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Freezing Step (freezing + step)
Selected AbstractsFreeze-drying of tert- butanol/water cosolvent systems: A case report on formation of a friable freeze-dried powder of tobramycin sulfateJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2002Sakchai Wittaya-Areekul Abstract A case study is presented in which a tert -butanol (TBA)/water cosolvent system was found to be a useful means of producing freeze-dried tobramycin sulfate that readily forms a loose powder upon agitation in a specialized application in which a critical quality attribute is the ability to pour the sterile powder from the vial. Both formulation and processing variables are important in achieving acceptable physical properties of the cake as well as minimizing residual TBA levels. Liquid/liquid phase separation was observed above critical concentrations of both drug and TBA, resulting in a two-layered lyophilized cake with unacceptable appearance, physical properties, and residual TBA levels. However, the choice of tobramycin sulfate and TBA concentrations in the single-phase region of the phase diagram resulted in a lyophilized solid that can readily be poured from vials. Crystallization of TBA before drying is critical to achieving adequately low residual TBA levels, and this is reflected in the effect of thermal history of freezing on residual TBA levels, where rapid freezing results in incomplete crystallization of TBA and relatively high levels of residual solvent. Annealing at a temperature above T,g of the system after an initial freezing step significantly reduces the level of residual TBA. Secondary drying, even at increased temperature and for extended times, is not an effective method of reducing residual TBA levels. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 1147,1155, 2002 [source] Maintenance of nonviral vector particle size during the freezing step of the lyophilization process is insufficient for preservation of activity: Insight from other structural indicatorsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2001Marion d.C. Molina Abstract The instability of nonviral vectors as liquid formulations has stimulated considerable interest in developing dehydrated formulations that would be resistant to shipping stresses and could be stored at room temperature. Recently, we reported that high sucrose/DNA ratios are capable of maintaining particle size during the freezing step of the lyophilization process and we suggested that the separation of individual particles within sugar matrices is responsible for the reported protection of nonviral vectors during the freezing step of a typical lyophilization protocol. The purpose of this study was to extend these observations to other nonviral vectors that incorporate different cationic components. Cationic lipid-based complexes composed of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), with helper lipid cholesterol (Chol) or dioleoylphosphatidyl-ethanolamine (DOPE), showed similar protection by sucrose. Formulations of a polyethylenimine (PEI)-based vector required much higher excipient/DNA ratios for size protection compared with protamine- and lipid-based vectors. At low sucrose/DNA ratios, zeta potentials for all complexes were significantly lowered during freezing. Similar results were obtained at high sucrose/DNA ratios, except for DOTAP,DOPE-containing vectors which maintained zeta potential values comparable to unfrozen controls. The changes in zeta potential values indicate that complexes are altered during freezing despite the maintenance of particle size as determined by light scattering. Furthermore, these changes might explain the observed reduction in transfection activity and provide new information about the effects of physicochemical changes of nonviral vectors during the freezing step of lyophilization. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1445,1455, 2001 [source] RHEOLOGICAL CHARACTERIZATION OF WET FOOD FOAMSJOURNAL OF TEXTURE STUDIES, Issue 2 2007B. EDGAR CHÁVEZ-MONTES ABSTRACT Incorporating air bubbles into foods is a technical challenge, and in all cases, the fabrication of a foam goes through a "wet foam" stage, where bubbles are diluted in the food matrix and require stabilization. Sometimes, the end product is itself a wet foam, and a popular example is ice cream. This article describes a study of structural aspects of wet foams, where the continuous phase is a fluid, by means of dynamic rheological tests. The effects of formulation and processing conditions on aerated food foams are studied, and an example is presented for ice cream mix. The incorporation of gas bubbles at volume fractions of 50% or less modifies moderately the bulk rheological properties, and their effect can be predicted by the foam limit case. The continuous phase dominates to a great part the bulk's rheological behavior, and in the case of food systems, it stems from the presence of polysaccharide thickeners. PRACTICAL APPLICATIONS This work presents an alternative approach to study the rheological properties of short life and difficult-to-sample products, such as wet food foams, in a rheo-reactor. Through the analysis of mechanical properties in oscillatory regime, the structure and stability of wet food foams can be characterized immediately after being fabricated in situ. This work presents new insights on the foaming step of ice cream mix (decoupled from the freezing step), and shows how the mechanical properties are affected by the incorporation ofbubbles, by process conditions and by the presence of thickeners and emulsifiers. This work can be a valuable guide to decide on optimal process and formulation to fabricate wet food foams (e.g., ice cream, aerated desserts) with specific mechanical properties and stability. [source] Collapse temperature of solutions important for lyopreservation of living cells at ambient temperature,BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010Geer Yang Abstract In this study, the collapse temperature was determined using the freeze-drying microscopy (FDM) method for a variety of cell culture medium-based solutions (with 0.05,0.8,M trehalose) that are important for long-term stabilization of living cells in the dry state at ambient temperature (lyopreservation) by freeze-drying. Being consistent with what has been reported in the literature, the collapse temperature of binary water-trehalose solutions was found to be similar to the glass transition temperature (T,g , ,30°C) of the maximally freeze-concentrated trehalose solution (,80,wt% trehalose) during the freezing step of freeze-drying, regardless of the initial concentration of trehalose. However, the effect of the initial trehalose concentration on the collapse temperature of the cell culture medium-based trehalose solutions was identified to be much more significant, particularly when the trehalose concentration is less than 0.2,M (the collapse temperature can be as low as ,65°C). We also determined that cell density from 1 to 10,million cells/mL and ice seeding at high subzero temperatures (,4 and ,7°C) have negligible impact on the solution collapse temperature. However, ice seeding does significantly affect the ice crystal morphology formed during the freezing step and therefore the drying rate. Finally, bulking agents (mannitol) could significantly affect the collapse temperature only when trehalose concentration is low (<0.2,M). However, improving the collapse temperature by using a high concentration of trehalose might be preferred to the addition of bulking agents in the solutions for freeze-drying of living cells. We further confirmed the applicability of the collapse temperature measured with small-scale (2,µL) samples using the FDM system to freeze-drying of large-scale (1,mL) samples using scanning electron microscopy (SEM) data. Taken together, the results reported in this study should provide useful guidance to the development of optimal freeze-drying protocols for lyopreservation of living cells at ambient temperature for easy maintenance and convenient wide distribution to end users, which is important to the eventual success of modern cell-based medicine. Biotechnol. Bioeng. 2010;106: 247,259. © 2010 Wiley Periodicals, Inc. [source] | ||||||||||