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  • 1
    Electronic Resource
    Electronic Resource
    Bioreactor based on suspended particles of immobilized enzyme (1993)
    Springer
    Annals of biomedical engineering 21 (1993), S. 57-65 
    Details
    ISSN: 1573-9686
    Keywords: Immobilized enzyme reactor ; Particle suspension ; Secondary flows ; Blood deheparinization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A bioreactor for blood detoxification was developed in which oscillation-induced secondary flows suspend particles of immobilized enzyme in a reactor operating at clinically useful flowrates. Torsional oscillation of the reactor about its axis created a pair of counterrotating toroidal vortices which were readily observed in flow-visualization studies. Oscillation frequencies were selected to provide spatially uniform particle dispersion, as assessed visually. As a model system, blood deheparinization by reactors containing heparinase immobilized to agarose particles was investigated. Identical deheparinization profiles were observed in the continuous-flow reactor and in independent batch studies, done in well mixed test tubes of blood, demonstrating that the oscillating reactor design minimizes external mass transfer limitations. Identical heparin neutralization profiles and rates were also observed in the first and the second of consecutive heparin neutralization studies (0–2h and 2–4h, respectively) demonstrating an effective half-life of the immobilized enzyme in the oscillating reactor of at least 4 h. No significant decrease in red or white blood cell count, platelet count, or hematocrit, and clinically acceptable levels of plasma hemoglobin and activated complement were observed with 2 h (20 passes) ofin vitro recirculation of human blood through the reactor. High, stable efficacy, operational stability, and excellent biocompatibility are attributed to secondary flow induced liquid-particle mixing within the oscillating reactor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368165
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics of immobilized heparinase in human blood (1993)
    Springer
    Annals of biomedical engineering 21 (1993), S. 67-76 
    Details
    ISSN: 1573-9686
    Keywords: Immobilized enzyme reactor ; Heparinase kinetics ; Blood deheparmization ; Bioreactor modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Immobilized enzyme reactors can form the basis of useful blood detoxification systems. One such reactor was developed for heparin neutralization by immobilized heparinase. In this article, reactor kinetics were studied under clinically relevant conditions. Heparin neutralization was assessedin vitro in whole human blood using (a) a well-mixed batch reactor, and (b) an oscillating, continuous-flow reactor. The kinetics of heparin neutralization in human blood were first order over the entire range of heparin and enzyme concentrations and particle fractions tested. The kinetic rate was not sensitive to physiological variations in the concentration of antithrombin, a heparin binding protein in blood. Enzyme activity did not decrease significantly over the 2 hour test period. Kinetic control of the system with minimal intraparticle diffusional limitations was suggested by the Thiele moduli (0.11–0.67) and effectiveness factors (0.98±0.01). The ratio kcat/Km obtained in batch studies was 0.0028±0.0008 cm3/μg-min. A continuous-flow oscillating reactor within a closed recirculation loop performed as a single well mixed batch reactor; there was a short mixing time of recirculating blood when compared to reaction time. A model based on this mixing pattern and the kinetics obtained in independent batch studies accurately predicted heparin neutralization profiles observed in the continuous-flow system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368166
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  • 3
    Electronic Resource
    Electronic Resource
    Composition of cell-polymer cartilage implants (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 605-614 
    Details
    ISSN: 0006-3592
    Keywords: tissue engineering ; cartilage regeneration ; polyglycolic acid ; glycosaminoglycan ; collagen ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cartilage implants for potential in vivo use for joint repair or reconstructive surgery can be created in vitro by growing chondrocytes on biodegradable polymer scaffolds. Implants 1 cm in diameter by 0.176 cm thick were made using isolated calf chondrocytes and polyglucolic acid (PGA). By 6 weeks, the total amount of glycosaminoglycan (GAG) and collagen (types I and II) increased to 46% of the implant dry weight; there was a corresponding decrease in the mass of PGA. Implant biochemical and histological compositions depended on initial cell density, scaffold thickness, and the methods of cell seeding and implant culture. Implants seeded at higher initial cell densities reached higher GAG contents (total and per cell), presumably due to cooperative cell-to-cell interactions. Thicker implants had lower GAG and collagen contents due to diffusional limitations.Implants that were seeded and cultured under mixed conditions grew to be thicker and more spatially uniform with respect to the distribution of cells, matrix, and remaining polymer than those seeded and/or cultured statically. Implants from mixed cultures had a 20-40-μm thick superficial zone of flat cells and collagen oriented parallel to the surface and a deep zone with perpendicular columns of cells surrounded by GAG Mixing during cell seeding and culture resulted in a more even cell distribution ad enhanced nutrient diffusion which could be related to a more favorable biomechanical environment for chondrogenesis. Cartilage with appropriate for and function for in vivo implantation ca thus be created by selectively stimulating the growth and differentiated function of chondrocytes (i.e., GAG and collagen synthesis) through optimization of the in vitro culture environment. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260430710
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of chondrocyte growth in cell-polymer implants (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 597-604 
    Details
    ISSN: 0006-3592
    Keywords: chondrocyte ; cartilage ; tissue engineering ; cell growth kinetics ; culture conditions ; diffusional limitations ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In vitro cultivation of cartilage cells (chondrocytes) on biodegradable polyglycolic acid (PGA) scaffolds resulted in implants which could potentially be used to repair damaged joint cartilage or for reconstructive surgery. Cell growth kinetics were studied to define conditions under which the cellularity of implants made from isolated calf chondrocytes reached that of the parent calf cartilage. In static cultures, condrocyte growth rates decreased as either implant thickness or implant cell density increased. Over 4 weeks of cultivation, implant permeability to glucose decreased to 3% that of the plain polymer scaffold; this effect was attributed to the decrease in effective implant porosity associated with cartilage tissue regeneration.In a well-mixed culture, implants 1 cm in diameter by 0.3 cm thick maintained high cell growth rates over 7 weeks and hard normal cell densities. Regenerated cartilage with these dimensions is large enough to resurface small joints such as the trapezium bone at the base of the human thumb. Such implants could not be grown statically, since cell growth stopped at 3-4 weeks and cell densities remained below normal. Optimization of the tissue culture environment is thus essential in order to cultivate clinically useful cartilage implants in vitro. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260430709
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  • 5
    Electronic Resource
    Electronic Resource
    Cultivation of cell-polymer tissue constructs in simulated microgravity (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 46 (1995), S. 306-313 
    Details
    ISSN: 0006-3592
    Keywords: tissue engineering ; chondrocyte ; polymer scaffold ; microgravity bioreactor ; rotating vessel ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Tissue-engineered cartilage was cultivated under conditions of simulated microgravity using rotating bioreactors. Rotation randomized the effects of gravity on inoculated cells (chondrocytes) and permitted their attachment to three-dimensional (3D) synthetic, biodegradable polymer scaffolds that were freely suspended within the vessel. After 1 week of cultivation, the cells regenerated a cartilaginous extracellular matrix (ECM) consisting of glycosaminoglycan (GAG) and collagen types I and II. Tissue constructs grown in simulated microgravity had higher GAG contents and thinner outer capsules than control constructs grown in turbulent spinner flasks. Two fluid dynamic regimes of simulated microgravity were identified, depending on the vessel rotation speed: (i) a settling regime in which the constructs were maintained in a state of continuous free-fall close to a stationary point within the vessel and (ii) an orbiting regime in which the constructs orbited around the vessel spin axis. In the settling regime, the numerically calculated relative fluid-construct velocity was comparable to the experimentally measured construct settling velocity (2-3 cm/s). A simple mathematical model was used in conjunction with measured construct physical properties to determine the hydrodynamic drag force and to estimate the hydrodynamic stress at the construct surface (1.5 dyn/cm2). Rotating bioreactors thus provide a powerful research tool for cultivating tissue-engineered cartilage and studying 3D tissue morphogenesis under well-defined fluid dynamic conditions. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260460403
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  • 6
    Electronic Resource
    Electronic Resource
    Cultivation of cell-polymer cartilage implants in bioreactors (1993)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 51 (1993), S. 257-264 
    Details
    ISSN: 0730-2312
    Keywords: bioreactor ; chondrocyte ; chondrogenesis ; tissue engineering ; cartilage ; joint repair ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Cartilage implants for potential use in reconstructive or orthopedic surgery can be created by growing isolated cartilage cells (chondrocytes) in vitro on synthetic, biodegradable polymer scaffolds. The scaffolds provide specific three-dimensional structures which support cell proliferation and biodegrade in a controlled fashion in parallel to cellular regeneration of cartilaginous tissue. Cartilage implants based on chondrocytes and fibrous polyglycolic acid scaffolds were recently shown to closely resemble normal cartilage histologically as well as with respect to cell density and matrix composition (collagen, glycosaminoglycan) [Freed et al., J Biomed Mater Res 27:11-23, 1993a]. These findings form the basis for developing straightforward procedures to obtain implants for clinical use from small, autologous cartilage specimens without any limitations in terms of availability of donor tissue or implant dimensions.Chondrocyte growth and cartilage matrix regeneration on polymer scaffolds are interdependent and also depend on in vitro tissue culture conditions. Under static culture conditions, cell growth rates are diffusionally limited due to increasing cell mass and decreasing effective implant porosity resulting from cartilage matrix regeneration. Optimization of the in vitro culture environment is thus essential for the cultivation of large, clinically useful cartilage implants. Preliminary studies indicate that major improvements can be achieved using bioreactors that provide efficient mass transfer and controlled shear rates at the cell and implant surfaces. © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240510304
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  • 7
    Electronic Resource
    Electronic Resource
    Neocartilage formation in vitro and in vivo using cells cultured on synthetic biodegradable polymers (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 11-23 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Cartilaginous implants for potential use in reconstructive or orthopedic surgery were created using chondrocytes grown on synthetic, biodegradable polymer scaffolds. Chondrocytes isolated from bovine or human articular or costal cartilage were cultured on fibrous polyglycolic acid (PGA) and porous poly(L)lactic acid (PLLA) and used in parallel in vitro and in vivo studies. Samples were taken at timed intervals for assessment of cell number and cartilage matrix (sulfated glycosaminoglycan [S-GAG], collagen). The chondrocytes secreted cartilage matrix to fill the void spaces in the polymer scaffolds that were simultaneously biodegrading. In vitro, chondrocytes grown on PGA for 6 weeks reached a cell density of 5.2 × 107 cells/g, which was 8.3-fold higher than at day 1, and equalled the cellularity of normal bovine articular cartilage. In vitro, the cell growth rate was approximately twice as high on PGA as it was on PLLA; cells grown on PGA produced S-GAG at a high steady rate, while cells grown on PLLA produced only minimal amounts of S-GAG. These differences could be attributed to polymer geometry and biodegradation rate. In vivo, chondrocytes grown on both PGA and PLLA for 1-6 months maintained the three-dimensional (3-D) shapes of the original polymer scaffolds, appeared glistening white macroscopically, contained S-GAG and type II collagen, and closely resembled cartilage histologically. These studies demonstrate the feasibility of culturing isolated chondrocytes on biodegradable polymer scaffolds to regenerate 3-D neocartilage. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820270104
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  • 8
    Electronic Resource
    Electronic Resource
    Joint resurfacing using allograft chondrocytes and synthetic biodegradable polymer scaffolds (1994)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 28 (1994), S. 891-899 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Cartilage implants which could potentially be used to resurface damaged joints were created using rabbit articular chondrocytes and synthetic, biodegradable polymer scaffolds. Cells were serially passaged and then cultured in vivo on fibrous polyglycolic acid (PGA) scaffolds. Cell-PGA constructs were implanted in vivo as allografts to repair 3-mm diameter, full thickness defects in the knee joints of adult rabbits, and cartilage repair was assessed histologically over 6 months. In vitro, chondrocytes proliferated on PGA and regenerated cartilaginous matrix. Collagen and glycosaminoglycan (GAG) represented 20 to 8% of the implant dry weight (dw), respectively, at the time of in vivo implantation; the remainder was PGA and unspecified components. Implants based on passaged chondrocytes had 1.7-times as much GAG and 2.6-times as much collagen as those based on primary chondrocytes. In vivo, cartilaginous repair tissue was observed after implantation of PGA both with and without cultured chondrocytes. Six month repair was qualitatively better for cell-PGA allografts than for PGA alone, with respect to: (1) surface smoothness, (2) columnar alignment of chondrocytes, (3) spatially uniform GAG distribution, (4) reconstitution of the subchondral plate, and (5) bonding of the repair tissue to the underlying bone. These pilot studies demonstrate that it is feasible to use cell-polymer allografts for joint resurfacing in vivo. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820280808
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