Freeze-drying Step Research Articles

Optimization of dye adsorption capacity and mechanical strength of chitosan aerogels through crosslinking strategy and graphene oxide addition

Chitosan (CS) aerogels were prepared by freeze-drying as potential adsorbents for water purification, and the effect of the strategy of crosslinking was investigated by varying the amount of crosslinker (glutaraldehyde) and the sequence of steps for the preparation of the aerogel. Two procedures were compared, in which the crosslinking step was carried out before or after the freeze-drying of the starting CS solution. When crosslinking was postponed after the freeze-drying step, the adsorption capacity towards an anionic dye, such as indigo carmine, considerably increased (up to +45%), reaching values as high as 534.4 ± 30.5 mg g−1. The same crosslinking strategy ensured a comparable improvement also in nanocomposite aerogels containing graphene oxide (GO), which was added to enhance the mechanical strength and provide adsorption capacity towards cationic dyes. Besides possessing good mechanical strength (compressive modulus higher than 1 MPa), the CS/GO aerogels were able to bind also cationic pollutants such as methylene blue. The maximum uptake capacity increased from 4.3 ± 1.6 to 168.6 ± 9.6 mg of cationic dye adsorbed per gram of adsorbent with respect to pristine CS aerogels.

Visualization of crust formation during hot-air-drying via micro-CT

Nowadays, hot-air-drying (HAD) is the most common process for the production of dried fruits and vegetables till now. It is well known that HAD has a big influence on product structure leading to effects like shrinkage or case-hardening. While shrinkage has already been documented throughout the drying process, case-hardening or the formation of a crust has only been shown for the dried product. In this study, a three-step approach consisting of a HAD-, a freezing-, and a freeze-drying step is used to show the development of a crust of carrot discs throughout a HAD process. With this method, the crust structures created during HAD were preserved and could be analyzed in a dry state with cone-beam micro-CT measurements. Crust thickness increased significantly during HAD and crust formation started before a relative moisture content of X/X0 = 0.5.

Oil spill cleanup employing magnetite nanoparticles and yeast-based magnetic bionanocomposite

Oil spill is a serious environmental concern, and alternatives to remove oils from water involving biosorbents associated to nanoparticles is an emerging subject. Magnetite nanoparticles (MNP) and yeast magnetic bionanocomposite (YB-MNP) composed by yeast biomass from the ethanol industry were produced, characterized, and tested to remove new motor oil (NMO), mixed used motor oil (MUMO) and Petroleum 28 °API (P28API) from water following the ASTM F726–12 method, which was adapted by insertion of a lyophilization step to ensure the accuracy of the gravimetric approach. Temperature, contact time, the type and the amount of the magnetic material were the parameters evaluated employing a fractional factorial design. It was observed the removal of 89.0 ± 2.6% or 3522 ± 118 g/kg (NMO) employing MNP; 69.1 ± 6.2% or 2841 ± 280 g/kg (MUMO) with YB-MNP; and 55.3 ± 8.2% or 2157 ± 281 g/kg (P28API) using MNP. The temperature was the most significant parameter in accordance with the Pareto's graphics (95% confidence) for all oil samples considered in this study as well as the two magnetic materials. Contact time and the interaction between the materials and temperature were also relevant. The D-Optimals designs showed that the NMO and P28API responded in a similar way for all evaluated parameters, while the uptake of MUMO was favored at higher temperatures. These behaviors demonstrate the influence of oil characteristics and the intermolecular forces between the oil molecules on the mechanism dragging process performed by the attraction between magnetite nanoparticles and a 0.7 T magnet. It was clear that this kind of experiment is predominantly a physic phenomenon which cannot be described as adsorption process.

Two-Step Synthesis of Cobalt Iron Alloy Nanoparticles Embedded in Nitrogen-Doped Carbon Nanosheets/Carbon Nanotubes for the Oxygen Evolution Reaction.

There is a vital need to explore highly efficient and stable non-precious-metal catalysts for the oxygen evolution reaction (OER) to reduce the overpotential and further improve the energy-conversion efficiency. Herein, we report a unique and cost-effective lyophilization and thermal treatment two-step procedure to synthesize a high-performance hybrid consisting of CoFe alloy nanoparticles embedded in N-doped carbon nanosheets interspersed with carbon nanotubes (CoFe-N-CN/CNTs) hybrid. The lyophilization step during the catalyst preparation leads to a uniform dispersion of carbon-like precursors and avoids the agglomeration of metal particles. In addition, the inserted CNTs and doped N in this hybrid provide a good electrical conductivity, an abundance of chemically active sites, good mass transport capability, and effective gas adsorption/release channels. All these lead to a high specific surface area of 240.67 m2 g-1 , favorable stability, and remarkable OER activities with an overpotential of only 285 mV at a current density of 10 mA cm-2 and a Tafel slope of 51.09 mV dec-1 in 1.0 m KOH electrolyte, which is even superior to commercial IrO2 catalysts. The CoFe-N-CN/CNTs hybrid thus exhibits great potential as a highly efficient and earth-abundant anode OER electrocatalyst.

Characterization of low-abundance species in the active pharmaceutical ingredient of CIGB-300: A clinical-grade anticancer synthetic peptide.

CIGB-300 is a first-in-class synthetic peptide-based drug of 25 amino acids currently undergoing clinical trials in cancer patients. It contains an amidated disulfide cyclic undecapeptide fused to the TAT cell-penetrating peptide through a beta-alanine spacer. CIGB-300 inhibits the CK2-mediated phosphorylation leading to apoptosis of tumor cells in vitro, and in vivo in cancer patients. Despite the clinical development of CIGB-300, the characterization of peptide-related impurities present in the active pharmaceutical ingredient has not been reported earlier. In the decision tree of ICHQ3A(R2) guidelines, the daily doses intake, the abundance, and the identity of the peptide-related species are pivotal nodes that define actions to be taken (reporting, identification, and qualification). For this, purity was first assessed by reverse-phase chromatography (>97%) and low-abundance impurities (≤0.27%) were collected and identified by mass spectrometry. Most of the impurities were generated during peptide synthesis, the spontaneous air oxidation of the reduced peptide, and the lyophilization step. The most abundant impurity, with no biological activity, was the full-length peptide containing Met17 transformed into a sulfoxide residue. Interestingly, parallel and antiparallel dimers of CIGB-300 linked by 2 intermolecular disulfide bonds exhibited a higher antiproliferative activity than the CIGB-300 monomer. Likewise, very low abundance trimers and tetramers of CIGB-300 linked by disulfide bonds (≤0.01%) were also detected. Here we describe for the first time the presence of active dimeric species whose feasibility as novel CIGB-300 derived entities merits further investigation.

Toward multiplexed quantification of biomolecules on surfaces using time-of-flight secondary ion mass spectrometry.

Accurate detection and quantification of individual molecules is important for the development of improved diagnostic methods as well as biochemical characterization of disease progression and treatments. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a surface analysis technique capable of imaging the distribution of specific molecules on surfaces with a high spatial resolution (<1 μm) and high sensitivity. ToF-SIMS is particularly suitable for detection of molecules up to ∼2 kDa, including lipids, whereas larger molecules, such as peptides and proteins, are fragmented during analysis, which makes them difficult to identify. In this study, an approach for extending the molecular detection capability of ToF-SIMS is presented, based on the specific binding of functionalized liposomes to molecular targets on the sample surface and subsequent detection of the liposomes by ToF-SIMS. Furthermore, by using different recognition elements conjugated to liposomes with different lipid compositions, simultaneous detection of different targets was accomplished. This multiplexing capability was investigated for two types of recognition elements (antibodies and cholera toxin) and for target molecules immobilized on surfaces using two frequently applied surface functionalization strategies: a supported lipid bilayer aimed to mimic a cell membrane and a polyethylene glycol modified surface, commonly employed in bioanalytical sensor applications. The efficacy of the conjugation protocols and the specificity of the recognition mechanism were confirmed using quartz crystal microbalance with dissipation monitoring, while fluorescence microscopy was used to validate the ToF-SIMS data and the reliability of the freeze-drying step required for ToF-SIMS analysis. The results demonstrated specific binding of the two types of liposomes to each target and showed a concentration-dependent binding to the targets on the different model surfaces. In particular, the possibility to use the contrasts in the mass spectra of SIMS to identify the concentration dependent coverage of different liposomes opens up new opportunities for multiplexed detection and quantification of molecules at biotechnology relevant interfaces.

Safety and efficacy of Lactococcuslactis NCIMB 30160 as a feed additive for all animal species.

Following a request from European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the proposed modification of the terms of the authorisation regarding the formulation of the product Lactococcus lactis NCIMB 30160. The applicant has proposed to modify the manufacturing process by replacing one ingredient in the freeze‐drying step with polyethylene glycol (PEG 4000), a product authorised in the EU as a food additive. The use of PEG 4000 as an excipient in formulations with Lactococcus lactis NCIMB 30160 would not change the previous conclusions regarding the safety for the target animals, consumers and users. The FEEDAP Panel concludes that the additive is safe for target species and for consumers of products from animals fed the treated silage. The additive is not a skin irritant but is a potential skin/respiratory sensitiser. In the absence of data, the Panel is unable to conclude on the safety for the environment of the proposed use of PEG 4000 as excipient in formulations of the additive. The FEEDAP Panel sees no reason to reconsider the conclusions on efficacy previously drawn that the additive containing L. lactis NCIMB 30160 has the potential to improve the production of silage from all forages by increasing lactic acid content and the preservation of dry matter, by reducing the pH and moderately the loss of protein, as determined by ammonia‐N.

Coupling Mo2C@C core-shell nanocrystals on 3D graphene hybrid aerogel for high-performance lithium ion battery

Hybrid aerogel by dispersing Mo2C@C core-shell nanocrystals into three-dimensional (3D) graphene (Mo2C@C-GA) has been successfully prepared through two-step methods. Firstly, carbon-coated MoO2 nanocrystals uniformly anchor on 3D graphene aerogel (MoO2@C-GA) via hydrothermal reaction. Then the MoO2@C-GA precursor is transformed into Mo2C@C-GA after the following carbonization process. Furthermore, the freeze-drying step plays an important role in the resulting pore size distribution of the porous networks. Moreover, graphene aerogels exhibit extremely low densities and superior electrical properties. When evaluated as anode material for lithium ion battery, Mo2C@C-GA delivers excellent rate capability and stable cycle performance when compared with C-GA and Mo2C nanoparticles. Mo2C@C-GA exhibits the initial discharge capacity of 1461.4 mA h g−1 at the current density of 0.1 A g−1, and retains a reversible capacity of 1089.8 mA h g−1 after 100 cycles at a current density of 0.1 A g−1. Even at high current density of 5 A g−1, a discharge capacity of 623.5 mA h g−1 can be still achieved. The excellent performance of Mo2C@C-GA could be attributed to the synergistic effect of Mo2C@C nanocrystals and the 3D graphene conductive network.

Standing wave design and optimization of a simulated moving bed chromatography for separation of xylobiose and xylose under the constraints on product concentration and pressure drop

The feasibility of a simulated moving bed (SMB) technology for the continuous separation of high-purity xylobiose (X2) from the output of a β-xylosidase X1→X2 reaction has recently been confirmed. To ensure high economical efficiency of the X2 production method based on the use of xylose (X1) as a starting material, it is essential to accomplish the comprehensive optimization of the X2-separation SMB process in such a way that its X2 productivity can be maximized while maintaining the X2 product concentration from the SMB as high as possible in consideration of a subsequent lyophilization step. To address this issue, a suitable SMB optimization tool for the aforementioned task was prepared based on standing wave design theory. The prepared tool was then used to optimize the SMB operation parameters, column configuration, total column number, adsorbent particle size, and X2 yield while meeting the constraints on X2 purity, X2 product concentration, and pressure drop. The results showed that the use of a larger particle size caused the productivity to be limited by the constraint on X2 product concentration, and a maximum productivity was attained by choosing the particle size such that the effect of the X2-concentration limiting factor could be balanced with that of pressure-drop limiting factor. If the target level of X2 product concentration was elevated, higher productivity could be achieved by decreasing particle size, raising the level of X2 yield, and increasing the column number in the zones containing the front and rear of X2 solute band.

Composite Alginate-Hyaluronan Sponges for the Delivery of Tranexamic Acid in Postextractive Alveolar Wounds

The management of wounds in patients on anticoagulant therapy who require oral surgical procedures is problematic and often results in a nonsatisfactory healing process. Here, we report a method to prepare an advanced dressing able to avoid uncontrolled bleeding by occluding the postextractive alveolar wounds, and simultaneously, capable of a fast release of tranexamic acid (TA). Composite alginate/hyaluronan (ALG/HA) sponge dressings loaded with TA were prepared by a straightforward internal gelation method followed by a freeze-drying step. Both blank and drug-loaded sponges were soft, flexible, and elegant in appearance and nonbrittle in nature. Scanning electron microscopy analysis confirmed the porous nature of these dressings. The integration of HA influenced the microstructure, reducing the porosity, modifying the water uptake kinetic, and increasing the resistance to compression. TA release from ALG/HA sponges showed a controlled release up to 3 h, and it was faster in the presence of HA. Finally, an in vitro clotting test performed on human whole blood confirmed that the TA-loaded sponges significantly reduce the blood clotting index by 30% compared with ALG/HA20 sponges. These results suggest that, if placed in a socket cavity, these dressings could give a relevant help to the blood hemostasis after dental extractions, especially in patients with coagulation disorders.

Quantification of six potential unspecific human biomarkers of 1-vinyl-2-pyrrolidone exposure in Sprague-Dawley rat urine using gas chromatography coupled with triple mass spectrometry.

The monomer 1-vinyl-2-pyrrolidone (VP) is a substance with excellent solvent features. It is used in a wide variety of pharmaceutical, cosmetic, food industrial or technical applications and produced on an industrial scale. Since VP has caused adenocarcinoma of the nasal cavity and liver cell carcinoma in long-term experiments with rats, a human biomarker would be appreciated for risk assessment. A sensitive analytical electron ionization gas chromatography/tandem mass spectrometry (GC/MS/MS) method for the determination of six possible biomarkers for VP in urine was established and validated. Two isotope-labeled internal standards (ISTD) were used for quantification. A simple and easy to use freeze-drying step was performed prior to derivatization with N-tert-butyldimethylsilyl-N-methyltrifluoracetamide (MTBSTFA) and following sample extraction for cleanup purposes. A calibration curve with six calibration standards ranging from 50μg/L to 2000μg/L (10-fold higher for H-OPAA) in urine was prepared. Validation results were satisfactory with recoveries ranging from 88.2 to 110.2 % with two exceptions for the lowest quality control for two substances without ISTD (126.4 % and 139.3 %). Three of the substances could be identified as VP metabolites in an exposure study with Sprague-Dawley (SD) rats. A quick and easy to use method has been established for six target molecules investigated for a better understanding of the metabolism of VP. Two of three substances identified as metabolites of VP could serve as a nonspecific human biomarker for VP exposure as shown with an excerpt of an exposure study performed in SD rats.

The pharmaceutical applications of a biopolymer isolated from Trigonella foenum-graecum seeds: Focus on the freeze-dried matrix forming capacity

The aim of the present study was to evaluate the funtion of fenugreek seed mucilage (FSM) as potential matrix forming agent for orodispersible pharmaceutical lyophilisates. The FSM was isolated and characterized. FSM colloidal dispersions were prepared and the rheological evaluation was performed. Oral lyophilisates (OLs) with different FSM concentrations, containing meloxicam as model drug were prepared by freeze drying method. The OLs were characterized and compared to gelatin containing tablets, prepared under the same conditions.The FSM dispersions revealed shear thinning flow type. Based on colloidal dispersions' rheological properties, five FSM concentrations were taken forward to the lyophilization step. Completely dry and elegant tablets were obtained. Texture analysis indicated highly porous structures, confirmed by SEM analysis, which explain the fast disintegration properties. All the prepared tablets disintegrated in less than 47 s. The disintegration process was prolonged by the increase in FSM content, due to the high viscosity the polymer creates in aqueous media. FSM tablets presented longer disintegration times, as compared to gelatin tablets, but also higher crushing strength. Considering the fast disintegration and the high crushing strength, FSM is a good candidate as matrix forming agent for fast disintegrating dosage forms or other freeze-dried preparations.

Effects of Chamber Pressure and Partial Pressure of Water Vapor on Secondary Drying in Lyophilization.

Secondary drying is the final step of lyophilization before stoppering, during which water is desorbed from the product to yield the final moisture content. We studied how chamber pressure and partial pressure of water vapor during this step affected the time course of water content of aqueous solutions of polyvinylpyrrolidone (PVP) in glass vials. The total chamber pressure had no effect when the partial pressure of water vapor was very low. However, when the vapor phase contained a substantial fraction of water vapor, the PVP moisture content was much higher. We carried out dynamic vapor sorption experiments (DVS) to demonstrate that the higher PVP moisture content was a straightforward result of the higher water vapor content in the lyophilizer. The results highlight that the partial pressure of water vapor is extremely important during secondary drying in lyophilization, and that lower chamber pressure set points for secondary drying may sometimes be justified as a strategy for ensuring low partial pressure of water vapor, especially for lyophilizers that do not inject dry gas to control pressure. These findings have direct application for process transfers/scale ups from freeze-dryers that do not inject dry gas for pressure control to those that do, and vice versa.

Evaluation of a novel system for analyzing hydrophilic blood metabolites

Metabolomics has recently been developed, and there have been a considerable number of metabolomics-based biomarker studies in the medical research field. Therefore, as a first step toward the practical use of metabolite biomarkers, a simple and quick sample preparation method involving metabolite extraction, metabolite measurement, and data analysis needs to be developed. In this study, we evaluated whether the use of simpler metabolite extraction methods would facilitate the stable analysis of hydrophilic blood metabolites during liquid chromatography/triple quadrupole mass spectrometry (LC/QqQMS)-based metabolome analysis. As a result, the anion and cation metabolites in plasma were stably analyzed via a methanol-based extraction procedure followed by ultrafiltration, and it was also confirmed that a lyophilization step was not necessary. When extraction was performed without a lyophilization step, approximately >50% and >80% of the detected metabolites had relative standard deviation values of <20% during LC/QqQMS-based anion and cation analyses, respectively. In addition, the plasma levels of l-valine, l-leucine, l-isoleucine, l-tyrosine, and l-phenylalanine were quantitatively measured using the corresponding stable isotopes; the SCLAM-2000, a fully automatic pre-treatment system for LC/MS that can be connected online to an LC/MS device; and an extraction procedure based on the simple procedure that we developed. Our findings suggest that simpler pretreatment procedures can be employed during LC/QqQMS-based metabolomics and might aid searches for metabolite biomarker candidates, the validation of metabolite biomarker candidates, and the practical use of metabolite biomarkers.

Development of a DNA-liposome complex for gene delivery applications

The association structures formed by cationic liposomes and DNA (Deoxyribonucleic acid)-liposome have been effectively utilized as gene carriers in transfection assays. In this research study, cationic liposomes were prepared using a modified lipid film hydration method consisting of a lyophilization step for gene delivery applications. The obtained results demonstrated that the mean particle size had no significant change while the polydispersity (PDI) increased after lyophilization. The mean particle size slightly reduced after lyophilization (520±12nm to 464±25nm) while the PDI increased after lyophilization (0.094±0.017 to 0.220±0.004). In addition. The mean particle size of vesicles increases when DNA is incorporated to the liposomes (673±27nm). According to the Scanning Electron Microscopy (SEM) and transmission electron microscopy (TEM) images, the spherical shape of liposomes confirmed their successful preservation and reconstitution from the powder. It was found that liposomal formulation has enhanced transfection considerably compared to the naked DNA as negative control. Finally, liposomal formulation in this research had a better function than Lipofectamine® 2000 as a commercialized product because the cellular activity (cellular protein) was higher in the prepared lipoplex than Lipofectamine® 2000.

Large-scale production and isolation of Candida biofilm extracellular matrix.

The extracellular matrix of biofilm is unique to the biofilm lifestyle, and it has key roles in community survival. A complete understanding of the biochemical nature of the matrix is integral to the understanding of the roles of matrix components. This knowledge is a first step toward the development of novel therapeutics and diagnostics to address persistent biofilm infections. Many of the assay methods needed for refined matrix composition analysis require milligram amounts of material that is separated from the cellular components of these complex communities. The protocol described here explains the large-scale production and isolation of the Candida biofilm extracellular matrix. To our knowledge, the proposed procedure is the only currently available approach in the field that yields milligram amounts of biofilm matrix. This procedure first requires biofilms to be seeded in large-surface-area roller bottles, followed by cell adhesion and biofilm maturation during continuous movement of the medium across the surface of the rotating bottle. The formed matrix is then separated from the entire biomass using sonication, which efficiently removes the matrix without perturbing the fungal cell wall. Subsequent filtration, dialysis and lyophilization steps result in a purified matrix product sufficient for biochemical, structural and functional assays. The overall protocol takes ∼11 d to complete. This protocol has been used for Candida species, but, using the troubleshooting guide provided, it could be adapted for other fungi or bacteria.

Monocationic salts of carrageenans: Preparation and physico-chemical properties

Highly pure monocationic forms of κ-, ι-, λ-carrageenans and furcellaran were prepared with the aid of successive dialysis and ion exchange steps. Two approaches were used to obtain the samples: direct exchange of the galactan-bound cations with the aid of ion-exchange resin and generation of H+-forms of the polysaccharides followed by neutralization process. The galactan samples were characterized by 1H-NMR, 13C-NMR, pulsed-field-gradient stimulated echo 1H-NMR, FTIR, FT-Raman spectroscopy, ICP-OES, size exclusion chromatography, viscometry, static and dynamic rheometry methods. The ability of cations to enhance gelation follows the order of Li+ < Na+ ≪ Mg2+, Ca2+ < NH4+ < K+ for κ-type carrageenan and NH4+, Li+ < Na+ < K+ < Ca2+ for ι-carrageenan samples prepared by ion exchange. Pure K+-forms of κ-carrageenan and furcellaran form gels of moderate gel strength at 1.5%, but also Ca2+-ι-carrageenan affords workable gels. Mixed cationic content using both mono- and divalent cations promotes gel formation of κ-carrageenan more effectively compared to furcellaran. κ-Carrageenan forms exceptionally strong gels (G′ > 1 × 105 Pa) in the presence of equal amounts of Rb+ and Sr2+ ions. The rheological properties are notably pH-dependent. Among the monocationic samples, Ba2+-forms of κ-carrageenan and furcellaran yield the strongest gels in alkaline media, whereas Rb+- and Cs+-forms show the highest gelling capacities under acidic conditions. The widely employed method involving excessive dialysis against water as the final purification step causes cation depletion, acidification of the carrageenan sample and significant degradation during the freeze-drying step.

Improvement of POC-CCA Interpretation by Using Lyophilization of Urine from Patients with Schistosoma mansoni Low Worm Burden: Towards an Elimination of Doubts about the Concept of Trace.

BackgroundAccurate diagnostic techniques for schistosomiasis are essential for prevalence determination and identification of positive patients. A point-of-care test for detecting schistosome circulating cathodic antigen (POC-CCA) has been evaluated for its accuracy in different endemic regions. This reagent strip/dipstick based assay has showed high sensitivity for individuals with high or moderate worm burden, but the interpretation of light infections is less clear, especially for trace readings.Methodology/Principal FindingsWe introduced a urine lyophilization step to the POC-CCA assay to improve its sensitivity and clarify the interpretation of traces. We evaluated POC-CCA sensitivity and specificity within individuals with low parasite burdens in a Brazilian endemic area where a high number of traces were detected. Patients that were positive for other helminths were also evaluated for cross reactions. In all cases, a combined parasitological diagnosis using Kato-Katz (24 slides) and Saline Gradient (1 g of feces) were used as reference. At baseline, diagnosis by POC-CCA (1–2 cassettes) showed 6% sensitivity, inaccurately predicting a low prevalence of Schistosoma mansoni infections (2 POC-CCA positives/32 egg positives). After urine lyophilization, the sensitivity was increased significantly (p < 0.05). Prevalence rates changed from 2% to 32% (27 POC-CCA positives/32 egg positives), equivalent to parasitological techniques. Most of the trace readings changed to positive after lyophilization while some negatives turned into traces. Cross reaction analysis confirmed the specificity of POC-CCA.Conclusions/SignificanceTrace readings cannot be primarily defined as positive or negative cases. It is critical to verify case-by-case by concentrating urine 10 fold by lyophilization for the diagnosis. Following lyophilization, persistent trace readings should be read as negatives. No trained technician is needed and cost is restricted to the cost of a lyophilizer and the electricity to run it.

Fisetin yeast-based bio-capsules via osmoporation: effects of process variables on the encapsulation efficiency and internalized fisetin content.

Osmoporation is an innovative method that can be used with food-grade yeast cells of Saccharomyces cerevisiae as natural encapsulating matrices. This technique overcomes barriers that difficult encapsulation and enables the internalization of fragile bioactive molecules such as fisetin into yeasts. In the present study, we assessed the effects of concentration, osmotic pressure, and temperature on the encapsulation efficiency (EE) and internalized fisetin content (IF). Two different quantification strategies were investigated: direct extraction (DE) without cell washing or freeze-drying steps and indirect extraction (IE) performed after washings with ethanol and freeze-drying. Our results showed that osmoporation improved EE (33%) and IF (1.199mg). The best experimental conditions were found by using DE. High-resolution images showed that the yeast cell envelope was preserved during osmoporation at 30MPa and 84% of yeast cells remained viable after treatment. Washing cells with organic solvent led to decreased EE (0.65%) and IF (0.023mg). This was probably due to either damages caused to yeast cell envelope or fisetin dragged out of cell. Overall, the results demonstrated the adequacy and relevant biotechnological potential of yeasts as encapsulating matrices for hydrophobic compounds. This fresh biotechnological approach has proven to be a promising tool for the production of bioactive-rich food products.

Carbon nanotube scaffolds with controlled porosity as electromagnetic absorbing materials in the gigahertz range.

Control of the microscopic structure of CNT nanocomposites allows modulation of the electromagnetic shielding in the gigahertz range. The porosity of CNT scaffolds has been controlled by two freezing protocols and a subsequent lyophilization step: fast freezing in liquid nitrogen and slow freezing at -20 °C. Mercury porosimetry shows that slowly frozen specimens present a more open pore size (100-150 μm) with a narrow distribution whereas specimens frozen rapidly show a smaller pore size and a heterogeneous distribution. 3D-scaffolds containing 3, 4, 6 and 7% CNT were infiltrated with epoxy and specimens with 2, 5 and 8 mm thicknesses were characterized in the GHz range. Samples with the highest pore size and porosity presented the lowest reflected power (about 30%) and the highest absorbed power (about 70%), which allows considering them as electromagnetic radiation absorbing materials.