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Nowadays, application of porous polydimethylsiloxane (PDMS) structure in biomedical is becoming widespread, and many methods have been established to create such structure. Although the pores created through these methods are mostly developed on the outer surface of PDMS membrane, this study offers a simple and cost-efficient technique for creating three-dimensional (3D) microporous PDMS structure with appropriate pore size for endothelial cell culture. In this study, combination of gas foaming and particulate leaching methods, with NaHCO3 as effervescent salt and NaCl as progen are used to form a 3D PDMS sponge. The in situ chemical reaction between NaHCO3 and HCl resulted in the formation of small pores and channels. Moreover, soaking the samples in HCl solution temporarily improved the hydrophilicity of PDMS, which then facilitated the penetration of water for further leaching of NaCl. The surface chemical modification process was performed by (3-aminopropyl)triethoxysilane to culture endothelial cells on porous PDMS matrix. The results are an indication of positive response of endothelial cells to the fabricated PDMS sponge. Because of simplicity and practicality of this method for preparing PDMS sponge with appropriate pore size and biological properties, the fabricated matrix can perfectly be applied to future studies in blood-contacting devices., (© 2015 International Union of Biochemistry and Molecular Biology, Inc.)

Four sulfur-oxidizing bacteria (Thiobacillus thioparus, Acidithiobacillus thiooxidans PTCC1717, Acidithiobacillus ferrooxidans PTCC1646, and Acidithiobacillus ferrooxidans PTCC1647) were used as biorecognition elements in a hydrogen sulfide biosensing system. All the experiments were performed in 0.1 M phosphate buffer solution containing 1-20 ppm H2S with optimum pH and temperature for each species. Although H2 S was applied to the biosensing system, the dissolved O2 content decreased. Dissolved O2 consumed by cells in both free and immobilized forms was measured using a dissolved oxygen sensor. Free bacterial cells exhibit fast response (<200 Sec). Immobilization of the cells on polyvinyl alcohol was optimized using an analytical software. Immobilized A. ferrooxidans and A. thiooxidans retained more than 50% of activity after 30 days of immobilization. According to the data, A. thiooxidans and A. ferrooxidans are appropriate species for hydrogen sulfide biosensor., (© 2014 International Union of Biochemistry and Molecular Biology, Inc.)

In the present study, a new online monitoring method for the determination of the CO₂ sensitivity of micro-organisms, based on the values of the respiration factors [OTR (oxygen transfer rate) and CTR (carbon dioxide transfer rate)], obtained by using the RAMOS (respiratory activity monitoring system) device considering a variety of aeration rates in the measuring flask, is investigated. Based on the data of the OTR, obtained by RAMOS under a variety of specific aeration rates, the proposed new method was developed as an online monitoring method for CO₂ sensitivity of micro-organisms in shaken bioreactors. A maximum accumulated CO₂ concentration of 12% was derived in applied methods, provided that the cultivation system is carried out under optimal conditions. Additionally, to predict these conditions, an unsteady-state gas transfer model in shaken bioreactors would be very advantageous. The data of OTR obtained using the RAMOS device were analysed and recalculated by a programme considering the calibration factor (Cf). The major advantage of the new method is the possibility to determine the metabolic activity, regardless of manual sampling.

Influence of carbon dioxide on growth and product kinetics of industrially important micro-organisms is essential for the interpretation of a bioprocess. In this research, the CO₂ effects on productivity and growth rate of micro-organisms have been studied by using a variety of kplug. The applied method is based on a different concentration of CO₂ in the headspace of ventilation flasks. The presented method is simple, inexpensive and shows similar results compared to large-scale fermentation regarding the evolution of CO₂ in a batch system. For the investigation of the proposed method, experiments employing Arxula adeninivorans LS3, Corynebacterium glutamicum (DM1730 and ATCC WT13032) and Hansenula polymorpha DSM70277 as model organisms in the ventilation flasks are performed. The fermentations in the RAMOS (respiratory activity monitoring system) device were carried out with a normal aeration rate (1 vvm) and under the same operating conditions as the ventilation flask f1. The modified unsteady-state model was used to predict the operation conditions of a biological system in the ventilation flasks. In the present study, a novel and easy method for the quantification of CO₂ sensitivity of micro-organisms in shaken bioreactors (called ventilation flask) was achieved.

In the present study, the special shake flasks, so-called ventilation flasks, are equipped with oxygen sensors and then an unsteady-state gas transfer model for shake flasks was developed and experimentally investigated for a wide range of gas transfer resistances (kplug). For the validation of our unsteady-state model to simulate the gas transfer in a biological system in the ventilation flasks, a strain of Corenobacterium glutamicum DM1730 was used as a model organism. For further easy processing, the resulting total mass-transfer resistance (kplug) is described as a function of the mass flow through the sterile plug (OTRplug) by an empirical equation. This equation is introduced into a simulation model that calculates the gas partial pressures in the headspace of the flask. Additionally, the gas transfer rates through the sterile closure and gas/liquid interface inside the flask are provided. This unsteady-state model would be a very useful method for scaling up from a shake flask to a fermentor; comparing the results of the gas concentration in the gas phase, there is good agreement between the introduced unsteady-state model and experimental results for the biological system.

In shaken bioreactors equipped with a sterile closure (e.g. a cotton plug), a realistic understanding and estimation of gas transfer is advantageous to avoid oxygen limitation or carbon dioxide inhibition of a microbial culture. Therefore, in the present study, an unsteady-state gas-transfer model for shake flasks was developed and experimentally investigated for a wide range of gas-transfer resistances (k(plug)). The introduced approach is based on the model of Henzler and co-workers [Henzler and Schedel (1991) Bioprocess Eng. 7, 123-131; Mrotzek, Anderlei, Henzler and Büchs (2001) Biochem. Eng. J. 7, 107-112], which describe the spatially resolved gas partial pressures inside the sterile closure, affecting the local gas diffusion coefficients and convective Stefan flow. For further easy processing the resulting total mass-transfer resistance (k(plug)) is described as a function of the mass flow through the sterile plug (OTR(plug)) by an empirical equation. This equation is introduced into a simulation model which calculates the gas partial pressures in the head space of the flask. Additionally, the gas-transfer rates through the sterile closure and gas/liquid interface inside the flask is provided. Simulations indicate that neglecting the oxygen in the head space volume of the flask under initial conditions (simple steady-state assumption) may lead to an underestimation of the oxygen transfer into the liquid phase. The extension of error depends on the conditions. A good agreement between the introduced unsteady-state model and experimental results for the sulfite oxidation as a chemical model system confirmed the validity and usefulness of the proposed unsteady-state approach.