Industrial scale barrier technology for preservation of...

Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Process of storage or protection

Reexamination Certificate

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C422S001000, C422S041000, C422S309000, C252S501100, C252S521600, C435S243000

Reexamination Certificate

active

06306345

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to preservation of sensitive biological materials in the form of dehydrated powder stored at temperatures above 0° C. More particularly, the invention relates to a technological process for integrating the following steps: preservation of the biological materials by foam formation, subsequent drying and milling of the foam to form a dry powder, and formulation of mixed dry powder product (cereals) for different practical applications.
2. Description of the Related Art
The preservation and storage of solutions or suspensions of biologically active materials, viruses, cells and small multicellular specimens is important for food and microbiological industries, agriculture, medical and research purposes. Storage of these dehydrated biologically active materials carries enormous benefits, such as reduced weight and reduced storage space, and increased stability.
Suggestions in the prior art for providing preservation of sensitive biological materials in dehydrated form include freeze-drying and vacuum or air-desiccation. Both, freeze-drying and desiccation preservation methods have positive and negative characteristics. While freeze-drying methods are scaleable to industrial quantities, conventional vacuum and air-desiccation methods do not yield preparations of biological materials which are scalable to industrial quantities. Freezing and other steps of the freeze-drying process are very damaging to many sensitive biological materials. The freeze-drying process is very long, cost ineffective, and cannot be performed using barrier technology to ensure sterility of the material.
Some of the problems associated with preservation by freezing and drying have been addressed by addition of protectant molecules, especially carbohydrates, which have been found to stabilize biological materials against the stresses of freezing and drying. However, despite the presence of protectants, the long-term stability after freeze-drying may still require low temperature storage, in order to inhibit diffusion-dependent destructive chemical reactions. Thus, further innovations have been sought to provide long-term storage of labile biological materials at ambient temperatures.
Storage of dried materials at ambient temperatures would be cost effective when compared to low temperature storage options. Furthermore, ambient temperature storage of biological materials such as vaccines and hormones would be extremely valuable in bringing modem medical treatments to third world countries where refrigeration is often unavailable. As the many benefits of shelf preservation of biological specimens have come to be appreciated, researchers have endeavored to harness vitrification as a means of protecting biological materials against degradative processes during long-term storage. Consequently, this technology of achieving the “glass” state has been anticipated to emerge as a premier preservation technique for the future.
A glass is an amorphous solid state that may be obtained by substantial undercooling of a material that was initially in the liquid state. Diffusion in vitrified materials, or glasses, occurs at extremely low rates (e.g. microns/year). Consequently, chemical or biological changes requiring the interaction of more than one moiety are practically completely inhibited. Glasses normally appear as homogeneous, transparent, brittle solids, which can be ground or milled into a powder. Above a temperature known as the glass transition temperature (Tg), the viscosity drops rapidly and the glass becomes deformable and the material turns into a fluid at even higher temperatures. The optimal benefits of vitrification for long-term storage may be secured only under conditions where Tg is greater than the storage temperature. The Tg is directly dependent on the amount of water present, and may therefore be modified by controlling the level of hydration; the less water, the higher the Tg.
Unfortunately, the advantages of vitrification technology as a means of conferring long-term stability to labile biological materials at ambient temperatures has not been fully utilized. Conventional methods of ambient temperature preservation by dessication are designed for laboratory processing of very small quantities of materials. Recently, V. Bronshtein developed an alternative method of preservation by foam formation (U.S. Pat. No. 5,766,520) that is compatible with large-scale commercial operations. Preservation by foam formation overcomes the technical problems related to scaling up desiccation and vitrification preservation processes. For this reason, preservation by foam formation is attractive as a scalable method for long-term storage of biological materials.
The present invention solves instrumentation problems related to preservation by foam formation and processing operations. Specially designed devices and instruments must be employed to reproducibly produce a dehydrated, shelf-stable, foams and uniform powder of the preserved materials. The instruments should integrate the ability to execute a barrier scalable preservation of biological material by desiccation, subsequent transformation of the dry material into powder form (for example by milling) and usage of dry powders to formulate products that may contain mixtures of different biological materials.
SUMMARY OF THE INVENTION
The present invention relates to a barrier method for preserving a biological solution or suspension as a foam or powder. The method comprises the following steps: drying the biological solution or suspension in a chamber at non-damaging temperatures by first boiling the sample under vacuum to form a mechanically stable foam, second dehydrating the foams at elevated temperature to obtain the glass transition temperature required to insure stability of preserved materials during storage, and crushing (and/or milling) the mechanically stable foam to form a powder.
The method further provides that the biological solution or suspension may be combined with a protectant prior to drying. Similar to other methods of preservation in the dry state, sugars, polyols and their polymers can be used to protect the material from the damaging effect of desiccation. More specifically, the protectant comprises a mixture comprising a monosaccharide, a disaccharide, and a polymer. The monosaccharide may be selected from the group consisting of non-reducing derivatives of fructose, glucose, sorbose, piscose, ribulose, xylulose, erythulose, and the like. Such derivatives may be obtained by methylating, ethylating, chlorinating or otherwise modifying the reducing groups.
Prior to milling the foams it may optionally be further dried under conditions sufficient to increase its stability at a desired storage temperature. The increased stability obtained during this secondary drying procedure may be performed inside the drying chamber or outside the drying chamber during warehouse storage. Alternatively, the foam may be further dried under conditions sufficient to increase its glass transition temperature above a desired storage temperature. These further drying steps may be applied after the foam has been crushed to form a powder.
A means for crushing the foam may be incorporated into the chamber. The crushing means may comprise a mill selected from the group consisting of a brush mill, a rotating blade mill, a pulverizing mill, a rotary attrition mill, a jet mill, an incremental cutting action mill, a ball mill, a hammer mill, a rotary tubular mill, a homogenizer, and a sonicator. Alternatively, the crushing means may comprise a deformable container inside the chamber, wherein the drying step is conducted inside of the deformable container. Where drying is conducted in a deformable container, crushing may be accomplished by mechanically deforming the deformable container. To maintain sterility, consistent with barrier technology, the deformable container may be sealed prior to deforming the container.
A variation of the deformable container of the present invention is a gas-permeable

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