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PubMed2006

Feasibility of static secondary ion mass spectrometry to study physicochemical interactions between organic components and silver in thermographic systems.

Chemical engineering of high-technology products requires elucidation of intermolecular interactions in complex materials. As part of an extensive study on thermographic systems, static secondary ion mass spectrometry (S-SIMS) was used to probe the physicochemical behaviour of active compounds, such as different tone modifiers and stabilisers, on silver. In particular, the feasibility of detecting adsorption and/or binding of individual additives and mixtures to silver was examined. Substrates prepared by sputter coating silver on silicon wafers were exposed to solutions of the studied compounds in 2-butanone. The signal intensities measured with S-SIMS for the ad-layers showed reproducibility to within 10%. Radical ions containing silver such as [M-H+Ag]+ * were used as evidence for the formation of bonds in the solid. Also the [M-H+2Ag]+ ions could be assigned to chemisorbed species while [M+Ag]+ ions could be formed by adduct ionisation of molecules with co-ejected Ag+ ions. The signal intensities of [M-H+Ag]+ * and [M-H+2Ag]+ ions were used to monitor the adsorption quantitatively as a function of time.

Journal Article↗
PubMed1988

Liposome-encapsulated hemoglobin: a synthetic red cell.

Liposome-encapsulated hemoglobin (LEH) is being developed at the Naval Research Laboratory as a universally transfusable oxygen-carrying blood replacement. A chemical engineering scale-up feasibility study has been completed recently. We report here the development of an encapsulation method which produces liters of phospholipid/cholesterol liposomes containing at least 16 g% hemoglobin in a few hours. The 0.2 micron liposomes are produced with a Microfluidizer TM (Microfluidics Corp., Newton, MA) adapted for this purpose, and then washed and sterile filtered using a Pellicon (Millipore, Bedford, MA) tangential flow filtration device. Previously, production limitations and lack of sterility have been serious barriers to toxicity testing for all the researchers engaged in related investigations. The biophysical properties of the LEH thus produced are ideal for use as a blood substitute, resembling those of red blood cells. The oxygen-binding affinity of LEH can be maintained at the level of fresh whole blood for many weeks by co-encapsulation of pyridoxal-5-phosphate. The circulation persistence time of liposomes is a function of the type of phospholipid. We have developed a formulation which has a circulation persistence time of 15-20 hours. The LEH oxygen binding characteristics, circulation half-life and its lipid composition dependence, scale-up preparation method, and a sterilization method are presented.

Animals↗
PubMed1992

Maximisation of perfusion systems and process comparison with batch-type cultures. Maximisation of perfusion cultures.

A comparison of cell yields and monoclonal antibody productivity from the same hybridoma has been made in a wide range of cell bioreactors including both batch and continuous perfusion cultures. The most productive systems were based on porous microcarriers in fixed and fluidised beds which can be operated with a high degree of efficiency and reliability from the physico-chemical engineering point of view. Further improvements should be possible by improving the physiological environment in dense cell cultures, as indicated by the preliminary studies that are described. These include experimental data showing the relationship between monoclonal antibody production rates with glucose, glutamine, ammonia, and oxygen levels in microporous beads. The results strongly indicate that perfusion processes that are scaleable in both volume and cell density can significantly reduce production costs. Manufacturers of biologicals from animal cells now have a choice between the proven batch-type processes and reliable perfusion systems based on microporous beads.

Animals↗
PubMed2006

Modeling of the pyruvate production with Escherichia coli: comparison of mechanistic and neural networks-based models.

Three different models: the unstructured mechanistic black-box model, the input-output neural network-based model and the externally recurrent neural network model were used to describe the pyruvate production process from glucose and acetate using the genetically modified Escherichia coli YYC202 ldhA::Kan strain. The experimental data were used from the recently described batch and fed-batch experiments [ Zelić B, Study of the process development for Escherichia coli-based pyruvate production. PhD Thesis, University of Zagreb, Faculty of Chemical Engineering and Technology, Zagreb, Croatia, July 2003. (In English); Zelić et al. Bioproc Biosyst Eng 26:249-258 (2004); Zelić et al. Eng Life Sci 3:299-305 (2003); Zelić et al Biotechnol Bioeng 85:638-646 (2004)]. The neural networks were built out of the experimental data obtained in the fed-batch pyruvate production experiments with the constant glucose feed rate. The model validation was performed using the experimental results obtained from the batch and fed-batch pyruvate production experiments with the constant acetate feed rate. Dynamics of the substrate and product concentration changes was estimated using two neural network-based models for biomass and pyruvate. It was shown that neural networks could be used for the modeling of complex microbial fermentation processes, even in conditions in which mechanistic unstructured models cannot be applied.

Acetates↗
PubMed1969

Some experiences in the estimation of parameters in non-linear differential equations.

The author describes a procedure developed by himself and his colleagues for obtaining estimates of the parameters of rate equations, together with information about confidence regions for the estimates. The program has been used successfully for processing results from the chemical engineering industry, with highly non-linear model systems, particularly since temperature was a variable, and the "rate constants" were non-linear combinations of other constants. In biochemical situations, in which investigations are almost always at constant temperature, the non-linearity should not be so extreme, and the procedure may well be capable of dealing with more than 5 to 7 parameters for which it is recommended.

Journal Article↗
PubMed1995

Methods for reducing the ammonia in hybridoma cell cultures.

The factors which limit the proliferation of eukaryotic cells in vitro are still not well known. Ammonia is believed to be toxic for mammalian cell proliferation and secretion. We have tried two approaches to reducing the ammonia in the medium. We first limited the ammonia produced by the cells by replacing glutamine by glutamate. Then, we used two chemical engineering methods to eliminate accumulated ammonia. In one the used medium was passed through a natural cation exchanger: the clinoptilolite. In the other, the culture medium was passed through a hydrophobic microporous hollow fiber module. Replacing the glutamine by glutamate reduced the medium ammonia concentration. The physicochemical removal of ammonia induced a better cell growth, but not a better specific antibody secretion.

Ammonia↗
PubMed1985

Possibilities of liposomes as dynamic dosage form in dermatology.

Local application of substances in different vehicles for the care of the skin and the treatment of skin diseases have been used since antiquity. With the present state of technology a modern dosage form allowing chemical engineering can be devised. Liposomes which consist of lipid bilayers engulfing an aqueous solution fulfill the sophisticated requirements. With a lipid and an aqueous compartment these liposomes can contain lipophilic and hydrophilic medicaments. The lipid composition and the incorporation of charged carrier protein molecules can be varied, affecting the rate of drug release to the skin. In this way active substances are either retained on the skin (pertinent to sunscreening agents) or liberated from the liposome depot to the skin layers (corticosteroids). The highly organized membrane structures containing lysine or hydrolysine can be fixed to the skin enzymatically avoiding temporal removal from the skin and supporting depot function and protective film function. Studying the surface lipid and epidermal lipid composition, lipid membranes can be composed which do not cause hypersensitivity reactions and form a substitute in case of deficient barrier function of the skin.

Dermatologic Agents↗
PubMed1995

Liquid emulsion membranes: principles, problems and applications in fermentation processes.

Liquid emulsion membranes (LEMs) have developed into a versatile technique for a variety of applications involving selective and controlled transport of biochemicals. Biological applications cover the controlled delivery of drugs from capsules, detoxification of the circulatory system, recovery of useful compounds from waste streams and selective separation of products from fermentation broths. This review traces the development of LEMs, discusses their key features, advantages and limitations, describes methods of modelling LEM systems and highlights some applications with industrial potential. Two kinds of LEM systems are considered. The first type are agitated emulsions, which are relatively easy to prepare and use but may be limited in their selectivity and long-term stability. Supported liquid membranes (SLMs) are a recent development; they use porous solid supports and have excellent stability and selectivity. Their chemical engineering aspects and applications in fermentation processes are considered.

Journal Article↗
PubMed2005

Mitochondrially targeted vitamin E and vitamin E mitigate ethanol-mediated effects on cerebellar granule cell antioxidant defense systems.

Ethanol (EtOH) disrupts the structure and function of the developing nervous system, sometimes leading to birth defects associated with fetal alcohol syndrome (FAS). Animal FAS models indicate that cellular membrane peroxidation, intracellular oxidant accumulation, and suppression of endogenous antioxidant enzymes contribute to the toxic effects of EtOH. Mitochondrially targeted vitamin E (MitoVit E), a chemically engineered form of vitamin E (VE) designed to accumulate in the mitochondria, has been shown to inhibit intracellular oxidant accumulation and cell death more effectively than VE. In previous investigations, we have shown that, in vivo, VE reduces neuronal death in the developing cerebellum of EtOH-exposed animals, and, in vitro, VE prevents apoptotic and necrotic death of EtOH-exposed cerebellar granule cells (CGCs). The present investigation shows that, in a FAS CGC model, 1 nM MitoVit E renders significant neuroprotection against EtOH concentrations as high as 1600 mg/dL. The present study also demonstrates that, in this same model, MitoVit E mitigates EtOH-induced accumulation of intracellular oxidants and counteracts suppression of glutathione peroxidase/glutathione reductase (GSH-Px/GSSG-R) functions, protein expression of gamma-glutamylcysteine synthetase (gamma-GCS), and total cellular glutathione (GSH) levels. In the presence and absence of EtOH, VE amplifies the protein expression levels of gamma-GCS, an enzyme that performs the rate-limiting step for GSH synthesis, and total GSH levels. These results suggest that MitoVit E and VE ameliorate EtOH toxicity through non-oxidant mechanisms-modulations of endogenous cellular proteins-and antioxidant means.

Animals↗
PubMed2005

Biocatalysis in semi-aqueous and nearly anhydrous conditions.

In the past few years there have been prolific advances in activating enzymes for nonaqueous biocatalysis. Molecular dynamics simulations complement recent experimental results and offer new insights into the deleterious effects of organic solvents, such as water stripping and active-site penetration. Methods for activating enzymes in semi-aqueous or nonaqueous media include protein engineering, chemical modification, and co-lyophilization with non-buffer salts. Enzyme immobilization on novel polymeric supports and the use of zeolite molecular sieves can also increase solvent tolerance, enhance activity, and improve enantioselectivity. The recent implementation of enzymes in ionic liquids has also led to better long-term stability relative to traditional organic solvents and the simultaneous solubilization of enzymes, cofactors and substrates.

Catalysis↗
PubMed2006

The Gurnham equation in characterizing the compressibility of pharmaceutical materials.

Limitations of the Heckel equation in characterizing material compression behavior have been well reported. In this work, the Gurnham equation, which was first introduced in chemical engineering, is proposed as an alternate method of evaluating the compressibility of pharmaceutical powders. The Gurnham equation was adapted for tablet compression and the estimated slope parameter c was proposed to represent material compressibility. Data from the compression of four commonly used excipients (microcrystalline cellulose, corn starch, lactose monohydrate, and dibasic calcium phosphate dihydrate) and one drug (acetaminophen) were evaluated using the Gurnham equation. Using compression data at different peak pressures, linear relationships between porosity and lnPressure of the five materials were obtained. The determined parameter c expresses the compressibility of materials. The analysis of previous experimental data, including granulations, mixtures and co-processed materials also indicates that c might be a representative parameter for material compressibility.

Acetaminophen↗
PubMed2006

Local film thinning due to concentration gradient of an insoluble surfactant at an interface.

The local thinning of a viscous liquid film on a substrate driven by a surface (or interfacial) tension gradient due to a concentration gradient of a monolayer of an insoluble surfactant initially non-uniformly distributed at a liquid interface relevant to chemical engineering, biomedical and other applications is investigated. A simple model is presented for the temporal evolution of the profiles of radial variation in the thickness of a thin liquid film, the effects of gravity and capillarity due to deformation of the interface in slowing down the film thinning process being allowed. As time increases, the surfactant spreads and the radius of its front increases inversely with decrease in the two-third power of the film thickness at the center. The model describes well not only the published experimental results but also those obtained by other authors using numerical simulations of a set of coupled partial differential equations.

Journal Article↗
PubMed1990

Effect of intravenous drug administration mode on drug distribution in a tumor slab: a finite Fourier transform analysis.

Cancer therapy using chemotherapeutic drugs frequently involves injection of the drug into the body through some intravenous mode of administration, viz, continuous (drip) infusion or single/multiple bolus injection(s). An understanding of the effect of the various modes of administration upon tumor penetration of drug is essential to rational design of drug therapy. This paper investigates drug penetration into a model tumor of slab geometry (between two capillaries) in which the overall transport rate of drug is limited by intra-tumor transport characterized by an effective diffusion coefficient. Employing the method of Finite Fourier Transforms (FFT), analytical solutions have been obtained for transient drug distribution in both the plasma and the tumor following three modes of administration, viz, continuous infusion, single bolus injection and equally-spaced equal-dose multiple bolus injections, of a given amount of drug. The qualitative trends exhibited by the plasma drug distribution profiles are consistent with reported experimental studies. Two concepts, viz, the dimensionless decay constant and the plasma/tumor drug concentration trajectories, are found to be particularly useful in the rational design of drug therapy. The dimensionless decay constant provides a measure of the rate of drug decay in the plasma relative to the rate of drug diffusion into the tumor and is thus characteristic of the tumor/drug system. The magnitude of this parameter dictates the choice of drug administration mode for minimizing drug decay in the plasma while simultaneously maximizing drug transport into the tumor. The concentration trajectories provide a measure of the plasma drug concentration relative to the tumor drug concentration at various times following injection. When the tumor drug concentration exceeds the plasma drug concentration, the drug will begin to diffuse out of the tumor. Knowledge of the time at which this diffusion reversal occurs is especially useful for optimum scheduling of subsequent bolus injections in a multiple bolus dosing regimen. There are no reported applications of the FFT method to solve repeated input functions in either the chemical engineering or pharmaceutical science literature. Thus, the application of FFT method to solve multiple bolus injections is a unique one. Use of this FFT based analysis as a predictor tool can limit the number of costly experiments which are being done now to achieve this purpose. Even though the model in its present form is simplified, the analysis thereof has nevertheless led to a better understanding of the various factors that must be taken into account for rational design of drug therapy.

Drug Administration Routes↗
PubMed2001

A new numerical procedure to determine the VLE curve.

A fast and accurate (to any required precision) numerical method is presented to calculate the vapour-liquid equilibrium for any subcritical temperature from a given equation of state. The calculations are made using the popular program MATHEMATICA, and we think that this method could be very useful in chemical physics and chemical engineering applications, as well as for teaching purposes.

Journal Article↗
PubMed2001

Dynamic optimization of chemical processes using ant colony framework.

Ant colony framework is illustrated by considering dynamic optimization of six important bench marking examples. This new computational tool is simple to implement and can tackle problems with state as well as terminal constraints in a straightforward fashion. It requires fewer grid points to reach the global optimum at relatively very low computational effort. The examples with varying degree of complexities, analyzed here, illustrate its potential for solving a large class of process optimization problems in chemical engineering.

Journal Article↗
PubMed2001

Probing hydration and the stability of protein solutions--a colloid science approach.

The stability of protein solutions is a topic of much theoretical and practical interest. The theory of Derjaguin, Landau, Verweey and Overbeek (DLVO theory) has long been used by colloid scientists and chemical engineers to define conditions leading to stability of dispersion, but has found very little application by protein chemists. We apply DLVO theory to demonstrate that protein solution stability appears to be closely related to the presence of the hydration layer, rather than to significant inter-molecular net repulsive force. A novel but simple formalism is then developed which indicates, via computation of a newly defined parameter ('site relaxation time'), that estimated 'dwell times' for water molecules on a protein surface are of a magnitude adequate to account for such a role.

Colloids↗
PubMed2003

Toxicokinetic modeling and its applications in chemical risk assessment.

In recent years physiologically based pharmacokinetic (PBPK) modeling has found frequent application in risk assessments where PBPK models serve as important adjuncts to studies on modes of action of xenobiotics. In this regard, studies on mode of action provide insight into both the sites/mechanisms of action and the form of the xenobiotic associated with toxic responses. Validated PBPK models permit calculation of tissue doses of xenobiotics and metabolites for a variety of conditions, i.e. at low-doses, in different animal species, and in different members of a human population. In this manner, these PBPK models support the low-dose and interspecies extrapolations that are important components of current risk assessment methodologies. PBPK models are sometimes referred to as physiological toxicokinetic (PT) models to emphasize their application with compounds causing toxic responses. Pharmacokinetic (PK) modeling in general has a rich history. Data-based PK compartmental models were developed in the 1930's when only primitive tools were available for solving sets of differential equations. These models were expanded in the 1960's and 1970's to accommodate new observations on dose-dependent elimination and flow-limited metabolism. The application of clearance concepts brought many new insights about the disposition of drugs in the body. In the 1970's PBPK/PT models were developed to evaluate metabolism of volatile compounds of occupational importance, and, for the first time, dose-dependent processes in toxicology were included in PBPK models in order to assess the conditions under which saturation of metabolic and elimination processes lead to non-linear dose response relationships. In the 1980's insights from chemical engineers and occupational toxicology were combined to develop PBPK/PT models to support risk assessment with methylene chloride and other solvents. The 1990's witnessed explosive growth in risk assessment applications of PBPK/PT models and in applying sensitivity and variability methods to evaluate model performance. Some of the compounds examined in detail include butadiene, styrene, glycol ethers, dioxins and organic esters/aids. This paper outlines the history of PBPK/PT modeling, emphasizes more recent applications of PBPK/TK models in health risk assessment, and discusses the risk assessment perspective provided by modern uses of these modeling approaches.

Animals↗