bluuebunny/crossref_metadata_2025_split huggingface dataset:
Controlling Diffusion of Solutes Through Ionically Crosslinked Alginate Hydrogels Designed for Tissue Engineering
Authors: Kuo Catherine K. , Ma Peter X. 
Published: April 2011

AbstractTissue engineering aims at creating new tissues as alternatives to organ transplants. Our approach is to incorporate cells into biodegradable polymer scaffolds designed to temporarily support new tissue formation. An important requirement of scaffolds is homogeneity. Homogeneity ensures structural integrity, uniform distribution of cells, and uniform porosity throughout the scaffold. Controlling pore sizes is necessary to regulate exchange of nutrients and waste products for cells. Pores too large can provide entryway to immune cells that can harm allogenic cells and developing tissue. We have fabricated three-dimensionally defined, homogeneous, ionically crosslinked alginate gels with a controlled slow-gelation system involving CaCO3 and D-glucono-δ-lactone. We varied the structural parameters and alginate types of these gels to control the diffusion of glucose, vitamin B12 and FITC-dextran (molecular weights of 180, 1355 and 9500, respectively) through the gels. Experiments were performed with gel discs placed between side-by-side donor and receptor chambers in a humidified incubator at 37°C. Samples were taken periodically and measured on a UV-Vis spectrophotometer. Generally, diffusion coefficient (D) increased with decreasing solute size. Varying structural parameters of the gels did not have a significant effect on diffusivity of vitamin B12. In contrast, for gels made with a Ca2+ to carboxyl molar ratio of 0.36, D of FITCdextran increased from (2.88 ± 0.52)×10-7 to (4.66 ± 0.48)×10-7 cm2/sec as alginate concentration decreased from 3.2% to 1.5%, respectively. D of FITC-dextran also increased from (3.17 ± 0.30)×10-7 to (4.66 ± 0.48)×10-7 cm2/sec as crosslinking density decreased for 1.5% alginate gels from a Ca2+ to carboxyl molar ratio of 0.72 to 0.36, respectively. D was highest for alginate gels with the highest guluronic acid content. Controlling diffusivity allows alginate gels with specific properties to be fabricated for tissue engineering scaffolding and other biomedical applications.
Bioactive Glass Paste in Molars of Mini-Pigs: An In Vivo Study
Authors: Efflandt Sarah E. , Lopes Manuela , Ko Ching-Chang , Perdigao Jorge , Douglas William H. , Francis Lorraine F. 
Published: April 2011

AbstractBioactive glass powder in the MgO-CaO-P2O5-SiO2 system was mixed with water to create a bioactive glass paste. The paste was then placed in 8 cavities in molars of Sinclair mini-pigs, isolated using a light-cure composite filling, and left in vivo for 4 weeks. Additionally, 4 controls were run where the bioactive glass was placed in an inert polymer substrate and then incubated at 37°C for 4 weeks. Specimens were cut longitudinally in two halves and prepared for chemical and x-ray analyses. Qualitative results showed that the paste in the molars stayed intact while there was little or no paste left in the polymer substrate after cutting. This observation suggested that the paste in the natural tissue had structural integrity which could be caused by chemical changes and/or mineralization encouraged by contact with dentinal tubule fluid. X-ray analysis did not reveal any crystallinity in the paste at 4 weeks, but chemical alterations were confirmed by electron microprobe analysis. The chemical inhomogeneity of the individual elemental maps revealed the formation of Ca-P-rich/Si-poor areas. These distinct chemical variations were not seen in chemical analyses run on the bioactive glass paste in its initial state.
Analysis of Electrostatic Effects on the Success of Retroviral-Mediated Gene Delivery
Authors: Davis Howard E. , Morgan Jeffrey R. , Yarmush Martin L. 
Published: April 2011

AbstractRecombinant retroviruses are a commonly used gene delivery tool in human gene therapy clinical trials as they permanently integrate the therapeutic DNA into the genome of the target cell. Despite their widespread use, however, retroviral gene transfer efficiencies remain disappointingly low. In the years since their initial development as vectors, it has become clear that the physicochemical properties of the recombinant retrovirus, as well as the properties of the target tissue, have a major impact on the success of gene transfer. In particular, the interaction between the native negative charge present on the vector and target cell membranes results in a significant electrostatic barrier which must be overcome in order for the transduction process to begin. Using a recently developed retrovirus adsorption assay, we have demonstrated that this electrostatic interaction is the dominant interaction during the initial steps of transduction. We have also established that cationic polymers enhance adsorption, and ostensibly transduction, by neutralizing this electrostatic barrier. Interestingly, we also found that this enhanced adsorption could be demonstrated even in the absence of a cellular receptor for the virus, suggesting that the first step of transduction does not involve binding of the virus to currently identified receptors, but is either a non-specific adsorption process or involves binding to an, as of yet, uncharacterized class of receptor. Based upon our finding that virus adsorption is non-gp70 mediated, we propose a new physical model of this initial step of transduction which is diffusion-limited, receptor and envelope independent, and modulable by positively charged compounds. Our findings may have significant implications for other gene and drug delivery systems which interact directly with target tissues at the level of the cell membrane.
Small Molecule Diffusion and Solubility in Adhesives Used for Transdermal Drug Delivery: Infrared-Attenuated Total Reflectance (IR-ATR) Studies.
Authors: Cantor Adam S. 
Published: April 2011

AbstractA key factor in designing a drug-in-adhesive transdermal drug delivery system is to understand the rate at which the drug and small-molecule excipients can diffuse in the adhesive matrix. The solubility of these components in the adhesive matrix is also of great importance. Results will be presented discussing the use of infrared-attenuated total reflectance (IR-ATR) spectroscopy as a method to measure both diffusion and solubility of small molecules in adhesives. In this method, the donor layer is either a doped adhesive or a free liquid that is placed in contact with a receptor layer which is an undoped adhesive in contact with an IR-ATR crystal. The IR-ATR crystal detects as a function of time any molecules that diffuse from the donor layer into and through the receptor layer.Examples will be discussed of several different experiments that can be performed with this technique. Diffusion coefficients are presented here for testosterone and terpineol in an isooctyl acrylate based adhesive using a doped adhesive donor layer. Diffusion and solubility of liquids in several adhesives has been determined using the experiment where a free liquid is used as the donor. Solubility and diffusion coefficients determined using an oversaturated doped layer containing dispersed, as well as dissolved solute, are presented here for testosterone and for progesterone. Finally diffusion from a doped layer of one adhesive to an undoped layer of a different adhesive was performed as a partition measurement. The parameters that can be extracted from each of these experiments, as well as the limitations of each type of experiment will be discussed.
Nanoparticles and Polymeric Vesicles From New Poly-L-Lysine Based Amphiphiles
Authors: Uchegbu Ijeoma F. , Tetley Laurence , Wang Wei 
Published: April 2011

AbstractNanoparticles and polymeric vesicles for drug delivery and other industrial applications have been prepared by the probe sonication of poly-L-lysine graft copolymer amphiphiles in aqueous media. The amphiphiles, which have a poly-L-lysine backbone and varied levels of both hydrophilic methoxypolyethylene glycol (Mw ∼ 5,000) and hydrophobic palmitoyl pendant groups, were prepared from 2 different molecular weight poly-L-lysine hydrobromide samples (Mw ∼4,000 and ∼20,000 respectively). Poly-L-lysine based amphiphilic polymers (PLPs) were characterised using light scattering, 1H NMR and an assay for the level of free amino groups. Steric factors appear to limit the final level of lysine group modification that can be achieved and even an excess amount of grafting reactants still resulted in the production of polymers in which 22 – 26 mole% of the lysine terminal amino groups remain unsubstituted. Polymeric unilamellar vesicles (220 – 570nm in diameter) imaged by electron microscopy were produced by probe sonication of PLP, cholesterol. Vesicle formation was possible over a narrow spectrum of polymer architecture and was favoured by a low molecular weight and a low level of palmitoyl substitution. A vesicle formation index (F') has thus been derived for this PLP, cholesterol system = Where H = %molar level of unreacted L-lysine units, L = %molar level of substituted palmitoyl units and DP = square root of the degree of polymerisation of the polymer. Probe sonication of an aqueous dispersion of PLP samples resulted in the production of stable nanoparticles (80 -170nm in diameter) as imaged by electron microscopy. Nanoparticles were able to encapsulate the hydrophilic fluorophore fluorescein isothiocyanate (FITC)-dextran and encapsulation increased as the level of unreacted lysine terminal amino groups in PLP increased thus increasing as the level of hydrophilic domains increased. The size of both the nanoparticles and the vesicles was directly influenced by the molecular weight of PLP. PLPs of molecular weight 32,000 – 48,000 and 89,000 – 140,000 resulted in nanoparticles of 85 – 114 nm and 125 – 167 nm in diameter respectively and PLP of molecular weight 25,000 and 89,000 gave rise to polymeric vesicles of 252 nm and 570 nm in diameter respectively.
Mechanism of Carrier Photoexcitation in Semiconducting Polymers: The Role of Electron Photoemission in “Photoconductivity” Measurements
Authors: Moses Daniel , Miranda Paulo B. , Soci Cesare , Heeger Alan J. 
Published: April 2011

ABSTRACTUltrafast photoinduced absorption by infrared-active vibrational modes (IRAV) is used to detect charged photo-excitations (polarons) in solid films of conjugated luminescent polymers. Experiments, carried out in zero applied electric field, show that polarons are generated within 100 fs with quantum efficiencies of approximately 10%. The ultrafast photoinduced IRAV Absorption, the weak pump-wavelength dependence, and the linear dependence of charge density on pump intensity indicate that both charged polarons and neutral excitons are independently generated even at the earliest times. Measurements of the excitation profile of the transient and steady-state photoconductivity of poly(phenylene vinylene) and its soluble derivatives over a wide spectral range up to hν = 6.2 eV indicate an apparent increase in the “photoconductivity” at hν > 3-4 eV that arises from external currents generated by electron photoemission (PE). After quenching the PE by addition of CO2+SF6 (90%:10%) into the sample chamber, the bulk photoconductivity is nearly independent of photon energy in all polymers studied, in a good agreement with the IRAV spectra. The single threshold for photoconductivity is spectrally close to the onset of π-π* absorption, behavior that is inconsistent with a large exciton binding energy.
Photoinduced Enhancement of Photoluminescence Intensity in PPV Films
Authors: Gobato Yara Galvão , Marletta Alexandre , Souza Jucimar M. , Pereira Ernesto , Faria Roberto M. , Guimarães Francisco E.G. 
Published: April 2011

ABSTRACTPoly(p-phenylene vinylene) (PPV) films are usually photodegraded in air. We report on the enhancement of photoluminescence (PL) intensity of PPV films induced by Ar ion laser in the presence of air. The PL spectra were measured as function of laser power, time exposure and sample thickness. The initial PL intensity increases up to 300% without significant changes in peak positions by optimizing such parameters. This effect is accompanied by a blue-shift in the absorption spectrum resulting in shortened effective conjugation length and by a formation of defects such as carbonyl groups. Mechanisms for the observed photoluminescence intensity enhancements are suggested.
Third Order Non-Linear Optical Properties of Polyphenylene Vinylene Derivatives in the Infrared Range
Authors: Dubitsky Yuri A. , Zaopo Antonio , Zappettini Andrea , Facchini Giulia , Amore Franco D , Pietralunga Silvia , Martinelli Mario 
Published: April 2011

ABSTRACTThe non-linear optical properties of poly[1,4-phenylene-1-phenyl vinylene], poly[1,4-phenylene-1,2-di(4′-phenoxyphenyl) vinylene], poly[2,5-dioctyloxy-1,4-phenylene vinylene] and poly[2- methoxy -5- (2'-ethylhexyloxy)-1,4-phenylene vinylene] MEH-PPV with different molecular weights were studied by the Third Harmonic Generation (THG) technique. The dispersion of the χ3 coefficient was measured in the wide infra red range from 1.2 up to 2.1 μm. It was shown that the highest χ3 value, observed for the high molecular weight MEH-PPV (Mw 230.000), reaches the maximum of 8x10-11 esu at 1.77 μm. At the same time, the medium molecular weight MEH-PPV (Mw 95.000) demonstrated not significantly different χ3 value of 6x10-11 esu. The dispersion of the χ3 coefficient was compared to the absorption of the third harmonic beam and strong χ3 enhancement relative to the excitonic absorption was observed. However, a surprising shift of about 70 nm towards the longer wavelengths between the two peaks was always observed for all studied PPV derivatives. The results of THG measurements were compared to those obtained by conventional Zscan technique in the same range. It was shown that the THG χ3 values in infrared range were up to one order of magnitude lower than those of direct Z-scan measurements.
The Synthesis, Condensation, and Luminescence of Stilbenoid Oligomers with Alkoxysilane End Groups
Authors: Detert H. , Sugiono E. 
Published: April 2011

ABSTRACTA synthetic route to highly luminescent organic semiconductors with curable alkoxysilyl groups is described. Monodisperse oligo(phenylenevinylene)s are rigidly connected to di- and triethoxysilanes via Heck reactions or via cross-metathesis. Hydrolysis of the silicic esters yields silanols condensing to linear and cyclic oligo-OPV-siloxanes or to three-dimensional networks, thus allowing the transformation of small molecules to fluorescent materials with well-defined chromophores. Transparent films are obtained by casting of soluble cyclosiloxanes and from OPV-silanetriols, the latter can be cured to insoluble networks.
Design, Synthesis and Charaterization of Polymers Derived from Fluorene for Application in RGB Polymer Light-Emitting-Diodes
Authors: Beaupré Serge , Leclerc Mario , Lévesque Isabelle , D'Iorio Marie 
Published: April 2011

ABSTRACTIn order to obtain efficient blue, green and red light-emitters as active layers in polymer light-emitting diode (PLEDs), we report herein the design, the synthesis, and the characterization of new polyesters and copolymers derived from fluorene. We will focus on a new approach to obtain a stable, high luminance blue emitter via polyesters derived from fluorene. The versatile synthetic approach allows the easy design of a whole class of new and tunable electroactive and photoactive aromatic polyesters. Poly(1,6-hexane- 9,9′,9′,9′′,9′′-hexahexyl-7,2′;7′,2′′-terfluorene-2,7′′-dicarboxylate) (PTFHHC6) and Poly(1,6-hexane-2,7-Bis(1,1′-biphenylen-4-yl-4′-dicarboxylate)-9,9-dioctylfluorene) (PE-BP-DOF-BP) exhibit strong emission in the blue range, both in solution and in the solid state. Moreover, these polyesters present some advantages over other polyfluorene derivatives. For example, their solid-state fluorescence spectrum does not show the formation of any excimer and does not vary upon thermal treatment. We will also present copolymers derived from fluorene which emit green light and a new approach to obtain red polymer light-emitting-diode will also be shown. Optical properties such as light absorption, light emission and quantum yield of fluorescence in solution as well as electrical properties such as cyclic voltammogram and conductivity in-situ are reported. Finally, some of the polymers presented have been tested in PLEDs devices and the preliminary results seem promising for the development of multicoloured displays made from the same class of polyfluorene derivatives.
Electronic Properties of Polymer-Fullerene Solar Cells
Authors: Dyakonov V. , Riedel I. , Deibel C. , Parisi J. , Brabec C. J. , Sariciftci N. S. , Hummelen J.C. 
Published: April 2011

ABSTRACTWe studied the electronic transport properties of conjugated polymer/fullerene based solar cells by means of temperature and illumination intensity dependent current-voltage characteristics, admittance spectroscopy and light-induced electron spin resonance. The short-circuit current density increases with temperature at all light illumination intensities applied, i.e., from 100 mW/cm2to 0.1 mW/cm2(white light), whereas a temperature independent behavior was expected. An increase of the open-circuit voltage from 850 mV to 940 mV was observed, when cooling down the device from room temperature to 100 K. The fill factor depends strongly on temperature with a positive temperature coefficient in the whole temperature range. In contrast, the light intensity dependence of the fill factor shows a maximum of 52% at intermediate illumination intensities (3 mW/cm2) and decreases subsequently, when increasing the intensity up to 100 mW/cm2. Further studies by admittance spectroscopy revealed two frequency dependent contributions to the device capacitance. One, as we believe, originates from trapping states located at the interface between composite and metal electrode with an activation energy of EA=180 meV, and the other one is from very shallow bulk states with EA=10 meV. The origin of the latter is possibly the thermally activated conductivity. The photo-generation of charge carriers and their fate in these blends have been studied by light-induced electron spin resonance. We can clearly distinguish between photo-generated electrons and holes in the composites due to different spectroscopic splitting factors (g-factors). Additional information on the environmental axial symmetry of the holes located on the polymer chains as well as on a lower, rhombic, symmetry of the electrons located on the methanofullerene molecules has been obtained. The origin of the signals and parameters of the g-tensor have been confirmed from studies on a hole doped polymer.
Ultrafast Energy And Electron Transfer In Conjugated Oligomer-Fullerene Molecules
Authors: Hal P.A. van , Janssen R.A.J. , Lanzani G. , Cerullo G. , Zavelani-Rossi M. , Silvestri S. De 
Published: April 2011

ABSTRACTThe intramolecular photoinduced energy and electron transfer within a fullereneoligothiophene-fullerene triad with nine thiophene units (C60-9T-C60) and an oligo(p-phenylene vinylene)-fullerene dyad with four phenyl groups (OPV4-C60) is investigated with femtosecond pump-probe spectroscopy with sub-10 fs and 200 fs time resolution in solvents of different polarity. Photoexcitation of the π-conjugated oligomer moiety in the triad and dyad results in an ultrafast singlet-energy transfer reaction to create the fullerene singlet-excited state with a time constant of 150-190 fs, irrespective of the polarity of the medium. In a polar solvent, intramolecular electron transfer occurs from the oligomer moiety to the C60 moiety with a time constant of 10-13 ps as a secondary reaction, subsequent to the ultrafast singlet-energy transfer. The charge-separated state has a lifetime of 50-80 ps and recombines to the ground state.
Electron Accepting Oligomers and Polymers: Chain Scission Under Quaternization Conditions
Authors: Dudis Douglas S. , Mckellar B. Robert 
Published: April 2011

ABSTRACTThe methylation of polybenzobisthiazole in dimethylsulfate produces an ndopable polymer which has previously been shown to have high electrical conductivity. The reaction conditions have been shown to chemically degrade the polymer chains, decreasing the molecular weight to about 20% of the original value. A methylationdemethylation scheme has been used to clarify the degree of chain scission.
Inorganic-organic Hybrid Materials (ORMOCERs) for Multilayer Technology – Passivation and Dielectric Behavior
Authors: Houbertz R. , Fröhlich L. , Schulz J. , Popall M. 
Published: April 2011

ABSTRACTInorganic-organic hybrid polymers (ORMOCER®s) have been synthesized by sol-gel processing. The materials can be functionalized such that their physical and chemical properties can be reproducibly tailored towards the desired application, i.e., electronics, optics (passives/actives) or passivation technology. Besides, the materials which show negative resist behavior, can be patterned by UV exposure with good resolution. The materials are well-suited for thin and thick film technology using conventional coating technology, applied in multi-layer technology. We here particularly focus on materials for passivation against environmental influences, which additionally exhibit very good dielectric properties.
Steady State Photoconductivity in Conjugated Polymers
Authors: Sitch C. D. , Halliday D. P. , Monkman A. P. 
Published: April 2011

ABSTRACTVisible and ultraviolet photoconductivity (PC) measurements have been performed on thick (7[.proportional]m) and thin (170nm) films of poly[2-methoxy, 5 ethyl (2' hexyloxy) paraphenylenevinylene] (MEH-PPV) sandwiched between indium tin oxide (ITO) and semitransparent gold (Au) electrodes. PC spectra were obtained for samples under different bias polarities and for illumination through the ITO electrode and through the Au electrode. The results obtained indicate that the absorbed photons form excitons that dissociate extrinsically at or near the electrodes to form hole polarons or intrinsically at higher photon energies in the bulk polymer.
The influence of nanostructure formation on properties for Cr implanted PET
Authors: Yuguang Wu , Tonghe Zhang , Huixing Zhang , Xiaoji Zhang , Ping Cui , Gu Zhou 
Published: April 2011

ABSTRACTPolyethylene terephthalate (PET) has been modified by Cr ion implantation with a dose range from 1×1016to 2×1017ions /cm2 using a metal vapor vacuum arc MEVVA source. The surface morphology was observed by atomic force microscopy (AFM). The Cr atom precipitation was found. The changes of the structure and composition have been observed with transmission electron microscope (TEM). The TEM photos revealed the presence of Cr nano-meter particles on the implanted PET. It is believed that the change would cause the improvement of the conductive properties and wear resistance. The electrical properties of PET have been improved after metal ion implantation. The resistivity of Cr ion implanted PET decreased obviously with an increase of ion dose. When the metal ion dose with 2×1017cm−2 was implanted into PET, the resistivity of PET could be less than 0.1 Ωm. But when Si or C ions with same dose are implanted PET, the resistivity of PET would be up to several Ωm. The result show that the resistivity of Cr ion implanted sample is obviously lower than that of Si- and C-implanted one. After Cr implantation, the surface hardness and modulus could be increased. The property of the implanted PET has modified greatly. The hardness and modulus of Cr implanted PET with dose of 2×1017/cm2 is 9.5 and 3.1 times greater than that of pristine PET. So we can see that wear resistance improved greatly. The Cr ion beam modification mechanism of PET will be discussed.