Dispersion effects in preparative polymethacrylate monoliths operated in radial-flow columns

Monolithic media have found widespread use as excellent tools for fast analytical separations of small molecules, proteins, pDNA and viruses. Polymethacrylate monoliths with large channels are attractive for capturing large molecules, like immunoglobulins, DNA, and viruses. For preparative purposes, these monoliths are operated in radial flow mode. Band spreading in monoliths is extremely low and mostly dominated by the contribution of extra column effects. The model used here had a single axial dispersion coefficient which lumps together extra column effects and the intrinsic band spreading of the monolithic material to characterize the adsorption of proteins and pDNA on polymethacrylate ion-exchange monoliths. Due to the fact that the performance of the monolith was unaffected by the velocity within the applied range, and due to highly favourable adsorption isotherms, a constant pattern model could be applied to predict preparative runs on radial flow units assuming axial flow for modelling.     

Dispersion effects in preparative polymethacrylate monoliths operated in radial-flow columns

Monolithic media have found widespread use as excellent tools for fast analytical separations of small molecules, proteins, pDNA and viruses. Polymethacrylate monoliths with large channels are attractive for capturing large molecules, like immunoglobulins, DNA, and viruses. For preparative purposes, these monoliths are operated in radial flow mode. Band spreading in monoliths is extremely low and mostly dominated by the contribution of extra column effects. The model used here had a single axial dispersion coefficient which lumps together extra column effects and the intrinsic band spreading of the monolithic material to characterize the adsorption of proteins and pDNA on polymethacrylate ion-exchange monoliths. Due to the fact that the performance of the monolith was unaffected by the velocity within the applied range, and due to highly favourable adsorption isotherms, a constant pattern model could be applied to predict preparative runs on radial flow units assuming axial flow for modelling.     

Biofiltration of toluene vapors using a model support

Vermiculite was used as biofiltration model support to study the degradation of toluene vapors. Thermal Gravimetric Analysis, cell respirometry, microcosms tests and qualitative data from Scanning Electron Microscopy (SEM) were used to estimate all the parameters (biofilm surface area, biofilm thickness, active and total biofilm density and maintenance coefficient) involved in a steady state biofiltration model. A global error of 9.7% between experimental data and the mathematical model for three different Empty Bed Residence Time (EBRT) was obtained.     

Use of ceramic monoliths as stationary phase in affinity chromatography

The use of coated ceramic monoliths as support for affinity chromatography is described. Ceramic monoliths are robust active matrix supports and present a very small pressure drop. Monoliths are coated with a very thin agarose gel layer and activated using a standard activation process for agarose beads. Experiments demonstrate that enzyme adsorption occurs exclusively on the outside surface of the agarose coating since enzyme molecules are too large to fit into the porous matrix. Adsorption and desorption rates are large and production of enzyme per unit monolith volume justifies further exploring this separation process for large throughput operation.     

Evaluation of dynamic response and biomechanical properties of isolated blood vessels

In this study we present the experimental and mathematical model for a precise assessment of isolated blood vessels dynamic response under a sudden change of blood pressure. Only the end points within the time interval of the considered dynamic response of the blood vessel, or so-called “alternate steady states” of the processes, were usually considered in various studies. These studies do not provide an insight how the process variables change between these alternate steady states. Isolated blood vessels (rat abdominal aorta) were used to determine how the process dynamics can be described in detailed quantitative terms by mathematical parameters. The experimental model and mathematical procedures presented in this study describe precisely (at a high sensitivity level) the time history of the pressure and the diameter change in between alternate steady states, when an abrupt change of blood pressure occurs at the vessel outlet. Also, the experimental model and mathematical procedures were used to determine changes in the stress–strain law, caused by the action of L-arginine. The presented experimental design and mathematical model can be used for assessment of isolated blood vessel dynamic responses under different stimuli, such as drug effects, electrostimulation etc.     

Multi-type Galton-Watson process as a model for proliferating human tumour cell populations derived from stem cells: estimation of stem cell self-renewal probabilities in human ovarian carcinomas

A mathematical model for proliferation of tumour cell populations is developed. The cell population is assumed to be organized in a hierarchy of decreasing proliferative potential and increasing degree of differentiation. Using some elements of the theory of Multi-type Galton-Watson processes, a method is proposed for the estimation of Psr, the probability of self-renewal of tumour stem cells, from the experimental distribution of clonal unit sizes obtained in cell culture studies. Six data sets from patients with advanced adenocarcinoma of the ovary are used to demonstrate the method. Reasonable estimates are obtained, and the theoretical colony size distributions predicted by the model appear to be in good qualitative agreement with the experimental ones, and lend support to a stem cell model of tumour growth. The possible significance of Psr as a prognostic factor is briefly discussed.     

Multi-Type Galton-Watson Process As A Model For Proliferating Human Tumour Cell Populations Derived From Stem Cells: Estimation of Stem Cell Self-Renewal Probabilities In Human Ovarian Carcinomas

Abstract. A mathematical model for proliferation of tumour cell populations is developed. the cell population is assumed to be organized in a hierarchy of decreasing proliferative potential and increasing degree of differentiation. Using some elements of the theory of Multi-type Galton-Watson processes, a method is proposed for the estimation of P_sr, the probability of self-renewal of tumour stem cells, from the experimental distribution of clonal unit sizes obtained in cell culture studies. Six data sets from patients with advanced adenocarcinorna of the ovary are used to demonstrate the method. Reasonable estimates are obtained, and the theoretical colony size distributions predicted by the model appear to be in good qualitative agreement with the experimental ones, and lend support to a stem cell model of tumour growth. the possible significance of P_sr as a prognostic factor is briefly discussed.     

Mathematical Modelling of the MAP Kinase Pathway Using Proteomic Datasets

The advances in proteomics technologies offer an unprecedented opportunity and valuable resources to understand how living organisms execute necessary functions at systems levels. However, little work has been done up to date to utilize the highly accurate spatio-temporal dynamic proteome data generated by phosphoprotemics for mathematical modeling of complex cell signaling pathways. This work proposed a novel computational framework to develop mathematical models based on proteomic datasets. Using the MAP kinase pathway as the test system, we developed a mathematical model including the cytosolic and nuclear subsystems; and applied the genetic algorithm to infer unknown model parameters. Robustness property of the mathematical model was used as a criterion to select the appropriate rate constants from the estimated candidates. Quantitative information regarding the absolute protein concentrations was used to refine the mathematical model. We have demonstrated that the incorporation of more experimental data could significantly enhance both the simulation accuracy and robustness property of the proposed model. In addition, we used the MAP kinase pathway inhibited by phosphatases with different concentrations to predict the signal output influenced by different cellular conditions. Our predictions are in good agreement with the experimental observations when the MAP kinase pathway was inhibited by phosphatase PP2A and MKP3. The successful application of the proposed modeling framework to the MAP kinase pathway suggests that our method is very promising for developing accurate mathematical models and yielding insights into the regulatory mechanisms of complex cell signaling pathways.     

Protein adsorption onto monoliths: A surface energetics study

This part of work was done to explore the basic understanding of the adsorption chromatography by determining the interaction of selected model proteins (n = 5) to monolithic chromatographic materials, with varying densities of butyl and phenyl ligands. Surface energetics approach was applied to study the interaction behavior. The physicochemical properties of the proteins and monolithic chromatographic materials were explored by contact angle and zeta potential values. These values were used to study protein to monolith interaction under various operating conditions. Surface energetics approach allowed the calculation of interaction energy as a function of distance, i.e. energy minimum values. Calculations were performed at various conditions to analyze the effect of major operating parameters on the interaction strength. The interaction strength exposed the hydrophobic nature of the monoliths which increases with increasing ligand density. Further, interaction energy of proteins were higher with monolith with butyl ligand compared to monolith with phenyl ligand. For instance, lactoferrin interaction to monoliths with butyl represents more interaction, i.e. 24.38 kT as compared to monoliths with phenyl i.e. 23.28 kT, keeping lambda as 0.2 nm and salt concentration as 100 mM of ammonium sulphate. Hence, more energy and time will be consumed for elution of proteins immobilized to monoliths with butyl. Similarly, the effect of solid surface for proteins immobilization, effect of ligand density and effect of lambda showed some interesting insights on the interaction behavior. The knowledge generated from the present work will help in the basic understanding as well as development of an efficient, low cost downstream processing design and may mimic the real chromatographic experiments.     

Stochastic models for X chromosome inactivation

Summary A multivariate Gaussian model for mammalian development is presented with the associated biological and mathematical assumptions. Many biological investigations use the female mammal X chromosome to test hypotheses and to estimate parameters of the developmental system. In particular, Lyon's (1961) hypotheses are used as a basis of the mathematical model. Experimental mouse data and three sets of human experimental data are analyzed using the hypothesized Gaussian model. The estimated biological parameters are consistent with some current biological theories.     

Enantioseparation of glycyl-dipeptides by CEC using particle-loaded monoliths prepared by ring-opening metathesis polymerization (ROMP)

Novel particle-loaded monolithic capillary electrochromatography (CEC) phases for chiral separations were prepared via ring-opening metathesis polymerization (ROMP) within the confines of fused silica columns with 200 microm i.d. using norborn-2-ene (NBE), 1,4,4a,5,8,8a-hexahydro-1,4,5,8,exo,endo-dimethanonaphthalene (DMN-H6) as monomers, 2-propanol and toluene as porogens, RuCl2(PCy3)2(CHPh) as initiator and silica-based particles containing the chiral selector. By suspending silica particles bearing the chiral selector in the polymerization mixture, particle-based monoliths are easily prepared. This approach has several advantages compared to particle-based separation media: (i) the concept of particle-based monoliths is broadly applicable, as any silica-based chiral phase can be used; (ii) they are inexpensive to prepare; and (iii) the manufacturing process is very simple, no sophisticated packing procedures or the preparation of end frits are required. To show the usefulness of this concept for chiral CEC, the chiral separation performance of particle-loaded CEC monoliths bearing teicoplanin aglycone, chemically bonded to 3 microm silica gel, was investigated for a set of glycyl-dipeptides. Particle-loaded ROMP CEC monoliths showed good separation performance for glycyl-dipeptides.     

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.     

Construction of pancreas–muscle–liver microphysiological system (MPS) for reproducing glucose metabolism

Although in vitro models are widely accepted experimental platforms, their physiological relevance is often severely limited. The limitation of current in vitro models is strongly manifested in case of diseases where multiple organs are involved, such as diabetes and metabolic syndrome. Microphysiological systems (MPS), also known as organ-on-a-chip technology, enable a closer approximation of the human organs and tissues, by recreating the tissue microenvironment. Multiorgan MPS, also known as multiorgan-on-a-chip or body-on-a-chip, offer the possibility of reproducing interactions between organs by connecting different organ modules. Here, we designed a three-organ MPS consisting of pancreas, muscle, and liver, to recapitulate glucose metabolism and homeostasis by constructing a mathematical model of glucose metabolism, based on experimental measurement of glucose uptake by muscle cells and insulin secretion by pancreas cells. A mathematical model was used to modify the MPS to improve the physiological relevance, and by adding the liver model in the mathematical model, physiological realistic glucose and insulin profiles were obtained. Our study may provide a methodological framework for developing multiorgan MPS for recapitulating the complex interaction between multiple organs.     

Modeling amino acid metabolism in mammalian cells-toward the development of a model library

Amino acids are necessary to mammalian cell cultures both for protein synthesis and as an energy source. In this study, we present an unstructured mathematical model describing (i) cell growth and death kinetics and (ii) metabolism of glucose and 19 amino acids for HEK-293 and CHO IFN-gamma cell cultures. The proposed mathematical framework is in good agreement with experimental data for both cell lines. It accommodates the inclusion of expressions for other cellular activities, such as the production of recombinant viral vectors or proteins, and can be used as the basis for the development of a model library for mammalian cell cultures.     

Multifrequency Analysis of Single Inductive Coil Measurements Across a Gel Phantom Simulation of Internal Bleeding in the Brain

The present study is part of an ongoing effort to develop a simple diagnostic technology for detecting internal bleeding in the brain, which can be used in lieu or in support of medical imaging and thereby reduce the cost of diagnostics in general, and in particular, would make diagnostics accessible to economically disadvantaged populations. The study deals with a single coil inductive device to be used for detecting cerebral hemorrhage. It presents a first-order experimental study that examines the predictions of our recently published theoretical study. The experimental model employs a homogeneous cylindrical phantom in which internal head bleeding was simulated by way of a fluid inclusion. We measured the changes in amplitude and phase across the coil with a network vector analyzer as a function of frequency (100–1,000 MHz), volume of blood simulating fluid, and the site of the fluid injection. We have developed a new mathematical model to statistically analyze the complex data produced in this experiment. We determined that the resolution for the fluid volume increase following fluid injection is strongly dependent on frequency as well as the location of liquid accumulation. The experimental data obtained in this study supports the predictions of our previous theoretical study, and the statistical analysis shows that the simple single coil device is sensitive enough to detect changes due to fluid volume alteration of two milliliters. Bioelectromagnetics. 2020;41:21–33 © 2019 Bioelectromagnetics Society     

A comparison of mathematical model predictions to experimental measurements for growth and recombinant protein production in induced cultures of Escherichia coli

Recombinant cell growth and protein synthesis by a recombinant Escherichia coli under various inducing conditions are compared to the predictions of a mathematical model. The mathematical model used was a combination of two literature models: (1) an empirical kinetic model for recombinant growth and product formation and (2) a genetically structured model of the lac promoter-operator on a multicopy plasmid. The experimental system utilized was recombinant E. coli CSH22 bearing the temperature-sensitive plasmid pVH106/172, which codes for the synthesis of beta-galactosidase and the other lac operon genes under the control of a lac promoter. Mathematical model predictions for recombinant beta-galactosidase yield and specific growth rate were compared with fermentation measurements of these same quantities for conditions of chemical induction with cyclic AMP and IPTG, copy number amplification (by shifting culture temperature), and combined chemical induction and copy number amplification. The model successfully predicted experimental product yields for most cases of chemical induction even though the product yields varied from 0.34 x 10(3) to 1500 x 10(3) units/g cell mass. The kinetic model also correctly predicted a decline in the specific growth rate with increasing levels of plasmid and recombinant protein. The model was less successful at predicting product amplification at high copy numbers. A comparison of model predictions and experimental results was also used to investigate some of the assumptions used in constructing the mathematical models.     

A green approach toward antibody purification: a sustainable biomimetic ligand for direct immobilization on (bio)polymeric supports

This paper presents a sustainable strategy for improving the capture of antibodies by affinity chromatography. A novel biomimetic ligand (4‐((4‐chloro‐6‐(3‐hydroxyphenoxy)‐1,3,5‐triazin‐2‐yl)oxy)naphthalen‐1‐ol) (TPN‐BM) was synthesized using a greener and simple protocol to overcome solubility limitations associated with ligand 22/8, known as artificial protein A. Furthermore, its subsequent immobilization on chitosan‐based monoliths induced by plasma surface activation allowed the design of a fast and efficient chromatographic platform for immunoglobulin G (IgG) purification. The TPN‐BM functionalized monoliths exhibited high‐binding capacity (160 ± 10 mg IgG per gram of support), and a selective capture of monoclonal antibodies directly from mammalian crude extracts in 85 ± 5% yield and 98% of purity. The synthesis of ligand TPN‐BM and the routes followed for monoliths preparation and functionalization were inspired in the green chemistry principles allowing the reduction of processing time, solvents and purification steps involved, turning the integrated system attractive from an economical and chemical point of view. Copyright © 2013 John Wiley & Sons, Ltd.