Freeze surface treatments

For biotechnological purposes, it is necessary not only that cells remain viable but also that adhesion is maintained so that a cell can be found in the expected position. The adhesion pattern that a cell has adopted before freezing is crucial to successful cryo-preservation. Adhesion patterns can be visualised by (TIRF microscopy, [63]) mentioned above and also by confocal laser scanning fluorescence (CLSM, [64]) microscopy. We have investigated the adhesion patterns of fibroblasts as a function of adhesion time and various surface treatments [65]. Some examples are shown in Fig. 19. 

Polyethylene, as LDPE, LLDPE or a mixture or blend involving combinations of LDPE, MDPE, HDPE, EVA, etc., finds a wide usage in bags, sacks, sachets, overwraps, shrink wraps, stretch wraps, etc. Most deep freeze packs, for example, use LDPE or an LDPE mixture which is produced from a reel on a form fill seal type machine. However, as many of these packs are up to 100% printed, even ink of 2-5 Pm could be considered as a separate layer which modifies some of the physical and chemical properties. As all polyolefins need a surface (oxidative) treatment to ensure a good print key, this or any other surface treatment process may further modify the film properties. 

Materials. Na-Kaolinite A homoionic sample of kaolinite was prepared from a well-crystallized sample purchased from Source Clays, University of Missouri, using a standardized technique (14) which involved repeated washing with distilled water and by treatment with NaCl solutions to remove exchangeable ions such as Ca, and freeze-drying of the final product. Nitrogen specific surface area of this kaolinite was estimated to be 9.4nr/g and X-ray analysis showed the characteristic pattern of kaolinite. 

Enbrel is a product now approved for medical use that is based upon this strategy. The product is an engineered hybrid protein consisting of the extracellular domain of the TNF p75 receptor fused directly to the Fc (constant) region of human IgG (see Box 13.2 for a discussion of antibody structure) The product is expressed in a CHO cell line from which it is excreted as a dimeric soluble protein of approximately 150 kDa. After purification and excipient addition (mannitol, sucrose and trometamol), the product is freeze-dried. It is indicated for the treatment of rheumatoid arthritis and is usually administered as a twice-weekly s.c. injection of 25 mg product reconstituted in WFI. Enbrel functions as a competitive inhibitor of TNF, a major pro-inflammatory cytokine. Binding of TNF to Enbrel prevents it from binding to its true cell surface receptors. The antibody Fc component of the hybrid protein confers an extended serum half-life on the product, increasing it by fivefold relative to the soluble TNF receptor portion alone. 

For quenching experiments, which were necessary to freeze-in the equilibrium states between the phase bands, the samples were reheated in a vacuum furnace under 500 mbar N2 to the original annealing temperature and dropped onto a copper plate kept below 470 K (200°C). With this treatment the Group 5 transition metal nitrides underwent a slight change in surface composition because it was impossible to adjust the appropriate nitrogen pressures. This, however, did not influence the compositions at the interface boundaries inside the diffusion couples. 

Treatment of Com. Ten microliters of an 80% acetone solution, containing 100 fig. of C14-gibberellin, was applied with a micropipet near the middle of the upper surface of the first leaf, followed by 10 fjl. of 0.1% Tween 20 and 50% ethyl alcohol in order to increase absorption of the radioactive material. The drop of solution was kept from running down by means of lanolin paste. Four normal and four dwarf com plants were thus treated, while untreated plants were kept as controls. The same number of dwarf plants was treated with 0.05 fic. of C14-5-aminotriazole in order to compare the pattern of translocation of gibberellin with that of a compound whose movement has been studied previously (4). The treated plants and controls were then placed in the growth chamber, and one or two specimens were harvested at the end of 1, 2, and 7 days, freeze-dried, and autoradiographed. 

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