An Aqueous Polymer Two-Phase System as Carrier in the Spray-Drying of Biological Material

This investigation describes a novel concept in the formulation of carrier systems for the spray-drying of biological materials. As carrier material a system composed of poly(vinyl pyrrolidone) (PVP) and dextran was used. This system yields an aqueous two-phase system in which each phase is enriched in one of the polymers. By varying the composition of the system, the effective structure of a “stirred” system can be varied, covering the entire range from dextran continuous to PVP continuous. This facilitates encapsulation of either of these polymers in a spray-drying operation. In an attempt to investigate the spray-drying from such a system, the surface composition of the spray-dried powder obtained from various compositions of the two-phase system was analyzed by electron spectroscopy for chemical analysis (ESCA), providing information on the distribution of the polymers in the powder and thus also in the spray droplets. The two-phase system was applied for the spray-drying of live bacteria. The survival rate of the bacteria depended on the composition of the two-phase system. The storage stability of the bacteria in these formulations was investigated after storage at room temperature under dry conditions for 4 weeks, and it was found that the survival rate was 10–45%. The results therefore show that this type of formulation holds promise for future applications for micro-organisms as well as other sensitive biological materials such as proteins.