Modulating stiffness with photo-switchable supramolecular hydrogels

Stimuli-responsive hydrogels are attractive materials with many applications towards biomedicine,biology, construction, and manufacturing. Materials that can be cured or annealed rapidly at room temperature are of particular interest. In this work we develop a class of supramolecular coumarin-functionalised hydrogels formedviahost-guest mediated self-assembly with cucurbit[8]uril thatcan photo-switch to covalent gels and reversibly toggle between the two states. A principle ad-vantage of such materials is their ability to maintain a homogeneous chemical composition and crosslink density while selectively modulating stiffness with light. An investigation of the photo-reversibility of these functional materials elucidated that hydroxyethyl cellulose-coumarin based gels were soft and could only switch from a physical state to a covalent one, while hyaluronic acid-coumarin based gels were softer and could be photo-reversed back into a physical state after covalent curing.A.T. acknowledges The Winston Churchill Foundation of the United States. R.A.F. acknowledges the Cambridge Commonwealth European and International Trust. C.C.P. acknowledges the Engineering and Physical Sciences Research Council. G.W. acknowledges the Leverhulme Trus

Coordination cages as permanently porous ionic liquids

Porous materials are widely used in industry for applications that include chemical separations and gas scrubbing. These materials are typically porous solids, although the liquid state can be easier to manipulate in industrial settings. The idea of combining the size and shape selectivity of porous domains with the fluidity of liquids is a promising one and porous liquids composed of functionalized organic cages have recently attracted attention. Here we describe an ionic-liquid, porous, tetrahedral coordination cage. Complementing the gas binding observed in other porous liquids, this material also encapsulates non-gaseous guests—shape and size selectivity was observed for a series of isomeric alcohols. Three gaseous chlorofluorocarbon guests, trichlorofluoromethane, dichlorodifluoromethane and chlorotrifluoromethane, were also shown to be taken up by the liquid coordination cage with an affinity that increased with their size. We hope that these findings will lead to the synthesis of other porous liquids whose guest-uptake properties may be tailored to fulfil specific functions

The impact of surgically induced ischaemia on protein levels in patients undergoing rectal cancer surgery

The goal of targeted therapy has driven a search for markers of prognosis and response to adjuvant therapy. The surgical resection of a solid tumour induces tissue ischaemia and acidosis, both potent mediators of gene expression. This study investigated the impact of colorectal cancer (CRC) surgery on prognostic and predictive marker levels. Tumour expression of thymidylate synthase, thymidine phosphorylase, cyclin A, vascular endothelial growth factor (VEGF), carbonic anhydrase-9, hypoxia inducible factor-1α, and glucose transporter-1 (GLUT-1) proteins was determined before and after rectal cancer surgery. Spectral imaging of tissue sections stained by immunohistochemistry provided quantitative data. Surgery altered thymidylate synthase protein expression (P=0.02), and this correlated with the change in the proliferation marker cyclin A. The expression of hypoxia inducible factor-1α, VEGF, and GLUT-1 proteins was also different following surgery. Colorectal cancer surgery significantly impacts on intratumoral gene expression, suggesting archival specimens may not accurately reflect in situ marker levels. Although rectal cancer was the studied model, the results may be applicable to any solid tumour undergoing extirpation in which molecular markers have been proposed to guide patient therapy

The effect of surgically induced ischaemia on gene expression in a colorectal cancer xenograft model

Delays in tissue fixation following tumour vascular clamping and extirpation may adversely affect subsequent protein and mRNA analysis. This study investigated the effect of surgically induced ischaemia in a xenograft model of a colorectal cancer on the expression of a range of prognostic, predictive, and hypoxic markers, with a particular emphasis on thymidylate synthase. Vascular occlusion of human tumour xenografts by D-shaped metal clamps permitted defined periods of tumour ischaemia. Alterations in protein expression were measured by immunohistochemistry and spectral imaging, and changes in mRNA were measured by reverse transcriptase–polymerase chain reaction. Thymidylate synthase expression decreased following vascular occlusion, and this correlated with cyclin A expression. A similar reduction in dihydropyrimidine dehydrogenase was also seen. There were significant changes in the expression of several hypoxic markers, with carbonic anhydrase-9 showing the greatest response. Gene transcriptional levels were also noted to change following tumour clamping. In this xenograft model, surgically induced tumour ischaemia considerably altered the gene expression profiles of several prognostic and hypoxic markers, suggesting that the degree of tumour ischaemia should be minimised prior to tissue fixation

Anisotropic silica colloids for light scattering

Anisotropic silica particles were used as model scattering enhancers and directly compared to their spherical counterparts. Furthermore, silica rods were assembled into micron-sized scattering particles. This allows for use in pigment formulations.</p

Anisotropic silica colloids for light scattering

Anisotropic silica particles were used as model scattering enhancers and directly compared to their spherical counterparts. Furthermore, silica rods were assembled into micron-sized scattering particles. This allows for use in pigment formulations.</p

Changes Across Time in Spike Rate and Spike Amplitude of Auditory Nerve Fibers Stimulated by Electric Pulse Trains

We undertook a systematic evaluation of spike rates and spike amplitudes of auditory nerve fiber (ANF) responses to trains of electric current pulses. Measures were obtained from acutely deafened cats to examine time-related changes free from the effects of hair-cell and synaptic adaptation. Such data relate to adaptation that likely occurs in ANFs of cochlear-implant users. A major goal was to determine and compare rate adaptation observed at different pulse rates (primarily 250, 1000, and 5000 pulse/s) and describe them using decaying exponential models similar to those used in acoustic studies. Rate-vs.-time functions were best described by two-exponent models and produced time constants similar to (although slightly greater than) the “rapid” and “short-term” components described in acoustic studies. There was little dependence of these time constants on onset spike rate, but pulse-rate effects were noted. Spike amplitude changes followed a time course different from that of rate adaptation consistent with a process related to ANF interspike intervals. The fact that two time constants governed rate adaptation in electrically stimulated and deafened fibers suggests that future computational models of adaptation should not only include hair cell and synapse components, but also components determined by fiber membrane characteristics

Different Scattering Regimes in Two-Dimensional Bose-Einstein Condensates

Conference Name: NATO Advanced Study Institute on Quantum Communication and Information TechnologiesDate of Conference: 3-14 June 2003Chapter 14Motivated by the recent efforts to produce low-dimensional condensates, we study the ground-state density profiles of two-dimensional Bose-Einstein condensed atoms at zero temperature within a mean-field theory. The interplay between the tight harmonic confinement in the axial direction and collisional properties of the condensate atoms help identify three distinct regimes of experimental interest. Each regime is described by a different atom-atom coupling which depends on the density of the condensate as the system starts to be influenced by two-dimensional collisions. We trace the regions of experimentally accessible system parameters for which the crossover between different dimensionality behaviors in the scattering properties may become observable