Preservation of bioactive materials by freeze dried foam
This invention provides methods and compositions to preserve bioactive materials in a dried foam matrix. Methods provide non-boiling foam generation and penetration of preservative agents at temperatures near the phase transition temperature of the membranes.
1. A method for preparing a stable dry foam composition comprising a bioactive material, wherein the bioactive material comprises a lipid membrane, which method comprises:
preparing a formulation comprising the bioactive material, and a polyol or polymer, in a solvent; determining the phase transition temperature of the lipid membrane;
adjusting the formulation to a temperature of the phase transition temperature of the lipid membrane;
expanding the formulation into a foam; and,
drying the foam by evaporation or by freezing the foam and drying the foam by sublimation, thereby preparing a stable dry foam composition of the bioactive material.
2. The method of claim 1 , wherein the bioactive material is selected from the group consisting of vaccines, bacteria, viruses, liposomes, platelets, and cell suspensions.
3. The method of claim 1 , wherein expanding the formulation comprises, degassing the formulation, boiling the formulation, forming a gas by chemical reaction, expanding bubbles suspended in the formulation, or injection, of bubbles into the formulation.
4. The method of claim 1 , wherein adjusting to the phase transition temperature comprises adjusting the formulation to a temperature ranging from about 2° C. to about 45° C.
5. The method of claim 1 , further comprising holding the formulation at the phase transition temperature for about 10 minutes to about 60 minutes.
6. The method of claim 1 , further comprising increasing the temperature of the formulation to a drying temperature that is less than or about a glass transition temperature of the dry foam.
7. The method of claim 1 , further comprising filling the formulation into a container, wherein the container comprises an etched or fritted bottom interior.
8. The method of claim 1 , further comprising administering the stable composition to a mammal as a reconstituted liquid or as a ground powder.
9. The method of claim 1 , wherein:
the bioactive material comprises a live attenuated influenza virus;
the formulation comprises about 40% sucrose, 5% gelatin, 0.02% block copolymers of polyethylene and polypropylene glycol, and 25 mM 7 . 2 pH KP04 buffer;
the method further comprises aliquoting the formulation into glass lyophilization vials;
adjusting the phase transition temperature comprises holding the vials at about 15° C. for about 30 minutes;
expanding the formulation comprises providing a vacuum of about 50 mTorr for about one hour;
the method further comprises increasing the temperature to about 33° C. and holding the temperature and pressure for about 48 hours; and,
the method further comprises sealing the vials.
10. The method of claim 1 , wherein said drying is by sublimation.
11. The method of claim 1 , wherein said step of adjusting the formulation to the temperature comes before said step of expanding the formulation into a foam.
12. The method of claim 1 , further comprising holding the formulation at the membrane phase transition temperature for at least 10 minutes.
13. The method of claim 1 , wherein said step of drying comprises freeze-drying.