Rheology and ultrasound scattering from aggregated red cell suspensions in shear flow

The shear flow dynamics of reversible red cell aggregates in dense suspensions were investigated by ultrasound scattering, to study the shear disruption processes of Rayleigh clusters and examine the effective mean field approximation used in microrheological models. In a first section, a rheo-acoustical model, in the Rayleigh scattering regime, is proposed to describe the shear stress dependence of the low frequency scattered power in relation to structural parameters. The fractal scattering regime characterizing the anisotropic scattering from flocs of size larger than the ultrasound wavelength is further discussed. In the second section, we report flow-dependent changes in the low-frequency scattering coefficient in a plane-plane flow geometry to analyze the shear disruption processes of hardened or deformable red cell aggregates in neutral dextran polymer solution. Rheo-acoustical experiments are examined on the basis of the rheo-acoustical model and the effective medium approximation. The ability of ultrasound scattering technique to determine the critical disaggregation shear stress and to give quantitative information on particle surface adhesive energy is analyzed. Lastly, the shear-thinning behavior of weakly aggregated hardened or deformable red cells is described.     

A mesoscale mechanical model of cellular interactions

Computational models of cell mechanics allow the precise interrogation of cell shape change. These morphological changes are required for cells to survive in diverse tissue environments. Here, we present a mesoscale mechanical model of cell-substrate interactions using the level set method based on experimentally measured parameters. By implementing a viscoelastic mechanical equivalent circuit, we accurately model whole-cell deformations that are important for a variety of cellular processes. To effectively model shape changes as a cell interacts with a substrate, we have included receptor-mediated adhesion, which is governed by catch-slip bond behavior. The effect of adhesion was explored by subjecting cells to a variety of different substrates including flat, curved, and deformable surfaces. Finally, we increased the accuracy of our simulations by including a deformable nucleus in our cells. This model sets the foundation for further exploration into computational analyses of multicellular interactions.     

Escape of autocrine ligands into extracellular medium: experimental test of theoretical model predictions

We have developed an experimental system for testing mathematical model predictions concerning escape of autocrine ligands into the extracellular bulk medium. This system employs anti-receptor blocking antibodies against the epidermal growth factor receptor (EGFR)/transforming growth factor alpha (TGFalpha) receptor/ligand pair. TGFalpha was expressed under the control of a tetracycline-repressed promoter, together with a constitutively expressed human EGFR in B82 mouse fibroblast cells. This expression system allowed us to vary TGFalpha synthesis rates over a roughly 300-fold range by adjusting tetracycline concentration. TGFalpha accumulation in the extracellular bulk medium was then measured as a function of cell density, TGFalpha synthesis rate, and anti-EGFR blocking antibody concentration. Consistent with model predictions, amounts of ligand in the medium on a per cell basis were found to diminish as cell density was increased but with reduced dependence on cell density at higher ligand synthesis rates. Similarly consistent with model predictions, higher ligand synthesis rates also decreased the effect of anti-receptor blocking antibodies. Our investigation has established that we can successfully analyze and understand autocrine ligand secretion behavior from the basis of our theoretical model.     

Rheology of concentrated suspensions of deformable elastic particles such as human erythrocytes

New models for the viscosity of concentrated suspensions of deformable elastic particles are developed using the differential effective medium approach (DEMA). The models are capable of describing the rheological behavior of un-aggregated suspensions of human red blood cells (RBCs). With the increase in shear rate, a shear-thinning behavior is predicted similar to that observed in the case of un-aggregated suspensions of RBCs. A decrease in relative viscosity and an enhancement of shear-thinning behavior is predicted when either the particle rigidity (elastic modulus) is decreased or the continuous medium viscosity is increased. These predictions are similar to those observed in suspensions of human RBCs. The proposed models are evaluated using experimental data on normal and hardened human RBC suspensions in protein-free saline.     

Bioreactor for the study of defined interactions of toxic metals and biofilms

A novel bioreactor system constructed for studies of the interactions of heavy metals and microbial cells at the solid-solution interface is described. The applicability of this experimental system to meet the severe constraints imposed on such an apparatus by the requirements for an unambiguous interpretation of data and for mathematical modeling of these interactions was explored with the trace metal lead and with the marine bacterium Pseudomonas atlantica. A chemically defined medium composed of the major components of seawater, simple salts required for growth, glucose, and the single amino acid glycine was derived. It supported a maximum growth rate several times less than that in a complex medium, but provided growth to high cell densities and the formation of biopolymer and supported the development of a monolayer biofilm. The use of such a medium in conjunction with our bioreactor system minimized trace metal contamination while allowing quantification of the partitioning of lead onto various reactor surfaces. Lead adsorption by reactor walls and model surfaces was linear with equilibrium led concentration up to 6 X 10(-6) mol/liter. Equilibrium lead adsorption due to P. atlantica biofilm surfaces ranged from 20 to 40% at a total lead concentration of 10(-6) mol/liter depending upon solution pH and ionic composition, indicating that biofilms can play an important role in controlling toxic metal concentrations in natural systems.     

Bioreactor for the study of defined interactions of toxic metals and biofilms.

A novel bioreactor system constructed for studies of the interactions of heavy metals and microbial cells at the solid-solution interface is described. The applicability of this experimental system to meet the severe constraints imposed on such an apparatus by the requirements for an unambiguous interpretation of data and for mathematical modeling of these interactions was explored with the trace metal lead and with the marine bacterium Pseudomonas atlantica. A chemically defined medium composed of the major components of seawater, simple salts required for growth, glucose, and the single amino acid glycine was derived. It supported a maximum growth rate several times less than that in a complex medium, but provided growth to high cell densities and the formation of biopolymer and supported the development of a monolayer biofilm. The use of such a medium in conjunction with our bioreactor system minimized trace metal contamination while allowing quantification of the partitioning of lead onto various reactor surfaces. Lead adsorption by reactor walls and model surfaces was linear with equilibrium led concentration up to 6 X 10(-6) mol/liter. Equilibrium lead adsorption due to P. atlantica biofilm surfaces ranged from 20 to 40% at a total lead concentration of 10(-6) mol/liter depending upon solution pH and ionic composition, indicating that biofilms can play an important role in controlling toxic metal concentrations in natural systems.     

A model for studies of mechanical interactions between the human spine and rib cage

A three-dimensional mathematical model useful for studies of the mechanics of the human skeletal thorax is described. To construct this model, rib cage elements are incorporated into a previously reported model of the thoracolumbar spine. The vertebrae and bony portions of the ribs and sternum are idealized as rigid bodies. The behavior of the discs, ligaments and costal cartilages are modelled by deformable elements. Appropriate geometric and stiffness property data are assigned to the elements of the model. In constructing the model, it was found that the mechanical response of the costo-vertebral joint is strongly influenced by articulation geometry. Although rigid bodies were used to model calcified portions of the ribs, the model predicted rib cage deformations in close agreement with those measured experimentally. These studies indicate that the rigid body motion of calcified portions of the rib makes a major contribution to the deformation of the rib cage in response to certain types of loadings. Quantitative results are also reported on the roles the rib cage plays in bending responses of the spine, the lateral stability of the spine, and the production and correction of several scoliotic deformities.     

Nonlocal shear deformable shell model for postbuckling of axially compressed microtubules embedded in an elastic medium

Buckling and postbuckling analysis is presented for axially compressed microtubules (MTs) embedded in an elastic matrix of cytoplasm. The microtubule is modeled as a nonlocal shear deformable cylindrical shell which contains small scale effects. The surrounding elastic medium is modeled as a Pasternak foundation. The governing equations are based on higher order shear deformation shell theory with a von Kármán-Donnell-type of kinematic nonlinearity and include the extension-twist and flexural-twist couplings. The thermal effects are also included and the material properties are assumed to be temperature-dependent. The small scale parameter e ₀ a is estimated by matching the buckling load from their vibrational behavior of MTs with the numerical results obtained from the nonlocal shear deformable shell model. The numerical results show that buckling load and postbuckling behavior of MTs are very sensitive to the small scale parameter e ₀ a. The results reveal that the MTs under axial compressive loading condition have an unstable postbuckling path, and the lateral constraint has a significant effect on the postbuckling response of a microtubule when the foundation stiffness is sufficiently large.     

Optimisation of synthetic medium composition for levorin biosynthesis by Streptomyces levoris 99/23 and investigation of its accumulation dynamics using mathematical modelling methods

The composition of a synthetic culture medium for levorin biosynthesis by Streptomyces levoris 99/23 was optimised using mathematical modelling methods. The optimal concentrations of the medium components were established by means of an optimum composition design at three factor variation levels. An adequate regression model was obtained. Levorin biosynthesis by Streptomyces levoris 99/23 in the optimised synthetic medium was over 38% higher than in the initial medium. The antibiotic biosynthesis dynamics in the optimised culture medium was studied by means of a non-linear differential equation system. The resultant model was valid.     

Description of dynamic lung fluid transport phenomena by linear non-equilibrium thermodynamic equations

We propose a mathematical model of dynamic lung transvascular fluid flow based on linear non-equilibrium thermodynamic equations. The model makes use of experimental results concerning lung fluid balance during hydrodynamic and hypooncotic loading. An ‘inexact problem’ solution method was employed to solve the mathematical problem and to obtain coefficients of mass transfer. Transport features dependent on the system's condition and on boundary phase surface phenomena were also considered. A complex analysis of such a multi-unit system as the lung is useful for the evaluation of fluid balance mechanisms and their application to the development of artificial mass exchange devices.     

Substrates’ and products’ inhibition in fructanase production by a new Kluyveromyces marxianus CF15 from Agave tequilana fructan in a batch reactor

This study focuses on fructanase production in a batch reactor by a new strain isolated from agave juice (K. marxianus var. drosophilarum) employing different Agave tequilana fructan (ATF) concentrations as substrate. The experimental data suggest that the fructanase production may be inhibited or repressed by high substrate (50 g/L) and ethanol (20.7 g/L) concentrations present in culture medium. To further analyze these phenomena an unstructured kinetic mathematical model taking into account substrate and products inhibition was proposed and fitted. The mathematical model considers six reaction kinetics and the ethanol evaporation, and predicts satisfactorily the biomass, fructan, glucose, fructose, ethanol, and fructanase behavior for different raw material initial concentrations. The proposed model is the first to satisfactorily describe the production of fructanase from branched ATF with a new strain of K. marxianus.

     

Automatic image recognition to determine morphological development and secondary metabolite accumulation in hairy root networks

This study focuses on the morphological development and secondary metabolite production of the red pigments from the group of betacyanins in hairy roots of Beta vulgaris. We demonstrate a working, medium throughput, customized, automatic image recognition solution for hairy roots on agar plates including the evaluation of 12 experimental samples. Image acquisition is conducted under comparable para‐meters using a tripod with light emitting diode background lighting and a digital single lens reflex camera. The server‐based image recognition system developed together with Wimasis GmbH, Munich, Germany helps to obtain not only quantitative values for morphological parameters, such as segment lengths and widths or metabolite concentrations, but also global parameters of root growth, such as total root length or the number of branching points. Using timed diagrams the development of the total root length, the total number of branching points, and the mean pigment concentration during the cultivation period were determined. The generated data present the basis for detailed mathematical modeling in order to achieve a structured growth model for hairy roots. A mathematical model for growth of hairy roots can be used to decrease experimental efforts as well as to optimize cultivation conditions and the bioreactor design.     

Dynamics and modeling on fermentative production of poly (β-hydroxybutyric acid) from sugars via lactate by a mixed culture of Lactobacillus delbrueckii and Alcaligenes eutrophus

The mixed culture system was considered in the present research where sugars such as glucose were converted to lactate by Lactobacillus delbrueckii and the lactate was converted to poly β-hydroxybutyrate (PHB) by Alcaligenes eutrophus in one fermentor. For the modeling of the effect of NH₃ concentration on the cell growth of A. eutrophus and PHB production rates, metabolic flux distributions were computed at two culture phases of cell growth and PHB production periods. It was found that the NADPH, generated through isocitrate dehydrogenate in TCA cycle, was predominantly utilized for the reaction from α-ketoglutalate to glutamate when NH₃ was abundant, while it tended to be utilized for the PHB production through acetoacetyl CoA reductase as NH₃ concentration decreased. This phenomenon was reflected in the development of mathematical model. In the mixed culture experiments, the two phases were observed, namely the lactate production phase due to L. delbrueckii and the lactate consumption phase due to A. eutrophus. The lactate concentration could be estimated on-line by the amount of NaOH solution and HCl solution supplied to keep the culture pH at constant level. Several mixed culture experiments were conducted to see the dynamics of the system. Finally, a mathematical model which can describe the dynamic behavior of the present mixed culture was developed and the model parameters were tuned for fitting the experimental data. The model may be used for several purposes such as control, optimization, and understanding process dynamics etc.     

Modeling of transient flow through a viscoelastic preparative chromatography packing

The common method for purification of macromolecular bioproducts is preparative packed‐bed chromatography using polymer‐based, compressible, viscoelastic resins. Because of a downstream processing bottleneck, the chromatography equipment is often operated at its hydrodynamic limit. In this case, the resins may exhibit a complex behavior which results in compression–relaxation hystereses. Up to now, no modeling approach of transient flow through a chromatography packing has been made considering the viscoelasticity of the resins. The aim of the present work was to develop a novel model and compare model calculations with experimental data of two agarose‐based resins. Fluid flow and bed permeability were modeled by Darcy's law and the Kozeny–Carman equation, respectively. Fluid flow was coupled to solid matrix stress via an axial force balance and a continuity equation of a deformable packing. Viscoelasticity was considered according to a Kelvin–Voigt material. The coupled equations were solved with a finite difference scheme using a deformable mesh. The model boundary conditions were preset transient pressure drop functions which resemble simulated load/elution/equilibration cycles. Calculations using a homogeneous model (assuming constant variables along the column height) gave a fair agreement with experimental data with regard to predicted flow rate, bed height, and compression–relaxation hysteresis for symmetric as well as asymmetric pressure drop functions. Calculations using an inhomogeneous model gave profiles of the bed porosity as a function of the bed height. In addition, the influence of medium wall support and intraparticle porosity was illustrated. The inhomogeneous model provides insights that so far are not easily experimentally accessible. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:958–967, 2013     

Using multi-matching system based on a simplified deformable model of the human iris for iris recognition

1 Introduction Iris recognition technology is based on the stableand distinctive iris patterns, and has attracted a lot ofattention recently. Nowadays it has become a most im-portant biometric solution for personal identification. Since the 1990s, much work on iris recognition hasbeen done and great progress has been made. Some pre-dominant algorithms for iris recognition have beenproposed. Daugman generated an iris code by quantizingthe local phase angle using a set of 2-D Gabor f…     

Optimization of multiple inducers effect on protease biosynthesis by Rhizopus oryzae

Effect of additional chemicals at different culture conditions was studied in detail on newly isolated Rhizopus oryza (RO, IIT KGP) to maximize protease synthesis. The surfactants and metal ions when added to the basal medium individually were acted as inducers. The combined effect of these inducers on protease production was also studied in detail and a semiempirical mathematical model based on the data obtained was proposed to optimize their effects. A 2.5 fold increase in the protease production was possible by optimizing the two variable inducers system.     

Mechanism and mathematical modeling of electro-enzymatic denitrification

In this study, a novel nitrate reduction method using an electro-enzymatic system was investigated to treat an aqueous solution containing high concentrations of nitrate. This system was comprised of working electrodes and their counter electrodes, where enzymes for nitrate removal were located inside the microorganisms. A nitrate reduction mechanism for the electro-enzymatic system was proposed and a mathematical model was developed. The modeling results were compared to the experimental results and all the experimental results fit well with the model; thus, the derived mathematical model can be used for reactor control and effluent prediction.