PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Freeze Drying”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed2004

Investigation of freeze-drying sublimation rates using a freeze-drying microbalance technique.

This study was to investigate the effects of different freeze-drying factors on the rate of sublimation. The experiments were carried out in a custom-built freeze-drying microbalance to accurately monitor the sample temperature and control the chamber pressure. Twenty-four experiments were conducted based on a full factorial design by changing four factors: freezing rate (fast freezing or slow freezing), chamber temperature (35, 0, or -35 degrees C), chamber pressure (30 or 1000 mTorr), and the presence or absence of an annealing process. Lactate dehydrogenase (LDH), a tetrameric protein, was selected as a model protein for this study. The statistical analysis of the experimental results revealed that chamber temperature, analogous to the shelf temperature, in this experiment system, had the greatest impact on the sublimation rate. High chamber temperature resulted in high sublimation rate, regardless of the chamber pressure and thermal history of the sample. Chamber pressure was an important factor affecting the sublimation rate. In addition, both chamber temperature and chamber pressure had significant impact on sample temperature during freeze-drying. Annealing the samples was the most critical step to preserve good freeze-dried cake structure.

Air Pressure↗
PubMed2006

Physical characterization of pharmaceutical formulations in frozen and freeze-dried solid states: techniques and applications in freeze-drying development.

Physical characterization of formulations in frozen and freeze-dried solid states provides indispensable information for rational development of freeze-dried pharmaceutical products. This article provides an overview of the physical characteristics of formulations in frozen and freeze-dried solid states, which are essential to both formulation and process development. Along with a brief description of techniques often used in physical characterization for freeze-drying development, applications of and recent improvements to these techniques are discussed. While most of these techniques are used conventionally in physical characterization of pharmaceuticals, some techniques were designed or modified specifically for studies in freeze-drying. These include freeze-drying microscopy, freeze-drying X-ray powder diffractometry and cryoenvironmental scanning microscopy, which can be used to characterize the physical properties of the formulation under conditions similar to the real vial lyophilization process. Novel applications of some conventional techniques, such as microcalorimetry and near infrared (NIR) spectroscopy, which facilitated freeze-drying development, receive special attention. Research and developmental needs in the area of physical characterization for freeze-drying are also addressed, particularly the need for a better understanding of the quantitative correlation between the molecular mobility and the storage stability (shelf life).

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↗
PubMed2006

Preparation of 3-D regenerated fibroin scaffolds with freeze drying method and freeze drying/foaming technique.

Although three-dimensional fibroin scaffolds have been prepared with freeze drying method, the porosity and pore sizes still can not satisfy the requirement of tissue engineering. In this article, fibroin porous scaffold with high porosity and > 100 microm diameter interconnected pores was firstly prepared with freeze drying method through adjusting fibroin concentration. The morphology of different scaffolds lyophilized from different fibroin concentration was observed by SEM. A novel freeze drying improved method, freeze drying/foaming technique, was also devised to prepare fibroin scaffolds at different fibroin concentrations. Using the said method, the porosity and pore size of fibroin scaffolds prepared from 12% concentration were 85.8 +/- 4% and 109 +/- 20 microm respectively with yield strength up to 450 +/- 6 KPa while the porosity and pore size of fibroin scaffolds prepared from 8% concentration were 96.9 +/- 3.6% and 120 +/- 30 microm respectively with yield strength up to 30 +/- 1 KPa. The freeze drying/foaming technique produced scaffolds with a useful combination of high yield strength, interconnected pores, and pore sizes greater than 100 microm in diameter. Through adjusting fibroin concentration and thawing time, the porosity, pore sizes and mechanical properties could be controlled to satisfy the different requirements of tissue engineering. The results suggested that fibroin scaffolds prepared with the above methods could be formed for utility in biomaterial application.

Animals↗
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↗
PubMedDate not supplied

Intravial distribution of moisture during the secondary drying stage of freeze drying.

Particularly for proteins that may be damaged by overdrying, the distribution of residual moisture in the dried product may be as important as the mean water content. Protein at the top of the cake could be "overdried" even though the mean water content was optimal. Theoretical studies suggest that, particularly for large fill depths, the residual moisture near the top of the cake is much lower than the moisture near the bottom, at least during and immediately after freeze drying. This work is an experimental study of the distribution of moisture within a vial as a function of time in secondary drying (mean residual water content of about 3%-6%) for dextran, human serum albumin, and bovine somatotropin. A core sample of the dried product was taken and sectioned into "top," "middle," and "bottom" sections. These three "core sections" and the remaining "outer" section (i.e., near the vial wall) were assayed for moisture. In general, the moisture content in the top section is less than the moisture content in the bottom section, but the "outer" section is consistently found to be lowest in moisture content. This observation suggests that drying was faster along the walls of the vial than in the core region, resulting in a highly curved ice-vapor interface. It is proposed that faster drying along the vial walls is a result of the observed product shrinkage during drying which provides a low resistance pathway for vapor escape along the vial wall. Product temperature measurements support the above speculation.

Freeze Drying↗
PubMed1997

Stabilization of gene delivery systems by freeze-drying.

Freeze-drying of three different forms of gene delivery systems was performed using a controlled two-step drying process and 10% sucrose as lyoprotectant. Complexes of pCMVL plasmid with transferrin-conjugated polyethylenimine, adenovirus-enhanced transferrinfection consisting of pCMVL/transferrin-polylysine complexes linked to inactivated adenovirus particles, and a recombinant, E1-defective adenovirus expressing a luciferase reporter gene were tested. Three weeks after freeze-drying the reagents were rehydrated with water and tested for transfection activity. Luciferase gene expression levels were retained at high levels in all three systems, in contrast to reagents stored in solution. The use of the lyoprotectant was essential. In the absence of sucrose the transfection activities dropped by a factor of 100-1000. The data suggest freeze-drying as a useful method for stabilization and storage of standardized batches of transfection agents.

Journal Article↗
PubMed1983

Clinical evaluation of freeze-dried bone allografts in periodontal osseous defects. Part III. Composite freeze-dried bone allografts with and without autogenous bone grafts.

Freeze-dried bone allografts (FDBAs) were evaluated alone and in combination with various types of autogenous bone in the treatment of periodontal osseous defects. A total of 381 defects were evaluated by surgical reentry approximately 1 year after grafting. Reentry data were compared with similar data obtained when the grafts were placed. Osseous regeneration and pocket reduction were rated as complete, greater than 50%, less than 50%, or failed. Complete or greater than 50% regeneration was considered successful. When compared with FDBAs, composite freeze-dried bone allografts/autogenous bone grafts (FDBA/ABGs) appear to offer significantly improved results in both osseous regeneration and pocket reduction. Use of composite FDBA/ABGs resulted in significant improvement in the treatment of combination one/two-wall defects and furcation involvements. A trend of improvement was seen with two-wall defects. The surgical data indicated that complete wound closure and the use of antibiotics enhanced graft success. The results also indicated that the presence of endodontically obturated teeth may be a consideration in the success or failure of the graft.

Adolescent↗