Functional Colloidosomes: Tunable Permeability and Stimilus-Responsive Release
Abstract
Self-assembly of colloidal particles in the liquid interface of double emulsion droplets can be used to fabricate "colloidosome" microcapsules, which have great potential as vehicles for the controlled delivery of drugs or other cargoes. We have developed
Pickering emulsion-based microcapsules that dissolve rapidly upon a pH change under mild solution conditions through the use of
responsive particles made from polymers with pH-switchable solubility. These capsules combine the sturdiness and pore size control
of colloidosomes with the option of triggered disassembly known from stimulus-responsive Pickering emulsions. Modifications on the
capsule preparation method allow the generation of a novel class of aqueous core colloidosomes that combine the benefit of low
capsule permeability (good cargo retention) with the option of a stimulus-triggered fast release in a target environment. The capsule
permeability prior to release can be controlled by three different methods. Complete or partial dissolution of the capsule walls in
response to a mild pH change is achieved in each case. Protein stability against aggregation is significant both in the context of disease markers and the integrity of therapeutic agents. In
biotechnology, irreversible protein aggregation is a frequently prevalent problem in the production, formulation, shipping, and storage
of therapeutic proteins because aggregation reduces the protein's efficacy. Typical aggregation studies require monitoring over
the course of days, weeks or months. This study presents a convenient, accurate and quick (~30 min) way of inferring information
about medium-specific protein aggregation tendencies from stable protein samples. Salt-induced protein aggregation is studied with
dynamic light scattering (DLS) in solutions of lysozyme and bovine serum albumin (BSA) containing different sodium salts. The same
ions are used in a second measurement series assessing the effect of more dilute electrolytes on protein diffusivity in
non-aggregating protein dispersions. Both aggregation and stable diffusion exhibit strong ion specificity along the lines of the
Hofmeister series: chaotropic counterions act as the strongest coagulants and, in stable protein solutions, lead to the lowest
"protein interaction parameter (ν)". Within this common qualitative trend, lysozyme and BSA solutions show marked
differences, including the sign of ν for most counterions tested. Despite the different nature of lysozyme and BSA, a strong
correlation is found in both cases between the ion-specific interaction parameter and the protein's aggregation tendency as
indicated by the salt concentration required for fast aggregation.