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  • Polymer and Materials Science  (5)
  • Key words Articular chondrocytes • Hydrostatic ¶pressure • Alginate • Oxygen partial-pressure • Redifferentiation  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Die Redifferenzierung von dedifferenzierten Gelenkknorpelzellen in Alginatkultur (2000)
    Springer
    Der Orthopäde 29 (2000), S. 91-99 
    Details
    ISSN: 1433-0431
    Keywords: Schlüsselwörter Gelenkknorpelzellen • Hydrostatischer ¶Druck • Alginat • Sauerstoffpartialdruck •¶Redifferenzierung ; Key words Articular chondrocytes • Hydrostatic ¶pressure • Alginate • Oxygen partial-pressure • Redifferentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary One of the goals in the field of tissue engineering is the development of artificial cartilage for the treatment of cartilage defects. Therefore autologous chondrocytes are seeded on different artificial matrices to test their possible use as implants (resorption, antigenicity, toxicity and their integration in the tissue). One of the main problems in these experiments is that usually the amount of available chondrocytes is too low for treating large-scale defects or for comparing different matrices. An in-vitro-multiplication of the cells is needed which causes the chondrocytes to dedifferentiate and become fibroblast-like. Therefore parameters which induce a redifferentiation are of great interest. The objective of this study was to determine the influence of intermittent hydrostatic pressure and low oxygen partial pressure on the redifferentiation of dedifferentiated bovine articular chondrocytes in monolayer and three-dimensional alginate bead culture. The redifferentiation process was monitored by immunocytochemical detection of newly synthesized collagen type II. The viability of the cells was determined by the trypanblue exclusion test. The chondrocytes were dedifferentiated by a two week culture in plastic flasks with an oxygen level of 20 %. After this they were subcultured in monolayer or three-dimensional alginate culture and subjected to three different stimuli for three weeks in order to redifferentiate: 1.) 20 % O2 (= 20,26 kPa Po2) + 5 % CO2 + 75 % N2; 2.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2; 3.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2 + 8 h/d of intermittent hydrostatic pressure (frequency: 3 bar absolute for 30 min and 1 bar absolute for 2 min). In the monolayer there was no detectable collagen type II found by immunocytochemistry under either of the three culture conditions. Therefore a redifferentiation of dedifferentiated chondrocytes was not possible in monolayer cultures with the tested parameters. In the three-dimensional alginate culture there was no immunocytochemical staining of collagen type II found in the beads cultured with 20 % oxygen. With 5 % oxygen we found a strong collagen type II-production by chondrocytes throughout the whole bead. The intermittent hydrostatic pressure combined with 5 % oxygen lead to a decreased collagen type II-production compared to cells subjected to 5 % oxygen only. Also chondrocytes closer to the edge of these beads were more often immunopositive and seemed to produce more immunoreactive collagen type II. The viability of the chondrocytes in the alginate culture was close to 90 % after three weeks. Our experiments showed that oxygen partial pressure is an important parameter in the cultivation of articular chondrocytes. Reduced partial oxygen pressure promoted or induced the redifferentiation of dedifferentiated chondrocytes in alginate culture.
    Notes: Zusammenfassung Im Bereich des sog. „tissue engineering“ wird derzeit an einem künstlichen Knorpelersatz gearbeitet, der zur Deckung von Defekten im Gelenkknorpel verwendet werden soll. Meist werden dabei verschiedene künstliche Matrices in vitro mit autologen Chondrozyten besiedelt und auf ihre Verwendbarkeit als Implantat (Resorbierbarkeit, Antigenität, Toxizität und Integration in bestehendes Gewebe) hin untersucht. Oft ist bei diesen Untersuchungen die zur Verfügung stehende autologe Knorpelzellmenge zu gering, um größere Defekte behandeln oder verschiedene Matrices miteinander vergleichen zu können. Daher ist eine In-vitro-Vermehrung der Chondrozyten notwendig, bei der die Zellen jedoch gleichzeitig dedifferenzieren und fibroblastenartig werden. Deshalb ist es von Interesse, Parameter zu untersuchen, die eine Redifferenzierung induzieren. Das Ziel dieser Untersuchung war es, den Einfluss von intermittierendem hydrostatischem Druck und niedrigem Sauerstoffpartialdruck auf die Redifferenzierung von Rindergelenkknorpelzellen im Monolayer und in dreidimensionaler (3-D-)Alginatkultur zu testen. Der Redifferenzierungsprozess wurde durch immunzytochemischen Nachweis von Typ-II-Kollagen überprüft. Die Vitalität der Zellen wurde mit Hilfe des Trypan-Blau-Ausschlusstests bestimmt. Die Chondrozyten wurden durch 2wöchige Kultur in Plastikflaschen bei 20 % O2 dedifferenziert. Danach wurden sie als Monolayer oder 3-D-Alginatkultur subkultiviert und für 3 Wochen 3 unterschiedlichen Stimuli zum Zwecke der Redifferenzierung ausgesetzt: 1.) 20 % O2 (= 20,26 kPa Po2) + 5 % CO2 + 75 % N2; 2.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2; 3.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2 + 8 h intermittierende hydrostatische Druckbelastung (Frequenz: 30 min Belastung bei 3 bar absolut und 2 min Entlastung bei 1 bar absolut) pro Tag. Im Monolayer konnte nach 3 Wochen für keine der 3 Kulturbedingungen immunzytochemisch neusynthetisiertes Typ-II-Kollagen nachgewiesen werden. Daher scheint eine Redifferenzierung der dedifferenzierten Chondrozyten im Monolayer unter den untersuchten Bedingungen nicht möglich zu sein. In der 3-D-Alginatkultur wurde bei den bei 20 % O2 gehaltenen Chondrozyten kein immunzytochemisch detektierbares Typ-II-Kollagen gefunden. Bei 5 % O2 war eine starke Typ-II-Produktion in der gesamten Kugel zu verzeichnen. Im Vergleich zu diesen zeigten Chondrozyten aus Kugeln, die zusätzlich noch mit intermittierendem hydrostatischem Druck behandelt wurden, eine geringere Typ-II-Kollagenproduktion (sowohl im Bezug auf die Menge der Immunfärbung als auch auf die Anzahl der Typ-II-produzierenden Zellen) und eine Häufung der positiven Zellen im Randbereich der Kugel. Die Vitalität der Zellen in den Alginatkugeln lag nach 3 Wochen bei ca. 90 %. Unsere Untersuchungen haben gezeigt, dass der Sauerstoffpartialdruck ein wichtiger Parameter in der Kultivierung von Gelenkknorpelzellen darstellt. Ein reduzierter Sauerstoffpartialdruck förderte oder induzierte die Redifferenzierung von dedifferenzierten Chondrozyten in Alginatkultur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003716
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of poly(3,3-bisethoxymethyl oxetane) and poly(3,3-bisazidomethyl oxetane) and their block copolymers (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 37 (1989), S. 267-281 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The homopolymers, poly(3,3-bisethoxymethyl oxetane) (polyBEMO), poly(3,3-bisazidomethyl oxetane) (polyBAMO), and triblock copolymers based on these homopolymers and a statistical copolymer center block composed of BAMO and 3-azidomethyl-3-methyl oxetane AMMO were synthesized and characterized by differential scanning calorimetry, modulus-temperature, optical microscopy, membrane osmometry, and solution and melt viscosity. The values of K and a for the Mark-Houwink equation were found to be 7.29 × 10-3 mL/g and 0.80, respectively, for polyBEMO at 25°C using number-average molecular weights. Glass transition temperatures were in the range -25 to -40°C and melting temperatures were between 65 and 90°C for all polymers. The melting temperature was found to increase as expected with molecular weight. Melt viscosities of triblock copolymers with polyBAMO end blocks were at least an order of magnitude lower than those with polyBEMO end blocks and clear optically, suggesting that the polyBAMO-based triblock copolymers formed one phase in the melt, while the polyBEMO-based triblock materials (milk white) phase separated. The addition of filler raised the melt viscosity to a level between that predicted by the Guth-Smallwood and the Mooney equations.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1989.070370121
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  • 3
    Electronic Resource
    Electronic Resource
    Multiple endotherm melting behavior in relation to the morphology of poly[3,3- bis(ethoxymethyl) oxetane] (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 40 (1990), S. 1379-1390 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two crystalline melting peaks have been observed by differential scanning calorimetry for low molecular weight poly[3,3-bis(ethoxymethyl) oxetane] (polyBEMO) samples, Mn 〈 1 × 104 g/mol, whereas only one melting peak has been observed for samples of higher molecular weight, Mn 〈 1 × 104 g/mol. Crystallization of low molecular weight samples at large supercoolings produces the lower melting form while low supercooling or annealing favors the higher melting species. Enthalpy of fusion values obtained by DSC for a multiple melting endotherm sample range from 28 to 39 J/g for crystallization temperatures from 58 to 35°C, respectively. Optical microscopy studies indicate that the lower melting peak corresponds to a spherulitic type morphology and the higher melting peak correlates to a fine grained crystal structure. Wide angle X-ray powder diffraction studies do not detect differences in the crystal structures of samples exhibiting either one or two melting peaks, which suggests that the multiple melting phenomenon is due to differences in morphology rather than the presence of different crystal forms.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1990.070400724
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  • 4
    Electronic Resource
    Electronic Resource
    Evaluation of the area under linear loss modulus-temperature curves (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 1617-1623 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The area under the linear loss modulus-temperature curves, LA, has been shown to be related to the chemical composition of the material. In addition, it can be significantly affected by morphology in multicomponent polymer systems. To characterize LA quantitatively, base-line corrections for instrumental contributions to LA were evaluated by several different methods and the results compared. In some instances, the calculation method affects only the LA magnitude, while general trends are unchanged; whereas in others, qualitative differences also become important. Not all of the methods described can be utilized universally. However, a straight-line-type of base line, similar to that which is used in infrared spectroscopy and differential scanning calorimetry, provides a widely applicable means of quantifying the loss area.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1991.070430905
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  • 5
    Electronic Resource
    Electronic Resource
    Factors which affect the glass transition and damping capability of polymers (1991)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 2 (1991), S. 49-56 
    Details
    ISSN: 1042-7147
    Keywords: Damping ; Glass transition ; IPNs ; Loss modulus ; Morphology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The shape of the glass transition plays a critical role in the engineering performance of polymers in sound and vibration damping, as well as other applications. The transition may be affected by fillers, plasticizers, blending, IPN formation, etc. A collection of data, both original and literature, is presented which illustrates how the phenomenon works. Emphasis is placed on the role of the area under the linear loss modulus-temperature curve, which may be evaluated in a fashion similar to other spectroscopic techniques. In addition, the loss area can be significantly affected by morphological factors.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1991.220020107
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  • 6
    Electronic Resource
    Electronic Resource
    The influence of the equilibrium melting temperature on the supermolecular morphology of several polymers (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 48 (1993), S. 1321-1329 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: At a constant isothermal crystallization temperature (Tc), the crystalline morphologies of several polymers have been found to be a function of the melt-liquid temperature (T1). At a constant Tc below a critical crystallization temperature (T*c [about 0.9 T*m(K)], a transition from a nonspherulitic to a spherulitic morphology occurs when the melt liquid is heated above a melt-liquid transition temperature, (Tlt) [approximately 1.03 Tm (K)], where Tm is the observed melting temperature of the sample. The melt-liquid transition temperature, Tlt, which experimentally affects the visible morphology of a semicrystalline polymer, is apparently indistinguishable from the thermodynamic melting temperature, T*m, determined by the Hoffman-Weeks procedure. The X-ray powder diffraction patterns of spherulitic and nonspherulitic morphologies were identical, independent of the heating-cooling cycle. This suggests that the transition that occurs at TIt does not affect the arrangement of polymer molecules in the crystallite, but only the manner in which the crystallites are arranged in the supermolecular morphology. The evidence suggests, at least for the polymers studied, that a residual order exists in the melt until the T*m or TIt of the particular polymer is reached. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070480802
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