Chemoprophylaxis Effect of EGCG on the Recurrence of Colorectal Cancer: A Systematic Review and Meta-Analysis.

BACKGROUND AND AIMS: The recurrence rate of Colorectal Cancer (CRC) after cure is always high. The purpose of this study was to investigate whether green tea extract (-)-Epigallocatechin gallate (EGCG) has an effective preventive effect on the recurrence of CRC. METHODS: We conducted a systematic literature review and meta-analysis of the effects of taking EGCG or placebo on disease recurrence in patients after colon polyp removal. RESULTS: Five Randomized Controlled Trials (RCTs) were included in this review. A double-blind drug trial involving 1389 participants involved EGCG and placebo. The results showed no significant publication bias or heterogeneity in the five studies (I2 = 38%; p = 0.17). Patients taking EGCG had a lower recurrence rate of CRC than those in the placebo group. The results were statistically significant (Z=2.83, p < 0.05). CONCLUSION: This study demonstrated that long-term EGCG can prevent CRC recurrence to a certain extent.

Neutron reflectivity characterization of the photoacid reaction-diffusion latent and developed images of molecular resists for extreme ultraviolet lithography.

Lithographic feature size requirements have approached a few radius of gyration of photoresist polymers used in thin-film patterning. Furthermore, the feature dimensions are commensurate with the photoacid diffusion length that defines the underlying latent image. Smaller imaging building blocks may enable reduced feature sizes; however, resolution limits are also dependent upon the spatial extent of the photoacid-catalyzed reaction diffusion front and subsequent dissolution mechanism. The reaction-diffusion front was characterized by neutron reflectivity for ccc stereoisomer-purified, deuterium-labeled tert-butoxycarbonyloxy calix[4]resorcinarene molecular resists. The spatial extent of the reaction front exceeds the size of the molecular resist with an effective diffusion constant of (0.13 ± 0.06) nm(2)/s for reaction times longer than 60 s, with the maximum at shorter times. Comparison to a mean-field reaction-diffusion model shows that a photoacid trapping process provides bounds to the spatial and extent of reaction via a reaction-limited mechanism whereas the ratio of the reaction rate to trapping rate constants recovers the effective diffusion peak. Under the ideal step-exposure conditions, surface roughness was observed after either positive- or negative-tone development. However, negative-tone development follows a surface-restructuring mechanism rather than etch-like dissolution in positive-tone development.

Photoresist latent and developer images as probed by neutron reflectivity methods.

Photoresist materials enable the fabrication of advanced integrated circuits with ever-decreasing feature sizes. As next-generation light sources are developed, using extreme ultraviolet light of wavelength 13.5 nm, these highly tuned formulations must meet strict image-fidelity criteria to maintain the expected performance gains from decreases in feature size. However, polymer photoresists appear to be reaching resolution limits and advancements in measurements of the in situ formed solid/solid and solid/liquid interface is necessary. This Review focuses on the chemical and physical structure of chemically amplified photoresists at the lithographic feature edge at length scales between 1 nm and 100 nm. Neutron reflectivity measurements provide insight into the nanometer-scale composition profiling of the chemical latent image at an ideal lithographic line-edge that separates optical resolution effects from materials processing effects. Four generations of advanced photoresist formulations were examined over the course of seven years to quantify photoresist/photoacid and photoresist/developer interactions on the fidelity of lithographic features. The outcome of these measurements complement traditional resist design criteria by providing the effects of the impacts of the photoresist and processing on the feature fidelity. These physical relations are also described in the context of novel resist architectures under consideration for next-generation photolithography with extreme-ultraviolet radiation.

Investigation of thermally responsive block copolymer thin film morphologies using gradients.

We report the use of a gradient library approach to characterize the structure and behavior of thin films of a thermally responsive block copolymer (BCP), poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA), which exhibits chemical deprotection and morphological changes above a thermal threshold. Continuous gradients in temperature and film thickness, as well as discrete substrate chemistry conditions, were used to examine trends in deprotection, nanoscale morphology, and chemical structure. Thermal gradient annealing permitted the extraction of transformation rate constants (k(t)) for the completion of thermal deprotection and rearrangement of the film morphology from a single BCP library on hydroxyl and alkyl surfaces, respectively. The transformation rate constants ranged from 1.45 × 10(-4) s(-1) to 5.02 × 10(-5) s(-1) for temperatures between 185 and 140 °C for hydroxyl surfaces. For the same temperature range, the alkyl surfaces yielded k(t) values ranging from 4.76 × 10(-5) s(-1) to 5.73 × 10(-6) s(-1), an order of magnitude slower compared to hydroxyl surfaces. Activation energies of the thermal deprotection and film transformation on these surfaces were also extrapolated from linear fits to Arrhenius behavior. Moreover, we noted a morphology shift and orientation transformation from parallel lamellae to perpendicular cylinders at the free surface because of changes in volume fraction and surface energetics of the initially symmetric BCP. Using gradient techniques, we are able to correlate morphological and chemical structure changes in a rapid fashion, determine kinetics of transitions, and demonstrate the effect of surface chemistry on the deprotection reaction in thermally responsive BCP thin films.

Manipulation of the asymmetric swelling fronts of photoresist polyelectrolyte gradient thin films.

The depth profile of swelling polyelectrolyte layers is characterized by a static bulk layer and an asymmetric profile with position and shape parameters that describe the intermediate and solution side of the interfacial region. The characteristic width in the solution-side region exceeds the dimensions of the individual chains and therefore is comprised of weakly associated polymers. Contrary to that observed for polyelectrolyte gels and brushes stabilized by cross-links or by covalent bonds to the substrate, respectively, these swelling layers exhibit a more complex response to monovalent and divalent salts. Salt causes an initial contraction of the solution-side interface; layer expansion and polymer dissolution follow at higher salt concentration. The swelling layers measured by neutron reflectivity with mass change verified by quartz crystal microbalance exhibit nonequilibrium responses to the salt concentration, as observed through this interplay between swelling and dissolution. Further, the asymmetric profiles approach, but do not reach, symmetric shapes as expected by mean field equilibrium interfaces. These measurements, motivated by technological needs of photoresist materials, highlight the significance of hydrophobic interactions in determining the structure of associating polymer molecules at the lithographic feature edge.

Effect of deprotection extent on swelling and dissolution regimes of thin polymer films.

The response of unentangled polymer thin films to aqueous hydroxide solutions is measured as a function of increasing weakly acidic methacrylic acid comonomer content produced by an in situ reaction-diffusion process. Quartz crystal microbalance with energy dissipation and Fourier transform infrared spectroscopy measurements are used to identify four regimes: (I) nonswelling, (II) quasiequilibrium swelling, (III) swelling coupled with partial film dissolution, and (IV) film dissolution. These regimes result from chemical heterogeneity in local composition of the polymer film. The acid-catalyzed deprotection of a hydrophobic group to the methacrylic acid tends to increase the hydrophilic domain size within the film. This nanoscale structure swells in aqueous base by ionization of the methacrylic acid groups. The swollen film stability, however, is determined by the hydrophobic matrix that can act as physical cross-links to prevent dissolution of the polyelectrolyte chains. These observations challenge current models of photoresist film dissolution that do not include the effects of swelling and partial film dissolution on image quality.