Thermoresponsive macroporous scaffolds prepared by emulsion templating.

A versatile method to prepare non-covalently crosslinked polyHIPEs hydrogels from oil-in-water high internal phase emulsions (HIPEs) whose aqueous phase contained thermo-responsive linear polymers is described. The interconnected pore structure of the polyHIPEs is maintained by reversible physical aggregation of thermo-responsive polymer chains in an aqueous environment. This method to prepare interconnected porous hydrogels using a thermal trigger in the guise of thermo-responsive polymers by emulsion templating requires no chemical reaction during solidification of the template. This particular feature could provide a safer route to injectable scaffolds as issues of polymerisation/crosslinking chemistry and residual initiator fragments or monomers do not arise.

Ionic liquids as internal phase for non-aqueous polyHIPEs.

Stable high internal phase emulsions (HIPEs) with the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide as dispersed phase were prepared and polymerised thermally into polyHIPEs. All polyHIPEs exhibited pore morphologies similar to that of polyHIPEs obtained with an aqueous dispersed phase. PolyHIPEs containing the dispersed phase possess a low T(g) and are thermally stable in excess of 200 °C, offering the potential for new porous materials where water as dispersed phase is chemically or physically undesirable.

Bioresponsive small molecule polyamines as noncytotoxic alternative to polyethylenimine.

Nonviral gene therapy continues to require novel synthetic vectors to deliver therapeutic nucleic acids effectively and safely. The majority of synthetic nonviral vectors employed in clinical trials to date have been cationic liposomes; however, cationic polymers are attracting increasing attention. One of the few cationic polymers to enter clinical trials has been polyethylenimine (PEI); however, doubts remain over its cytotoxicity, and in addition it displays lower levels of transfection than viral systems. Herein, we report on the development of a series of small molecule analogues of PEI that are bioresponsive to the presence of pDNA, forming poly(disulfide)s that are capable of efficacious transfection with no associated toxicity. The most effective small molecule developed, a cyclic disulfide based upon a spermine backbone, is shown to form very well-defined polyplexes (100-200 nm in diameter) that mediate murine lung transfection in vivo to within an order of magnitude of in vivo jetPEI, and at the same time display a much improved cytotoxicity profile.

Inducing pH responsiveness via ultralow thiol content in polyacrylamide (micro)gels with labile crosslinks.

Here we present the synthesis and characterization of pH responsive polyacrylamide microgels, synthesized via free radical polymerization of acrylamide and bis (acryloylcystamine) (BAC). The gels were made with ultralow amounts of thiol functional groups incorporated into the polymer. The resulting gel monoliths were mechanically chopped into microgel particles with size distributions ranging from 80 to 200 mum. The gels exhibit an interesting reversible pH-dependent rheological behavior which led to gelling of the colloidal suspension when the pH was increased, and a low-viscosity suspension was obtained when the pH was taken back to the original value. The viscosity of the colloidal system containing MBA crosslinked microgels remained insensitive to pH. This observation motivated further analysis; viscosity measurements of the highly viscous (gel-like) state of the BAC crosslinked microgel colloidal suspension were carried out to further understand the rheological behavior of the colloidal system. Electrophoretic mobility measurements as function of pH of the BAC and MBA crosslinked colloidal polyacrylamide microgel suspensions were performed. The swelling behavior of the microgels for both colloidal systems was also determined as function of pH using static light scattering. This swelling behavior was used to rationalize the observed rheological behavior. The work presented here demonstrates that free thiol groups present within a polymer gel matrix confer pH responsive behavior to the gel in solution. The viscosity of a BAC crosslinked microgel suspension was also measured under reducing conditions. The viscosity of the microgel suspension reduced with time, due to the breakage of the disulfide bonds in the crosslinkers.

Amplified fluorescence quenching in high ionic strength media.

We report a new cationic poly(phenylene ethynylene) (PPE) derivative that exhibits strong amplified fluorescence quenching in the presence of electron-deficient species, yielding high Stern-Volmer coefficients of 4.7 × 10 M in aqueous solutions. Importantly, with the addition of appropriate non-ionic surfactants, the polymer is found to retain its excellent sensitivity even when transferred to high ionic strength buffered media, which have previously been shown to suppress the amplified quenching effect in other polyelectrolyte systems. The cationic PPE derivative yields Stern-Volmer coefficients as high as 10 M in 25 mM buffer solutions of both tris(hydroxymethyl) aminomethane (Tris) and sodium acetate containing 150 mM sodium chloride, the optimal conditions for many enzymes such as phosphatases. The ability to maintain high Stern-Volmer coefficients in high ionic strength buffered media extends the applicability of ionic conjugated polymers to high sensitivity detection in biological media, and thus greatly enhances their versatility as biological sensors.

Cytotoxicity of polycations: Relationship of molecular weight and the hydrolytic theory of the mechanism of toxicity.

The mechanism of polycation cytotoxicity and the relationship to polymer molecular weight is poorly understood. To gain an insight into this important phenomenon a range of newly synthesised uniform (near monodisperse) linear polyethylenimines, commercially available poly(l-lysine)s and two commonly used PEI-based transfectants (broad 22kDa linear and 25kDa branched) were tested for their cytotoxicity against the A549 human lung carcinoma cell line. Cell membrane damage assays (LDH release) and cell viability assays (MTT) showed a strong relationship to dose and polymer molecular weight, and increasing incubation times revealed that even supposedly "non-toxic" low molecular weight polymers still damage cell membranes. The newly proposed mechanism of cell membrane damage is acid catalysed hydrolysis of lipidic phosphoester bonds, which was supported by observations of the hydrolysis of DOPC liposomes.

Sonochemical degradation of N-methylpyrrolidone and its influence on single walled carbon nanotube dispersion.

Sonicating pure N-methyl pyrrolidone (NMP) rapidly produces contaminating organic nanoparticles, at increasing concentration with time, as investigated by AFM, as well as UV-vis, IR and NMR spectroscopies. The contamination issue affects carbon nanotube, and likely other nanomaterial, dispersions processed by sonication in organic solvents.

Quantitative analysis and optimization of gravure printed metal ink, dielectric, and organic semiconductor films.

Here we demonstrate the optimization of gravure printed metal ink, dielectric, and semiconductor formulations. We present a technique for nondestructively imaging printed films using a commercially available flatbed scanner, combined with image analysis to quantify print behavior. Print speed, cliché screen density, nip pressure, the orientation of print structures, and doctor blade extension were found to have a significant impact on the quality of printed films, as characterized by the spreading of printed structures and variation in print homogeneity. Organic semiconductor prints were observed to exhibit multiple periodic modulations, which are correlated to the underlying cell structure.

The synthesis of [2], [3] and [4]rotaxanes and semirotaxanes.

The cucurbituril-catalysed synthesis of [2], [3] and [4]semirotaxanes allows access to regioselectively pure, 1,3-disubstituted mono-, bis- and tris-triazoles in high yield after dethreading.

Enantioselective molecularly imprinted polymers via ring-opening metathesis polymerisation.

Enantioselective molecularly imprinted polymers (MIPs) have been synthesised via ROMP for the first time.

Formation of oligotriazoles catalysed by cucurbituril.

The catalytic activity of cucurbituril in 1,3-dipolar cycloadditions has been applied to the synthesis of oligotriazoles.

Phosphorylation status of thymidine kinase 1 following antiproliferative drug treatment mediates 3'-deoxy-3'-[18F]-fluorothymidine cellular retention.

BACKGROUND: 3'-Deoxy-3'-[18F]-fluorothymidine ([18F]FLT) is being investigated as a Positron Emission Tomography (PET) proliferation biomarker. The mechanism of cellular [18F]FLT retention has been assigned primarily to alteration of the strict transcriptionally regulated S-phase expression of thymidine kinase 1 (TK1). This, however, does not explain how anticancer agents acting primarily through G2/M arrest affect [18F]FLT uptake. We investigated alternative mechanisms of [18F]FLT cellular retention involving post-translational modification of TK1 during mitosis. METHODS: [18F]FLT cellular retention was assessed in cell lines having different TK1 expression. Drug-induced phosphorylation of TK1 protein was evaluated by MnCl2-phos-tag gel electrophoresis and correlated with [18F]FLT cellular retention. We further elaborated the amino acid residues involved in TK1 phosphorylation by transient transfection of FLAG-pCMV2 plasmids encoding wild type or mutant variants of TK1 into TK1 negative cells. RESULTS: Baseline [18F]FLT cellular retention and TK1 protein expression were associated. S-phase and G2/M phase arrest caused greater than two-fold reduction in [18F]FLT cellular retention in colon cancer HCT116 cells (p<0.001). G2/M cell cycle arrest increased TK1 phosphorylation as measured by induction of at least one phosphorylated form of the protein on MnCl2-phos-tag gels. Changes in [18F]FLT cellular retention reflected TK1 phosphorylation and not expression of total protein, in keeping with the impact of phosphorylation on enzyme catalytic activity. Both Ser13 and Ser231 were shown to be involved in the TK1 phosphorylation-modulated [18F]FLT cellular retention; although the data suggested involvement of other amino-acid residues. CONCLUSION: We have defined a regulatory role of TK1 phosphorylation in mediating [18F]FLT cellular retention and hence reporting of antiproliferative activity, with implications especially for drugs that induce a G2/M cell cycle arrest.

Robust and Operationally Simple Synthesis of Poly(bis(2,2,2-trifluoroethoxy) phosphazene) with Controlled Molecular Weight, Low PDI, and High Conversion.

Synthetically straightforward conditions have been developed for the preparation of poly(bis 2,2,2-trifluoroethoxy)phosphazene with low PDI (<1.15) at high conversion (75-99%) and on a multigram scale. A combination of 31P NMR and GPC analyses demonstrate that molecular weight increases linearly as a function of monomer consumption, exhibiting first order kinetics with respect to monomer concentration up to high monomer conversion. Thus, the molecular weight can be controlled by varying the initiator (H2O) to monomer ratio.

Multifunctional structural energy storage composite supercapacitors.

This paper addresses the challenge of producing multifunctional composites that can simultaneously carry mechanical loads whilst storing (and delivering) electrical energy. The embodiment is a structural supercapacitor built around laminated structural carbon fibre (CF) fabrics. Each cell consists of two modified structural CF fabric electrodes, separated by a structural glass fibre fabric or polymer membrane, infused with a multifunctional polymeric electrolyte. Rather than using conventional activated carbon fibres, structural carbon fibres were treated to produce a mechanically robust, high surface area material, using a variety of methods, including direct etching, carbon nanotube sizing, and carbon nanotube in situ growth. One of the most promising approaches is to integrate a porous bicontinuous monolithic carbon aerogel (CAG) throughout the matrix. This nanostructured matrix both provides a dramatic increase in active surface area of the electrodes, and has the potential to address mechanical issues associated with matrix-dominated failures. The effect of the initial reaction mixture composition is assessed for both the CAG modified carbon fibre electrodes and resulting devices. A low temperature CAG modification of carbon fibres was evaluated using poly(3,4-ethylenedioxythiophene) (PEDOT) to enhance the electrochemical performance. For the multifunctional structural electrolyte, simple crosslinked gels have been replaced with bicontinuous structural epoxy-ionic liquid hybrids that offer a much better balance between the conflicting demands of rigidity and molecular motion. The formation of both aerogel precursors and the multifunctional electrolyte are described, including the influence of key components, and the defining characteristics of the products. Working structural supercapacitor composite prototypes have been produced and characterised electrochemically. The effect of introducing the necessary multifunctional resin on the mechanical properties has also been assessed. Larger scale demonstrators have been produced including a full size car boot/trunk lid.

Ion-responsive alginate based macroporous injectable hydrogel scaffolds prepared by emulsion templating.

Ion-responsive biocompatible macroporous hydrogels with a well-defined highly interconnected open porous structure were synthesised using oil-in-water (o/w) high internal phase emulsion (HIPE) templating. Methacrylate-modified alginate was crosslinked in the continuous minority water phase and the oil internal phase removed to produce macroporous hydrogel monoliths. The physical dimensions, pore and pore throat size as well as water uptake of the alginate polyHIPE hydrogel can be controllably tuned by ion-responsive behaviour towards Ca2+ ions. The ionic crosslinks formed are fully reversible and be dissolved using sodium citrate to remove Ca2+ ions through chelation. The polyHIPE hydrogels possess mechanical properties with storage moduli up to 20 kPa and are biocompatible as shown by cytotoxicity assays. The hydrogel can be extruded through a hypodermic needle causing it to break into small pieces (about 1 to 3 mm in diameter) while retaining the interconnected pore morphology after injection. Furthermore, these hydrogel fragments can be reformed into a coherent scaffold under mild conditions using an alginate solution containing Ca2+ ions.

Examination of the effect of increasing the number of intra-disulfide amino functional groups on the performance of small molecule cyclic polyamine disulfide vectors.

Establishing structure-activity relationships is vital if the efficacy of non-viral vectors is to match that of their viral counter-parts. Recently, we reported on the ability of a series of small molecule, cyclic polyamine disulfides to condense and cage plasmid DNA (pDNA) by a process of thermodynamically controlled templated polymerization, leading to a series of corresponding pDNA-polyplex nanoparticles able to mediate high levels of transfection with no associated cytotoxicities. The leading cyclic polyamine disulfide was shown to be the spermine tetra-amine disulfide (TetraN-3,4,3). Herein we report on the significantly more challenging syntheses of cyclic disulfides with longer polyamine motifs. Two new cyclic polyamine disulfides, based on hexa- and octa-amine inserts, were prepared and their transfection efficacies and cytotoxicities compared with our previously reported cyclic tri- and tetra-amine disulfides. The new cyclic hexa- and octa-amine disulfides prove more effective at transfection in vitro, especially of lung epithelial A549 cell line. By contrast, our original cyclic tetra-amine disulfide remains the most efficient agent for the transfection of lung epithelial cells in vivo following intra-nasal administration. Hypothetical mechanistic reasons are presented to explain this outcome. Our data in toto support the concept of shorter cyclic polyamine disulfides as preferred agents for polycation-mediated controlled condensation and functional delivery of pDNA to lung epithelial cells in vivo.

Inhibition of mitogen-activated protein kinase (MAPK) and cyclin-dependent kinase 2 (Cdk2) by platinum(II) phenanthroline complexes.

UNLABELLED: Inhibition of protein kinases in the fight against disease remains a constant challenge for medicinal chemists, who have screened multitudes of predominantly planar organic scaffolds, natural and synthetic, to identify potent-albeit not always selective-kinase inhibitors. Herein, in an effort to investigate the potential biological utility of metal-based compounds as inhibitors against the cancer-relevant targets mitogen-activated protein kinase and cyclin-dependent kinase 2, we explore various parameters in planar platinum(II) complexes with substituted phenanthroline ligands and aliphatic diamine chelate co-ligands, to identify combinations that yield promising inhibitory activity. The individual ligands' steric requirements as well as their pattern of hydrogen bond donors/acceptors appear to alter inhibitory potency when modulated. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12154-011-0059-5) contains supplementary material, which is available to authorized users.

Coordination chemistry of amide-functionalised tetraazamacrocycles: structural, relaxometric and cytotoxicity studies.

Three different tetraazamacrocyclic ligands containing four amide substituents that feature groups (namely allyl, styryl and propargyl groups) suitable for polymerisation have been synthesised. Gadolinium(III) complexes of these three ligands have been prepared as potential monomers for the synthesis of polymeric MRI contrast agents. To assess the potential of these monomers as MRI contrast agents, their relaxation enhancement properties and cytotoxicity have been determined. A europium(III) complex of one of these ligands (with propargyl substituents) is also presented together with its PARACEST properties. In addition, to gain further insight into the coordination chemistry of the tetra-propargyl substituted ligand, the corresponding zinc(II) and cadmium(II) complexes have been prepared. The X-ray crystal structures of the tetra-propargyl ligand and its corresponding gadolinium(III), zinc(II) and cadmium(II) complexes are also presented.