Preservation of bioactive materials by freeze dried foam

DETAILED DESCRIPTION The present invention includes methods and compositions for preserving bioactive materials in storage.
The methods generally provide, e.
g.
, processes of expanding a formulation of the bioactive material and a polyol into a foam followed by drying the foam into a stable dry foam composition.
The methods can variously include, e.
g.
, freezing of the foam before drying, inclusion of foaming agents in the formulation, holding the formulation at the phase transition temperature of a lipid membrane to enhance penetration of protective agents, and/or expansion of the formulation at pressures between about 200 Torr and 25 mTorr.
A stable dry foam composition to preserve bioactive materials having lipid membranes can be prepared using the methods of the invention.
The methods generally include, e.
g.
, preparing a formulation of a polyol or polymer in a solvent (such as water or an alcohol) with the bioactive material, cooling the formulation to a temperature of about the phase transition temperature of the lipid membrane, expanding the formulation into a foam, and drying the foam by evaporation or sublimation to prepare a stable dry foam composition of the lipid membrane containing bioactive material.
For example, a formulation of a live attenuated influenza virus with about 40% sucrose, 5% gelatin, 0.
02% block copolymers of polyethylene and polypropylene glycol, and 25 mM 7.
2 pH KPO.
sub.
4 buffer can be aliquoted into glass lyophilization vials, cooled at a phase transition temperature of about 15.
degree.
C.
for about 30 minutes, expanded in a vacuum of about 50 mTorr for about one hour, and exposed to a drying temperature of about 33.
degree.
C.
for about 48 hours before sealing the vials.
The dry foam composition prepared by such a process can remain stable for at least about 2 years in storage at about 25.
degree.
C.
Another method of the invention calls for expanding the formulation into a foam at vacuum pressures higher than those described in the prior art.
For example, a formulation of a bioactive material (including membranes or not) in a solvent with a polyol or polymer, can be expanded into a foam (without requiring foaming agents) by exposure to a pressure less than 25 Torr, less than 8 Torr, less than 400 mTorr, or between about 200 mTorr and 25 mTorr, and the foam physically stabilized and dried by evaporation or sublimation of the solvent from the foam to prepare a dry foam composition