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At least 19 recordsLinked to original sources
PubMed1985

Critical-point drying versus freeze drying for scanning electron microscopy: a quantitative and qualitative study on isolated hepatocytes.

Critical-point drying and freeze drying were compared both quantitatively and qualitatively as preparative procedures for scanning electron microscopy. Isolated hepatocytes were used as model cells. Nomarski differential interference contrast microscopy was used for light microscopic measurements of the hepatocytes in the unfixed, the glutaraldehyde fixed, the glutaraldehyde + OsO4 fixed, the critical-point dried and the freeze dried states. Critical-point dried hepatocytes were found to shrink to 38% of glutaraldehyde + OsO4 fixed volume, whereas optimal freeze dried hepatocytes (frozen in water saturated with chloroform and freeze dried at 183 K for 84 h) were found to shrink to 51% of glutaraldehyde + OsO4 fixed volume. Transmission and scanning electron micrographs of the critical-point dried cells showed well-preserved ultrastructure and surface structure. Micrographs of the freeze dried cells showed ultrastructure destroyed by internal ice crystals and surface structure destroyed by external ice crystals. Double-fixed isolated hepatocytes were shown to swell during storage in buffer and to shrink during storage after critical-point drying. For low magnification scanning electron microscopy (up to about 3000 times) both critical-point drying and freeze drying can be used. However, for high magnification scanning electron microscopy, critical-point drying is superior to freeze drying.

Animals↗
PubMed1979

Binding of concanavalin-A to critical-point-dried and freeze-dried human lymphocytes.

When human lymphocytes are treated with concanavalin-A (con A) and hemocyanin, the hemocyanin marker, which demonstrates con A binding sites, can be visualized by scanning (SEM) and transmission electron microscopy (TEM) on both critical-point-dried and freeze-dried cells. The ability to visualize the hemocyanin marker by SEM, its quantity and distribution, were all similar in lymphocytes prepared by both drying procedures. By TEM, hemocyanin was seen adjacent to the plasma membrane on critical-point-dried lymphocytes. In contrast, freeze-dried cells showed hemocyanin labeling at some distance from the plasma membrane (40-70 nm) as well as adjacent to it. The distribution of hemocyanin corresponded to the thickness of the amorphous coat seen on fixed, freeze-dried cells. Therefore, the extracellular coat on freeze-dried lymphocytes is a carbohydrate-containing glycocalyx.

Concanavalin A↗
PubMed1992

Enzyme histochemistry and immunohistochemistry with freeze-dried or freeze-substituted resin-embedded tissue.

Freeze-drying or freeze-substitution, combined with low-temperature resin-embedding, represents a new approach to the optimum preservation of tissue for enzyme histochemistry and immunohistochemistry. This method, which avoids tissue fixation, combines excellent tissue morphology with the preservation of enzyme activity and immunoreactivity and allows high-resolution enzyme histochemical and immunohistochemical studies to be performed. The activity of a wide range of enzymes can be demonstrated in sections of freeze-dried or freeze-substituted resin-embedded tissue. Enzymes are retained in situ with high activity, accurate localization and no diffusion. Immunohistochemical studies can also be performed on resin sections, and antigens--especially labile antigens--are immobilized in situ without denaturation and can be demonstrated with high sensitivity and accurately localized. This method allows the localization and distribution of enzymes and antigens to be studied in relation to excellent histological and cytological detail.

Animals↗
PubMed1988

Comparison of the effects of critical point-drying and freeze-drying on cytoskeletons and microtubules.

We have compared the effects of critical point-drying (CPD) and freeze-drying (FD) on the morphology of Triton-resistant cytoskeletons and microtubules by scanning (SEM) and transmission electron microscopy (TEM). In general, cytoskeletons attached to Formvar films suffer less structural damage than cells or cytoskeletons attached to glass, because the Formvar film absorbs some of the stress associated with shrinkage during drying. However, as seen in stereo-pair electron micrographs, the three-dimensional structure of cytoskeletons prepared by FD is better preserved and shows fewer artefacts than those prepared by CPD. CPD specimens are flatter, often have a concave and apparently collapsed nuclear matrix and show large cracks both in the perinuclear zone and through the cytoskeleton. At least some of the damage appears to be due to residual water in the CO2 used as the substitution fluid, because cytoskeletons dried with a water filter attached to the CPD apparatus show substantially less damage than those dried without the filter. Freeze-dried cytoskeletons consist mostly of unbroken, smooth filaments and have no perinuclear open space. Comparison of the effects of drying on the diameters of in vitro polymerized microtubules showed that the diameter of microtubules is reduced after drying, but that FD causes significantly less shrinkage than CPD. Addition of 0.2% tannic acid to the glutaraldehyde fixative significantly reduces the shrinkage of CPD microtubules, but has no effect on FD microtubules. The observations on microtubules support the hypothesis that drying-induced shrinkage is the result of both pressure and solvent evaporation and they indicate that tannic acid stabilizes samples against the former but not the latter.

Cytoskeleton↗
PubMed1989

A comparison of freeze-dried bone allograft and demineralized freeze-dried bone allograft in human periodontal osseous defects.

This study was conducted to clinically compare freeze-dried bone allograft (FDBA) and demineralized freeze-dried bone allograft (DFDBA). Twenty-two defects (11 intrapatient pairs) in 9 patients were grafted with either DFDBA or FDBA. Evaluations were based on standardized radiographs, presurgical and postsurgical soft tissue measurements using the cemento-enamel junction as a fixed reference point, and osseous measurements at the time of surgery. Grafted sites were re-entered at a minimum of 6 months following placement. A mean osseous repair of 1.7 mm (59%) occurred with DFDBA and 2.4 mm (66%) with FDBA. A mean clinical attachment gain of 1.7 mm was obtained with DFDBA and 2.0 mm with FDBA. Probing depths decreased a mean of 2.00 mm with both DFDBA and FDBA. These findings reveal no significant differences between the two materials in primarily intraosseous defects when evaluated at a minimum 6 months postsurgery.

Adult↗
PubMed1992

Scanning electron microscopy of freeze-dried preparations: relationship of morphology to freeze-drying parameters.

The structure of the freeze-dried plug of several biological preparations was examined using scanning electron microscopy (SEM). A variety of carbohydrate preparations were frozen at two different cooling rates of 150 degrees C per minute and 1 degree C per minute. After lyophilization, residual moisture analysis demonstrated that under conditions of rapid freezing a drier product could be obtained. SEM observations showed the lyophilised plug structure of rapidly frozen material consisted of a fine amorphous meshwork, while material frozen slowly consisted of a leafy amorphous material. Freeze-dried mannitol preparations were shown to be of a crystalline nature. In most instances, rapidly frozen material was easier to reconstitute after lyophilization. SEM of proteinaceous preparations which had been frozen at differing rates also showed a variety of different appearances which were probably related to the direction of ice growth. During ice growth formation the migration of buffers and salts towards the surface may occur. Localised high salt/buffer areas may cause deterioration of the product and reduce shelf life. SEM observations were made on the freeze-dried plug of preparations which had collapsed during the lyophilization process. Typically, the basal region of the plug had a more solid structure than the open meshwork of successfully dried material.

Biological Products↗
PubMedDate not supplied

[Stabilization of dextranase from Penicillium funiculosum and Fusarium solani during heating and freeze-drying].

Freeze-drying of highly purified dextranse from Penicillium funiculosum and Fusarium solani was accompanied by 90% losses of enzyme activity and solubility. Many carbohydrates were tested as stabilizers, e.g. glucose, maltose, lactose, polyglucine, dextranase hydrolyzate of polyglucine as well as mannitol and ammonium sulfate. Polyglucine, its hydrolyzate, and glucose proved most effective stabilizers. The stabilizing effect of polyglucine hydrolyzate of dextranase during its heating and freeze-drying was compared. The effective concentration of the stabilizer during freeze-drying was 10 times lower than during heating.

Dextranase↗
PubMed1992

Formulation and stability of freeze-dried proteins: effects of moisture and oxygen on the stability of freeze-dried formulations of human growth hormone.

This research presents the results of a series of stability studies on freeze-dried formulations of human growth hormone (hGH). Chemical decomposition via methionine oxidation and asparagine deamidation as well as irreversible aggregation are characterized by HPLC. Water sorption isotherms, DSC thermograms, and pulsed proton NMR data are also obtained. No glass transition temperatures are observed in the temperature range of the stability studies. The pulsed NMR data suggest onset of greater mobility in the solid at a water content slightly higher than BET "monolayer" level. Stability of freeze-dried solids at 25 degrees C and 40 degrees C is studied as a function of residual moisture and exposure to oxygen. Formulations with and without a glycine/mannitol excipient system are studied. Significant levels of chemical decomposition and irreversible aggregation occur under most conditions with the effects of residual water content and "headspace oxygen" strongly dependent on the formulation. At low water content with minimal oxygen in the vial headspace, the glycine/mannitol formulation yields optimum stability. However, for either high water content or high oxygen content in the vial, stability of hGH without excipients is superior. The qualitative effect of residual moisture on stability depends on the temperature of the stability study. Generally, the stability of a sample adjusted to a given water content by desorption (during freeze-drying) is identical to the stability of a sample prepared by sorption of water on to a previously highly dried sample.

Calorimetry, Differential Scanning↗
PubMed1990

Biohazards in pharmaceutical freeze drying.

Among freeze-dried drugs there are many which may imperil manufacturing personnel, e.g. cytostatic drugs possessing carcinogenic effects. Production zones must be specially adapted for handling such drugs. There are many risks endangering a freeze-drying operation--power or water supply failure, but also improperly established freeze-drying cycle. A production batch of a rare, expensive and sensitive product represents a big value; modern equipment therefore features sophisticated automation, overriding possible human error. Problem of particulate contamination is less severe with vials stoppered inside the vacuum chamber, but rubber closures still may become a source of haze. Back-migration of oil from vacuum pumps may be another source. Economy of industrial freeze-drying may be much improved if freezing sequence, drying rate, adjustment of vacuum by "bleeding" nitrogen are tailored specially for each particular product.

Drug Contamination↗