article

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Graphical abstract

665 KiB

Open AccessArticle

Structural Analysis of Aromatic Liquid Crystalline Polyesters

by Henry Hall, Samiul Ahad, Robert Bates, Maria Bertucci, Cristina Contreras, Alexandru Dospinoiu, Guangxin Lin, Nancy Singletary and Arpad Somogyi

Polymers 2011, 3(1), 367-387; https://doi.org/10.3390/polym3010367 - 27 Jan 2011

Cited by 4 | Viewed by 10342

Abstract

Laboratory preparations of liquid crystalline prepolymers, distillates accompanying prepolymers, final polymers, and sublimates accompanying final polymers were examined. NaOD/D₂O depolymerization of prepolymers and polymers back to monomers with integration of the ¹H NMR spectra showed up to 6% excess of [...] Read more.

Laboratory preparations of liquid crystalline prepolymers, distillates accompanying prepolymers, final polymers, and sublimates accompanying final polymers were examined. NaOD/D₂O depolymerization of prepolymers and polymers back to monomers with integration of the ¹H NMR spectra showed up to 6% excess of carboxyls over phenol groups, caused partly by loss of the low-boiling comonomer hydroquinone through distillation during prepolymerization and leaving anhydride units in the polymer chain. ESI⁻ MS and MS/MS of hexafluoroisopropanol extracts of the prepolymer detected small molecules including some containing anhydride groups; ESI⁺ MS showed the presence of small cyclic oligomers. ¹H NMR (including TOCSY) spectra provided more quantitative analyses of these oligomers. The final polymerization increases the length of the polymer chains and sublimes out the small oligomers. Anhydride linkages remaining in the polymer must make LCP’s more susceptible to degradation by nucleophilic reagents such as water, alkalis, and amines. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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552 KiB

Open AccessReview

New Strategies in the Development of Antimicrobial Coatings: The Example of Increasing Usage of Silver and Silver Nanoparticles

by Menno L. W. Knetsch and Leo H. Koole

Polymers 2011, 3(1), 340-366; https://doi.org/10.3390/polym3010340 - 26 Jan 2011

Cited by 578 | Viewed by 33365

Abstract

Bacterial infection from medical devices is a major problem and accounts for an increasing number of deaths as well as high medical costs. Many different strategies have been developed to decrease the incidence of medical device related infection. One way to prevent infection [...] Read more.

Bacterial infection from medical devices is a major problem and accounts for an increasing number of deaths as well as high medical costs. Many different strategies have been developed to decrease the incidence of medical device related infection. One way to prevent infection is by modifying the surface of the devices in such a way that no bacterial adhesion can occur. This requires modification of the complete surface with, mostly, hydrophilic polymeric surface coatings. These materials are designed to be non-fouling, meaning that protein adsorption and subsequent microbial adhesion are minimized. Incorporation of antimicrobial agents in the bulk material or as a surface coating has been considered a viable alternative for systemic application of antibiotics. However, the manifestation of more and more multi-drug resistant bacterial strains restrains the use of antibiotics in a preventive strategy. The application of silver nanoparticles on the surface of medical devices has been used to prevent bacterial adhesion and subsequent biofilm formation. The nanoparticles are either deposited directly on the device surface, or applied in a polymeric surface coating. The silver is slowly released from the surface, thereby killing the bacteria present near the surface. In the last decade there has been a surplus of studies applying the concept of silver nanoparticles as an antimicrobial agent on a range of different medical devices. The main problem however is that the exact antimicrobial mechanism of silver remains unclear. Additionally, the antimicrobial efficacy of silver on medical devices varies to a great extent. Here we will review existing antimicrobial coating strategies and discuss the use of silver or silver nanoparticles on surfaces that are designed to prevent medical device related infections. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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Open AccessArticle

Influence of Initial Substrate Concentration of the Belouzov-Zhabotinsky Reaction on Transmittance Self-Oscillation for a Nonthermoresponsive Polymer Chain

by Yusuke Hara and Rumana A. Jahan

Polymers 2011, 3(1), 330-339; https://doi.org/10.3390/polym3010330 - 26 Jan 2011

Cited by 17 | Viewed by 7465

Abstract

We succeeded in causing transmittance self-oscillations of a novel self-oscillating polymer chain induced by the Belouzov-Zhabotinsky (BZ) reaction under constant conditions. The novel polymer chain was composed of a biocompatible and non-thermoresponsive poly-vinylpyrrolidone (PVP) main-chain, covalently-bonded to the ruthenium catalyst (Ru(bpy)₃) [...] Read more.

We succeeded in causing transmittance self-oscillations of a novel self-oscillating polymer chain induced by the Belouzov-Zhabotinsky (BZ) reaction under constant conditions. The novel polymer chain was composed of a biocompatible and non-thermoresponsive poly-vinylpyrrolidone (PVP) main-chain, covalently-bonded to the ruthenium catalyst (Ru(bpy)₃) of the BZ reaction. We investigated the influence of initial substrate concentrations of the three BZ substrates on the transmittance self-oscillation of the novel polymer solution. As a result, we demonstrated that the width of the transmittance self-oscillation is significantly affected by these initial concentrations. However, the amplitude of the transmittance self-oscillation is hardly affected by the BZ substrate conditions. Furthermore, the period of the self‑oscillation has a good linear relationship to the concentration of the BZ substrates. Therefore, the period of the self-oscillation can be controlled by the selection of the initial concentrations of the BZ substrates. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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Open AccessArticle

Poly(alkyl methacrylate) Tooth Coatings for Dental Care: Evaluation of the Demineralisation-Protection Benefit Using a Time-Resolved In Vitro Method

by Birthe V. Nielsen, Thomas G. Nevell, Eugen Barbu, James R. Smith, Gareth D. Rees and John Tsibouklis

Polymers 2011, 3(1), 314-329; https://doi.org/10.3390/polym3010314 - 19 Jan 2011

Cited by 1 | Viewed by 10499

Abstract

An in vitro method for the time-resolved quantification of acid-mediated tooth demineralisation has been developed and evaluated against putative non-permanent protective formulations based on a series of poly(alkyl methacrylate)s. Using a thermostatted carousel, dentally relevant substrates consisting of hydroxyapatite discs or sections of [...] Read more.

An in vitro method for the time-resolved quantification of acid-mediated tooth demineralisation has been developed and evaluated against putative non-permanent protective formulations based on a series of poly(alkyl methacrylate)s. Using a thermostatted carousel, dentally relevant substrates consisting of hydroxyapatite discs or sections of bovine teeth have been exposed to aqueous citric acid under controlled conditions, before and after being treated with the polymeric coatings. The dissolution of phosphate was monitored by the determination of ³¹P by Inductively Coupled Plasma—Mass Spectrometry and by the spectrophotometric phosphovanadomolybdate method. Dose-response plots constructed for both groups of treated substrates have revealed that the coatings significantly reduce erosion rates but are less effective at inhibiting tooth demineralisation than the standard fluoride treatment. The approach has enabled an evaluation of the erosion-protection efficiency of each coating. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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548 KiB

Open AccessReview

Design of Autonomous Gel Actuators

by Shingo Maeda, Yusuke Hara, Satoshi Nakamaru and Shuji Hashimoto

Polymers 2011, 3(1), 299-313; https://doi.org/10.3390/polym3010299 - 11 Jan 2011

Cited by 7 | Viewed by 8650

Abstract

In this paper, we introduce autonomous gel actuators driven by chemical energy. The polymer gels prepared here have cyclic chemical reaction networks. With a cyclic reaction, the polymer gels generate periodical motion. The periodic motion of the gel is produced by the chemical [...] Read more.

In this paper, we introduce autonomous gel actuators driven by chemical energy. The polymer gels prepared here have cyclic chemical reaction networks. With a cyclic reaction, the polymer gels generate periodical motion. The periodic motion of the gel is produced by the chemical energy of the oscillatory Belouzov-Zhabotinsky (BZ) reaction. We have succeeded in making synthetic polymer gel move autonomously like a living organism. This experimental fact represents the great possibility of the chemical robot. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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Open AccessArticle

Structural and Mechanical Hysteresis at the Order-Order Transition of Block Copolymer Micellar Crystals

by Theresa A. LaFollette and Lynn M. Walker

Polymers 2011, 3(1), 281-298; https://doi.org/10.3390/polym3010281 - 11 Jan 2011

Cited by 15 | Viewed by 8896

Abstract

Concentrated solutions of a water-soluble block copolymer (PEO)₂₀-(PPO)₇₀-(PEO)₂₀ show a thermoreversible transition from a liquid to a gel. Over a range of concentration there also exists an order-order transition (OOT) between cubically-packed spherical micelles and hexagonally-packed cylindrical micelles. [...] Read more.

Concentrated solutions of a water-soluble block copolymer (PEO)₂₀-(PPO)₇₀-(PEO)₂₀ show a thermoreversible transition from a liquid to a gel. Over a range of concentration there also exists an order-order transition (OOT) between cubically-packed spherical micelles and hexagonally-packed cylindrical micelles. This OOT displays a hysteresis between the heating and cooling transitions that is observed at both the macroscale through rheology and nanoscale through small angle neutron scattering (SANS). The hysteresis is caused by the persistence of the cubically-packed spherical micelle phase into the hexagonally-packed cylindrical micelle phase likely due to the hindered realignment of the spherical micelles into cylindrical micelles and then packing of the cylindrical micelles into a hexagonally-packed cylindrical micelle phase. This type of hysteresis must be fully characterized, and possibly avoided, for these block copolymer systems to be used as templates in nanocomposites. Full article

(This article belongs to the Special Issue Nano-Structures of Block Copolymers)

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1104 KiB

Open AccessReview

Functionalization of Block Copolymer Vesicle Surfaces

by Stefan Egli, Helmut Schlaad, Nico Bruns and Wolfgang Meier

Polymers 2011, 3(1), 252-280; https://doi.org/10.3390/polym3010252 - 11 Jan 2011

Cited by 89 | Viewed by 16777

Abstract

In dilute aqueous solutions certain amphiphilic block copolymers self-assemble into vesicles that enclose a small pool of water with a membrane. Such polymersomes have promising applications ranging from targeted drug-delivery devices, to biosensors, and nanoreactors. Interactions between block copolymer membranes and their surroundings [...] Read more.

In dilute aqueous solutions certain amphiphilic block copolymers self-assemble into vesicles that enclose a small pool of water with a membrane. Such polymersomes have promising applications ranging from targeted drug-delivery devices, to biosensors, and nanoreactors. Interactions between block copolymer membranes and their surroundings are important factors that determine their potential biomedical applications. Such interactions are influenced predominantly by the membrane surface. We review methods to functionalize block copolymer vesicle surfaces by chemical means with ligands such as antibodies, adhesion moieties, enzymes, carbohydrates and fluorophores. Furthermore, surface-functionalization can be achieved by self-assembly of polymers that carry ligands at their chain ends or in their hydrophilic blocks. While this review focuses on the strategies to functionalize vesicle surfaces, the applications realized by, and envisioned for, such functional polymersomes are also highlighted. Full article

(This article belongs to the Special Issue Nano-Structures of Block Copolymers)

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1338 KiB

Open AccessArticle

Synthesis of Novel π-Conjugated Rod-Rod-Rod Triblock Copolymers Containing Poly(3-hexylthiophene) and Polyacetylene Segments by Combination of Quasi-Living GRIM and Living Anionic Polymerization

by Tomoya Higashihara, Cheng-Liang Liu, Wen-Chang Chen and Mitsuru Ueda

Polymers 2011, 3(1), 236-251; https://doi.org/10.3390/polym3010236 - 10 Jan 2011

Cited by 15 | Viewed by 9786

Abstract

The first successful synthesis of a new rod-rod-rod triblock copolymer, polyacetylene(PA)-b-poly(3-hexylthiophene)(P3HT)-b-PA could be synthesized by a combination of quasi-living Grignard metathesis (GRIM) and living anionic polymerization. We first confirmed that poly(4-tolyl vinyl sulfoxide) (PTVS), which is a soluble precursor [...] Read more.

The first successful synthesis of a new rod-rod-rod triblock copolymer, polyacetylene(PA)-b-poly(3-hexylthiophene)(P3HT)-b-PA could be synthesized by a combination of quasi-living Grignard metathesis (GRIM) and living anionic polymerization. We first confirmed that poly(4-tolyl vinyl sulfoxide) (PTVS), which is a soluble precursor for PA, could be synthesized by living anionic polymerization in THF at −78 °C, initiated with 3-methyl-1,1-diphenylpentyllithium as the initiator in the presence of in situ-generated lithium enolate. The molecular weights (MWs) and polydispersities (PDIs) were well controlled (MW = 5,200–27,000, PDI = 1.10–1.22), respectively. A coil-rod-coil triblock copolymer, PTVS-b-P3HT-b-PTVS, (6,000-12,500-6,000) could also be synthesized, initiated with a P3HT-based difunctional macroinitiator in the presence of lithium enolate. GPC-RALLS and ¹H NMR analyses confirmed a high degree of structural homogeneity of PTVS-b-P3HT-b-PTVS. A thermal transformation reaction of the polymer was carried out in the film state at 170 °C for 2 h to afford PA-b-P3HT-b-PA quantitatively, as monitored by TGA and FT-IR analyses. The optical and electronic properties as well as the morphological behavior of the block copolymers were investigated by UV-vis spectroscopy, conductivity measurement, and AFM observation. Full article

(This article belongs to the Special Issue Conductive Polymers)

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496 KiB

Open AccessArticle

Partially Fluorinated Sulfonated Poly(ether amide) Fuel Cell Membranes: Influence of Chemical Structure on Membrane Properties

by Ying Chang, Yeong-Beom Lee and Chulsung Bae

Polymers 2011, 3(1), 222-235; https://doi.org/10.3390/polym3010222 - 07 Jan 2011

Cited by 12 | Viewed by 10107

Abstract

A series of fluorinated sulfonated poly (ether amide)s (SPAs) were synthesized for proton exchange membrane fuel cell applications. A polycondensation reaction of 4,4’-oxydianiline, 2-sulfoterephthalic acid monosodium salt, and tetrafluorophenylene dicarboxylic acids (terephthalic and isophthalic) or fluoroaliphatic dicarboxylic acids produced SPAs with sulfonation degrees [...] Read more.

A series of fluorinated sulfonated poly (ether amide)s (SPAs) were synthesized for proton exchange membrane fuel cell applications. A polycondensation reaction of 4,4’-oxydianiline, 2-sulfoterephthalic acid monosodium salt, and tetrafluorophenylene dicarboxylic acids (terephthalic and isophthalic) or fluoroaliphatic dicarboxylic acids produced SPAs with sulfonation degrees of 80–90%. Controlling the feed ratio of the sulfonated and unsulfonated dicarboxylic acid monomers afforded random SPAs with ion exchange capacities between 1.7 and 2.2 meq/g and good solubility in polar aprotic solvents. Their structures were characterized using NMR and FT IR spectroscopies. Tough, flexible, and transparent films were obtained with dimethylsulfoxide using a solution casting method. Most SPA membranes with 90% sulfonation degree showed high proton conductivity (>100 mS/cm) at 80 °C and 100% relative humidity. Among them, two outstanding ionomers (ODA-STA-TPA-90 and ODA-STA-IPA-90) showed proton conductivity comparable to that of Nafion 117 between 40 and 80 °C. The influence of chemical structure on the membrane properties was systematically investigated by comparing the fluorinated polymers to their hydrogenated counterparts. The results suggest that the incorporation of fluorinated moieties in the polymer backbone of the membrane reduces water absorption. High molecular weight and the resulting physical entanglement of the polymers chains played a more important role in improving stability in water, however. Full article

(This article belongs to the Special Issue Conductive Polymers)

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749 KiB

Open AccessReview

Recent Advances in Ocular Drug Delivery Systems

by Noriyuki Kuno and Shinobu Fujii

Polymers 2011, 3(1), 193-221; https://doi.org/10.3390/polym3010193 - 06 Jan 2011

Cited by 166 | Viewed by 24425

Abstract

Transport of drugs applied by traditional dosage forms is restricted to the eye, and therapeutic drug concentrations in the target tissues are not maintained for a long duration since the eyes are protected by a unique anatomy and physiology. For the treatment of [...] Read more.

Transport of drugs applied by traditional dosage forms is restricted to the eye, and therapeutic drug concentrations in the target tissues are not maintained for a long duration since the eyes are protected by a unique anatomy and physiology. For the treatment of the anterior segment of the eye, various droppable products to prolong the retention time on the ocular surface have been introduced in the market. On the other hand, direct intravitreal implants, using biodegradable or non-biodegradable polymer technology, have been widely investigated for the treatment of chronic vitreoretinal diseases. There is urgent need to develop ocular drug delivery systems which provide controlled release for the treatment of chronic diseases, and increase patient’s and doctor’s convenience to reduce the dosing frequency and invasive treatment. In this article, progress of ocular drug delivery systems under clinical trials and in late experimental stage is reviewed. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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615 KiB

Open AccessReview

Bio-Decorated Polymer Membranes: A New Approach in Diagnostics and Therapeutics

by Patric Baumann, Pascal Tanner, Ozana Onaca and Cornelia G. Palivan

Polymers 2011, 3(1), 173-192; https://doi.org/10.3390/polym3010173 - 06 Jan 2011

Cited by 28 | Viewed by 10169

Abstract

Today, demand exists for new systems that can meet the challenges of identifying biological entities rapidly and specifically in diagnostics, developing stable and multifunctional membranes, and engineering devices at the nanometer scale. In this respect, bio-decorated membranes combine the specificity and efficacy of [...] Read more.

Today, demand exists for new systems that can meet the challenges of identifying biological entities rapidly and specifically in diagnostics, developing stable and multifunctional membranes, and engineering devices at the nanometer scale. In this respect, bio-decorated membranes combine the specificity and efficacy of biological entities, such as peptides, proteins, and DNA, with stability and the opportunity to chemically tailor the properties of polymeric membranes. A smart strategy that serves to fulfill biological criteria is required, whereby polymer membranes come to mimic biological membranes and do not disturb but rather enhance the functioning and activity of a biological entity. Different approaches have been developed, exemplified by either planar or vesicular membranes, allowing insertion inside the polymer membrane or anchoring via functionalization of the membrane surface. Inspired by nature, but incorporating the strength provided by chemical design, bio-decorated polymer membranes represent a novel concept with great potential in diagnostics and therapeutics. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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734 KiB

Open AccessArticle

A Polyvinyl Alcohol-Polyaniline Based Electro-Conductive Hydrogel for Controlled Stimuli-Actuable Release of Indomethacin

by Tong-Sheng Tsai, Viness Pillay, Yahya E. Choonara, Lisa C. Du Toit, Girish Modi, Dinesh Naidoo and Pradeep Kumar

Polymers 2011, 3(1), 150-172; https://doi.org/10.3390/polym3010150 - 05 Jan 2011

Cited by 64 | Viewed by 14094

Abstract

Electro-conductive hydrogels based on poly(vinyl alcohol), crosslinked with diethyl acetamidomalonate as the hydrogel component, were engineered using polyaniline as the inherently conductive component, and fabricated in the form of cylindrical devices to confer electro-actuable release of the model drug indomethacin. The hydrogels were [...] Read more.

Electro-conductive hydrogels based on poly(vinyl alcohol), crosslinked with diethyl acetamidomalonate as the hydrogel component, were engineered using polyaniline as the inherently conductive component, and fabricated in the form of cylindrical devices to confer electro-actuable release of the model drug indomethacin. The hydrogels were characterized for their physicochemical and physicomechanical properties. Cyclic voltammetry was employed for electro-activity and conductivity analysis. Drug entrapment efficiency ranged from 65–70%. “ON-OFF” switchable drug release was obtained by periodically applying-removing-reapplying an electric potential ranging from 0.3–5.0 V for 60 seconds at hourly intervals and the cumulative drug release obtained ranged from 4.7–25.2% after four release cycles respectively. The electro-stimulated release of indomethacin was associated with the degree of crosslinking, the polymeric ratio and drug content. A Box-Behnken experimental design was constructed employing 1.2 V as the baseline potential difference. Thedevices demonstrated superior swellability and high diffusivity of indomethacin, in addition to high electrical conductivity with “ON-OFF” drug release kinetics via electrical switching. In order to investigate the electro-actuable release of indomethacin, molecular mechanics simulations using AMBER-force field were performed on systems containing water molecules and the poly(vinyl alcohol)-polyaniline composite under the influence of an external electric field. Various interaction energies were monitored to visualize the effect of the external electric field on the erosion of polyaniline from the co-polymeric matrix. This strategy allows the electro-conductive hydrogels to be suitably applied for controlled, local and electro-actuable drug release while sustaining a mild operating environment. Full article

(This article belongs to the Special Issue Conductive Polymers)

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1981 KiB

Open AccessArticle

Electrospraying, a Reproducible Method for Production of Polymeric Microspheres for Biomedical Applications

by Nathalie Bock, Maria A. Woodruff, Dietmar W. Hutmacher and Tim R. Dargaville

Polymers 2011, 3(1), 131-149; https://doi.org/10.3390/polym3010131 - 05 Jan 2011

Cited by 267 | Viewed by 18061

Abstract

The ability to reproducibly load bioactive molecules into polymeric microspheres is a challenge. Traditional microsphere fabrication methods typically provide inhomogeneous release profiles and suffer from lack of batch to batch reproducibility, hindering their potential to up-scale and their translation to the clinic. This [...] Read more.

The ability to reproducibly load bioactive molecules into polymeric microspheres is a challenge. Traditional microsphere fabrication methods typically provide inhomogeneous release profiles and suffer from lack of batch to batch reproducibility, hindering their potential to up-scale and their translation to the clinic. This deficit in homogeneity is in part attributed to broad size distributions and variability in the morphology of particles. It is thus desirable to control morphology and size of non-loaded particles in the first instance, in preparation for obtaining desired release profiles of loaded particles in the later stage. This is achieved by identifying the key parameters involved in particle production and understanding how adapting these parameters affects the final characteristics of particles. In this study, electrospraying was presented as a promising technique for generating reproducible particles made of polycaprolactone, a biodegradable, FDA-approved polymer. Narrow size distributions were obtained by the control of electrospraying flow rate and polymer concentration, with average particle sizes ranging from 10 to 20 µm. Particles were shown to be spherical with a homogeneous embossed texture, determined by the polymer entanglement regime taking place during electrospraying. No toxic residue was detected by this process based on preliminary cell work using DNA quantification assays, validating this method as suitable for further loading of bioactive components. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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440 KiB

Open AccessArticle

Gelatin Functionalization of Biomaterial Surfaces: Strategies for Immobilization and Visualization

by Sandra Van Vlierberghe, Els Vanderleyden, Veerle Boterberg and Peter Dubruel

Polymers 2011, 3(1), 114-130; https://doi.org/10.3390/polym3010114 - 05 Jan 2011

Cited by 41 | Viewed by 11072

Abstract

In the present work, the immobilization of gelatin as biopolymer on two types of implantable biomaterials, polyimide and titanium, was compared. Both materials are known for their biocompatibility while lacking cell-interactive behavior. For both materials, a pre-functionalization step was required to enable gelatin [...] Read more.

In the present work, the immobilization of gelatin as biopolymer on two types of implantable biomaterials, polyimide and titanium, was compared. Both materials are known for their biocompatibility while lacking cell-interactive behavior. For both materials, a pre-functionalization step was required to enable gelatin immobilization. For the polyimide foils, a reactive succinimidyl ester was introduced first on the surface, followed by covalent grafting of gelatin. For the titanium material, methacrylate groups were first introduced on the Ti surface through a silanization reaction. The applied functionalities enabled the subsequent immobilization of methacrylamide modified gelatin. Both surface modified materials were characterized in depth using atomic force microscopy, static contact angle measurements, confocal fluorescence microscopy, attenuated total reflection infrared spectroscopy and X-ray photo-electron spectroscopy. The results indicated that the strategies elaborated for both material classes are suitable to apply stable gelatin coatings. Interestingly, depending on the material class studied, not all surface analysis techniques are applicable. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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807 KiB

Open AccessReview

Chitosan-Based Hyaluronic Acid Hybrid Polymer Fibers as a Scaffold Biomaterial for Cartilage Tissue Engineering

by Norimasa Iwasaki, Yasuhiko Kasahara, Shintarou Yamane, Tatsuya Igarashi, Akio Minami and Shin-ichiro Nisimura

Polymers 2011, 3(1), 100-113; https://doi.org/10.3390/polym3010100 - 27 Dec 2010

Cited by 37 | Viewed by 12537

Abstract

An ideal scaffold material is one that closely mimics the natural environment in the tissue-specific extracellular matrix (ECM). Therefore, we have applied hyaluronic acid (HA), which is a main component of the cartilage ECM, to chitosan as a fundamental material for cartilage regeneration. [...] Read more.

An ideal scaffold material is one that closely mimics the natural environment in the tissue-specific extracellular matrix (ECM). Therefore, we have applied hyaluronic acid (HA), which is a main component of the cartilage ECM, to chitosan as a fundamental material for cartilage regeneration. To mimic the structural environment of cartilage ECM, the fundamental structure of a scaffold should be a three-dimensional (3D) system with adequate mechanical strength. We structurally developed novel polymer chitosan-based HA hybrid fibers as a biomaterial to easily fabricate 3D scaffolds. This review presents the potential of a 3D fabricated scaffold based on these novel hybrid polymer fibers for cartilage tissue engineering. Full article

(This article belongs to the Collection Polysaccharides)

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Polymers, Volume 3, Issue 1 (March 2011) – 35 articles , Pages 1-661

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