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  • 1
    Electronic Resource
    Electronic Resource
    Immobilization of poly(ethylene glycol) onto a poly(vinyl alcohol) hydrogel. 1. Synthesis and characterization (1991)
    s.l. : American Chemical Society
    Macromolecules 24 (1991), S. 6065-6072 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00023a003
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  • 2
    Electronic Resource
    Electronic Resource
    Metabolic activity of CHO fibroblasts in HEMA-MMA microcapsules (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 39 (1992), S. 672-678 
    Details
    ISSN: 0006-3592
    Keywords: microencapsulation ; MTT assay ; polyacrylate ; artificial membrane ; metabolic activity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Chinese hamster ovary (CHO) fibroblast cells were microencapsulated in polyacrylate membranes (HEMA-MMA: 75% HEMA) via an interfacial precipitation process. The CHO cells were observed to grow in large aggregates, attached to each other instead of to the capsule wall. When CHO cells were encapsulated at high density (4 × 106 cells/mL), the initial metabolic activity in microcapsules, as determined by the MTT assay, correlated with the polymer-cell extrusion ratio, presumably because of the dependence of encapsulation efficiency on the relative flow rates. However, there was a large variation in the metabolic activity among individual microcapsules throughout the present study. Capsules with low encapsulation efficiency (at a “seeding” density of 4 × 106 cells/mL) exhibited a rapid increase in the metabolic activity during the following week. When CHO cells were encapsulated at low density (4 × 105 cells/mL), there was only a small increase in the metabolic activity. Only a small fraction (∼5%) of the capsules exhibited a high level of metabolic activity and 40% of the capsules exhibited undetectable metabolic activity even after 2 weeks. We conclude that CHO cells, which served as model cells, survive the encapsulation process and retain an active metabolic state once enclosed by the HEMA-MMA membranes. However, the resultant microcapsules are extremely heterogeneous in the amount of retained metabolic activity.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260390612
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  • 3
    Electronic Resource
    Electronic Resource
    Viability and protein secretion from human Hepatoma (HepG2) cells encapsulated in 400-μm polyacrylate microcapsules by submerged nozzle-liquid jet extrusion (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 1199-1204 
    Details
    ISSN: 0006-3592
    Keywords: microencapsulation ; polyacrylate ; submerged jet ; mammalian cell ; HepG2 cells ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An interfacial precipitation process to encapsulate mammalian cells in hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) microcapsules of ∼ 750 in ∼m diameter was previously described. It was not possible to produce smaller capsules due to low shearing force. A new droplet generation scheme was developed by suspending the cell and polymer co-extrusion nozzle in a uniform co-axial fluid jet which enabled the production of 300 to 600-µm diameter capsules. HepG2 hepatoma cells in 400-µm-diameter HEMA-MMA capsules were able to retain their metabolic activity during and after the encapsulation process. The in vitro secretion of plasma proteins α1-acid glycoprotein, α1-antitrypsin, and fibrinogen by the encapsulated cells was retained. The encapsulated cells secreted less fibrinogen (340 kD) relative to α1-acid glycoprotein (42kD), indicating the sieving effect (but not absolute cut-off) of the HEMA-MMA membrane. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260441007
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  • 4
    Electronic Resource
    Electronic Resource
    Thrombin and albumin adsorption to PVA and heparin-PVA hydrogels. 2: Competition and displacement (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 89-95 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Thrombin adsorption to polyvinyl alcohol (PVA) was different from its adsorption to polyethylene (PE) - not so much in amount, but in its affinity. Thrombin was more easily displaced from polyethylene and its adsorption was more readily prevented by prior or simultaneous exposure to albumin. From PVA (or heparin-PVA), only ∼ 30% of the adsorbed protein could be removed by a series of eluents, including even harsh ones such as 2.5M NaOH and 6M guanidine;〉85% could be removed from PE. Thrombin adsorption to PVA was not affected by the presence of BSA in solution or at the surface, but was virtually prevented on PE by preexposure to or adsorption with BSA. Heparin-PVA was not much different than PVA in most of these experiments, but did exhibit a “Vroman effect”. In the absence of fibringen or antithrombin III, there was a maximum in thrombin adsorption from plasma at a plasma concentration of 1%. The behavior on this surface was dependent on both exposure time and protein concentration. These studies highlight the complexity of the interaction between plasma proteins and polymer surfaces (particularly hydrogel surfaces) and the difficulty of obtaining a clear picture of what happens when a single protein interacts with a polymer in the presence of other proteins. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820270112
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  • 5
    Electronic Resource
    Electronic Resource
    Preparation and thrombogenicity of alkylated polyvinyl alcohol coated tubing (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 577-592 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A polyvinyl alcohol hydrogel (PVA) was reacted with a CI8 isocyanate at 80°C in dimethyl formamide (DMF) in order to improve the platelet reactivity of the hydrogel through an inf hence on albumin adsorption or retention. A C, isocyanate was used as a control. Surface coverage by XPS appeared to be ∼100% for both C4 and C18 modified surfaces, although the limited solubility of C18 isocyanate in DMF may have resulted in a nonuniform surface. Relative to PVA or the solvent treated control, octadecylation resulted in increased albumin adsorption (from a single protein solution) and increased retention when the adsorbed albumin was exposed to a fibrinogen solution. However, octadecylation did not obviate the platelet reactivity problem in preliminary studies: systemic platelet counts were reduced by about half over 4 days in a canine AV shunt experiment and the initial rate of platelet destruction for C IR-PVA was greater (36%/ day) even than for the solvent-treated PVA. Surprisingly in preliminary studies butylation of PVA resulted in little or no thrombocytopenia and did not appear to increase significantly the fractional rate of platelet destruction relative to the shunt only blank. It is presumed that the nonspecific effect of alkylation (independent of chain length) was the dominant contribution to the reduced platelet reactivity. A similar effect of C18-PVA presumably would have been observed had the limited solubility of C18 isocyanate not precluded a uniform surface coverage.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820260503
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  • 6
    Electronic Resource
    Electronic Resource
    Measurement of the rate of thrombin production in human palsma in contact with different materials (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 675-693 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Thrombin production in plasma in contact with various materials was consistent with a first-order autocatalytic model (d[T]/dt = k,[T]; [TI] = thrombin concentration, t = time, k, = thrombin production rate constant) since the initial portion of a semilogarithmic plot of thrombin concentration against time was linear. Thrombin concentration was measured in clotting plasma (phospholipid enhanced or plateletrich plasma) using fluorogenic substrate (BMCA) by aliquot sampling at various intervals or more conveniently by monitoring cumulative fluorescence. The latter was generated by the action, on BMCA incubated in the clotting plasma, of the thrombin as it was generated. The thrombin concentration was determined from the first derivative of the S-shaped cumulative fluorescence curve. kp, was greater for glass (7.92 × 10-3 cm/than) for the other materials (polypropylene, polystyrene, polyethylene and PVA; kp, ∼3.1 × 10-3cm/s) in plasma with cephalin without flow. A kp, for heparin PVA could not be determined since the thrombin concentration was too low to be quantified. A larger difference between polyethylene and PVA was noted with platelet-rich plasma without flow while lower values (1.0 × cm/s) were noted in a flow system but at a higher surface to volume ratio. The first-order rate constant can be used in simple models relating production of thrombin at a wall of a tube to its mass transfer away from the wall in flowing blood. One such model predicts that the concentration of thrombin at the wall should become infinite at the point in the tube when the mass transfer coefficient equals kp. According to this model, kp on the order of cm/s would be a useful target for a nonthrombogenic material.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820260509
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  • 7
    Electronic Resource
    Electronic Resource
    Morphological assessment of hepatoma cells (HepG2) microencapsulated in a HEMA-MMA copolymer with and without Matrigel (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 1401-1418 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Hepatoma cells (HepG2), an anchorage-dependent cell line, were microencapsulated in a HEMA-MMA polyacrylate membrane to which the cells do not ad here. This environment was altered by the coencapsulation of Matrigel, a reconstituted extracellular matrix derived from the Engelbreth-Holm-Swarm (EHS) mouse tumor basement membrane, to provide sites for cell attachment. The effect on the cells of these two capsule microenvironments during a 2-week in vitro culture period was assessed by examining the spatial arrangement, morphology, and viability of the cells using light microscopy and scanning electron microscopy (SEM). In preparation for microscopy, dissolution of the polymer was prevented by the use of frozen sections embedded in a water-soluble compound. Similarly, freeze cleavage of conductively stained capsules permitted SEM observation of the capsule interior along with ultrastructural detail of the cells. In the absence of Matrigel, cells in HEMA-MMA capsules were found to form aggregates in intracapsular pockets with central necrosis occurring at day 7 in large aggregates. The coencapsulation of HepG2 cells with Matrigel, resulted in an initially uniform distribution of essentially individual cells with aggregates appearing later within the Matrigel. Many cells within these capsules had remained viable when examined up to day 14 with only limited cellular necrosis, implying a favorable environment for microencapsulated HepG2 cells. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820261102
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  • 8
    Electronic Resource
    Electronic Resource
    Thrombin and albumin adsorption to PVA and heparin-PVA hydrogels. I. Single protein isotherms (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 947-958 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: More radiolabeled thrombin was adsorbed to heparin-polyvinyl alcohol (PVA) than to PVA, consistent with a specific interaction with the immobilized heparin. The maximum surface concentration on heparin-PVA was estimated to be ∼450 nmol/m2 with an apparent affinity constant (Ka,) of 2.5μM-1; on PVA, the plateau concentration was 10 nmol/m2 with a Ka 〈 1 nM-1. There was little difference in bovine serum albumin (BSA) adsorption between PVA and heparin PVA. Interestingly, thrombin adsorption to polyethylene was indistinguishable from that to PVA despite the large difference in surface chemistry. BSA adsorbed to polyethylene with higher affinity than to the hydrogels, although the plateau concentrations were comparable. The adsorbed thrombin was biologically inactive at least towards chromogenic substrate, with the residual activity on PVA unaffected by subsequent incubations with antithrombin 111. PVA and heparin-PVA presented a heterogeneous and complex substrate for interaction with proteins. The adsorbed protein was likely present in multiple states depending on the groups with which it interacted.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820260709
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  • 9
    Electronic Resource
    Electronic Resource
    Microencapsulated human hepatoma (HepG2) cells: In vitro growth and protein release (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 1213-1224 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The feasibility of a microencapsulation process ultimately for cell transplantation was investigated by encapsulating human hepatoma (HepG2) cells in hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) membranes through an interfacial precipitation process. Changes in viability and metabolic activity as well as protein secretion by the encapsulated cells were studied in vitro. When encapsulated at either low or high density (1 or 5 × 106 cells/mL, respectively), HepG2 cells retained their active metabolic state and/or proliferated during the initial 1-week period, after which a significant drop in cell viability was obtained. Encapsulati of a biological attachment substrate, Matrigel, along with the cells, however, resulted in rapid proliferation in both low and high density capsules with prolonged maintenance of an active metabolic state. The secretion of four model proteins (α1-acid glycoprotein, α1-antitrypsin, haptaglobin and fibrinogen) was demonstrated during the 2-week study period for the Matrigel encapsulated cells. Furthermore, the encapsulated cells remained responsive to interleukin 6 (IL6), a physiological stimulator of plasma protein secretion, as determined by the elevated secretion of haptaglobin in response to IL6 treatment. We conclude that HEMA-MMA capsules, in the presence of an attachment substrate, provide a suitable environment for the growth and expression of differentiated functions of encapsulated hepatoma cells. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820271002
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  • 10
    Electronic Resource
    Electronic Resource
    Immobilization of poly(ethylene glycol) onto a poly(vinyl alcohol) hydrogel: 2. Evaluation of thrombogenicity (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 1383-1391 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Immobilized polyethylene glycol (PEG) reduced the amount of bovine serum albumin (BSA) adsorbed on polyvinyl alcohol (PVA) hydrogel, but did not reduce the platelet reactivity of the hydrogel surface. PEG, molecular weight (MW) 2000 or 5000, with or without a monomethoxy end group, was covalently bound to glutaraldehyde-crosslinked PVA either through a cyclic acetal or an urethane functional group with a surface coverage of 70% (as measured by x-ray photoelectron spectroscopy [XPS]). Immobilization of monomethoxy-PEG via a cyclic acetal reduced BSA adsorption to PVA from 11 ± 2 nmol/m2 to 3.9 ± 0.3 nmol/m2 and 3.3 ± 0.3 nmol/m2 for MW 2000 and 5000, respectively. Similarly, urethane bound PEG reduced adsorption to 3.5 ± 1.6 nmol/m2 for MW 2000 and 5.4 ± 1.0 nmol/m2 for MW 5000. Whole blood clotting times of PVA (using a Chandler loop) were not affected by covalently linked PEG, although the initial rate of thrombin generation at the surface, measured using a fluorogenic substrate, was marginally reduced; a rate constant of 4.2 ± 0.1 cm/sec and 3.5 ± 0.1 cm/sec were obtained for MW 2000 and 5000, respectively, compared to 5.6 ± 1.0 cm/sec for PVA. Ex vivo evaluation using a canine arteriovenous shunt revealed that the hydrogel, with or without bound PEG, reduced circulating platelet levels by 35-70% after 4 days. The initial fractional rate of platelet destruction determined from measurement of platelet cyclooxygenase activity, indicated that cyclic acetal or urethane bound PEG of either molecular weight had no effect on platelet consumption produced by PVA. The PEG hypothesis at least as it relates to platelet interactions may need to be evaluated further in the light of these results. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820271105
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