Quick Procedure to Evaluate the Oxygen Mass Transfer Resistance in Aerated Laboratory-scale Bioreactors

Oxygen transfer intensity is a major concern whenever conducting enzymatic reactions or bioprocesses, which require air for microbial growth or enzymatic oxidative steps. Agitation in bio-reaction units is directly related to oxygen transport from the gas phase to liquid phase followed by the oxygen uptake by the individual microbial cell or oxygen consumption in enzymatic oxidation reactions. In fact, activity of microorganisms or of the enzyme (oxidase) is monitored by the use of oxygen from supplied air. A limitation in the supplied oxygen, due to mass transport resistance or a consumption rate faster than the transported oxygen rate, may cause a decrease in the cell growing rate or a decrease of the overall enzymatic reaction rate. Consequently, a close control of the available oxygen in the liquid phase is implemented for any type of aerobic bioreactor, the amount of dissolved oxygen (DO) being continuously measured by means of DO-meters. As the solubility of oxygen in water is not very high (ca. 9 mg/L at 20 o C), its overall consumption rate is dependent on a large number of factors, the most important being the diffusion coefficient, temperature, gas-liquid mass transfer coefficient K L a , and the rate of microbial/enzymatic reactions. Oxygen transfer from gas phase to the reaction site (cells, enzyme) takes place in several steps. First, oxygen is transferred through the gas-liquid interface, then it is transported through bulk liquid and finally into the microbial cell. To improve the oxygenation rate, sophisticated mixing and air sparger systems are implemented on both laboratory and industrial scale bioreactors. Air under pressure is supplied through a tube end consisting in 'O' rings with very fine holes or orifices. The size of bubbles, which affects the mass transfer process, depends on the holes' size and type of sparger. For very fine and uniform bubbles with effective gas dispersion, a micro-sparger system is used instead of a sparger, consisting in highly porous ceramic material. Air dispersion in liquid phase is not only related to the sparger, but also on the type of impeller and mixing intensity. The appropriate position and type of the impeller can ensure the even distribution of the gas in the reactor. High agitation is favourable to the mixing, but a very high stirring speed may cause shear forces, damaging the cells and leading to a spotty aeration of the liquid. Special chapters are dedicated to mass transfer evaluation in the framework of bioreactor design and operation with various areas of applicability: industrial biosynthesis To optimise the aeration rate, knowing the gas-liquid mass transfer resistance is essential not only for a theoretical process analysis, but also for practical reasons related to bioprocess development. As the experimental observation can indicate only the overall oxygen uptake by the bioprocess, it is highly important to separate the contribution of the physical gas-liquid transport to its consumption in bio-reactions. Such analysis is possible only from separate determinations of the K L a coefficient and of the (bio)reaction rates. Experiments should be conducted in the absence of reaction, or under operating regimes at high aeration rates, making the whole process kinetically controllable. The volumetric mass transfer coefficient K L a is dependent on a large number of factors. This is why its precise evaluation is difficult due to its strong dependence on the liquid phase properties, mixing, gas solubility, operating conditions (temperature), sparger depth, aeration rate, vessel volume and geometry, baffles, liquid surface tension, etc

SILVER GREEN SYNTHESIS ON BACTERIAL CELLULOSE MEMBRANES USING TANNIC ACID

Silver nanoparticles were deposed on bacterial cellulose (BC) membranes using tannic acid as reducing agent. The synthesis of silver nanoparticles was confirmed by scanning electron microscopy (SEM), energy dispersive spectroscopy with X-ray (EDX) and UV-VIS spectroscopy. The antimicrobial activity of BC-silver films was tested against E. coli K12-MG1655, all the composites having a good antimicrobial activity. These composites could be used for antimicrobial wound dressings

Bacterial Cellulose—Carboxymethylcellulose Composite Loaded with Turmeric Extract for Antimicrobial Wound Dressing Applications

Bacterial cellulose (BC) is a biopolymer whose properties have been intensively studied, especially for biomedical applications. Since BC has no antimicrobial activity, it is necessary to use bioactive substances for developing wound healing applications. Another drawback of BC is the loss if its water retention capacity after dehydration. In order to overcome these problems, carboxymethyl cellulose (CMC) and turmeric extract (TE) were selected for the preparation of BC composites. Citric acid (CA) was used as the crosslinking agent. These composites were tested as potential antimicrobial wound dressing materials. TE-loaded BC–CMC composites were characterized in terms of their morphology, crystallinity, and thermal behavior. Swelling tests and curcumin-release kinetic analysis were also performed. All the composites tested had high swelling degrees, which is an advantage for the exudate adsorption from chronic wounds. The antibacterial potential of such composites was tested against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans). The in vitro cytotoxicity toward L929 fibroblast cells was studied as well. The obtained results allow us to recommend these composites as good candidates for wound dressing applications

Cnicus benedictus Oil as a Raw Material for Biodiesel: Extraction Optimization and Biodiesel Yield

Cnicus benedictus fruits were used as raw material to extract oil, and the resulting oil was converted into biodiesel. Two extraction methods were tested: batch extraction, and ultrasound assisted extraction. Response surface methodology was considered for the optimization of the process efficiency. The selected key independent variables were temperature, extraction time, and solid/liquid ratio for batch extraction and ultrasound intensity, temperature, and extraction time for the ultrasound assisted extraction, respectively. The optimal working conditions are different for the two extraction techniques, with respect to temperature, solid/liquid ratio, and extraction time, respectively, leading to higher extraction efficiency in the case of the ultrasound-assisted extraction. Cnicus benedictus oil obtained under the optimal extraction conditions was further esterified with methanol under acid catalysis to yield biodiesel. The biodiesel was characterized through 1H-NMR and the main fuel properties were determined

<i>Cnicus benedictus</i> Oil as a Raw Material for Biodiesel: Extraction Optimization and Biodiesel Yield

Cnicus benedictus fruits were used as raw material to extract oil, and the resulting oil was converted into biodiesel. Two extraction methods were tested: batch extraction, and ultrasound assisted extraction. Response surface methodology was considered for the optimization of the process efficiency. The selected key independent variables were temperature, extraction time, and solid/liquid ratio for batch extraction and ultrasound intensity, temperature, and extraction time for the ultrasound assisted extraction, respectively. The optimal working conditions are different for the two extraction techniques, with respect to temperature, solid/liquid ratio, and extraction time, respectively, leading to higher extraction efficiency in the case of the ultrasound-assisted extraction. Cnicus benedictus oil obtained under the optimal extraction conditions was further esterified with methanol under acid catalysis to yield biodiesel. The biodiesel was characterized through 1H-NMR and the main fuel properties were determined

Bacterial Cellulose Hybrid Composites with Calcium Phosphate for Bone Tissue Regeneration

Bacterial cellulose (BC) is a unique microbial biopolymer with a huge number of significant applications in the biomedical field, including bone tissue engineering. The present study proposes to obtain and characterize BC hybrid composites with calcium phosphate as biocompatible and bioactive membranes for bone tissue engineering. BC precursor membranes were obtained in static culture fermentation, and after purification, were oxidized to obtain 2,3-dialdehyde bacterial cellulose (DABC). Calcium phosphate-BC oxidized membranes were produced by successive immersion in precursor solutions under ultrasonic irradiation. The samples were characterized for their physicochemical properties using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy grazing incidence X-ray diffraction (GI-XRD), solid-state 13C nuclear magnetic resonance (CP/MAS 13C NMR), and complex thermal analysis. In vitro cell studies were also performed to evaluate the influence of modified morphological characteristics on cell adhesion and proliferation. The results showed an increase in porosity and biodegradability for DABC hybrid composites compared with BC. In vitro cell studies have revealed that both hybrid composites favor cell adhesion to the surface. The new BC and DABC hybrid composites with calcium phosphate could be considered promising materials for bone tissue regeneration

Antibacterial Activity of Bacterial Cellulose Loaded with Bacitracin and Amoxicillin: In Vitro Studies

The use of bacterial cellulose (BC) in skin wound treatment is very attractive due to its unique characteristics. These dressings&rsquo; wet environment is an important feature that ensures efficient healing. In order to enhance the antimicrobial performances, bacterial-cellulose dressings were loaded with amoxicillin and bacitracin as antibacterial agents. Infrared characterization and thermal analysis confirmed bacterial-cellulose binding to the drug. Hydration capacity showed good hydrophilicity, an efficient dressing&rsquo;s property. The results confirmed the drugs&rsquo; presence in the bacterial-cellulose dressing&rsquo;s structure as well as the antimicrobial efficiency against Staphylococcus aureus and Escherichia coli. The antimicrobial assessments were evaluated by contacting these dressings with the above-mentioned bacterial strains and evaluating the growth inhibition of these microorganisms