Bubble coalescence behaviour in biological media

Summary A twin bubble column was used to measure the k_La values for oxygen in model and cultivation media using the steady state method described previously (Adler et al. 1980). Desmophen and soy oil were used as antifoam agents together with model and/or cultivation media for Chaetomium cellulotyticum, Trichoderma reesei, Hansenula polymorpha, Saccharomyces cerevisiae and Escherichia coli. The bubble coalescence behavior is mainly influenced by antifoam agents and somewhat by protein and alcohol additives. In the range investigated (0.01 to 0.1%.), the k_La values are not influenced by the Desmophen concentration and only slighthly by the soy oil concentration (0.5 to 1.5%.). The coalescence behaviour was characterized by the ratio m_corr=(k_La)_corr/(k_La)_ref. A nutrient salt solution with Desmophen was used as a reference. The k_La measured in the investigated media were corrected by considering the differences in k_La's in the investigated and reference media. These m_corr values can directly be used for bubble columns close to the optimum aeration rate.Symbols a Specific gas/liquid interfacial area - c Concentration - k_L Mass transfer coefficient - k_La Volumetric mass transfer coefficient - W_SG Superficial gas velocity - E_G Relative gas hold-up     

Bubble coalescence in air-sparged bioreactors

Coalescence frequency has been measured in an air-sparged bubble column by observing the rate with which insoluble tracer gases were mixed within the dispersed gas phase. The effects of gas-sparge rate and salt concentration were examined. Coalescence frequencies increased with increasing gas-sparge rates approximately in proportion to the increase in gas-phase hold up. The coalescence frequency decreased with NaCI concentration to a minimum frequency about half the frequency observed in pure water. Bubble size distributions were also measured in the air-sparged column. The size distribution changed significantly over the same range of NaCI concentration as variations in the coalescence frequency were observed. The gas-sparge rate showed no effect on the bubble size.     

Foam behaviour of biological media

Summary A simple method was developed for evaluating foam stability. The influence of KCl and MgSO₄ on foam stability of bovine serum albumin foams was investigated. These salts increase foaminess, but diminish foam stability by the same degree. Thus there is little overall.     

Ultrasonic hysteresis in biological media

Summary Non-linear mechanical response of viscoelastic strain responding media to high amplitude stress-strain is examined from a phenomenological point of view and found to lead to results compatible with empirical observations of high intensity ultrasound irradiation of brain, liver, and eye lens tissues. The proposed hysteresis model provides for most of the observed dependencies such as an intensity dependent absorption coefficient, an absorption coefficient increasing linearly with frequency, and a dispersionless velocity of ultrasound in soft tissues (excluding lung). The non-linear compliance of tissues further predicts production of half-harmonic signals even in the absence of cavitation.     

Foam behavior of biological media

Summary The influence of the concentrations of NaCl, NaJ, KJ and/or Na₂SO₄ on the foaminess of BSA solutions is investigated. The foaminess increases with increasing salt concentrations as expected for NaCl, NaJ and Na₂SO₄. With KJ the foaminess exhibits an anomaly. The dependence of the foaminess on the pH is complex. In the presence of buffer there is a minimum at 4.81 and a maximum at 4.7. In the absence of buffer the foaminess reaches a maximum at pH 4 and a minimum at 3. The anomaly of BSA solutions is well-known but not yet fully understood.Symbols BSA Bovine Serum Albumin - C concentration - C_BSA concentration of BSA - C_BUFFER concentration of buffer - C_SALT concentration of salt - V_s equilibrium volume of the foam - V_tg volumetric gas flow rate - =V_s/V_tg foaminess     

Foam behavior of biological media

Summary The influence of the alcohol concentration on the foaminess, , of-BSA-solutions is considered. This effect is calculated by means of the function (C_BSA . f), where f=1 for pure protein solutions and f>1 for alcohol solutions. f is calculated by f = 2^TT_eff. Here, where T_T is the turbidity temperature change due to solvent structure effects and T_D, the temperature correction due to alcohol-protein interaction. The constants necessary to calculate T_T and T_D are tabulated. The agreement between the calculated and measured foaminess , as a function of the n-propanol concentration is satisfactory and for methanol or ethanol excellent.     

A framework for models of biological behaviour

Modelling is most clearly understood as a adjunct in the process of deriving predictions from hypotheses. By representing a hypothesised mechanism in a model we hope by manipulating the model to understand the hypotheses' consequences. Eight dimensions on which models of biological behaviour can vary are described: the degree of realism with which they apply to biology; the level of biology they represent; the generality or range of systems the model is supposed to cover; the abstraction or amount of biological detail represented; the accuracy of representation of the mechanisms; the medium in which the model is built; the match of the model behaviour to biological behaviour; and the utility of the model in providing biological understanding and/or technical insight. It is hoped this framework will help to clarify debates over different approaches to modelling, particularly by pointing out how the above dimensions are relatively independent and should not be conflated.     

Group behaviour in physical,chemical and biological systems

Groups exhibit properties that either are not perceived to exist, or perhaps cannot exist, at the individual level. Such ‘emergent’ properties depend on how individuals interact, both among themselves and with their surroundings. The world of everyday objects consists of material entities. These are, ultimately, groups of elementary particles that organize themselves into atoms and molecules, occupy space, and so on. It turns out that an explanation of even the most commonplace features of this world requires relativistic quantum field theory and the fact that Planck’s constant is discrete, not zero. Groups of molecules in solution, in particular polymers (‘sols’), can form viscous clusters that behave like elastic solids (‘gels’). Sol-gel transitions are examples of cooperative phenomena. Their occurrence is explained by modelling the statistics of inter-unit interactions: the likelihood of either state varies sharply as a critical parameter crosses a threshold value. Group behaviour among cells or organisms is often heritable and therefore can evolve. This permits an additional, typically biological, explanation for it in terms of reproductive advantage, whether of the individual or of the group. There is no general agreement on the appropriate explanatory framework for understanding group-level phenomena in biology.     

Nitric oxide delivery system for biological media

Developing an understanding of how chronically elevated levels of nitric oxide at sites of inflammation or infection can lead to cancer and other diseases requires ways to expose cells and biomolecules to controlled concentrations of NO for hours to days. To achieve this, a small (65ml) stirred reactor was fabricated that included a flat, porous poly(tetrafluoroethylene) membrane and a loop of poly(dimethylsiloxane) tubing for NO and O(2) delivery, respectively. It was equipped with probes for continuous monitoring of NO and O(2) concentrations. Transport through the membrane and tubing was characterized using separate O(2) depletion experiments. In experiments using only a 10% NO mixture and a buffer that was initially air-equilibrated, constant rates of accumulation were observed for NO(2)(-) (53±2μM/h; n=8), the end product of NO oxidation, as expected. Simultaneous delivery of NO and O(2) yielded steady NO concentrations of 0.7-2.3μM, depending on the tubing length and gas compositions. A model was developed that allows the steady NO and O(2) concentrations and the duration of the transients to be predicted to within a few percent. This system should be useful for exposing cells and biomolecules to concentrations of NO that mimic those in vivo.     

The isolation ofChromatium Okenii and its behaviour in different media

Summary An enrichment culture ofChromatium Okenii, obtained from mud of a ditch at Delft, was used for isolation of this species. The bacteria of the strain, isolated by making 5 successive shake cultures in an agar medium were, however, less than half the size ofChr. Okenii when cultivated under the same conditions as the bacteria in the original culture.By variation of the culture conditions for the pure strain, it appeared that in a mineral medium containing fairly high concentrations of sodium thiosulphate and fairly low concentrations of sodium malate, bacteria developed of nearly the same size as present in the enrichment culture. This supports the view ofWinogradsky that media of this type offer the most natural conditions to purple sulphur bacteria.It is, therefore, evident thatChr. Okenii is a highly pleomorphic species, and the consequences hereof for the differentiation of species within the genusChromatium were discussed.     

Microgravity dependence of excitable biological and physicochemical media

Neuronal tissue and especially the central nervous system (CNS) is an excitable medium. Self-organisation, pattern formation, and propagating excitation waves as typical characteristics in excitable media consequently have been found in neuronal tissue. The properties of such phenomena in excitable media do critically depend on the parameters (i.e., electromagnetic fields, temperature, chemical drugs) of the system and on small external forces to which gravity belongs. The spreading depression, a propagating excitation depression wave of neuronal activity, is one of the best described of the those wave phenomena in the CNS. Especially in the retina as a true part of the CNS it can be easily observed with optical techniques due to the high intrinsic optical signal of this tissue. Another of such waves in neuronal tissue is the propagating action potential in nerve fibres. In this paper, data from our laboratories concerning the influence of gravity on the velocity of propagating waves in excitable media are summarized mainly in terms of the retinal spreading depression and propagating action potentials. Additionally, we have used waves in gels of the Belousov-Zhabotinsky reaction as the physicochemical model system of biological activity as the properties of these waves follow the same theories as the spreading depression and action potentials and they have some striking similarities in wave behavior. Thus propagating Belousov-Zhabotinsky waves are described by their gravity dependence.