Silver nanoparticles coated with dodecanethiol used as fillers in non-cytotoxic and antifungal PBAT surface based on nanocomposites.

In the present study, we report the preparation of antifungal and non-cytotoxic polymer nanocomposites with potential application in biomedical materials. Dodecanethiol-protected silver nanoparticles (AgNPs-DDT) were synthesized by a reduction/precipitation method and dispersed in chloroform to obtain stable colloidal dispersions. PBAT-based nanocomposites containing 0.25, 0.5 and 2 wt% AgNPs-DDT were prepared by casting method. The incorporation of AgNPs-DDT in PBAT matrix resulted in nanocomposites which combine improved mechanical performance and antifungal properties with a non-cytotoxic characteristic.

Fabrication of nanopore and nanoparticle arrays with high aspect ratio AAO masks.

How to use high aspect ratio anodic aluminum oxide (AAO) membranes as an etching and evaporation mask is one of the unsolved problems in the application of nanostructured arrays. Here we describe the versatile utilizations of the highly ordered AAO membranes with a high aspect ratio of more than 20 used as universal masks for the formation of various nanostructure arrays on various substrates. The result shows that the fabricated nanopore and nanoparticle arrays of substrates inherit the regularity of the AAO membranes completely. The flat AAO substrates and uneven AAO frontages were attached to the Si substrates respectively as an etching mask, which demonstrates that the two kinds of replication, positive and negative, represent the replication of the mirroring of Si substrates relative to the flat AAO substrates and uneven AAO frontages. Our work is a breakthrough for the broad research field of surface nano-masking.

Effect of clay content and speed screw rotation on the crystallization and thermal behaviors of recycled PET/clay nanocomposites.

Nanocomposites of recycled poly(ethylene terephthalate) (rPET) containing 2.5 wt% and 5.0 wt% of montmorillonite modified with organophilic quaternary ammonium salt (DELLITE 67G) were prepared by melt compounding using a co-rotating twin-screw type extruder with two organoclay contents were used: 2.5 wt% and 5.0 wt% and were prepared using two different rotation speeds: 150 and 250 rpm. Thermal characterization (analysis) of the nanocomposites was performed using differential scanning calorimetry (DSC) analysis. The results from DSC measurements showed that the addition of organoclay affects recycled PET's crystallization for two screw rotation speeds studies. The nucleating effect of organoclay was investigated. Morphological analysis using Transmission Electron Microscopy (TEM) revealed the presence of fully exfoliated clay platelets in samples prepared at 150 rpm.

Medium optimization based on statistical methodologies for pristinamycins production by Streptomyces pristinaespiralis.

The optimization of nutrient levels for the production of pristinamycins by Streptomyces pristinaespiralis CGMCC 0957 in submerged fermentation was carried out using the statistical methodologies based on the Plackett-Burman design, the steepest ascent method, and the central composite design (CCD). First, the Plackett-Burman design was applied to evaluate the influence of related nutrients in the medium. Soluble starch and MgSO4 x 7H2O were then identified as the most significant nutrients with a confidence level of 99%. Subsequently, the concentrations of the two nutrients were further optimized using response surface methodology of CCD, together with the steepest ascent method. Accordingly, a second-order polynomial regression model was finally fitted to the experimental data. By solving the regression equation from the model and analyzing the response surface, the optimal levels for soluble starch and MgSO4 x 7H2O were determined as 20.95 and 5.67g/L, respectively. Under the optimized medium, the yield of pristinamycins in the shake flask and 5-L bioreactor could reach 1.30 and 1.01 g/L, respectively, which is the highest yield reported in literature to date.

Cultivation and modelling of encapsulated Saccharomyces cerevisiae in NaCS-PDMDAAC polyelectrolyte complexes.

The cultivation of encapsulated S. cerevisiae in NaCS-PDMDAAC polyelectrolyte complexes was studied. The results showed that the encapsulated microorganisms had the same growth trends as in its free cell culture and, thus, NaCS-PDMDAAC microcapsules were suitable for the encapsulation of these biological substances. The encapsulated S. cerevisiae cells were fermented sequentially for 16 batches. The highest cell density in the capsules reached 2.64 x 10(10) cells mL(-1) and the ethanol concentration was 47.0 g L(-1). A model of the cultivation of the encapsulated S. cerevisiae was developed.

Controlled release of biomolecules from temperature-sensitive hydrogels prepared by radiation polymerization.

Poly(acryloyl-L-proline methyl ester)-based hydrogels containing 1 and 5% of a crosslinking agent were studied as drug delivery systems. The drug loading properties were investigated by matrix incubation into solutions containing biomolecules with molecular weight ranging between 300 and 65,000 Da. The loading yield was found to depend on both the crosslinking degree and the molecular weight of the drug. In vitro release studies were carried out with both swollen and dry matrices loaded with gentamicin, isoniazid and insulin. Gentamicin and isoniazid were released by a bimodal Fickian diffusion with a remarkable burst that was found to depend on both matrix crosslinking degree and physical state. In vivo, the subcutaneous implantation into mice of the isoniazid loaded matrices allowed for an efficient drug release for 800 h. In vitro insulin was released from the swollen matrices for 1500 h by diffusional Fickian mechanism while the dry ones displayed a lag time followed by Fickian diffusion release. The subcutaneous implantation of the insulin-loaded matrices into diabetic mice induced a remarkable decrease in the glucose concentrations in blood. In particular, the dry 1% matrices were found to maintain a low glucose level for 700 h.

Supports for enzyme immobilization.

Macroporous silica gel, prepared from sodium silicate and hydrochloric acid, one grade of diatomaceous earth (celite 545) and nonporous glass were analyzed in terms of pore size by the mercury intrusion pressure method. The alkylamine derivatives of the above materials were examined for their suitability as supports for enzyme immobilization, using the enzyme glucose oxidase. The effectiveness of the immobilized enzyme was compared in relation to the free enzyme and particle size of the carrier. The immobilized enzyme exhibited a broader range of optimum pH and greater thermal stability, among some properties considered.

The conformation of SecA, as revealed by its protease sensitivity, is altered upon interaction with ATP, presecretory proteins, everted membrane vesicles, and phospholipids.

Interactions between SecA and cellular components involved in the translocation of secretory proteins across the cytoplasmic membrane of Escherichia coli were studied by examining changes in the sensitivity of SecA to staphylococcal protease V8. In the presence of ATP, the amino-terminal 95-kDa portion of the SecA molecule became highly resistant to V8 digestion. Adenosine 5'-(gamma-thio)triphosphate (ATP gamma S) and ADP were as effective as ATP. For the effect, ATP could be partly replaced by CTP and UTP, but not GTP, as in the case of the protein translocation reaction. In the presence of proOmpA, a presecretory protein, on the other hand, SecA became more sensitive to V8 digestion. The signal peptide region was involved in this effect. The V8-digestion profile in the presence of both proOmpA and ATP or ADP was the same as that in the presence of proOmpA alone. Consistently, proOmpA-induced discharge of ADP or ATP gamma S from SecA was observed by means of flow dialysis. SecA-deprived everted membrane vesicles and an E. coli phospholipid mixture were also effective in making SecA more sensitive to V8 digestion. Among the phospholipids, phosphatidylglycerol and cardiolipin were effective, whereas phosphatidylethanolamine was not. It is suggested that SecA directly interacts with these cellular components and the interactions result in changes in the conformation of SecA. The physiological significance of such interactions in protein secretion is discussed.