A Study of the Effect of Kosmotropic and Chaotropic Ions on the Release Characteristics of Lignin Microcapsules under Stimuli-Responsive Conditions

Abstract

Stimuli-responsive behavior of lignin microcapsules (LMCs) has been investigated along with the detailed characterization of their stability profiles. The disassembly of LMCs was found to be salt species-dependent, indicating the specific relevance of inherent kosmotropic and chaotropic characteristics. For the first time, a connection between the Hofmeister series and the stability profile of lignin microscale materials is established. LMCs showed excellent stability in water and under high temperature and pressure (autoclaving conditions). Active release is efficiently triggered by pH changes and balancing chaotropic and kosmotropic effects via salinity tuning.

Lignosulfonate Microcapsules for Delivery and Controlled Release of Thymol and Derivatives

“…For the generation of microcapsules from natural polyphenols (NPs), sonochemistry proved to be exceptionally useful, as demonstrated in various studies before [8,12,17,21,22]. Capsules were generated according to a protocol previously validated for SLS [12] starting from an oil-in-water (o/w) emulsion that was obtained by mixing and vigorously shaking a 1/1-mixture (v/v) of the following two solutions: a 5 mg/mL aqueous solution of softwood lignosulfonate (SLS) at pH = 12 and a 5 mg/mL solution of thymol derivative in olive oil spiked with 5% (m/m) of linoleic acid (LA). The alkaline environment was previously shown to be necessary to both guarantee highly amphiphilic character and full solubility of the oligomeric and polymeric lignins for reliable capsule generation [12].…”

“…This affects not only solubility and, thus, distribution of the actives between the oil and the water phase, but also the possible types of electronic interactions the actives can be undergone with the lignosulfonate shell material on the basis of the aromatic moieties present in the systems. An overview of such interactions and the effects of various conditions on their stability have also been discussed before for lignosulfonate capsules [12]. The lignosulfonate is principally capable of acting as surfactant, a fact exploited since decades by now [45][46][47]; chosen conditions adapted from earlier studies [12] represent optimised conditions in the absence of an active.…”

“…Figure 1 shows a Figure 1. Generic structure of softwood lignosulfonate (SLS) oligomers used before in softwood lignosulfonate-based microcapsules (SLS-MC)-generation [12].…”

“…Encapsulation by sonication is a recently developed technique for the synthesis of natural polyphenols microcapsules that requires minimum amounts of time for preparation and only generates minimum amounts of aqueous waste [6,8,12,17]. The energy evolved during sonication can, in fact, trigger supramolecular stacking interaction in natural polyphenolic macromolecules, such as tannins or lignins, most noteworthy also without the addition of crosslinking, and thus eventually only additionally stabilizing agents [18][19][20].…”

“…Such materials show high stability, not only in the isolated form, but also in cosmetic media and, therefore, are interesting vectors for innovative formulation in health, personal care, and cosmetics. The structural features of The mix of functional groups renders typical LSs water soluble over a wide pH range [12,13]. Moreover, LSs possess a very interesting toxicity profile towards plants, animals, and humans, and they are consequently used as technological additives, for example, as emulsifier in animal feeds [14,15].…”