Drying behaviour and visualization of surfactants after co-spray drying of surfactant-stabilized aqueous suspensions.

Surfactants are widely used in many industries as dispersants or flocculants for suspensions. As the addition of low concentrations of surfactant is sufficient to execute their effect, they barely alter the formulation composition. In this research it was examined whether surfactants, in particular polysorbate 80 (PS80), were suitable as suspension stabilizers for co-spray drying of drug-filler combinations. Therefore, their drying behaviour at different process and formulation settings was studied and mapped by means of fluorescently labelled PS80. Co-spray drying of 10% w/w aqueous suspensions stabilized with 0.1% w/w PS80 resulted in excessive loss of sticky powder in the conical lower part of the drying chamber and the powder conveyor ducts. Up to 16% of powder was lost in the first transporter (i.e. the first part of the conveyor ducts). The amount of powder deposited in the first transporter, and by extension the stickiness of the recovered powder, was correlated with the presence of PS80 on the surface of the spray dried particles. Redistribution of free surfactant molecules during droplet drying depended on the process and formulation parameters. Enrichment of PS80 at the particle surface was most pronounced after co-spray drying of liquid feedstocks with low suspended fraction at process conditions favouring rapid droplet drying.

Following the stability of amphiphilic nanoaggregates by using intermolecular energy transfer.

An intermolecular energy transfer system is developed for studying the stability of nanoaggregate(s) (NAs) in complex solution and cell culture by one- and two-photon fluorescence microscopy and optical imaging. The system allows facile addition of one or more tumor targeting molecules, one of which is exemplified here. NAs functionalized with an MRI and optical probe, with and without folic acid, remain stable in fetal bovine serum for at least 4 hours. HeLa cell cultures showed a clear difference between NAs non-targeted and targeted to folate receptors, with both NAs appearing to be taken up by the cells through different mechanisms. An MRI relaxivity, r1, of 9 mM-1 s-1 at 310 K and 1.4 T was measured associated with the increased rotational correlation time of the NAs. These NAs may have application in the targeted drug delivery of hydrophobic drugs such as doxorubicin (DOX).