Abstract
Background:
Disaccharides are in general first choice as formulation compounds when freezedrying microorganisms. Although polysaccharides and other biopolymers are considered too large to stabilize and interact with cell components in the same beneficial way as disaccharides, polymers have been reported to support cell survival. In the present study we compare the efficiency of sucrose, the polymers Ficoll, hydroxyethylcellulose, hydroxypropylmethylcellulose and polyvinylalcohol to support survival of three bacterial strains during freeze-drying. The initial osmotic conditions were adjusted to be similar for all formulations. Formulation characterization was used to interpret the impact that different compound properties had on cell survival.
Results:
Despite differences in molecular size, both sucrose and the sucrose based polymer Ficoll supported cell survival after freeze-drying equally well. All formulations became amorphous upon dehydration. Scanning electron microscopy and X-ray diffraction data showed that the discerned differences in structure of the dry formulations had little impact on the survival rates. The capability of the polymers to support cell survival correlated with the surface activity of the polymers in a similar way for all investigated bacterial strains.
Conclusion:
Polymer-based formulations can support cell survival as effectively as disaccharides if formulation properties of importance for maintaining cell viability are identified and controlled.