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.