Showing papers by "Harry R. Allcock published in 2005"
TL;DR: The electrospun nonwoven mats showed enhanced surface hydrophobicity compared to spun cast films with up to a 55 degrees increase in water contact angle and a low value of hysteresis was recorded for the superhydrophobic surfaces.
Abstract: Nanofibers of poly[bis(2,2,2-trifluoroethoxy)phosphazene] were produced by electrospinning from solutions in tetrahydrofuran, methylethyl ketone, and acetone. The fiber diameter varied from 80 nm to 1.4 μm by changes in the concentration of the polymer solution. The electrospun nonwoven mats showed enhanced surface hydrophobicity compared to spun cast films with up to a 55° increase in water contact angle. The hydrophobicity varied with fiber diameter and surface morphology, with contact angles to water being in the range of 135°−159°. A low value of hysteresis (<4°) was recorded for the superhydrophobic surfaces. The extremely high hydrophobicity of these mats is a combined result of a fluorinated surface and the inherent surface roughness of an electrospun mat.
188 citations
TL;DR: The in situ formation of HAp in the presence of polyphosphazenes, where HAp is chemically bonded to the polymer is illustrated, to show the effects of temperature, reaction chemistry and phase evolution on the kinetics, phase evolution and microstructural development of stoichiometric HAp.
136 citations
63 citations
TL;DR: The results showed that neuroblastoma cells adhere selectively to the +CAP microfeatures and that multiple properties can be achieved with a single material and that TFE can be used as both a -CAP and an insulation layer and PMCP as a conductive +CAP layer.
36 citations
TL;DR: Aqueous micellar solutions of PS–KPCPP block copolymers showed pH-dependent behavior, which makes them suitable for studies of guest retention and release in response to ion charge and pH.
Abstract: Amphiphilic diblock copolymers that contained hydrophilic poly[bis(potassium carboxylatophenoxy)phosphazene] segments and hydrophobic polystyrene sections were synthesized via the controlled cationic polymerization of Cl3PNSiMe3 with a polystyrenyl–phosphoranimine as a macromolecular terminator. These block copolymers self-associated in aqueous media to form micellar structures which were investigated by fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The size and shape of the micelles were not affected by the introduction of different monovalent cations (Li+, K+, Na+, and Cs+) into the stable micellar solutions. However, exposure to divalent cations induced intermicellar crosslinking through carboxylate groups, which caused precipitation of the ionically crosslinked aggregates from solution. This micelle-coupling behavior was reversible: the subsequent addition of monovalent cations caused the redispersion of the polystyrene-block-poly[bis(potassium carboxylatophenoxy)phosphazene] (PS–KPCPP) block copolymers into a stable micellar solution. Aqueous micellar solutions of PS–KPCPP copolymers also showed pH-dependent behavior. These attributes make PS–KPCPP block copolymers suitable for studies of guest retention and release in response to ion charge and pH. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2912–2920, 2005
35 citations
TL;DR: Elevated proportions (5 and 10% by weight) of polyphosphazene resulted in the inhibition of SHAp formation, which is attributed to the formation of viscous polymer solution coatings on the calcium phosphate precursors, retarding their reaction, and consequently inhibiting ShAp formation.
Abstract: The low temperature synthesis of composites potentially suitable as bone substitutes which form in vivo, was investigated. The composites were comprised of stoichiometric hydroxyapatite (SHAp) and water-soluble poly phosphazenes. These constituents were selected because of their biocompatibility, and were mixed as powders with a phosphate buffer solution (PBS) to form the composites. The effects of poly[bis(sodium carboxylatophenoxy)phosphazene] (Na-PCPP) or poly[bis(potassium carboxylatophenoxy) phosphazene] (K-PCPP) on stoichiometric hydroxyapatite (SHAp) formation from tetracalcium phosphate and anhydrous dicalcium phosphate were assessed. The kinetics and reaction chemistries of composite formation were followed by isothermal calorimetry, X-ray diffraction, infrared spectroscopy and scanning electron microscopy. In the presence of 1% by weight of polyphosphazenes, composites comprised of SHAp and calcium cross-linked polymer salts were formed. Thus a mechanism for binding between polymer chains was established. Elevated proportions (5 and 10% by weight) of polyphosphazene, however, resulted in the inhibition of SHAp formation. This is attributed to the formation of viscous polymer solution coatings on the calcium phosphate precursors, retarding their reaction, and consequently inhibiting SHAp formation.
26 citations
TL;DR: The incorporation of η6-arene, ferrocene, and ruthenocene side groups into phosphazene high polymers generates properties such as high melting behavior and electronic conductivity, and provides insights into reaction mechanisms and ring polymer equilibria as discussed by the authors.
Abstract: The incorporation of η6-arene, ferrocene, and ruthenocene side groups into phosphazene high polymers generates properties such as high melting behavior and electronic conductivity, and provides insights into reaction mechanisms and ring–polymer equilibria. The design and synthesis of these polymers is facilitated by model compound studies using small molecule cyclic phosphazenes.
13 citations
TL;DR: In this article, the synthesis of polyoctenamers with pendent functionalized cyclotriphosphazenes as amphiphilic lithium ion conductive membranes is described.
Abstract: The synthesis of novel polyoctenamers with pendent functionalized cyclotriphosphazenes as amphiphilic lithium ion conductive membranes is described Cyclotriphosphazene monomers were functionalized with one cycloocteneoxy substituent per ring Two different types of monomer units, one with oligoethyleneoxy cation coordination side groups and the other with hydrophobic fluoroalkoxy side groups, were then prepared The syntheses of these monomers, their ring-opening metathesis copolymerization, and the characteristics of the resultant polymers are discussed, with an emphasis on the dependence of ionic conductivity and hydrophobicity on polymer composition
13 citations
TL;DR: The hybrid networks showed high water uptake values and the release of Rose Bengal, Biebrich Scarlet, and FITC−albumin from the phosphazene−silicate matrix was studied over time as a function of network density.
Abstract: A method for the cross-linking of water-soluble polyphosphazenes via a sol−gel condensation is described. Precursor polymers were produced by covalently binding an organosilicon alkoxide to the terminus of pendent oligoethylenoxy chains on poly[bis(methoxyethoxyethoxy)phosphazene]. Subsequent hydrolysis and condensation of these precursors yielded hybrid silicate networks with covalently integrated polyphosphazenes. The hybrid networks showed high water uptake values (up to 1570 wt %). The release of Rose Bengal, Biebrich Scarlet, and FITC−albumin from the phosphazene−silicate matrix was studied over time as a function of network density. These hydrogels are of interest as potential materials for use in membranes or biomaterials.
9 citations
5 citations
01 Jan 2005
TL;DR: Fluoroalkoxyphosphazenes are also stable to ultraviolet and higher energy radiation, resistant to oxidation, and have glass transition temperatures in the range of -60 o C as mentioned in this paper.
Abstract: ®is insoluble in organic solvents under normal conditions whereas the polyphosphazene counterparts are easy to fabricate from solution or via melt or elastomer fabrication methods. Moreover, the interfacial properties of the fluoroalkoxyphosphazene polymers may be modified easily by surface reactions with a range of nucleophiles. A typical surface contact angle to water of spun cast or film cast [NP(OCH2CF3)2]n is in the region of 109 o . Other Properties. Fluoroalkoxyphosphazenes are also stable to ultraviolet and higher energy radiation, are resistant to oxidation, and have glass transition temperatures in the range of -60 o C. The single substituent polymers are microcrystalline, with the trifluoroethoxy derivative having a melting temperature of 242 o
16 Mar 2005
TL;DR: Immuno-fluorescence was used to show the presence of pre and postsynaptic markers, suggesting that MUS are the result of networking, and this cell line could prove as a useful model for synaptic dopaminergic pacing cell systems.
Abstract: The SK-N-BE(2c) is an I-type neuroblastoma that develops a strong pacing electrical response over time. This response is likely the result of a developing interconnected network, such that the regular pacemaker-like firing of individual cells becomes synchronous over time forming a multi unit spikes signal (MUS). Immuno-fluorescence was used to show the presence of pre and postsynaptic markers, suggesting that MUS are the result of networking. Hence this cell line could prove as a useful model for synaptic dopaminergic pacing cell systems
16 Mar 2005
TL;DR: In this paper, two polyphosphazenes were synthesized: poly[bis(trifluoroethoxy) phosphazene] (TFE) and poly[(methoxyethoxy-ethoxy 1.0(p-cresoxy)1.0 phosphazene) (PMPP) for patterned neural network systems.
Abstract: Two polyphosphazenes were synthesized: poly[bis(trifluoroethoxy)phosphazene] (TFE) and poly[(methoxyethoxyethoxy)1.0(p-cresoxy)1.0 phosphazene] (PMPP). These materials were selected due to their properties in order to provide a conductive cell friendly substrate to couple cells to electrode plates (PMPP) and an isolative cell unfriendly polymer to coat the rest of the system (TFE). Materials properties were tested and analyzed using well known physicochemical methods and cell selectivity was tested using a human derived neuroblastoma cell line (SK-N-BE(2c)). Materials proved to behave as expected, opening the door for the use of polyphosphazenes in patterned neural network systems