Browsing by Author "Hartley, PG"

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    Formation of liquid-crystalline structures in the bile salt–chitosan system and triggered release from lamellar phase bile salt–chitosan capsules
    (American Chemical Society, 2014-07-22) Tangso, KJ; Lindberg, S; Hartley, PG; Knott, RB; Spicer, P; Boyd, BJ
    Nanostructured capsules comprised of the anionic bile salt, sodium taurodeoxycholate (STDC), and the biocompatible cationic polymer, chitosan, were prepared to assess their potential as novel tailored release nanomaterials. For comparison, a previously studied system, sodium dodecyl sulfate (SDS), and polydiallyldimethylammonium chloride (polyDADMAC) was also investigated. Crossed-polarizing light microscopy (CPLM) and small-angle X-ray scattering (SAXS) identified the presence of lamellar and hexagonal phase at the surfactant–polymer interface of the respective systems. The hydrophobic and electrostatic interactions between the oppositely charged components were studied by varying temperature and salt concentration, respectively, and were found to influence the liquid-crystalline nanostructure formed. The hexagonal phase persisted at high temperatures, however the lamellar phase structure was lost above ca. 45 °C. Both mesophases were found to dissociate upon addition of 4% NaCl solution. The rate of release of the model hydrophilic drug, Rhodamine B (RhB), from the lamellar phase significantly increased in response to changes in the solution conditions studied, suggesting that modulating the drug release from these bile salt–chitosan capsules is readily achieved. In contrast, release from the hexagonal phase capsules had no appreciable response to the stimuli applied. These findings provide a platform for these oppositely charged surfactant and polymer systems to function as stimuli-responsive or sustained-release drug delivery systems. © 2014, American Chemical Society.
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    The interaction of cubosomes with supported phospholipid bilayers using neutron reflectometry and QCM-D
    (Royal Society of Chemistry, 2011-09-21) Shen, HH; Hartley, PG; James, M; Nelson, A; Defendi, H; McLean, KM
    We present the results of a study of the interaction of lyotropic liquid crystalline dispersions with supported lipid bilayers based on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) using a quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR). We investigated two types of phytantriol-based cubosome formulations, with subtly different internal nanostructures, with one formulation incorporating 2.5% of the biological lipid di-palmitoylphosphatidylserine (DPPS). The QCM-D data showed that cubosomes do not directly attach to the silica supporting surface but they can accumulate on the model membrane, confirming that there is an attractive interaction between POPC bilayers and the cubosome formulations. We have further used NR to quantify the amount of cubosomes adsorbed on the supported POPC bilayers and to examine the structural rearrangement of cubosomes on interaction with the supported lipid bilayer. The data show that the DPPS-containing cubosomes accumulate at the bilayer surface continuously for 15 hours. Pure phytantriol cubosomes accumulated over a longer time period (36 hours), but accumulated to a lesser degree overall. Furthermore, NR data revealed lipid exchange and structural rearrangements for both types of cubosomes, however, for the DPPS-containing cubosomes, these processes were greater in magnitude and faster. Confocal microscopy analysis of cubosome interactions with HeLa cells in vitro, showed increased membrane affinity for the DPPS-containing formulations, which were consistent with the NR and QCM-D observations. We interpret these observations as suggesting that membrane accumulation, cellular uptake and cytotoxicity of cubosome formulations are directly related to their DPPS content, and that this may be the result of increased propensity for liquid crystalline structural rearrangement, as postulated previously (H. H. Shen et al., Biomaterials, 2010, 31, 9473).© 2011, Royal Society of Chemistry
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    Nanofibrillar micelles and entrapped vesicles from biodegradable block copolymer/polyelectrolyte complexes in aqueous media
    (ACS Publications, 2013-07-09) Salim, NV; Hameed, N; Hanley, TL; Waddington, LJ; Hartley, PG; Guo, Q
    Here we report a viable route to fibrillar micelles and entrapped vesicles in aqueous solutions. Nanofibrillar micelles and entrapped vesicles were prepared from complexes of a biodegradable block copolymer poly(ethylene oxide)-block-poly(lactide) (PEO-b-PLA) and a polyelectrolyte poly(acrylic acid) (PAA) in aqueous media and directly visualized using cryogenic transmission electron microscopy (cryo-TEM). The self-assembly and the morphological changes in the complexes were induced by the addition of PAA/water solution into the PEO-b-PLA in tetrahydrofuran followed by dialysis against water. A variety of morphologies including spherical wormlike and fibrillar micelles, and both unilamellar and entrapped vesicles, were observed, depending on the composition, complementary binding sites of PAA and PEO, and the change in the interfacial energy. Increasing the water content in each [AA]/[EO] ratio led to a morphological transition from spheres to vesicles, displaying both the composition- and dilution-dependent micellar-to-vesicular morphological transitions. © 2013, American Chemical Society.
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    Neutron scattering studies on the formation and decomposition of gas hydrates near the ice point
    (Curran Associates, 2011-07-17) Klapproth, A; Piltz, RO; Kennedy, SJ; Peterson, VK; Garvey, CJ; Kozielski, P; Hartley, PG
    Gas hydrates pose a major risk of disruption to the marine pipelines of the oil and gas industry. At the temperatures and pressures in these pipelines gas hydrates can form large solid plugs. A clearer understanding of these processes would allow implementation of effective strategies to avoid production losses in gas pipelines. In-situ neutron powder diffraction was used to study hydrate growth and dissociation for 10% propane-methane gas and D2O ice and liquid water in the temperature and pressure range of 263 – 288 K and 3.0 – 4.8 MPa. Of our three samples one formed a mixed sI and sII hydrate while the other two formed single sII hydrate. Thermodynamic stability calculations could not accurately predict if a mixed hydrate would be formed. Our hydrate dissociation experiments question the relevance of anomalous hydrate preservation in our particular case. Furthermore these experiments elucidate the importance of the heat flow of the reaction processes and the role of a free liquid-gas interface. Copyright© (2011) by Hydrafact Ltd
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    Targeted detection of phosphatidylserine in biomimetic membranes and in vitro cell systems using annexin V-containing cubosomes
    (Elsevier, 2013-11-01) Shen, HH; Lake, V; Le Brun, AP; James, M; Duff, AP; Peng, Y; McLean, KM; Hartley, PG
    In this work we have formulated Annexin V (ANX) decorated phosphatidylserine containing phytantriol (PSPhy) cubosomes to act as probes for the enhanced detection of apoptotic membranes in both model and in vitro cell systems. Small angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (Cryo-TEM) indicated that ANX-containing PSPhy (ANX-PSPhy) cubosomes retain the Pn3m cubic symmetry and cubic phase nanoparticle characteristics of PSPhy cubosomes. The interaction of ANX-PSPhy cubosomes with apoptotic model and cellular membranes was also investigated using both quartz crystal microbalance with dissipation and confocal microscopy which confirmed that ANX-PSPhy cubosomes can selectively bind to apoptotic cells and model membranes. Neutron reflectometry has also been used to show strong binding of ANX-PSPhy cubosomes to a model apoptotic membrane, and in addition reveals changes in both the bilayer structure and in the internal structure of the cubosome in a region adjacent to the membrane as a result of material exchange. This material exchange between cubosome and apoptotic model bilayer was further demonstrated using Cryo-TEM. We have demonstrated that lipid bound protein, in this case Annexin V, can be used to target cubosome systems to biological surfaces in vitro. © 2013, Elsevier Ltd.