Optimum fiber spacing in a hollow fiber bioreactor

A high surface area hollow fiber reactor was developed for mammalian cell culture. The reactor employs an interfiber gel matrix of agar or collagen for cell support. A model was developed to predict cell density as a function of fiber spacing. Optimum spacings are calculated for two sizes of Celgard hollow fibers. Ehrlich Ascites Tumor (EAT) cells were grown to an estimated density of 1.1 x 10(8) viable cells/mL in the extracapillary space-corresponding to an overall reactor density of 7 x 10(7) cells/mL. On the basis of available kinetic and diffusivity data, the model predicts that lactate accumulation may limit cell growth in the early stage of medium utilization, while oxygen delivery becomes limiting at later stages.     

Kinetics of a hollow fiber dehydrogenase reactor

A hollow fiber module was used as a reactor for conversion of ethanol to acetaldehyde in the presence of horse liver alcohol dehydrogenase as catalyst. Mass transport rates for NAD⁺, the overall acetaldehyde generation rate, catalyst effectiveness factors, and the overall order of the reaction with respect to NAD⁺ concentration were measured. A coupled-substrate reactor with continuous in situ regeneration of cofactor was also examined. Two substrates of opposite redox state were added simultaneously to the feed stream. NADH and acetaldehyde concentrations were monitored in the effluent stream. The cofactor recycle number, or ratio of moles of product to moles of NADH produced, exceeded 10,000 under certain conditions. While decreasing the NAD⁺ concentration in the feed stream decreased reactor productivity somewhat, it greatly enhanced the ratio of product formed per mole of NAD⁺ fed to the reactor. It is suggested that high cofactor costs in dehydrogenase reactors may be overcome with efficient in situ regeneration and secondary recovery and recycling of cofactor from the process stream.     

Synthetic spider silk: a modular fiber

Spiders make their webs and perform a wide range of tasks with up to seven different types of silk fiber. These different fibers allow a comparison of structure with function, because each silk has distinct mechanical properties and is composed of peptide modules that confer those properties. By using genetic engineering to mix the modules in specific proportions, proteins with defined strength and elasticity can be designed, which have many potential medical and engineering uses.     

Bidirectional amyloid fiber growth for a yeast prion determinant

The polymerization of many amyloids is a two-stage process initiated by the formation of a seeding nucleus or protofibril. Soluble protein then assembles with these nuclei to form amyloid fibers. Whether fiber growth is bidirectional or unidirectional has been determined for two amyloids. In these cases, bidirectional growth was established by time lapse atomic-force microscopy. Here, we investigated the growth of amyloid fibers formed by NM, the prion-determining region of the yeast protein Sup35p. The conformational changes in NM that lead to amyloid formation in vitro serve as a model for the self-perpetuating conformational changes in Sup35p that allow this protein to serve as an epigenetic element of inheritance in vivo. To assess the directionality of fiber growth, we genetically engineered a mutant of NM so that it contained an accessible cysteine residue that was easily labeled after fiber formation. The mutant protein assembled in vitro with kinetics indistinguishable from those of the wild-type protein and propagated the heritable genetic trait [PSI(+)] with the same fidelity. In reactions nucleated with prelabeled fibers, unlabeled protein assembled at both ends. Thus, NM fiber growth is bidirectional.     

Mechanism of osmotic flow in a periodic fiber array

The classic analysis by Anderson and Malone (Biophys J 14: 957-982, 1974) of the osmotic flow across membranes with long circular cylindrical pores is extended to a fiber matrix layer wherein the confining boundaries are the fibers themselves. The equivalent of the well-known result for the reflection coefficient sigma0 = (1 - phi)2, where phi is the partition coefficient, is derived for a periodic fiber array of hexagonally ordered core proteins. The boundary value problem for the potential energy function describing the solute distribution surrounding each fiber is solved by defining an equivalent fluid annulus in which the pressures and osmotic forces are determined. This model is of special interest in the osmotic flow of water across a capillary wall, where recent experimental studies suggest that the endothelial glycocalyx is a quasiperiodic fiber array that serves as the primary molecular sieve for plasma proteins. Results for the reflection coefficient are presented in terms of two dimensionless numbers, alpha = a/R and beta = b/R, where a and b are the solute and fiber radii, respectively, and R is the outer radius of the fluid annulus. In general, the results differ substantially from the classic expression for a circular pore because of the large difference in the shape of the boundary along which the osmotic force is generated. However, as in circular pore theory, one finds that the reflection coefficients for osmosis and filtration are the same.     

Actin on multiple fronts to generate a muscle fiber

How the actin cytoskeleton is harnessed to fulfill its diverse cellular functions is a recurrent and intriguing question. In this issue of Developmental Cell, Kim et al. and Massarwa et al. describe a new role for F-actin, and more specifically the actin regulator WASp, in myoblast fusion in Drosophila.     

Nanocellulose,a tiny fiber with huge applications

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Stress-modulated collagen fiber remodeling in a human carotid bifurcation

This work concerns with the implementation of a new stress-driven remodeling model for simulating the overall structure and mechanical behavior of a human carotid bifurcation. By means of an iterative finite element based procedure collagen fiber direction and maximal principal stresses are computed. We find that the predicted fibers' architecture at the cylindrical branches and at the apex of the bifurcation correlates well with histological observations. Some insights about the mechanical response of the sinus bulb and the bifurcation apex are revealed and discussed. The results are compared with other, isotropic and orthotropic, models available in the literature.     

Plant cell immobilization in a dual hollow fiber bioreactor

Summary Lithospermum erythrorhizon was immobilized in a dual hollow fiber bioreactor (DHFBR) to maintain high cell density and to operate continuously. The cells grew well and its dry biomass density was 325 g/L of the void volume for the cell growth. Volumetric and specific productivities of phenolics were 221 mg/L.day and 0.68 mg/g.dry wt.day, respectively, which are 58 and 2 times of those of shake flask cultures.     

Enzymatic solubilization of a pectinaceous dietary fiber fraction from potato pulp: Optimization of the fiber extraction process

Upgrading of potato pulp, a byproduct stream from industrial manufacture of potato starch, is important for the continued economic competitiveness of the potato starch industry. The major part of potato pulp consists of the tuber plant cell wall material which is particularly rich in galactan branched rhamnogalacturonan I type pectin. In the work reported here, the release of high-molecular weight pectinaceous dietary fiber polysaccharides from starch free potato pulp was accomplished by use of a multicomponent pectinase preparation from Aspergillus aculeatus (Viscozyme^® L). The enzyme reaction conditions for the solubilization were optimized via a surface response design to be addition of 0.27% Viscozyme^® L by weight of potato pulp substrate dry matter, 1 h treatment at pH 3.5, 62.5 °C. Analysis of the molecular size and monomer composition of the enzymatically released fibers showed that they were rich in galactose and uronic acid indicating that the solubilized fibers were mainly made up of galactan branched rhamnogalacturonan I type pectin polymers.     

Dietary fiber

Dietary fiber is plant-derived material that is resistant to digestion by human alimentary enzymes. Fiber may be divided into two broad chemical classes: 1) non-alpha-glucan polysaccharides (cellulose, hemicelluloses, and pectins) and 2) lignins. Dietary fiber behaves within the gastrointestinal tract as a polymer matrix with variable physicochemical properties including susceptibility to bacterial fermentation, water-holding capacity, cation-exchange, and adsorptive functions. These properties determine physiological actions of fiber and are dependent on the physical and chemical composition of the fiber. Fiber undergoes compositional changes as a consequence of bacterial enzymatic action in the colon. Dietary fiber is of clinical significance in certain disorders of colonic function and in glucose and lipid metabolism. Dietary fiber increases stool bulk by acting as a vehicle for fecal water and by increasing fecal bacterial volume. Use of fiber in the treatment of constipation and uncomplicated diverticular disease is well established. By increasing stool bulk, fiber also reduces the fecal concentration of bile acids and other substances. Certain types of fiber decrease the rate of glucose absorption and attenuate postprandial rises in blood glucose and insulin. Plasma cholesterol levels are reduced by mucilaginous forms of fiber. This effect appears to be mediated in part by an increase in fecal acidic sterol excretion.     

Evaluation of a hepatocyte-entrapment hollow fiber bioreactor: a potential bioartificial liver

We have developed a hepatocyte entrapment hollow fiber bioreactor for potential use as a bioartificial liver. Hepatocytes were entrapped in collagen gel inside the lumen of the hollow fibers. Medium was perfused through the intraluminal region after contraction of the hepatocyte-entrapment gel. Another medium stream, comparable to the patient's blood during clinical application, passed through the extracapillary space. Viability of hepatocytes remained high after 5 days as judged by the rate of oxygen uptake and viability staining. Urea and albumin synthetic activities were also sustained. Transmission electron microscopic examination demonstrated normal ultrastructural integrity of hepatocytes in such a bioreactor. With its sort-term, extracorporeal support of acute liver failure, the current bioreactor warrants further investigation. (c) 1993 John Wiley & Sons, Inc.     

Hormones and the barnacle muscle fiber as a preparation

This minireview discusses the use of single barnacle muscle fibers as a model system for studying hormonal actions. The response of barnacle muscle fibers to serotonin, proctolin, octopamine, aldosterone and insulin is described. Recent data relating to the actions of these hormones on other invertebrate and vertebrate preparations is touched upon. The use of the barnacle muscle fiber as a preparation to investigate hormone-stimulated protein phosphorylation is emphasized.     

Ovule and suspension culture of a cotton fiber development mutant

Summary Growth and development of cotton fibers in a developmental mutant, Ligon-lintless, and its near isogenic wild type, Texas Marker-1, were compared in ovule and cell suspension cultures. In both organ and cell cultures the pattern of growth of fiber cells from the two genotypes mimicked the pattern ofin vivo growth. The timing of fiber cell initiation soon after anthesis in Ligon-lintless suggests that the fiber cells on this mutant are analogous to the commercially important lint fibers. Length distributions of elongated cells from cell suspension culture of Ligon-lintless and Texas Marker-1 indicate that the length attained in culture is affected by the genotype of the explant tissue.