Understanding the encapsulation and release of small molecular weight model actives from alginate fluid gels

The inclusion of actives within a range of biopolymer-based formulated gelled systems has been receiving significant attention. Among these, encapsulation in gelled microparticles has generated substantial interest, but such systems still face challenges for scalable production. Fluid gels are a class of soft-solid particles produced via high-shear approaches that are suitable for industrial manufacture. However, their use for the entrapment of species of therapeutic/nutritional activity has been scarcely investigated. The aim of this work was to study the encapsulation/retention of different small molecular weight actives of varied hydrophilicity/hydrophobicity within alginate fluid gels (AFG). The presence of an active during AFG formation did not interfere with gel particle dimensions nor bulk rheological behaviour. Following production, encapsulation of all actives within the fluid gel particles was very low, but significantly increased for the hydrophobic ones with storage. The rate and extent of hydrophobic active loading in the AFG particles were governed by the concentration of the former and gel particle size. Release studies under sink conditions revealed that hydrophobic active content within the AFG particles is not expelled and remains fully entrapped regardless of fluid gel particle size and storage period. A hypothesis suggesting that the loading of hydrophobic actives within the AFG particles is due to changes to the solvent quality of water, is presented. Overall, the current study offers insight into the use of alginate fluid gels as encapsulation media and presents original findings that can greatly support future efforts to expand the applicability of these industrially-relevant colloidal systems.