Gel freeze-drying

Ding SQ, Zeng YP, Jiang DL (2007) Fabrication of mullite ceramics with ultrahigh porosity by gel freeze drying. J Am Ceram Soc 90 2276-2279... 

Aloe vera gel (freeze-dried) produced no toxic effects in rats from either acute or sub-chronic oral doses (l-64mg/kg p.o. twice daily). In mice or rats, the preserved or fresh gel failed to cause any toxicity at doses up to 20 g/kg p.o. or i.p., and no toxic effects were found from a dose of 5 g/kg p.o. per day for 45 days. Life-long dosing of a freeze-dried filet of the leaves at 1% of the diet also failed to produce any deleterious effects. ... 

Y.H. Huang, O.L. Jiang, and J.X. Zhang, et al., Fabrication of Transparent Yttria Ceramics Through Gel-freezing Dry Method, J.inorg.Maier., 23[6 1135-1140(2008). 

Ereeze casting (59) is a hybrid of sHp casting, gel casting, and freeze drying in which a slurry is poured into a rigid mbber mold, frozen, and the frozen Hquid is removed by sublimation, ie, by freeze drying (see Cryogenics). 

Supercritical and Freeze Drying. To eliminate surface tension related drying stresses in fine pore materials such as gels, ware can be heated in an autoclave until the Hquid becomes a supercritical fluid, after which drying can be accompHshed by isothermal depressurization to remove the fluid (45,69,72) (see Supercritical fluid). In materials that are heat sensitive, the ware can be frozen and the frozen Hquid can be removed by sublimation (45,69). 

C. Isolation and purification of XK-62-2 100 g of the white powder obtained in the above step B are placed to form a thin, uniform layer on the upper part of a 5 cm0X 150 cm column packed with about 3 kg of silica gel advancely suspended in a solvent of chloroform, isopropanol and 17% aqueous ammonia (2 1 1 by volume). Thereafter, elution is carried out with the same solvent at a flow rate of about 250 ml/hour. The eluate is separated in 100 ml portions. The active fraction is subjected to paper chromatography to examine the components eluted. XK-62-2 is eluted in fraction Nos. 53-75 and gentamicin Cja is eluted in fraction Nos. 85-120. The fraction Nos. 53-75 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate Is then dissolved in a small amount of water. After freeze-drying the solution, about 38 g of a purified preparate of XK-62-2 (free base) is obtained. The preparate has an activity of 950 units/mg. Likewise, fraction Nos. 85-120 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate is then dissolved in a small amount of water. After freeze-drying the solution, about 50 g of a purified preparate of gentamicin Cja (free base) is obtained. 

Because most food matrices are water soluble, many efforts were directed to the formulation of lipophilic pigments (mainly carotenoids) into water-soluble formulations (powders or gels). For hydrophilic pigments like flavonoids, polar dried microcapsules are the most popular ways to stabilize their functionality. Extracts rich in P-carotene were encapsulated using three different encapsulation techniques (spray drying, drum drying, and freeze drying)." ... 

Figure 2. SDS-PAGE of culture supernatants. Freeze-dried samples were resuspended in distilled water, mixed with an equal volume of sampling buffer and heated to 100°C for 5 min. lOpl aliquots were applied to the gel. The right lane contains standards of Mr 14-66 kDa. Lanes 2, 3, 4 and 1 are increasing dilutions of the supernatant respectively.

Figure 8.7 Overview of the manufacture of Betaferon, a recombinant human IFN-(3 produced in E. coli. The product differs from native human IFN-(3 in that it is unglycosylated and cysteine residue 17 had been replaced by a serine residue. E. coli fermentation is achieved using minimal salts/glucose media and product accumulates intracellularly in inclusion body (IB) form. During downstream processing, the lbs are solubilized in butanol, with subseguent removal of this denaturant to facilitate product refolding. After two consecutive gel-filtration steps, excipients are added, the product is filled into glass vials and freeze-dried. It exhibits a shelf life of 18 months when stored at 2-8 °C...

Streptokinase is a 48 kDa extracellular bacterial protein produced by several strains of Streptococcus haemolyticus group C. Its ability to induce lysis of blood clots was first demonstrated in 1933. Early therapeutic preparations administered to patients often caused immunological and other complications, usually prompted by impurities present in these products. Chromatographic purification (particularly using gel filtration and ion-exchange columns) overcame many of these initial difficulties. Modern chromatographically pure streptokinase preparations are usually supplied in freeze-dried form. These preparations (still obtained by non-recombinant means) often contain albumin as an excipient. The albumin prevents flocculation of the active ingredient upon its reconstitution. 

In the first freeze drying plant [2.9] phosphorous pentoxide has been used to absorb the water vapor, but to day this technique is outdated. The development of refrigeration technology with compressors or NH3 absorption and the availability of LN2 has replaced water absorption by silica gel or similar products. Some trials aiming to revive this technology are detailed in Section 1.2.6. 

The RM of the dried product was measured at 50 °C over P205 or in an oven with circulating air at 50 °C, or in the same oven at 90 °C over silica gel. Identical measurements were made with fresh bones. For NMR measurements, a known amount of D20 was added to the bone in a glass container. After equilibrium between DzO and H20 was reached, a known amount of the product was taken from the solution and studied in a Perkin Elmer NMR-spectrometer. In Fig. 3.23 the water contents of fresh and freeze dried bones are listed measured by NMR and the gravimetric methods at 90 °C. The data show that only a certain amount of the total water can be removed at 90 °C, while another amount is so... 

The determination of the molecular weight of nanoparticles is performed by gel permeation chromatography (GPC). The experimental setup consists of a high performance liquid chromatography system with a size exclusion column and a refractive index detector. The nanoparticles are usually freeze-dried and dissolved in tetrahydrofuran for analysis on the system. Poly(styrene) or poly(methylmethacrylate) standards are used to calibrate the column, to enable the determination of number average molecular weight (Mn), as in... 

Finally, radiochemical methods of analysis may be used to follow rates of detritiation. This method is particularly useful for very slow reactions (where it is impractical to collect data for any appreciable extent of reaction) as an initial rate approach may then be employed. Separation difficulties, at least for aqueous solutions, may be overcome by using the freeze-drying method or the more recent countercurrent dialysis and Sephadex gel filtration techniques. ... 

Figure 1. Freeze-dried gel of A. xylinum cellulose ribbons deposited during normal growth. The arrows point to triple-stranded left-hand helical microfibrils averaging 36.8 3A in diameter (1). The sample was replicated with 17.3A Pt-C and backed with 90.2A of carbon. 

The gel from the purified tobacco pectin was formed on 1.3 cm ashless Whatman 50 filter paper discs which were frozen in propane at about — 190°C. These samples were then freeze-dried (90 min) at —70°C, replicated with 16.9A Pt/C at —178°C in a 5 x 10-8 torr. vacuum and backed with 146A of carbon. Finally, these samples were digested with 80% sulfuric acid, rinsed with deionized water, picked up from underneath with... 

Since the x-ray fiber diffraction measurements based on citrus pectin (32) were consistent with the TEM measurements of tobacco pectin, we prepared a gel from citrus pectin similar to the previous x-ray sample. This gel was then examined by TEM. Air-dried samples of this gel, shown in Figure 5, demonstrated long stretches of helix in the molecules lying on the surface. (In the freeze-dried gels—not shown—only short stretches of helix were visible.) The average filament width in the air-dried gel was found to be 14.2A. After correcting for the added size due to the Pt/C coating... 

In conclusion, we have demonstrated that high resolution TEM is a valuable complement to x-ray fiber diffraction analysis and chemical structural elucidation. Its application provided information about the organization of pectin in cell walls and in calcium-free gels. Using freeze-dried samples that were Pt/C replicated, we demonstrated tobacco pectin filaments in a gel to be of the same diameter as the filaments on the noncutinized lower epidermal surface of senescing Coker 319 tobacco leaves. These filaments were 7.1 3A and 4.6 4.8A, respectively, and roughly the same diameter, 7A, as fiber-diffraction modeled citrus pectin (32). Replicated... 

Figure 4A. Freeze-dried, Pt/C replicated gel prepared from deesterified tobacco pectin. (Bar = 10,000A.)...

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