bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled destruction of residual crosslinker in a silicone elastomer for drug delivery
Authors: Karlsson Anders , Singh Satish K. , Albertsson Ann‐Christine
Published: August 2002

In drug delivery systems that use silicone elastomers as a diffusion matrix for the active drug, it is common to crosslink the material by the hydrosilylation reaction. In this platinum‐catalyzed reaction, vinyl groups on a polymer add to the methyl siloxane hydride (MHS) groups on a low molecular mass crosslinker. With an excess of crosslinker, a fast curing is achieved and a fully crosslinked material is formed. Unreacted MHS groups were shown to remain in the elastomer after curing because of the excess crosslinker. In this work, a simple procedure was developed to eliminate the unreacted MHS groups from the final product. We found that storage of the product at +40°C and 75% relative humidity for a few weeks will effectively destroy the residual MHS groups in the elastomer. The effects of varying levels of humidity, oxygen, and temperature on this postcuring procedure were studied. The amount of MHS groups was measured with NMR and IR spectroscopy. We also found that the hardness of the material increased by approximately 25% as a consequence of this postcuring treatment. This increase is probably due to a secondary crosslinking reaction between MHS and silanol groups. Heat treatment at higher temperatures led to an even further increase in the hardness and compression modulus. Because no MHS groups remained in the elastomer when this heat treatment was started, it is apparent that another secondary crosslinking reaction is occurring, probably silanol condensation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2254–2264, 2002
The diffusion and bulk properties of polyurethane (PU) ‐based hydrophilic and hydrophobic membranes
Authors: Pulat Mehlíka , Akdoğan Ayten
Published: August 2002

In this study, the diffusion characteristics of diclofenac‐Na through hydrophobic and hydrophilic polyurethane (PU)‐based membranes are investigated. Hydrophilic polymers are obtained by graft copolymerization of PU with acriylamide (AAm) and itaconic acid (IA). The membranes are prepared by a solvent‐casting method and characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis. The diffusion measurements are performed using a diffusion cell for 10 h at 37°C. Permeability coefficients calculated from diffusion experiments are ∼3 times higher in hydrophilic membranes than hydrophobic PU membranes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 193–198, 2002
Structural change in mercerized cotton fibers on cellulase treatment
Authors: Haga T. , Takagishi T.
Published: August 2002

Cotton fibers treated with liquid ammonia and sodium hydroxide were hydrolyzed with crude cellulase. The structural change in the fibers due to the cellulase treatment was examined in relation to the apparent affinity of Congo Red. The cellulose III crystalline structure collapsed and generated intermediate‐molecular‐ordered regions on cellulase treatment. Adsorption of Congo Red occurred on the crystallite surfaces of cellulose II and cellulose III that was transformed from cellulose II. The fiber, the dominant crystallite phase of which was cellulose III that was transformed from cellulose II, had a considerably increased apparent affinity after cellulase treatment. The intermediate structure on the crystallite surface was associated with the adsorption of Congo Red in the cases of cellulose II and cellulose III. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1675–1680, 2001
Novel method for preparation of carboxylated nitrile rubber–natural rubber blends using bis(diisopropyl)thiophosphoryl polysulfides
Authors: Naskar Nityananda , Debnath Subhas Chandra , Basu Dipak Kumar
Published: August 2002

Bis(diisopropyl)thiophosphoryl trisulfide (DIPTRI) and bis(diisopropyl)thiophosphoryl tetrasulfide (DIPTET) are successfully used as a novel coupling agent and accelerator, respectively, to covulcanize an elastomer blend comprising polar carboxylated nitrile rubber (XNBR) and nonpolar natural rubber (NR). These compounds are capable of forming a chemical link between these dissimilar rubbers to produce a technologically compatible blend as judged by a swelling experiment. The blend vulcanizates thus produced exhibit enhanced physical properties that can further be improved by adopting the two‐stage vulcanization technique and also by judicious selection of the NR:XNBR ratio. The blend morphology assessed by scanning electron microcroscopy micrographs accounts for significant improvement in the physical properties of the blend vulcanizates, particularly in two‐stage vulcanization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1725–1736, 2001
Molecular weight effect on antimicrobial activity of chitosan treated cotton fabrics
Authors: Shin Y. , Yoo D.I. , Jang J.
Published: August 2002

The effect of the molecular weight of chitosan on antimicrobial activity was investigated using three chitosans of different molecular weights [1800 (water soluble), 100,000, and 210,000] and similar degrees of deacetylation (86–89%). Cotton fabrics were treated with chitosan by the pad–dry–cure method. The molecular weight dependence of the antimicrobial activity of chitosan was more pronounced at a low treatment concentration. Chitosans with molecular weight of 100,000 and 210,000 effectively inhibited Staphylococcus aureus at a 0.5% treatment concentration. Chitosan with a molecular weight of 1800 was effective against S. aureus at a 1.0% treatment concentration. Escherichia coli was effectively inhibited by chitosan with a molecular weight of 210,000 at a 0.3% treatment concentration and by chitosans with a molecular weight of 1800 and 100,000 at a 1.0% treatment concentration. Proteus vulgaris was effectively inhibited by chitosans with molecular weight of 100,000 and 210,000 at a 0.3% treatment concentration and by chitosan with a molecular weight of 1800 at a 0.5% treatment concentration. None of the chitosans significantly inhibited Klebsiella pneumoniae and Pseudomonas aeruginosa below a 1.0% treatment concentration. Chitosans with high molecular weights were more effective in inhibiting bacterial growth than chitosans with low molecular weights. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2495–2501, 2001
Effects of mixing time on phase structure and mechanical properties of poly(ethylene terephthalate)/ polycarbonate blends
Authors: García M. , Eguiazábal J. I. , Nazábal J.
Published: August 2002

The effects of interchange reactions on the solid‐state structure and mechanical properties of a 70/30 poly(ethylene terephthalate) (PET)/bisphenol A polycarbonate (PC) blend were studied. Increasing reaction levels were obtained by means of lower screw speeds in the extruder. The progressive production of copolymers with the reaction time increased the amount of each component in the other phase. The concomitant degradation of PET led to a maximum in ductility and tensile and impact strengths whereas the modulus of elasticity and the yield stress were held constant. The maximum in properties took place at a reaction time close to 2.6 min; at longer reaction times the negative effect of degradation began to overcome the positive effect of the interchange reactions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 121–127, 2001
Preparation of epoxy resin/acrylic composite latexes by miniemulsion polymerization method
Authors: Kawahara Hideaki , Goto Tokio , Ohnishi Kiyoshi , Ogura Hironao , Kage Hiroyuki , Matsuno Yoshizo
Published: August 2002

Epoxy resin/acrylic composite latexes were prepared by miniemulsion polymerization. Epoxy resins have a functional epoxy group in them and excellent characteristics, such as heat resistance and good adhesion. Acrylic latexes have weather and water resistance. Combining the epoxy resin and the acrylic latex was an attempt to actualize these advantages. The miniemulsion polymerization method was effective in obtaining the composite latex. A less than 500‐nm droplet size for the monomer preemulsion was necessary to obtain the latex in a stable manner. Dimethylaminoethylmethacrylate and methacrylic acid as the reactive functional monomer with an epoxy group were introduced to the latexes. The effect of the polymerization method of these functional groups on the properties of latexes and their films was investigated. The latex prepared by the two‐stage polymerization method had good polymerization stability, storage stability, and solvent resistance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 128–133, 2001
Effect of crosslink structures on dynamic mechanical properties of natural rubber vulcanizates under different aging conditions
Authors: Fan Ruliang , Zhang Yong , Huang Chen , Zhang Yinxi , Fan Yongzhong , Sun Kang
Published: August 2002

The effects of crosslink structures on the dynamic mechanical properties (DMPs) of unfilled and carbon black N330‐filled natural rubber (NR) vulcanizates cured with conventional (CV), semiefficient (SEV), and efficient (EV) cure systems and having about the same total crosslink densities were investigated before and after aerobic and anaerobic aging at 100°C. The three unfilled NR vulcanizates cured with the CV, SEV, and EV systems had about the same mechanical loss factor (tan δ) values at about 0°C but showed some apparent differences in the tan δ values in the order EV > SEV > CV at relatively high temperatures of 40–80°C before aging. However, N330‐filled NR vulcanizates gave higher tan δ values than the unfilled vulcanizates and showed little effect of the crosslink types on the tan δ at different temperatures over the glass‐transition temperature (Tg) before aging. Aerobic heat aging increased the Tg and tan δ values of the vulcanizates over a wide range of temperatures from −80 to 90°C that was mainly due to the changes in the total density and types of crosslinks. The unfilled vulcanizates cured with the CV system showed the greatest change in DMP because of their poor resistance to heat aging. Aerobic heat aging of NR vulcanizates caused a more significant change in the DMP than anaerobic heat aging because of the dominant effect of the oxidative degradation during aerobic heat aging on the main‐chain structure, crosslink structures, and DMPs of the vulcanizates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 710–718, 2001
Poly(ethylene terephthalate)/polypropylene reactive blends through isocyanate functional group
Authors: Bae Taek‐Yoon , Park Kang‐Yeol , Kim Dong‐Hyun , Suh Kyung‐Do
Published: August 2002

To evaluate the compatibilization effects of an isocyanate group on poly(ethylene terephthalate)/polypropylene (PET/PP) blends through a reactive blend, PP grafted with 2‐hydroxyethyl methacrylate‐isophorone diisocyanate (PP‐g‐HI) was prepared and blended with PET. In view of the blend morphology, the presence of PP‐g‐HI reduced the particle size of the dispersed phase by the reduced interfacial tension between the PP and PET phases, indicating the in situ copolymer (PP‐g‐PET) generated during the melt blending. The DSC thermograms for the cooling run indicated that the PET crystallization in the PP‐g‐HI rich phase was affected by the chemical reactions of PET and PP‐g‐HI. The improved mechanical properties for the PET/PP‐g‐HI blends were shown in the measurement of the tensile and flexural properties. In addition, the water absorption test indicated that the PET/PP‐g‐HI blend was more effective than the PET/PP blend in improving the water resistance of PET. The positive properties of PET/PP‐g‐HI blends stemmed from the improved compatibilization of the PET/PP blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1056–1062, 2001
Novel regenerable N‐halamine polymeric biocides. III. Grafting hydantoin‐containing monomers onto synthetic fabrics
Authors: Sun Yuyu , Sun Gang
Published: August 2002

A novel cyclic‐amine monomer, 3‐allyl‐5,5‐dimethylhydantoin (ADMH) was synthesized and characterized. ADMH alone could not be grafted onto ordinary polymers. However, the presence of triallyl‐1,3,5‐triazine‐2,4,6(1H,3H,5H)‐trione (TATAT) remarkably enhanced the ADMH grafting yield onto synthetic fabrics. The influences of reaction conditions on the grafting copolymerization were investigated. After chlorine bleach treatment, hydantoin units in the grafted copolymers were transformed into N‐halamine structures. Treated samples exhibited potent antibacterial activity against Escherichia coli, and the functional properties were shown to be durable and regenerable. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1517–1525, 2001
Solid‐state carbon‐13 NMR study of material composites based on sugarcane bagasse and thermoplastics polymers
Authors: Stael Giovanni Chaves , Tavares Maria Inês Bruno
Published: August 2002

The composites formed by sugarcane bagasse and thermoplastic polymers, such as polypropylene (PP), polyethylene (PE), and ethylene‐co‐vinyl acetate (EVA), have been analysed by carbon‐13 high‐resolution solid‐state nuclear magnetic resonance (NMR), employing crosspolarization magic angle spinning (CPMAS); variable contact‐time experiment and proton spin‐lattice relaxation time in the rotating frame. NMR responses showed that these techniques can be used to observe the degree of compatibility and homogeneity of different polymers composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2150–2154, 2001
Melt spinnable spandex fibers from segmented copolyetheresteraramids
Authors: Niesten M. C. E. J. , Krijgsman J. , Harkema S. , Gaymans R. J.
Published: August 2002

Spandex fibers were obtained by melt spinning segmented copolyetheresteramides with crystallizable aromatic diamide units of uniform length and poly(tetramethyleneoxide) segments. The aramid content was varied from 3 to 22 wt %, and the molecular weight of the polyether segment ranged from 1000 to 9000 g/mol. The influence of the spinning and drawing conditions on the fiber properties was investigated. The aromatic diamide units crystallize very fast. This made the melt spinning of the polymers easy. The aramide units were also found to be very effective in increasing the modulus. For a high elasticity a low aramid content was beneficial, and with a few percent a good elastic behavior is obtained. Orientation by drawing or a spin drawing process improves the elastic behavior. The elastic properties are compared to the values of commercial spandex fibers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2194–2203, 2001
Preparation of polymer/graphite conducting nanocomposite by intercalation polymerization
Authors: Chen Guo‐Hua , Wu Da‐Jun , Weng Wen‐Gui , Yan Wen‐Li
Published: August 2002

An in situ polymerization was conducted in the presence of expanded graphite obtained by rapid heating of the graphite intercalation compound (GIC) to form a polymer/expanded graphite conducting composite. Study showed that the graphite was dispersed in the form of nanosheets in the polymer matrix. The transition from an electrical insulator to an electrical semiconductor for the composite occurred when the expanded graphite content was 1.8 wt %, which was much lower than that of conventional conducting polymer composite. The composite exhibited high electrical conductivity of 10−2 S/cm when the graphite content was 3.0 wt %. This great improvement of conductivity could be attributed to the high aspect ratio (width‐to‐thickness) of the graphite nanosheets. Study suggested that extensive rolling of the blend greatly affected the conductivity of the composite. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2506–2513, 2001
Polyurethane–epoxy maleate of bisphenol a semi‐interpenetrating polymer networks
Authors: Cascaval Constantin N. , Ciobanu Constantin , Rosu Dan , Rosu Liliana
Published: August 2002

Semi‐interpenetrating polymer networks were synthesized starting from polyurethane (PU) and epoxy maleate of bisphenol A (EMBA). Differential scanning calorimetry and swelling measurements showed good miscibility and the presence of the strong intermolecular interactions within the synthesized networks. The physicomechanical properties increased against PU to a maximum value with the increasing of EMBA content up to 12 wt % and then decreased with further increasing EMBA content. Generally, with exception of the elongation at the limit of elasticity, the mechanical properties improved very much under action of the UV radiation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 138–144, 2002
Optimizing the balance between viscosity/modulus and impact in particulate composites
Authors: Sudduth Richard D.
Published: August 2002

The objective of this study was to develop some new concepts of importance when trying to optimize the viscosity/modulus and impact relative to the particle‐size distribution in suspensions and particulate composites. The results of this study appear to indicate that, conceptually, it is possible to significantly improve the viscosity versus the impact balance for material formulations by optimizing the particle‐size distribution. For binary particle‐size distributions, the influence of the preferred particle‐size distribution, as determined using a square‐root distribution, did not yield the most desirable particle‐size distribution if the particle‐to‐particle component of the interaction coefficient was high. However, if three or more particles were utilized in the distribution, then the optimum particle‐size distribution utilized can apparently be characterized using the square‐root distribution even when the particle–particle component, σpc, of the interaction coefficient, σ, was found to be quite high. In addition, this same square‐root particle‐size distribution can also satisfactorily predict a probability of impact that can remain consistently high as long as the particles utilized are well chosen and not too close in size. Thus, this preferred particle‐size distribution can be utilized to predict at least one of the preferred distributions to optimize the balance of properties between impact and the viscosity/modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 291–304, 2002
Manmade fibers one hundred years: Polymers and polymer design
Authors: Sikkema Doetze J.
Published: August 2002

A brief overview of a century of manmade fiber development (particularly technical, i.e., strong and high E‐modulus, fibers), emphasizing the last quarter century where the work increasingly grew in the direction of rational design of new structures, as the understanding of what makes a fiber do its job well grew. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 484–488, 2002
Swelling–shrinking hysteresis of poly(N‐isopropylacrylamide) gels in sodium dodecylbenzenesulfonate solutions
Authors: Sayil Çigdem , Okay Oguz
Published: August 2002

The swelling and shrinking behaviors of a series of poly(N‐isopropylacrylamide) (PNIPA) hydrogels are studied in aqueous solutions of sodium dodecylbenzenesulfonate (SDBS). Between 0 and 3 mol % 2‐acrylamido‐2‐methylpropanesulfonic acid sodium salt (AMPS) is used as an ionic comonomer in the hydrogel synthesis. It is shown that the collapsed PNIPA gels in water at 52°C start to swell above a critical SDBS concentration in the external solution. This critical concentration decreases as the ionic group content of PNIPA gel increases. A comparison of the swelling and shrinking experiments in SDBS solutions indicates strong hysteresis behavior of PNIPA gels. A more diluted solution is required to make a swollen gel start to reshrink than to cause gel swelling. The results show strong attractive forces between the isopropyl groups of the PNIPA network and the DB groups of SDBS molecules. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1228–1232, 2002
Transient occurrence of 27 kDa heat‐shock protein in the terminal tubule cells during postnatal development of the rat submandibular gland
Authors: Amano Osamu , Kudo Yoshinori , Shimada Mayumi , Wakayama Tomohiko , Yamamoto Miyuki , Iseki Shoichi
Published: August 2002

It has been suggested that the 27 kDa heat‐shock protein (Hsp27) plays a role at crucial cellular checkpoints for proliferation, apoptosis, and differentiation. We examined the immunolocalization of Hsp27 in the rat submandibular gland during postnatal development, wherein acinar cells proliferate and differentiate at earlier postnatal periods. At 2 weeks of age, weak Hsp27 immunoreactivity was distributed diffusely over all gland components. At 3 weeks, Hsp27 immunoreactivity disappeared in most parts of the acini and ducts, but was intensely accumulated in a small cell population located in the acinar center. This population was composed mostly of terminal tubule (TT) type I cells. At 4 weeks, the Hsp27‐immunopositive cell population in the acinar center was composed primarily of immature (type II) acinar cells, partly of immature (granulated) intercalated duct (ID) cells, and occasionally of apoptotic cells. After 5 weeks, all acinar components became mature and were no longer immunoreactive for Hsp27. When acinar cell differentiation was accelerated by administration of isoproterenol to 3‐week‐old rats for 7 days, the number of Hsp27‐positive cells was significantly lower than in the control gland at 4 weeks, confirming that Hsp27 expression is downregulated in mature acinar cells. These results suggest that at around 3–4 weeks in postnatal development, the centroacinar TT cells stop proliferating and begin to differentiate into acinar and ID cells, and occasionally undergo apoptosis. Hsp27 is transiently expressed in the centroacinar TT cells during this critical period, and thus may play a role in their differentiation into the immediate descendants. Anat Rec 264:358–366, 2001. © 2001 Wiley‐Liss, Inc.
Magnetic resonance spectroscopy of the human brain
Authors: Ross Brian , Bluml Stefan
Published: August 2002

Magnetic resonance (MR; synonymous with NMR = nuclear magnetic resonance) is a universal physical technique best known for non‐invasive detection and anatomical mapping of water protons (H). MR‐spectroscopy (MRS) records protons from tissue chemicals other than water, intrinsic phosphorus containing metabolites, sodium, potassium, carbon, nitrogen, and fluorine. MRS is therefore an imaging technique with the potential to record human and animal biochemistry in vivo. As a result of wide availability of MRI equipment in research laboratories and hospitals, MRS is a serious competitor with PET to define normal body composition and its perturbation by pharmacological and pathological events. This article describes practical aspects of in vivo MRS with particular emphasis on the brain, where novel metabolites have been described. A survey of these new aspects of neurochemistry emphasize their practical utility as neuronal and axonal markers, measures of energy status, membrane constituents, and osmolytes, as well as some xenobiotics, such as alcohol. The concept of multinuclear in vivo MRS is illustrated by diagnosis and therapeutic monitoring of several human brain disorders. Although these methods are currently most frequently encountered in human studies, as well as with transgenic and knockout mouse models, MRS adds a new dimension to anatomic and histopathologic descriptions. Anat Rec (New Anat) 265:54–84, 2001. © 2001 Wiley‐Liss, Inc.
Unfolding the human hippocampus with high resolution structural and functional MRI
Authors: Zeineh Michael M. , Engel Stephen A. , Thompson Paul M. , Bookheimer Susan Y.
Published: August 2002

The hippocampus is a region of the brain that is crucial to memory function. Functional neuroimaging allows for the noninvasive investigation of the neurophysiology of human memory by observing changes in blood flow in the brain. We have developed a technique that employs high‐resolution functional magnetic resonance imaging (fMRI) in combination with cortical unfolding to provide activation maps of the hippocampal region that surpass in anatomic and functional detail other methods of in vivo human brain mapping of the medial temporal lobe. We explain the principles behind this method and illustrate its application to a novelty‐encoding paradigm. Anat Rec (New Anat) 265:111–120, 2001. © 2001 Wiley‐Liss, Inc.
Risk factors for damage in childhood‐onset systemic lupus erythematosus: Cumulative disease activity and medication use predict disease damage
Authors: Brunner Hermine I. , Silverman Earl D. , To Theresa , Bombardier Claire , Feldman Brian M.
Published: August 2002

Objective

The Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR) Damage Index measures damage in adult patients with systemic lupus erythematosus (SLE), but its usefulness in patients with childhood‐onset SLE has not been examined. This study was conducted to evaluate the sensibility of the SLICC/ACR Damage Index, to investigate how cumulative disease activity is related to damage in childhood‐onset SLE, and to identify other risk factors for damage in childhood‐onset SLE.

Methods

Disease activity and damage in 66 patients with newly diagnosed childhood‐onset SLE were assessed retrospectively, and information on potential risk factors for damage (age, race, sex, medications, duration of disease, hypertension, body mass index, antiphospholipid antibodies, kidney disease, acute thrombocytopenia) was obtained. In addition, a group of physicians was surveyed to establish the sensibility of the SLICC/ACR Damage Index in childhood‐onset SLE.

Results

The SLICC/ACR Damage Index was found to have face, content, and construct validity when used in children. The mean SLICC/ACR Damage Index score of the patients was 1.76 (mean followup 3.3 years). Cumulative disease activity over time was the single best predictor of damage (R2 = 0.30). Other, possibly important risk factors for damage were corticosteroid treatment, the presence of antiphospholipid antibodies, and acute thrombocytopenia. It was determined that immunosuppressive agents may be protective.

Conclusion

The SLICC/ACR Damage Index, though useful in childhood‐onset SLE, may benefit from the introduction of weightings and redefinition of some of the items. Ongoing disease activity leads to disease damage, and treatment should be prompt. Prolonged use of high‐dose corticosteroids may further increase damage, but use of immunosuppressive agents may protect against disease damage; this latter finding may have potential implications for the treatment of childhood‐onset SLE and deserves further study. The relationship between disease activity and concomitant use of medication also requires further investigation.
Specific enzymatic treatment of bovine and human articular cartilage: Implications for integrative cartilage repair
Authors: Bos P. K. , DeGroot J. , Budde M. , Verhaar J. A. N. , van Osch G. J. V. M.
Published: August 2002

Objective

Chondrocyte death in articular cartilage wound edges and the subsequent lack of matrix‐producing cells in the interface area are considered to be a major cause of impaired cartilage wound healing and poor integrative cartilage repair. This study was undertaken to investigate whether enzymatic matrix digestion can be used to stimulate integrative cartilage repair via a mechanism of local increase in the amount of vital chondrocytes in cartilage wound edges.

Methods

Full‐thickness bovine articular cartilage samples were cultured in vitro for 14 days in standard medium. Samples were either left untreated or treated for 48 hours with 0.3% hyaluronidase or 30 units/ml highly purified collagenase VII. Nuclear and cytoplasmic changes were analyzed to determine cell viability, and the number of vital chondrocytes in wound edges was determined. Subsequently, we investigated whether increased chondrocyte density in the lesion edges resulted in better wound healing. Finally, full‐thickness human tibial plateau cartilage explants were tested with similar enzyme treatment protocols to determine the clinical value of our results.

Results

In bovine explants a rapid onset of chondrocyte death was observed in wound edges in all treatment groups. This led to low chondrocyte density in a band of 0–150 μm from the lesion edges in untreated and hyaluronidase‐treated explants. Treatment with 30 units/ml collagenase resulted in a significant increase in chondrocyte density in this area. The integration experiments demonstrated improved integration of the lesion edges after treatment with collagenase. In human articular cartilage an increase in chondrocyte density at the lesion edges could also be achieved, but only when proteoglycans were depleted from the wound edges prior to collagenase treatment.

Conclusion

Treatment with highly purified collagenase improves integrative cartilage repair, possibly by increasing the cell density at cartilage wound edges.
The scatter of documents over databases in different subject domains: How many databases are needed?
Authors: Hood William W. , Wilson Concepción S.
Published: August 2002

The distribution of bibliographic records in on‐line bibliographic databases is examined using 14 different search topics. These topics were searched using the DIALOG database host, and using as many suitable databases as possible. The presence of duplicate records in the searches was taken into consideration in the analysis, and the problem with lexical ambiguity in at least one search topic is discussed. The study answers questions such as how many databases are needed in a multifile search for particular topics, and what coverage will be achieved using a certain number of databases. The distribution of the percentages of records retrieved over a number of databases for 13 of the 14 search topics roughly fell into three groups: (1) high concentration of records in one database with about 80% coverage in five to eight databases; (2) moderate concentration in one database with about 80% coverage in seven to 10 databases; and (3) low concentration in one database with about 80% coverage in 16 to 19 databases. The study does conform with earlier results, but shows that the number of databases needed for searches with varying complexities of search strategies, is much more topic dependent than previous studies would indicate.
Maximum likelihood estimation of a latent variable time‐series model
Authors: Bartolucci Francesco , De Luca Giovanni
Published: August 2002

Recently, Fridman and Harris proposed a method which allows one to approximate the likelihood of the basic stochastic volatility model. They also propose to estimate the parameters of such a model maximising the approximate likelihood by an algorithm which makes use of numerical derivatives. In this paper we propose an extension of their method which enables the computation of the first and second analytical derivatives of the approximate likelihood. As will be shown, these derivatives may be used to maximize the approximate likelihood through the Newton–Raphson algorithm, with a saving in the computational time. Moreover, these derivatives approximate the corresponding derivatives of the exact likelihood. In particular, the second derivative may be used to compute the standard error of the estimator and confidence intervals for the parameters. The paper presents also the results of a simulation study which allows one to compare our approach with other existing approaches. Copyright © 2001 John Wiley & Sons, Ltd.
Statistical challenges in credit card issuing
Authors: Lucas Alan
Published: August 2002

The credit card industry is awakening to the fact that the vast amounts of data it has on its customers should be treated as a valuable asset and that extracting knowledge from this data is crucial if one wants to optimize ones credit book. The company I work for—Barclaycard has over 7 million customers and over 9 million credit cards in circulation and deals with over 300 million credit card transactions per annum—a tremen dous amount of data. This paper is intended to provide a flavour of some of the statistical work that is required to take advantage of this asset. The suggestions are only the tip of the iceberg. Credit cards are a complex business. A factor that makes up this complexity is that credit card customers use their cards for a number of non‐credit reasons, namely: payment convenience, smoothing of finances, paying regular bills, emergencies and spontaneous spending. Moreover, managing customers implies balancing revenue, churn and bad debt issues, and the explosion of competetion in recent years is making it more difficult to attract and retain profitable, low‐risk customers. In the paper I will examine the traditional statistical methodology behind the issue of credit, along with some of the problems that have been solved and some that are still outstanding. The paper then provides an overview of the new Customer Value Management paradigm, also known as Customer Relationship Management (CRM), highlighting the new challenges that have emanated from this and the implications for statisticians. Copyright © 2001 John Wiley & Sons, Ltd.
Increased mouse survival, tumor growth inhibition and decreased immunoreactive p53 after exposure to magnetic fields
Authors: Tofani Santi , Cintorino Marcella , Barone Domenico , Berardelli Michele , De Santi Maria Margherita , Ferrara Adriana , Orlassino Renzo , Ossola Piero , Rolfo Katia , Ronchetto Flavio , Tripodi Sergio Antonio , Tosi Piero
Published: August 2002

The possibility that magnetic fields (MF) cause antitumor activity in vivo has been investigated. Two different experiments have been carried out on nude mice bearing a subcutaneous human colon adenocarcinoma (WiDr). In the first experiment, significant increase in survival time (31%) was obtained in mice exposed daily to 70 min modulated MF (static with a superimposition of 50 Hz) having a time average total intensity of 5.5 mT. In the second independent experiment, when mice bearing tumors were exposed to the same treatment for four consecutive weeks, significant inhibition of tumor growth (40%) was reported, together with a decrement in tumor cell mitotic index and proliferative activity. A significant increase in apoptosis was found in tumors of treated animals, together with a reduction in immunoreactive p53 expression. Gross pathology at necroscopy, hematoclinical/hematological and histological examination did not show any adverse or abnormal effects. Since pharmacological rescue of mutant p53 conformation has been recently demonstrated, the authors suggest that MF exposure may obtain a similar effect by acting on redox chemistry connected to metal ions which control p53 folding and its DNA‐binding activity. These findings support further investigation aimed at the potential use of magnetic fields as anti‐cancer agents. Bioelectromagnetics 23:230–238, 2002. © 2002 Wiley‐Liss, Inc.
Genotoxicity of radiofrequency signals. I. Investigation of DNA damage and micronuclei induction in cultured human blood cells
Authors: Tice Raymond R. , Hook Graham G. , Donner Maria , McRee Donald I. , Guy Arthur W.
Published: August 2002

As part of a comprehensive investigation of the potential genotoxicity of radiofrequency (RF) signals emitted by cellular telephones, in vitro studies evaluated the induction of DNA and chromosomal damage in human blood leukocytes and lymphocytes, respectively. The signals were voice modulated 837 MHz produced by an analog signal generator or by a time division multiple access (TDMA) cellular telephone, 837 MHz generated by a code division multiple access (CDMA) cellular telephone (not voice modulated), and voice modulated 1909.8 MHz generated by a global system of mobile communication (GSM)‐type personal communication systems (PCS) cellular telephone. DNA damage (strand breaks/alkali labile sites) was assessed in leukocytes using the alkaline (pH>13) single cell gel electrophoresis (SCG) assay. Chromosomal damage was evaluated in lymphocytes mitogenically stimulated to divide postexposure using the cytochalasin B‐binucleate cell micronucleus assay. Cells were exposed at 37±1°C, for 3 or 24 h at average specific absorption rates (SARs) of 1.0–10.0 W/kg. Exposure for either 3 or 24 h did not induce a significant increase in DNA damage in leukocytes, nor did exposure for 3 h induce a significant increase in micronucleated cells among lymphocytes. However, exposure to each of the four RF signal technologies for 24 h at an average SAR of 5.0 or 10.0 W/kg resulted in a significant and reproducible increase in the frequency of micronucleated lymphocytes. The magnitude of the response (approximately four fold) was independent of the technology, the presence or absence of voice modulation, and the frequency (837 vs. 1909.8 MHz). This research demonstrates that, under extended exposure conditions, RF signals at an average SAR of at least 5.0 W/kg are capable of inducing chromosomal damage in human lymphocytes. Bioelectromagnetics 23:113–126, 2002. © 2002 Wiley‐Liss, Inc.
The intestinal epithelial stem cell
Authors: Marshman Emma , Booth Catherine , Potten Christopher S.
Published: August 2002

This article considers the role of the adult epithelial stem cell, with particular reference to the intestinal epithelial stem cell. Although the potential of adult stem cells has been revealed in a number of recent publications, the organization and control of the stem cell hierarchy in epithelial tissues is still not fully understood. The intestinal epithelium is an excellent model in which to study such hierarchies, having a distinctive polarity and high rate of cell proliferation and migration. Studies on the small intestinal crypt provide insight into the characteristics of the stem cells in normal and regenerating circumstances and demonstrate why a thorough understanding of these cells is an essential pre‐requisite for stem cell based therapeutic approaches. BioEssays 24:91–98, 2002. © 2002 John Wiley & Sons, Inc.
Synaptic modification in neural circuits: A timely action
Authors: Berninger Benedikt , Bi Guo‐Qiang
Published: August 2002

Long‐term modification of synaptic strength is thought to be the basic mechanism underlying the activity‐dependent refinement of neural circuits and the formation of memories engrammed on them. Studies ranging from cell culture preparations to humans subjects indicate that the decision of whether a synapse will undergo strengthening or weakening critically depends on the temporal order of presynaptic and postsynaptic activity. At many synapses, potentiation will be induced only when the presynaptic neuron fires an action potential within milliseconds before the postsynaptic neuron fires, whereas weakening will occur when it is the postsynaptic neuron that fires first. Such processes might be important for the remodeling of neural circuits by activity during development and for network functions such as sequence learning and prediction. Ultimately, this synaptic property might also be fundamental for the cognitive process by which we structure our experience through cause and effect relations. BioEssays 24:212–222, 2002. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/bies.10060
Putting its fingers on stressful situations: the heavy metal‐regulatory transcription factor MTF‐1
Authors: Lichtlen P. , Schaffner W.
Published: August 2002

It has been suggested that metallothioneins, discovered about 45 years ago, play a central role in heavy metal metabolism and detoxification, and in the management of various forms of stress. The metal‐regulatory transcription factor‐1 (MTF‐1) was shown to be essential for basal and heavy metal‐induced transcription of the stress‐responsive metallothionein‐I and metallothionein‐II. Recently it has become obvious that MTF‐1 has further roles in the transcriptional regulation of genes induced by various stressors and might even contribute to some aspects of malignant cell growth. Furthermore, MTF‐1 is an essential gene, as mice null‐mutant for MTF‐1 die in utero due to liver degeneration. We describe here the state of knowledge on the complex activation of MTF‐1, and propose a model with MTF‐1 as an interconnected cellular stress‐sensor protein involved in heavy metal metabolism, hepatocyte differentiation and detoxification of toxic agents. BioEssays 23:1010–1017, 2001. © 2001 John Wiley & Sons, Inc.
Conformational changes of enzymes adsorbed at liquid– solid interface: Relevance to enzymatic activity
Authors: Noinville S. , Revault M. , Baron M.‐H.
Published: August 2002

FTIR with attenuated total reflectance spectroscopy was used to study in situ adsorption of enzymes at water–solid interfaces to better understand how conformational changes may monitor enzymatic activity. Because the adsorption process depends on hydrophobic and electrostatic interactions, conformational changes were studied as a function of the nature of the adsorbing substrates, which are hydrophobic or hydrophilic in character. The adsorption kinetics of two examples of serine enzymes, α‐chymotrypsin (α‐chym) and Humicola lanuginosa lipase (HLL), were studied. The secondary structure and solvation of the adsorbed enzymes were both compared to the dissolved enzymes. The positively charged α‐ chym was adsorbed on a negatively charged hydrophilic support with minor structural changes, but the negatively charged lipase had no affinity for a similar support. Both enzymes were strongly retained on the hydrophobic support. The secondary and tertiary structures of the α‐chym adsorbed on the hydrophobic support were strongly altered, which correlates to the inhibition of enzymatic hydrolysis. The specific solvation obtained for the adsorbed HLL is consistent with the existence of the open conformer in relation to the enhanced enzymatic activity at the water–hydrophobic interface. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 67: 323–326, 2002
Analysis of biological wastewater treatment processes using multicomponent gas phase mass balancing
Authors: Gapes Daniel , Keller Jurg
Published: August 2002

A reactor system using off‐gas analysis was developed for analyzing wastewater treatment process reactions. Using a mass spectrometer for the gas analysis provides the ability to simultaneously measure several gas components (such as oxygen, nitrogen, carbon dioxide, and argon). One of the benefits of the reactor design was the precise control of the dissolved oxygen concentration, uncoupled from the system turbulence, which was controlled via a gas recycle loop. This feature allowed control of the turbulence within the reactor without any need for mechanical stirring. Using oxygen as the test gas, the reactor was shown to perform well in the measurement of oxygen uptake rate of nitrifying activated sludge. The oxygen uptake rate calculations were made using a simple calibration method developed for the reactor system. The reactor was able to provide precise and accurate results for this test case. Furthermore, the system was capable of measuring under dynamic process conditions, as well as when the process rates were constant (steady state). © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 76: 361–375, 2001.
Optimization of L‐phenylalanine production of Corynebacterium glutamicum under product feedback inhibition by elevated oxygen transfer rate
Authors: Shu Chin‐Hang , Liao Chii‐Cherng
Published: August 2002

Production feedback inhibition both on cell growth and on product formation of phenylalanine fermentation might be alleviated by elevated oxygen supply. Batch fermentations by a high phenylalanine producing strain Corynebacterium glutamicum CCRC 18335 at various initial phenylalanine concentrations (P0) ranging from 0 to 20 g/L and different oxygen transfer rate coefficients (KLa) ranging from 23 to 76 h−1 were studied. The fermentation parameters with respect to P0 were strongly dependent on KLa. Cell yield favored higher KLa and lower P0. Product yield with respect to varying phenylalanine concentration was evaluated by the relative oxygen availability (ROA). The optimal ROA for phenylalanine formation was strongly dependent on the product concentration. While P0 was low, the product inhibition was less significant and the maximum product yield occurred while ROA was at 0.5–0.6. While P0 was high, the product inhibition was significant and the maximum product yield occurred while ROA was at 0.8–0.9. These results suggest that the product feedback inhibition of phenylalanine fermentation processes can be alleviated by a gradual increase in oxygen supply rate while the increasing product concentration is taken into account. The strategy is demonstrated in a fed‐batch culture with elevated oxygen supply. The final phenylalanine concentration was 23.2 g/L, which was 45% better than that of the fed‐batch fermentation without elevated oxygen supply. Likewise, the maximum productivity was improved by 42% at 0.37 g/(L · h). © 2002 John Wiley & Sons, Inc. Biotechnol Bioeng 77: 131–141, 2002.
Use of isolated cyclohexanone monooxygenase from recombinant Escherichia coli as a biocatalyst for Baeyer–Villiger and sulfide oxidations
Authors: Zambianchi F. , Pasta P. , Carrea G. , Colonna S. , Gaggero N. , Woodley J. M.
Published: August 2002

The performance, in Baeyer–Villiger and heteroatom oxidations, of a partially purified preparation of cyclohexanone monooxygenase obtained from an Escherichia coli strain in which the gene of the enzyme was cloned and overexpressed was investigated. As model reactions, the oxidations of racemic bicyclo[3.2.0]hept‐2‐en‐6‐one into two regioisomeric lactones and of methyl phenyl sulphide into the corresponding (R)‐sulphoxide were used. Enzyme stability and reuse, substrate and product inhibition, product removal, and cofactor recycling were evaluated. Of the various NADPH regeneration systems tested, 2‐propanol/alcohol dehydrogenase from Thermoanerobium brockii appeared the most suitable because of the low cost of the second substrate and the high regeneration rate. Concerning enzyme stability, kosmotropic salts were the only additives able to improve it (e.g., half‐life from 1 day in diluted buffer to 1 week in 1 M sodium sulphate) but only under storage conditions. Instead, significant stabilization under working conditions was obtained by immobilization on Eupergit C (half‐life approximately 2.5 days), a procedure that made it possible to reuse the catalyst up to 16 times with complete substrate (5 g·L−1) conversion at each cycle. Reuse of free enzyme was also achieved in a membrane reactor but with lower efficiency. Water‐organic solvent biphasic systems, which would overcome substrate inhibition and remove from the aqueous phase, where reaction takes place, the formed product, were unsuccessful because of their destabilizing effect on cyclohexanone monooxygenase. More satisfactory was continuous substrate feeding, which shortened reaction times and, very importantly, yielded in the case of bicyclo[3.2.0]hept‐2‐en‐6‐one (10 g·L−1) both lactone products with high optical purity (enantiomeric excess ≥96%), which was not the case when all of the substrate was added in a single batch. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 489–496, 2002.
Effect of oxygen transfer on glycerol biosynthesis by an osmophilic yeast Candida magnoliae I2B
Authors: Sahoo Debendra K. , Agarwal Gopal P.
Published: August 2002

The influence of oxygen on glycerol production by an osmophilic yeast, Candida magnoliae I2B, was studied in a bioreactor. Oxygen transfer rates (OTRs) and volumetric oxygen transfer coefficients (kLa) were determined at different aeration and agitation rates. Cell growth as well as glycerol production was strongly affected by oxygen supply. Improvement in OTRs resulted in increased cell growth and glycerol yield. However, at high OTRs, there was a reduction in glucose uptake rate, indicating Pasteur Effect, and glycerol accumulation was also reduced at kLa of 253 h−1. The availability of oxygen per unit of cell mass was found to be the most important factor that controlled cell growth, glucose uptake, and glycerol yield. The overall productivity and yield of glycerol could be related with kLa. The biosynthesis of glycerol was found to both growth‐ and non‐growth‐associated, although glycerol was mainly produced in post‐exponential phase. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 545–555, 2002.