Polarization dependence of optically driven polydomain elastomer mechanics

We model how polarized and unpolarized light can cause mechanical response in polydomain nematic and related photoelastomers. The reduction of order by heating and the consequential large strains that are known from nematic elastomers can alternatively be caused by light-induced bending of rodlike dye molecules which then equally reduce the order of their nematic hosts. While there is no mechanical response to heating of polydomain elastomers, mechanical response to light is possible by the selective absorption of light according to how domains are aligned with respect to the polarization direction or with respect to the propagation direction in the case of unpolarized light. We find large contractions or elongations, depending on the nature of polarization. The responses are nonmonotonic with light intensity.

Semisoft elastic response of nematic elastomers to complex deformations

We consider a relaxed semisoft elastomer with its director oriented along the z axis that is first subjected to a large stretch in the x direction then to a slight x-z shear. We give a general argument that in any theory including director rotation, at the onset and end of the director rotation induced by these large stretches, there will be kinks in the stress-large strain curve (forming a stress-strain plateau) and zeros in the x-z shear modulus (C5) associated with small shears imposed on top of the stretches. We then find the analytical forms of the C5 -strain curves for a particular model of semisoftness (arising from compositional fluctuations) and show that it, together with the known stress-strain curve, provides the basis for a strong test of this theory. Finally, we consider the scope for other semisoft models and show that the compositional fluctuations model in fact yielded a generic form, that is, it is the most general quadratic free energy that does not explicitly include a final state direction other than the director. By introducing such additional directions, a large range of alternative models could be developed.

Biological functions and clinical implications of oestrogen receptors alfa and beta in epithelial tissues

For the past 10 years it is known that oestrogen functions through the activation of two oestrogen receptors (ERalpha and ERbeta). To the great surprise of endocrinologists, ERbeta was found to be widely distributed in tissues throughout the body including tissues previously considered as 'oestrogen insensitive'. The epithelium of the ventral prostate and lung as well as ovarian granulosa cells are ERalpha-negative but ERbeta-positive and in these tissues ERbeta seems to be involved in important physiological processes, like differentiation, extracellular matrix organization and stromal-epithelial communication. In tissues where both ERs are expressed, the two receptors seem to counteract each other. In the uterus, mammary gland and immune system, ERalpha promotes proliferation whereas ERbeta has pro-apoptotic and pro-differentiating functions. The challenge of the future will be to develop specific agonists, which can selectively activate/inactivate either ERalpha or ERbeta. These pharmaceuticals are likely to be of clinical importance in the prevention or treatment of various diseases.

Bleaching and stimulated recovery of dyes and of photocantilevers

We examine how intense optical beams can penetrate deeply into highly absorbing media by a nonlinear, photobleaching process. The role of stimulated recovery to the dye ground state can be important and is delineated. This analysis of nonlinear absorption processes is applicable in general to situations where chromophores are irradiated, for instance, in biology. We examine the implications for the bending of cantilevers made of heavily dye-loaded nematic photosolids, that is nematic glasses and elastomers that have large mechanical reactions to light. In particular we describe the bending of cantilevers sufficiently absorbing that they would not bend if Beer's law were applicable. We quantify the role of optically generated heat in determining the mechanical response and conclude that in general it is minor in importance compared with optical effects.

Mechanical response of smectic-C elastomers

The elastic response of a smectic-C elastomer to three deformations, namely imposed lambda(xx), lambda(xz), and lambda(zz), has been modeled using a nonlinear theory of a nematic elastomer with embedded smectic layers, and with the director tilt (in the x direction) at a fixed angle with respect to the smectic layer normal (z direction). The main focus is the elastic response after any soft mode of the sample. It is found that the elastomer contracts in the x direction under lambda(xz) shear. On stretching parallel to the layer normal it is found that there is a soft mode that acts to rotate the director toward the z direction. The deformation of the system after this soft mode can be reduced to shear and elongation in the plane of the layers. We make predictions of the mechanical response of the elastomer, in particular the length of the soft plateau and the asymptotic modulus for the elastomer when stretched parallel to the layer normal. Finally, since monodomain Sm-C elastomers are made by the deformation-induced alignment of polydomains, we describe these important systems. Qualitative behavior of the model is then compared to existing experimental literature on the mechanical alignment of polydomains.

Linear and nonlinear photoinduced deformations of cantilevers

Glassy and elastomeric nematic networks with dye molecules present can be very responsive to illumination, huge reversible strains being possible. If absorption is appreciable, strain decreases with depth into a cantilever, leading to bend that is the basis of micro-opto-mechanical systems (MOMS). Bend actually occurs even when Beer's law suggests a tiny penetration of light into a heavily dye-doped system. We model the nonlinear opto-elastic processes behind this effect. In the regime of cantilever thickness giving optimal bending for a given incident light intensity, there are three neutral surfaces. In practice such nonlinear absorptive effects are very important since heavily doped systems are commonly used.

Evaluation of the chromogenic Cica-beta-Test for detecting extended-spectrum, AmpC and metallo-beta-lactamases

BACKGROUND

Extended-spectrum, metallo- and AmpC beta-lactamases usually are sought subsequently to susceptibility testing, meaning that producers are not identified until 72 h after a clinical specimen is taken. Chromogenic tests might usefully shorten this delay, and we investigated the Cica-beta-Test for this purpose.

METHODS

Reference and clinical strains with known beta-lactamases, or controls, were grown with a cefpodoxime disc to promote conservation of resistance. The cultures were then tested with nitrocefin and with the Cica-beta-Test, which examines for hydrolysis of the chromogenic oxyimino-cephalosporin HMRZ-86 with and without specific inhibitors of extended-spectrum, metallo- and AmpC beta-lactamases.

RESULTS

were scored, as colour changes from yellow to red, with the tester blinded to the strain identity and the mechanism(s) present. Results Proportions of extended-spectrum, metallo- and AmpC beta-lactamase producers correctly identified by the Cica-beta-Test were 85%, 77% and 72%, respectively. Such performance should be achievable if testing colonies from a primary culture plate, 24 h after a specimen was taken. Greater precision, albeit at more delay, would be achieved if results were read in conjunction with antibiogram data available 48 h after the specimen was taken. Limitations were frequent confusion of Klebsiella oxytoca hyperproducing K1 enzyme with AmpC hyperproducers, and that isolates with NMC-A or KPC carbapenemases were wrongly inferred to have AmpC enzymes.

CONCLUSIONS

The Cica-beta-Test has the potential to provide useful therapeutic guidance, identifying isolates with potent beta-lactamases and informing early therapy; it will also help to monitor beta-lactamase epidemiology among multiresistant strains.

Efficacy of practised screening methods for detection of cephalosporin-resistant Enterobacteriaceae

OBJECTIVES

Enterobacteriaceae with extended-spectrum beta-lactamases (ESBLs) are now widespread and simple phenotypic tests are required to detect them in diagnostic laboratories. We investigated the performance of screening methods at 16 hospitals in South-East England.

METHODS

Sixteen laboratories in South-East England submitted 1195 consecutive Enterobacteriaceae isolates found to be resistant, by their routine methods, to any or all of cefpodoxime, ceftazidime and cefotaxime. These isolates were re-tested centrally with various cephalosporin/clavulanate combinations and with multiplex PCR for bla(CTX-M) and bla(AmpC) alleles.

RESULTS

Screening methods among the laboratories were the following: cefpodoxime discs alone (1 site); cefpodoxime, cefotaxime and ceftazidime discs (9 sites) or agar dilution (1 site); Phoenix (2 sites), Vitek 1 (1 site) and Vitek 2 (2 sites). A total of 8% of isolates submitted based on disc tests proved fully cephalosporin-susceptible, compared with 3% sent based on tests with automated systems and none of those sent based on agar dilution tests. Among isolates submitted solely on cefpodoxime resistance 256/372 (69%) proved cephalosporin-susceptible or had only borderline resistance with no clear mechanism demonstrable; this proportion decreased to 28/160 (18%) for those submitted on the basis of resistance to ceftazidime, 18/122 (15%) for those resistant to cefotaxime and 26/496 (5%) for those resistant to both cefotaxime and ceftazidime. The inference of ESBL production by Vitek 2 had the best agreement with reference laboratory results.

CONCLUSIONS

Many isolates found resistant only to cefpodoxime at the source sites proved not to have ESBLs or AmpC; screening with cefotaxime and ceftazidime allowed better specificity for identification of mechanism-based resistance, as did the automated systems. Cefpodoxime disc tests nevertheless remain a useful primary screen for laboratories prepared only to test one agent.

New developments in oestrogen signalling in colonic epithelium

Epidemiological studies show that oestrogen reduces the risk of colorectal cancer in postmenopausal women and ERβ (oestrogen receptor β)-selective ligands have been reported to be very effective treatment in animal models of inflammatory bowel disease. Several studies have shown that ERβ is the predominant ER in the colonic epithelium, but it is not clear whether the benefit of ERβ agonists in inflammatory bowel disease are due to their action on the colon epithelium itself, or on the immune system. In order to address this issue, we have compared colons of ERβ−/− and wild-type mice with regard to morphology, histology, proliferation and differentiation. We found that the number of proliferating cells was higher in ERβ−/− mice, and the migration of labelled cells from base to lumen of the crypts was faster. Additionally, immunohistochemical staining revealed fewer apoptotic cells (cleaved caspase 3-positive), a significant decrease in expression of the epithelial differentiation marker, cytokeratin CK20, the adherens junction protein, α-catenin, and the hemidesmosomal protein, plectin, in ERβ−/− mice. These findings suggest a role for ERβ in growth, organization and maintenance of the normal colonic crypt–villus architecture. The next step is to elucidate the molecular mechanisms that underlie the signalling of ERβ in normal cell growth and assess whether or not ERβ agonists will be useful drugs in the prevention or treatment of colorectal cancer. Dietary phyto-oestrogens are believed to play a role in protection against colorectal cancer. Lignans, such as enterolactone, an ER agonist, prevent cancer development in animal models. Since ERβ is the only ER in the colon, there is enough reason to speculate that phyto-oestrogens are acting through ERβ.