Sonochemically triggered self-assembly of lignins microcapsules for storage and delivery applications

Nanostructures of natural polymers have received steadily growing interest as a result of their peculiar properties and applications superior to their bulk counterparts. These nanostructures can be generated in aqueous medium, avoiding thus the use of eventually environmentally non-benign organic solvents. Along these lines, we achieved the encapsulation of active small molecules into micro- and nano-scaled capsules made out of lignins using sonochemistry. The ultrasound technique proved to be an essential tool in this production of nano- and micro-scaled features, since it offers simplified ways to achieve reactions and size-determining conditions. Starting from oil in water emulsions containing lignins and eventually actives to be incorporated, we present thus a rapid, simple, and robust method of one step assembly of lignins and their suitable coordination complexes into metal-free as well as iron-re-enforced nano- and microcapsules, LNCs, LMCs, Fe-LNCs and Fe-LMCs, respectively; assembly is generally driven mainly by physical interactions, with only marginal chemical modification during sonication (quantitative 31P NMR, gel permeation chromatography). Studies regarding effective loading and release capacities under various conditions show increased stability of Fe-LN(M)Cs with respect to LN(M)Cs as an additional effect of the complexation of the metal ions by the various phenolic OH groups in addition to the stacking interactions occurring in the LN(M)Cs. Fe-LN(M)Cs showed also reduced shell thickness and thus increased encapsulation efficiency and slower release kinetics when compared to corresponding LN(M)Cs.