Preparation and Characterization of Hybrid Nanocomposites Coated on LDPE

Summary: Hybrid organic‐inorganic nanocomposites containing hyperbranched structures were prepared through a dual‐curing process, which involves photopolymerization and condensation alkoxysilane groups. In particular, an oligomer containing PEO units and α,ω‐methacrylate groups was used together with a HBP bearing acrylic groups as the organic phase precursors. MEMO, as the organic‐inorganic linker, and TEOS, as inorganic phase precursor, were also employed. The kinetics of both photopolymerization and condensation reactions were investigated by double bond conversion analysis (via FT‐IR) and weight loss determination, respectively. The mobility of the organic phase was studied by means of DSC and DMTA and correlated with hybrid composition. TEM analyses performed on microtomed film slices indicated the formation of nanoscale silica domains. Hybrids were coated onto an LDPE film previously subjected to a plasma treatment, and substrate‐coating interfacial adhesion was investigated through stress‐strain and DMTA experiments.

Reaction scheme showing the insertion of furanic units in copolyester chains by ester interchange reaction.     

The Candida albicans PMM1 gene encoding phosphomannomutase complements a Saccharomyces cerevisiae sec 53-6 mutation

We have constructed an ordered-array genomic DNA library of the pathogenic dimorphic fungus Candida albicans which facilitates the rapid cloning of C. albicans genes by hybridisation. Using the Saccharomyces cerevisiae SEC53 gene encoding phosphomannomutase as a hybridisation probe we have cloned the C. albicans homologue, PMM1, and determined its sequence. This gene shows high similarity, both at the nucleotide (76.2%) and amino-acid (77.7%) level, to the S. cerevisiae SEC53 gene. We have used the C. albicans PMM1 gene, in single copy, to transform temperature-sensitive S. cerevisiae sec53-6 mutant cells, which are defective in PMM activity at 37°C, to growth at 37°C. The C. albicans PMM1 gene is thus the structural and functional equivalent of the SEC53 gene.     

Effectiveness of add-on pegylated interferon alfa-2a therapy in a lamivudine-treated patient with chronic hepatitis B

Hepatitis B virus (HBV) surface antigen (HBsAg) to anti-HBsAg (anti-HBs) antibody seroconversion is the best, final objective for all available chronic hepatitis B (CHB) treatments. Unfortunately, this goal is rarely obtained with the currently utilized therapeutic approaches. Here we describe the case of a CHB patient who was very successfully treated with a particular therapeutic schedule. The patient was initially treated with lamivudine for four years. Subsequently, pegylated interferon alpha-2a was introduced for a period of one year. During this period of combined therapies, the patient showed a flare of aminotransferase values followed by complete normalization of liver biochemistry parameters and HBsAg/anti-HBs seroconversion that persisted up to 24 months after all therapies had been stopped.     

Conditional inactivation of the E-cadherin gene in thyroid follicular cells affects gland development but does not impair junction formation

We have conditionally inactivated the E-cadherin gene in the thyroid follicular cells of mouse embryo to unravel its role in thyroid development. We used the Cre-loxP system in which the Cre-recombinase was expressed under the control of the tissue-specific thyroglobulin promoter that becomes active at embryonic d 15. At postnatal d 7, thyroid follicle lumens in the knockout mice were about 30% smaller with respect to control mice and had an irregular shape. E-cadherin was almost completely absent in thyrocytes, beta-catenin was significantly reduced, whereas no change in gamma-catenin was detected. alpha-Catenin was also reduced on the cell plasma membrane. Despite the dramatic loss of E-cadherin and beta-catenin, cell-cell junctions were not affected, the distribution of tight junction proteins was unaltered, and no increase of thyroglobulin circulating in the blood was observed. In addition, we found that other members of the cadherin family, the R-cadherin and the Ksp-cadherin, were expressed in thyrocytes and that their membrane distribution was not altered in the E-cadherin conditional knockout mouse. Our results indicate that E-cadherin has a role in the development of the thyroid gland and in the expression of beta-catenin, but it is not essential for the maintenance of follicular cell adhesion.     

Study of Organic Phase Mobility in Nanocomposite Organic‐Inorganic Coatings

Summary: Organic‐inorganic hybrids synthesized by a dual photopolymerization and condensation process from (i) two organic precursors, either poly(ethylene glycol) α,ω diacrylate ( = 600) (PEGDA) or bisphenol‐A‐ethoxylate(15EO/phenol)‐dimethacrylate (BEMA), (ii) the organic‐inorganic bridging monomer (methacryloyl‐oxypropyl‐trimethoxysilane, (MEMO)) and (iii) the inorganic precursor tetraethoxysilane (TEOS) were investigated by differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy (DMTA). It is found that progressive formation of the crosslinked network during the different steps of hybrid production results in changes of molecular mobility that show up in changes of the glass transition of the organic phase. While moving from the organic precursor to the final hybrid through the subsequent photopolymerization and condensation reactions, the transition is seen to broaden, decrease in intensity and shift to higher temperature. Excellent agreement of DSC and DMTA results is obtained. Dynamic mechanical analysis of the hybrids coated on PET film (coating thickness 10 and 40 µm) show an additional up‐shift of T_g, more marked in the case of the thinner hybrid coating. This result is attributed to molecular interactions at the substrate‐coating interface that locally hinder molecular mobility. The consequent increase of T_g is more evident when the coating layer is thin. The results show the potential of the DMTA technique in coating‐polymer substrate adhesion studies. Finally, the relaxation spectrum of the hybrids is sensitive to humidity absorbed from the environment and reversibly changes in absorption‐desorption cycles.

DMTA loss spectrum of‘free’ PEGDA‐based hybrid film, PET film with thick coating and PET film with thin coating.     

Scaffold for tissue engineering fabricated by non-isothermal supercritical carbon dioxide foaming of a highly crystalline polyester

Porous scaffolds of a random co-polymer of ω-pentadecalactone (PDL) and ε-caprolactone (CL) (poly(PDL–CL)), synthesized by biocatalysis, were fabricated by supercritical carbon dioxide (scCO₂) foaming. The co-polymer, containing 31 mol.% CL units, is highly crystalline (T_m = 82 °C, ΔH_m = 105 J g^?1) thanks to the ability of the two monomer units to co-crystallize. The co-polymer can be successfully foamed upon homogeneous absorption of scCO₂ at T > T_m. The effect of soaking time, depressurization rate and cooling rate on scaffold porosity, pore size distribution and pore interconnectivity was investigated by micro X-ray computed tomography. Scaffolds with a porosity in the range 42–76% and an average pore size of 100–375 μm were successfully obtained by adjusting the main foaming parameters. Process conditions in the range investigated did not affect the degree of crystallinity of poly(PDL–CL) scaffolds. A preliminary study of the mechanical properties of the scaffolds revealed that poly(PDL–CL) foams may find application in the regeneration of cartilage tissue.