bluuebunny/crossref_metadata_2025_split huggingface dataset:
Immobilization of glucose oxidase in thin polypyrrole films: Influence of polymerization conditions and film thickness on the activity and stability of the immobilized enzyme
Authors: Almeida Nicholas F. , Beckman Eric J. , Ataai Mohammad M. 
Published: December 2004

AbstractUsing monomers that polymerize to form electrically conducting polymers, one can control the thickness of the polymer film and the amount of enzyme that can be immobilized in the films. First, an investigation of the major variables that influence the immobilization of glucose oxidase by entrapment in polypyrrole films, prepared by electropolymerization from aqueous solutions containing the enzyme and monomer, was carried out. Then the optimized conditions were used to assess the effects of film thickness on the activity and stability of immobilized enzyme. For the films ranged in thickness from 0.1 μm to 1.6 μm, the resulting apparent activity and stability of the immobilized enzyme were found to be a strong function of the polymer film thickness. Above a thickness of 1.0 μm, the apparent activity of the immobilized enzyme increases linearly with increasing film thickness. The nonlinearity observed for films of thickness less than 1.0 μm can be attributed to the changes observed in the morphology of the resulting polypyrrole films. Furthermore, it was noted that when the glucose oxidase/polypyrrole films are stored in phosphate buffer, at 4°C, the observed rate of loss in apparent activity of the immobilized enzyme is highest for the first few days, also being higher for the thinner films. However, after the loosely entrapped enzyme is leached from the polymer film, the rate of loss in activity is very low indicating that the well‐entrapped enzyme, as well as the polypyrrole films, exhibit good stability. Finally, the reproducibility of the immobilization technique is excellent. © 1993 John Wiley & Sons, Inc.
Quantification of damage to suspended insect cells as a result of bubble rupture
Authors: Trinh Kim , Garcia‐Briones Miguel , Chalmers Jeffrey J. , Hink Fred 
Published: December 2004

AbstractIt is proposed that when cells are either attached to, or very near, a rupturing bubble, the hydrodynamic forces associated with the rupture are sufficient to kill the cells. Four types of experiments were conducted to quantify the number and location of these killed cells. We determined: (1) the number of cells killed as a result of a single, 3.5‐mm bubble rupture; (2) the number and viability of cells in the upward jet that results when a bubble ruptures; (3) the number of cells on the bubble film; and (4) the fate of cells attached to the bubble film after film rupture. All experiments were conducted with Spodoptera frugiperda (SF‐9) insect cells, in TNM‐FH and SFML medium, with and without Pluronic F‐68. Experiments indicate that approximately 1050 cells are killed per single, 3.5‐mm bubble rupture in TNM‐FH medium and approximately the same number of dead cells are present in the upward jet. It was also observed that the concentration of cells in this upward jet is higher than the cell suspension in TNM‐FH medium without Pluronic F‐68 by a factor of two. It is believed that this higher concentration is the result of cells adhering to the bubble interface. These cells are swept up into the upward jet during the bubble rupture process. Finally, it is suggested that a thin layer around the bubble containing these absorbed cells is the “hypothetical killing volume” presented by other researchers. © 1994 John Wiley & Sons, Inc.
Enhanced disruption of Candida utilis using enzymatic pretreatment and high‐pressure homogenization
Authors: Baldwin Clark V. , Robinson Campbell W. 
Published: December 2004

AbstractThe enhancement of the overall disruption of a native strain of Candida utilis (ATCC 9226) was studied using a combination of two methods, namely, pretreatment in the form of partial enzymatic lysis by Zymolyase followed by mechanical disruption in a Microfluidizer high‐pressure homogenizer. The cells were grown in both batch and continuous cultures to examine the effect of specific growth rate on disruption. Cell suspensions ranging in concentration from 7 to 120 g DW/L were disrupted with and without enzymatic pretreatment. For yeast grown in batch culture, final total disruption obtained using the combined protocol approached 95% with four passes at a pressure of 95 MPa, as compared with only 65% disruption using only mechanical homogenization. A modified model was developed to predict the fraction disrupted by the enzymatic pretreatment‐mechanical homogenization two‐stage process. Predicted disruptions agreed favorably with experimental observations (maximum deviation of 20%) over a wide range of operating conditions. © 1994 John Wiley & Sons, Inc.
A cellular automaton model for microcarrier cultures
Authors: Hawboldt Kelly A. , Kalogerakis Nicolas , Behie Leo A. 
Published: December 2004

AbstractIn order to achieve high cell densities anchoragedependent cells are commonly cultured on microcarriers, where spatial restrictions to cell growth complicates the determination of the growth kinetics. To design and operate large‐scale bioreactors for microcarrier cultures, the effect of this spatial restriction to growth, referred to as contact inhibition, must be decoupled from the growth kinetics. In this article, a cellular automaton approach is recommended to model the growth of anchorage‐dependent cells on microcarriers. The proposed model is simple to apply yet provides an accurate representation of contact‐inhibited cell growth on microcarriers. The distribution of the number of neighboring cells per cell, microcarrier surface areas, and inoculation densities are taken into account with this model. When compared with experimental data for Vero and MRC‐5 microcarrier cultures, the cellular automaton predictions were very good. Furthermore, the model can be used to generate contact‐inhibition growth curves to decouple the effect of contact‐inhibition from growth kinetics. With this information, the accurate determination of kinetic parameters, such as nutrient uptake rates, and the effects of other environmental factors, such as toxin levels, may be determined. © 1994 John Wiley & Sons, Inc.
Review: Tissue engineering in the nervous system
Authors: Bellamkonda Ravi , Aebischer Patrick 
Published: December 2004

AbstractThe nervous system presents a challenge to the field of tissue engineering because some of its complex neurochemical and neuroanatomical architecture is just beginning to be understood. A combination of advances in molecular neurobiology, gene transfer techniques, and the concomitant advances in the engineering of biomaterials at a molecular level, are making tissue engineering in the nervous system possible. Due to the vast range of fields that this highly interdisciplinary task spans, any review is bound to be somewhat limited. Given that, this review attempts to cover some solutions engineered for: (a) the functional replacement of a missing neuroactive component; (b) the rescue or regeneration of degenerated neural tissue; and (c) the building of intelligent neural cell‐based biosensors and simple in vitro neural circuits based on controlled neural cell attachment to electrically relevant substrates. © 1994 John Wiley & Sons, Inc.
Review: Bone tissue engineering: The role of interstitial fluid flow
Authors: Hillsley M. V. , Frangos J. A. 
Published: December 2004

AbstractIt is well established that vascularization is required for effective bone healing. This implies that blood flow and interstitial fluid (ISF) flow are required for healing and maintenance of bone. The fact that changes in bone blood flow and ISF flow are associated with changes in bone remodeling and formation support this theory. ISF flow in bone results from transcortical pressure gradients produced by vascular and hydrostatic pressure, and mechanical loading. Conditions observed to alter flow rates include increases in venous pressure in hypertension, fluid shifts occurring in bedrest and microgravity, increases in vascularization during the injury‐healing response, and mechanical compression and bending of bone during exercise. These conditions also induce changes in bone remodeling. Previously, we hypothesized that interstitial fluid flow in bone, and in particular fluid shear stress, serves to mediate signal transduction in mechanical loading‐ and injury‐induced remodeling. In addition, we proposed that a lack or decrease of ISF flow results in the bone loss observed in disuse and microgravity. The purpose of this article is to review ISF flow in bone and its role in osteogenesis. © 1994 John Wiley & Sons, Inc.
Long‐Term continuous culture of hepatocytes in a packed‐bed reactor utilizing porous resin
Authors: Miyoshi Hirotoshi , Yanagi Kennichi , Ohshima Norio , Fukuda Hideki 
Published: December 2004

AbstractAs part of our attempt to develop a hybrid artificial liver support system using cultured hepatocytes, we investigated the long‐term metabolic function of hepatocytes incubated in a packed‐bed type reactor using reticulated polyvinyl formal (PVF) resin as a supporting material. Long‐term (up to 1 week) perfusion culture experiments using the packed‐bed reactor (20 mm i.d.) loaded with 500 PVF resin cubes (mean pore size 250 μm, 2 × 2 × 2 mm), together with conventional monolayer culture experiments as controls, were performed in serum‐free or serum‐containing medium. Ammonium metabolism and urea synthesis activities were evaluated quantitatively based on reaction kinetic analyses. Initial rates of ammonium metabolism and urea‐N synthesis, as well as GPT enzyme activities, were adopted as indexes of the metabolic performance of the reactor and activities of the cultured hepatocytes.When serum‐free medium was used in the perfusion cultures, ammonium metabolic and urea‐N synthetic rates showed significant decay with elapse of the culture period, being less than 10% of those measured on day 1. This loss of activity was more prominent in the perfusion culture than in the monolayer cultures using this medium. In contrast, when serum‐containing medium was used, approximately 50% of these activities obtained on day 1 were maintained even at the end of the cultures both in the perfusion and monolayer culture experiments.We concluded that the packed‐bed reactor using PVF resin enabled high‐density culture of hepatocytes, and showed a satisfactory ability to maintain the metabolic function of immobilized hepatocytes for relatively long periods of up to 1 week. This type of reactor is thus considered to represent a breakthrough in overcoming the difficulties involved in the development of a hybridtype artificial liver support system. © 1994 John Wiley & Sons, Inc.
Growth of recombinant fibroblasts in alginate microcapsules
Authors: Chang P. L. , Hortelano G. , Awrey D. E. , Tse M. 
Published: December 2004

AbstractTo develop a novel strategy of nonautologous somatic gene therapy, we now demonstrate the feasibility of culturing genetically modified fibroblasts within an immunoprotective environment and the optimal conditions required for their continued survival in vitro. When mouse Ltk− fibroblasts transfected with the human growth hormone gene were enclosed within permselective microcapsules fabricated from alginate–polylysine–alginate, they continued to secrete human growth hormone at the same rates as the nonencapsulated cells. They also continued to proliferate in vitro for at least 1 month even though their viability gradually declined to about 50%. The viability can be improved by controlling for (a) temperature during encapsulation, (b) duration of treatment with polylysine, (c) duration of liquefying the core alginate with sodium citrate, and (d) cell density at the time of encapsulation. The best conditions leading to improved survival and maximum proliferation of cells within the microcapsules were obtained by encapsulating the cells at 4 to 10°C instead of room temperature, coating the microspheres with polylysine for 6 to 10 min instead of 20 min, liquefying the core alginate by treating with citrate for 20 min instead of 6 to 10 min, and using a concentration of 2 × 106 cells/mL of alginate for encapsulation. Under such conditions, normally adherent and genetically engineered mouse fibroblasts survived and proliferated optimally within the microcapsule environment. The encapsulated fibroblasts maintained their level of transgene expression while recombinant gene products such as human growth hormone could diffuse through the microcapsule membrane without impediment. The demonstration that genetically modified fibroblasts can survive and continue to deliver recombinant gene products from within these microcapsules and the optimization for their maximal viability and growth within microcapsules should increase the potential for success in using such microencapsulated recombinant cells for somatic gene therapy. © 1994 John Wiley & Sons, Inc.
Blueprint for a lipase support: Use of hydrophobic controlled‐pore glasses as model systems
Authors: Bosley John A. , Clayton John C. 
Published: December 2004

AbstractFor the commercial exploitation of lipase biocatalysis to be successful, it is essential that effective supports are selected for lipase immobilization. In this study hydrophobic controlled‐pore glasses have been used as model systems for the immobilization of Rhizomucor miehei lipase. The effect of pore diameter and surface chemistry on enzyme efficiency in a typical esterification reaction under essentially nonaqueous conditions has been examined. It has been found that pore diameters of at least 35 nm are needed for the lipase to be able to utilize the internal volume of the support particles in the immobilization process. Despite the small size of the substrates in the esterification reaction, even larger pores (>100 nm) are required for the lipase efficiency to become independent of pore diameter; below 100 nm lipase activity and efficiency are markedly reduced. It has also been shown that the chemical nature of the hydrophobic surface plays an important part in catalyst design. Although lipase will adsorb readily to a wide range of hydrophobic groups, the highest catalyst activities are obtained when the glass surface is derivatized to give long alkyl chains; the presence of unsaturated derivatives gonerally leads to a reduction in activity. © 1994 John Wiley & Sons, Inc.
Kinetics of adhesion and spreading of animal cells
Authors: Ramsden J. J. , Li S.‐Y. , Prenosil J. E. , Heinzle E. 
Published: December 2004

AbstractThe adhesion and spreading of cells at surfaces are well established phenomena which have been extensively observed using light or electron microscopy. The kinetics of both processes can be quantitatively measured by allowing the cells to attach themselves to the surface of a planar waveguide allows the number of cells per unit area and a parameter uniquely characterizing their shape, such as the area in contact with the surface, to be determined. Cells suspended in nutrient medium or pure phosphate buffer were allowed to attach to and spread on a metal oxide surface or a layer of fibronectin, and the kinetics of attachment and spreading have been measured. Attachment kinetics are the same in all cases, but spreading on the metal oxide requires nutrient medium, without which it does not occur. Spreading of cells attached to a layer of fibronectin in the absence of nutrient medium occurs at about a tenth of the rate of cells spreading on metal oxide in the presence of nutrient. © 1994 John Wiley & Sons, Inc.
Surfactant‐Modified lipase for the catalysis of the interesterification of triglycerides and fatty acids
Authors: Basheer Sobhi , Mogi Ken‐ichi , Nakajima Mitsutoshi 
Published: December 2004

AbstractThe lipase‐catalyzed intresterification of triglycerides and fatty acids in n‐hexane was studied. Initially, lipase Saiken was modified with a surfactant of sorbitan esters so that its dispersibility in hydrophobic organic media was improved. The surfactant‐modified lipase formed in the modification process carried out in a buffer solution has 1,3‐positional specificity and predominantly catalyzed the interesterification reaction in a microaqueous n‐hexane system. The modification technique converted inactive lipases to very active biocatalysts for the interesterification of triglycerides and fatty acids. The pH and the weight ratio of surfactant to enzyme used during the lipase modification process have shown significant effects in determining the recoveries of the protein and enzyme activity from the buffer solution, the protein content of the modified lipase complex after being freeze dried, and the interesterification activity of the complex. The water content in the reaction solution has strongly influenced the enzyme activity as well as the distribution of the products. © 1995 John Wiley & Sons, Inc.
Effects of calcium on development of anaerobic acidogenic biofilms
Authors: Huang J. , Pinder K. L. 
Published: December 2004

AbstractAnerobic biofilms with dominantly acidogenic bacteria were grown in fixed‐bed recycle reactors. The influence of calcium concentration in the culture medium on biofilm mass accumulation, immobilized calcium concentration, and biofilm‐specific activity was investigated. The results indicate that the biofilm mass accumulation was increased by the presence of calcium in the growth medium when calcium concentration was not higher than 120mg/L. Calcium accumulated in the biofilms increased in proportion to the calcium level in the feed. The biofilms for an increased input calcium concentration showed a trend of decrease in specific activity. The biofilms with a thickeness of less than 0.5 mm had the highest specific activity. The optimum calcium concentration for substrate consumption by the biofilms was 100 to 120 mg/L. The biofilms transferred from higher calcium medium to lower calcium medium were more susceptible to sloughing from their support surfaces, which indicates calcium's role in the stability of the biofilm structure. © 1995 John Wiley & Sons, Inc.
Production of poly(D‐3‐hydroxybutyrate) from CO2, H2, and O2 by high cell density autotrophic cultivation of Alcaligenes eutrophus
Authors: Tanaka Kenji , Ishizaki Ayaaki , Kanamaru Toshihisa , Kawano Takeharu 
Published: December 2004

AbstractHydrogen‐oxidizing bacterium, Alcaligenes eutrophus autotrophically produces biodegradable plastic material, poly(D‐3‐hydroxybutyrate), P(3HB), from carbon dioxide, hydrogen, and oxygen. In autotrophic cultivation of the microorganism, it is essential to eliminate possible occurrence of gas explosions from the fermentation process. We developed a bench‐plant scale, recycled‐gas, closed‐circuit culture system equipped with several safety features to perform autotrophic cultivation of A. eutrophus by maintaining the oxygen concentration in the substrate gas phase below the lower limit for a gas explosion (6.9%). The culture vessel utilized a baskettype agitator, resulting in a KL a value of 2970 h−1. Oxygen gas was also directly fed to the fermentor separately from the other gases. As a result, 91.3 g · dm−3 of the cells and 61.9 g · dm−3 of P(3HB) were obtained after 40 h of cultivation under this oxygen‐limited condition. The results compared favorably with those reported for mass production of P(3HB) by heterotrophic fermentation. © 1995 John Wiley & Sons, Inc.
Development of optimized transfectoma cell lines for production of chimeric antibodies in hollow fiber cell culture systems
Authors: Schläpfer Beatrice S. , Scheibler Marcel , Holtorf Anke‐Peggy , Van Nguyen Hai , Pluschke Gerd 
Published: December 2004

AbstractMethods for the selection of transfectoma cells that express large quantities of mouse–human chimeric antibodies have been develped. SP2/0 mouse myeloma cells were transfected with pSV2‐gpt and pSV2‐neo based immunoglobulin expression vectors. Double transfectants were selected using the xanthine–guanine phosphoribosyl transferase (gpt)and the neomycin (neo) selection marker genes. ELISA‐based screening of transfectoma clones resulted in the isolation of IgG‐producing transfectomas. Introduction of the kappa light‐chain 3′‐enhancer into the light‐chain expression vector significantly increased immunoglobulin expression, but only when the enhancer was located at its physiological site, 9 kb downstream of the kappa constant region exon. With some of the transfectomas, final yields of up to 80 mg/L of chimeric IgG were obtained in conventional flask cultures using serum‐free growth medium. A pilot‐scale AcuSyst Maximizer hollow fiber cell culture system was used for the production of gram amounts of chimeric IgG. Results obtained with different transfectoma clones in conventional culture were not fully predictive for yields in the hollow fiber system. In contrast, differences in productivity between individual clones in the laboratory‐scale Tecnomouse cell culture unit were comparable with those in the Maximizer system. Up to 200 mg of chimeric IgG were produced per day in one Maximizer bioreactor. © 1995 John Wiley & Sons, Inc.
Dielectrophoretic separation of cells: Continuous separation
Authors: Markx Gerard H. , Pethig Ronald 
Published: December 2004

AbstractDielectrophoresis is the movement of particles in non‐uniform alternating and direct current (AC, DC) electric fields. When nonuniform electric fields are created between microelectrodes, cells will redistribute themselves around the electrodes, the force holding the cells in place dependig on the local electric field and on the electrical properties of the cells themselves and the suspending medium. Steric drag forces produced by a gentle fluid flow in the chamber can be used to separate cells by selectively lifting cells from potential energy wells produced by the electric field. The technique is demonstrated in the batch separation of bacteria, yeast cells, and plant cells. Continuous separation and extraction of two cell types can be achieved by repeated reversing of the fluid flow direction in phase with the switching on and off of the applied voltage, and the efficacy of the technique is demonstrated for viable and nonviable (heat‐treated) yeast cells. © 1995 John Wiley & Sons, Inc.
Development of effective modified cellulase for cellulose hydrolysis process
Authors: Park Jin Won , Kajiuchi Toshio 
Published: December 2004

AbstractCellulase was modified with amphilic copolymers made of α‐allyl‐ω‐methoxy polyoxyalkylene (POA) and maleic acid anhydride (MAA) to improve the cellulose hydrolytic reactivity and cellulase separation. Amino groups of the cellulase molecule are covalently coupled with the MAA functional groups of the copolymer. At the maximum degree of modification (DM) of 55%, the modified cellulase activity retained more than 80% of the unmodified native cellulase activity. The modified cellulase shows greater stability against temperature, pH, and organic solvents, and demonstrated greater conversion of substrate than native cellulase does. Cellulase modification is also useful for controlling strong adsorption of cellulase onto substrate. Moreover, cellulase modified with the amphiphilic copolymer displays different separation characteristics which are new. One is a reactive two‐phase partition and another is solubility in organic solvents. It appears that these characteristics of modified cellulase work very effectively in the hydrolysis of cellulose as a total system, which constitutes the purification of cellulase from culture broth, hydrolysis of cellulose, and recovery of cellulase from the reaction mixture. © 1995 John Wiley & Sons, Inc.