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PubMed2000

Effect of freeze-drying and gamma irradiation on the mechanical properties of human cancellous bone.

Freeze-drying and gamma irradiation are commonly used for preservation and sterilization in bone banking. The cumulative effects of preparation and sterilization of cancellous graft material have not been adequately studied, despite the clinical importance of graft material in orthopaedic surgery. Taking benefit from the symmetry of the left and right femoral heads, the influence of lipid extraction followed by freeze-drying of a femoral head and a final 25-kGy gamma irradiation was determined, with the nonirradiated, nonprocessed counterpart as the control. Five hundred and fifty-six compression tests were performed (137 pairs for the first treatment and 141 pairs for the second). Mechanical tests were performed after 30 minutes of rehydration in saline solution. Freeze-dried femoral heads that had undergone lipid extraction experienced reductions of 18.9 and 20.2% in ultimate strength and stiffness, respectively. Unexpectedly, the work to failure did not decrease after this treatment. The addition of gamma irradiation resulted in a mean drop of 42.5% in ultimate strength. Stiffness of the processed bone was not modified by the final irradiation, with an insignificant drop of 24%, whereas work to failure was reduced by a mean of 71.8%. Freeze-dried bone was a bit less strong and stiff than its frozen control. Its work to failure was not reduced, due to more deformation in the nonlinear domain, and it was not brittle after 30 minutes of rehydration. Final irradiation of the freeze-dried bone weakened its mechanical resistance, namely by the loss of its capacity to absorb the energy (in a plastic way) and a subsequent greater brittleness.

Biomechanical Phenomena↗

PubMedDate not supplied

Effect of dextran molecular weight on protein stabilization during freeze-drying and storage.

The effect of dextran molecular weight on structural stability of freeze-dried products and protein stability in amorphous matrices was investigated during storage at elevated temperatures. Glucose-6-phosphate dehydrogenase (G6PDH) was freeze-dried in 10% (w/v) dextrans of five molecular weights (12 kD, 42 kD, 71 kD, 512 kD and 2000 kD) to residual water content of 0.027 ( 0.004 g/g dry mass. The molecular weight of dextrans affected the glass transition temperature (Tg) of freeze-dried products and the recovery of enzyme activity after freeze-drying. As the molecular weight of dextrans increased from 12 kD to 2000 kD, the Tg increased from 100 degrees C to 120 degrees C, whereas the recovery of protein activity decreased from 85 +/- 4 % to 70 +/- 5%. The inactivation of freeze-dried protein during storage followed a bi-phasic first-order kinetics. The stability of amorphous matrices and protein increased significantly as the molecular weight increased from 12 kD to 512 kD. However, at a higher molecular weight (2000 kD), the stability was reduced. In a separate experiment, the stability of dried dextran/protein samples was studied during heating from 30 degrees C to 99 degrees C at 0.2 degrees C/min and subsequent incubation at 99 degrees C. Dextran with an average molecular weight of 512 kD was again found to provide the best protection. Mechanisms that cause the differences in protein stability among different molecular weight dextrans remain unclear.

Cryopreservation↗

PubMed1998

Characterization of the sucrose/glycine/water system by differential scanning calorimetry and freeze-drying microscopy.

The objective of this study was to characterize the thermal properties of systems containing various ratios of amorphous and crystalline components using both differential scanning calorimetry (DSC) and freeze-drying microscopy. The glycine/sucrose system was used as a model system, since it is routinely used in protein formulations. DSC analysis revealed that the addition of glycine to sucrose solutions resulted in a decrease in the glass transition (T'g) of the system. The T'g of a pure sucrose solution (7% w/v) decreased from -32.3 to -51.5 degrees C for a mixture containing a sucrose/glycine ratio of 2:5. The glass transition of the sucrose/glycine mixture decreased linearly as more glycine was added to the system. This decrease in glass transition resulted in severe collapse during freeze-drying of these mixtures above T'g. However, collapse was not observed during freeze-drying if the DSC thermogram of the sucrose/glycine mixture exhibited a transition resulting from recrystallization of the amorphous glycine. Mixtures having a sucrose/glycine ratio of 3:4 and 2:5 had a glass transition of -48 degrees C and -51.5 degrees C, respectively. Despite their low glass transition temperatures, these samples freeze-dried readily at a product temperature > T'g using a fast freeze-drying cycle (primary drying at a shelf temperature of +20 degrees C and chamber pressure of 100 mTorr) without any sign of collapse. The crystallization of the amorphous glycine from the frozen mixture of sucrose and glycine provided support during freeze-drying which prevented the macroscopic collapse of the final product. Freeze-drying microscopy visually revealed the crystallization and allowed for prediction of cake quality upon lyophilization. Although the freeze-drying microscope is not as sensitive as the DSC in detecting all transitions (it cannot detect a glass transition), it clarifies the interpretation of DSC, and together they provide valuable information regarding the relevance of each of the transitions to the final freeze-dried product elegance.

Calorimetry, Differential Scanning↗

PubMed2004

Freeze-dried irradiated bone brittleness improves compactness in an impaction bone grafting model.

BACKGROUND: Defatted bone chips with or without freeze-drying and irradiation have mechanical advantages as compared to fresh-frozen controls in in vitro models of impaction. These improved results have been ascribed to replacement of viscous bone marrow by saline and embrittlement of the freeze-dried bone by irradiation. MATERIAL AND METHODS: To determine which of these hypotheses is correct, we compared the development of stiffness and compactness of morselized bone graft that had been: 1) fat-reduced with saline, and 2) fresh-frozen, solvent-detergent defatted, 3) freeze-dried irradiated and 4) not irradiated. We used 12 osteoarthrotic femoral heads to prepare these four batches of morselized bone, and impacted 18 samples from each batch in a cylinder. The frozen bone grafts were tested after thawing at room temperature for 2 hours and the freeze-dried grafts were tested after 30 minutes of rehydration. We monitored the development of compactness and stiffness of the material during impaction. RESULTS: The stiffness of the freeze-dried irradiated bone was greater than that of the other three series after 10, 50 and 150 impactions. The freeze-dried bone chips that were not irradiated and the chips defatted with saline alone were less stiff than the fresh-frozen control after 150 impactions. INTERPRETATION: The brittleness of freeze-dried irradiated bone, caused by loss of the capacity to absorb energy in a plastic way, increases the compactness and stiffness of the morselized grafts. Washing bone with saline alone or treating bone with solvent-detergent but no irradiation had no similar mechanical advantage and the bone did not impact better than fresh-frozen undefatted bone in our model.

Aged↗

PubMed2003

[Experimental study of repairing segmental bone defect with reconstituted freeze-dried bone allograft].

OBJECTIVE: To study the effect of basic fibroblast growth factor (bFGF) and hyaluronic acid gel (HAG) combined with freeze-dried bone allograft in repairing segmental bone defect and to explore their mechanism. METHODS: The 15 mm segmental bone/periosteum defects were created on bilateral radius in 50 New Zealand rabbits and were treated with four different kinds of implants on 25 radius respectively (group A: bFGF and HAG combined with freeze-dried bone; group B: bFGF combined with freeze-dried bone; group C: HAG combined with freeze-dried bone; group D: simple freeze-dried bone as a control). The repair of defect was observed radiologically and histologically and were analyzed by radionuclide bone imaging and measurement of calcium contents at different periods. RESULTS: The new bone formation, bone metabolic activity and calcium contents of defects were higher in group A than in group B (P < 0.05), and were higher in group B than in groups C and D (P < 0.05). There were no significant difference between groups C and D. The bone defects healed in the 8th week in group A, in the 10th week in group B, but did not healed in the 10th week in groups C and D. CONCLUSION: As an osteogenetic factor, bFGF promotes the new bone formation; as a slow-release carrier, HAG enhances the effectiveness of bFGF. The combination of bFGF, HAG and freeze-dried bone allograft can repair the segmental bone defect more effectively.

Animals↗

PubMed2001

Phase transitions of glycine in frozen aqueous solutions and during freeze-drying.

PURPOSE: To study the solid-state and phase transitions of glycine, (i) in frozen aqueous solutions, and (ii) during freeze-drying. METHODS: X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC) were used to analyze the frozen systems. In situ freeze-drying in the sample chamber of the diffractometer enabled characterization of phase transitions during freeze-drying. RESULTS: Transitions in frozen systems. Rapid (20 degrees C/min) or slow (2 degrees C/min) cooling of aqueous solutions of glycine (15% w/w) to -70 degrees C resulted in crystallization of beta-glycine. Annealing at -10 degrees C led to an increase in the amount of the crystalline phase. When quench-cooled by immersing in liquid nitrogen, glycine formed an amorphous freeze-concentrate. On heating, crystallization of an unidentified phase of glycine occurred at approximately -65 degrees C which disappeared at approximately -55 degrees C, and the peaks of beta-glycine appeared. Annealing caused a transition of beta- to the -gamma- form. The extent of this conversion was a function of the annealing temperature. Slower cooling rates and annealing in frozen solutions increased the crystalline beta-glycine content in the Iyophile. Freeze-drying of quench-cooled solutions led to the formation of gamma-glycine during primary drying resulting in a lyophile consisting of a mixture of beta- and -gamma-glycine. The primary drying temperature as well as the initial solute concentration significantly influenced the solidstate of freeze-dried glycine only in quench-cooled systems. CONCLUSIONS: The cooling rate, annealing conditions and the primary drying temperature influenced the solid-state composition of freeze-dried glycine.

Calorimetry, Differential Scanning↗

PubMed1976

Freeze-drying equipment.

Illustrated presentation of a sophisticated research freeze-drying apparatus, fitted with many controls including a program controller. With this machine, it is possible to remove samples from any part of the chamber, at any time, without interfering with the freeze-drying process. By this ability to sample, the apparatus makes it possible to study, during the freeze-drying process, the influence on the dried product of many parameters and to reproduce in the chamber the same drying conditions offered by the production-scale machines. The figures include one of a production-scale machine, and a patented device for automatic loading and unloading of the freezers and the freeze-dryers.

Freeze Drying↗

PubMed2005

[Rabbit urethral defect repair with freeze-dried acellular bladder submucosa].

OBJECTIVE: To evaluate the result of urethral defect repair using freeze-dried acellular bladder submucosa. METHODS: The freeze-dried acellular bladder submucosa was obtained from human cadaveric bladder submucosa using freeze-thawed enzymatic treatment and the freeze-drying technique. 18 male New Zealand rabbits were used in this experiment. A defect of 1.0 cm x 0.5 cm was created in the ventral urethra of the animal. The acellular matrix was grafted to the urethral defect in 14 rabbits. The other 4 animals underwent a sham operation as the controls. From postoperative one to twenty-four weeks, the animals underwent retrograde urethrography at certain intervals. The grafts of the acellular matrix were taken and prepared for histological evaluation. RESULTS: No obvious urethral stricture was observed in the 14 matrix-grafted animals. Histological examinations of the specimens showed progressive infiltration of cells and vascular vessels. Complete epithelization was obtained at 2 weeks. The orientation of collagen fibers in the matrix-grafted area tended to be regular with time. CONCLUSIONS: Freeze-dried acellular bladder submucosa may be a suitable material for urethral defect repair, which induces urethral mucous cells to migrate, grow and epithelialize.

Animals↗

PubMed2005

Spray freeze drying to produce a stable Delta(9)-tetrahydrocannabinol containing inulin-based solid dispersion powder suitable for inhalation.

The purpose of this study is to investigate whether spray freeze drying produces an inhalable solid dispersion powder in which Delta(9)-tetrahydrocannabinol (THC) is stabilised. Solutions of THC and inulin in a mixture of tertiary butanol (TBA) and water were spray freeze dried. Drug loads varied from 4 to 30 wt.%. Various powder characteristics of the materials were determined. Stability of THC was determined and compared with freeze dried material. The powders, dispersed with an inhaler based on air classifier technology, were subjected to laser diffraction analysis and cascade impactor analysis. Highly porous particles having large specific surface areas (about 90 m(2)/g) were produced. At high drug loads, THC was more effectively stabilised by spray freeze drying than by freeze drying. Higher cooling rates during spray freeze drying result in improved incorporation. Fine particle fractions of up to 50% were generated indicating suitability for inhalation. It was concluded that spray freeze drying from a water-TBA mixture is a suitable process to include lipophilic drugs (THC) in inulin glass matrices. High cooling rates during the freezing process result in effective stabilisation of THC. The powders can be dispersed into aerosols with a particle size appropriate for inhalation.

Administration, Inhalation↗

PubMedDate not supplied

Folic acid content in thermostabilized and freeze-dried space shuttle foods.

This study was designed to determine whether freeze-dried and thermostabilized foods on a space shuttle contain adequate folate and to investigate any effects of freeze-drying on folacin. Frozen vegetables were analyzed after three states of processing: thawed; cooked; and rehydrated. Thermostabilized items were analyzed as supplied with no further processing. Measurable folate decreased in some freeze-dried vegetables and increased in others. Folacin content of thermostabilized food items was comparable with published values. We concluded that although the folacin content of some freeze-dried foods was low, adequate folate is available from the shuttle menu to meet RDA guidelines.

Folic Acid↗

PubMed1993

Survival differences among freeze-dried genetically engineered and wild-type bacteria.

Because the death mechanisms of freeze-dried and air-dried bacteria are thought to be similar, freeze-drying was used to investigate the survival differences between potentially airborne genetically engineered microorganisms and their wild types. To this end, engineered strains of Escherichia coli and Pseudomonas syringae were freeze-dried and exposed to air, visible light, or both. The death rates of all engineered strains were significantly higher than those of their parental strains. Light and air exposure were found to increase the death rates of all strains. Application of death rate models to freeze-dried engineered bacteria to be released into the environment is discussed.

Air↗

PubMed1963

Preservation of bacteria by circulating-gas freeze drying.

Water-washed Serratia marcescens and Escherichia coli were freeze dried in a circulating-gas system at atmospheric pressure. This convective procedure resulted in a substantially higher survival of organisms than could be obtained by the vacuum method of freeze drying. There was little or no decrease in cell viability during convective drying when the residual moisture content was 15% or higher. Below this level, survival declined with decreasing moisture content. A detailed comparison of the convective and vacuum methods indicated that the advantage gained by freeze drying bacteria in air accrues in the early period of sublimation, at which time cells were found to be sensitive to vacuum drying but insensitive to air drying. An explanation for this difference is proposed, based upon the kinetics of water removal in the two processes. In brief, it is suggested that the convective method permits samples to be dried more uniformly; and regional over-drying, which may be deleterious even if transient, is thus avoided in achieving the optimal level of moisture.

Atmospheric Pressure↗

PubMed1977

Freeze drying cattle blood typing reagents.

A system is described for freeze drying and storage of reagents (antisera) used in cattle blood typing tests. Reagents were freeze-dried in evacuated bottles at the desired dilution for rapid reconstitution to use in test procedures. Reagents not in current use were dried in bulk lots and stored in polyethylene film bags. All freeze drying procedures were performed with readily available commercial equipment. A computer program was developed to produce a current inventory of reagent supplies and projections of the number of samples which can be typed.

Animals↗

PubMed2005

Storage stability assessment of freeze-dried royal jelly by furosine determination.

The effect of freeze-drying and the assessment of the storage stability of freeze-dried royal jelly (RJ) were investigated by the determination of furosine and blocked lysine. The level of furosine in the RJ samples collected from cells at different times (1, 2, and 3 days after grafting) showed that the Maillard reaction had already occurred in the hive as indicated by the increase in furosine: from 9.6 to 20.8 mg/100 g of protein. Freeze-dried RJ was more prone to the early stage of the Maillard reaction than fresh RJ, as confirmed by the significantly higher furosine values found after 12 months, both at 4 degrees C (253.4 versus 54.9 mg/100 g of protein) and at room temperature (884.3 versus 332.5 mg/100 g of protein). After 18 months at room temperature, the lyophilized samples reached a furosine level of 1440.4 mg/100 g of protein, which corresponded to the blocked lysine levels, amounting to 24% of total lysine.

Animals↗

PubMed2004

Freeze-dried sperm fertilization leads to full-term development in rabbits.

To date, the laboratory mouse is the only mammal in which freeze-dried spermatozoa have been shown to support full-term development after microinjection into oocytes. Because spermatozoa in mice, unlike in most other mammals, do not contribute centrosomes to zygotes, it is still unknown whether freeze-dried spermatozoa in other mammals are fertile. Rabbit sperm was selected as a model because of its similarity to human sperm (considering the centrosome inheritance pattern). Freeze- drying induces rabbit spermatozoa to undergo dramatic changes, such as immobilization, membrane breaking, and tail fragmentation. Even when considered to be "dead" in the conventional sense, rabbit spermatozoa freeze-dried and stored at ambient temperature for more than 2 yr still have capability comparable to that of fresh spermatozoa to support preimplantation development after injection into oocytes followed by activation. A rabbit kit derived from a freeze-dried spermatozoon was born after transferring 230 sperm-injected oocytes into eight recipients. The results suggest that freeze-drying could be applied to preserve the spermatozoa from most other species, including human. The present study also raises the question of whether rabbit sperm centrosomes survive freeze-drying or are not essential for embryonic development.

Animals↗

PubMed1999

Effect of freeze-dried soybean curd (tofu) on various bodily functions.

The present study was designed to examine the effect of freeze-dried soybean curd (tofu) on various bodily functions. The dietary experiment consisted of 4 days of a non-prescribed ordinary diet, 10 days of an experimental diet that contained 190 g of meat contributing about 38 g of protein (hereinafter referred to as the "meat period"), and 39 days of an experimental diet that contributed vegetable protein, i.e., freeze-dried tofu, corresponding to the protein that 190 g of meat would provide (hereinafter referred to as the "freeze-dried tofu period"). Three eggs (about 150 g) and 180 ml of cow's milk were prescribed for the daily diet, and staple and other foods were dispensed freely during both the meat and the freeze-dried tofu periods. The results showed that serum cholesterol levels and diastolic blood pressure significantly decreased in the freeze-dried tofu period as compared with the meat period. Freeze-dried tofu was found to be a valuable food for preventing lifestyle-related chronic diseases.

Adult↗

PubMed2005

Bioequivalence of liquid and freeze-dried recombinant human follicle-stimulating hormone.

OBJECTIVE: The bioequivalence and tolerability of freeze-dried and liquid formulations of recombinant human follicle-stimulating hormone (r-hFSH) filled-by-mass were assessed in a crossover, open-label, randomised, single-centre, phase I bioequivalence study. METHODS: Following pituitary down-regulation with the gonadotrophin-releasing hormone agonist goserelin, healthy adult volunteers (18years-45years of age) received single subcutaneous injections of r-hFSH , 300 IU, from freeze-dried and liquid formulations in random order, separated by a 7-day washout period. Blood was obtained over 144 h for pharmacokinetic analysis. MAIN OUTCOME MEASURES: These were peak serum FSH concentrations (Cmax,), time to peak concentration (Tmax) and area under the concentration-time curve from zero to the last measurable concentration (AUCJ), local and systemic tolerability. RESULTS: Of 44 volunteers who underwent down-regulation, 39 (18 men, 21 women) completed the study. Cmax and AUClast were similar with the freeze-dried (mean 9.51 IU/L and 844 IU.h/L, respectively) and liquid (mean 8.99 IU/L and 841 IUh/L, respectively) formulations, whereas T was significantly higher with the liquid formulation (median 12h vs 15h, p = 0.0183). The 90% confidence intervals for the ratio of the treatment means for Cnw and AUC,=, were within the pre-defined bioequivalence range of 0.8-1.25. CONCLUSION: Both formulations were well tolerated with regard to both systemic and local adverse events. The freeze-dried and liquid formulations of r-hFSH are bioequivalent and show no significant differences in tolerability. Thus, the liquid formulation is expected to provide comparable efficacy and tolerability to the freeze-dried formulation in clinical use.

Adolescent↗

PubMed2002

Freeze-dried and resin-embedded biological material is well suited for ultrastructure research.

Transmission electron micrographs of different biological material, cryofixed, freeze-dried and embedded in Spurr's resin, in Epon, or in Lowicryl, are presented. The structure preservation obtained either without or with application of chemical fixatives after drying showed that freeze-dried embedded specimens are particularly well suited for new morphological, immunocytochemical and microanalytical studies aimed at detecting the life-like subcellular distribution of mobile macromolecules and ions. The results also indicate that the removal of cell water by freeze-drying from the areas of best cryofixation is relatively slow. Ultrathin sections of well cryofixed biological material embedded after freeze-drying in Spurr's resin or Epon reveal cellular plasma phases with very fine granularities and well defined membranes in negative contrast. This may be due to the preservation of the original structure of cellular macromolecules with a considerable amount of their hydration water. Sublimation studies with differently hydrated and cryofixed macromolecules are suggested to settle this issue.

Acrylic Resins↗