Organic–Inorganic Multilayer Microcarriers with Superior Mechanical Properties for Potential Active Delivery in Fast-Moving Consumer Goods

This study introduces an eco-friendly approach to fabricating superstrong, core-shell, composite microcapsules, offering a sustainable alternative to traditional insoluble microplastic-based materials like melamine-formaldehyde. These microcapsules were engineered with a thick CaCO3 shell formed via crystal ripening in the presence of water-soluble poly(acrylic acid), encasing a hexylsalicylate oil core armored by hydrophilic SiO2 nanoparticles. An additional polydopamine layer was deposited via oxidative autopolymerization at pH 8.5 for improved structural and surface properties of the resulting microcapsules. These microcapsules (D 3,2 = 8.8 ± 0.3 μm) were spherical, with a relatively smooth surface, and exhibited unique mechanical properties, which are essential to broaden their applications in industry. Remarkably, compression tests showed a mean rupture stress of 73.5 ± 5.0 MPa, which dramatically surpasses any other inorganic/synthetic microcarrier reported in the literature. In addition, only 10-20% of the core active was released within 2 h into a mixed water-propanol medium used as an accelerated release test, where the solubility of the active oil is high, with full release over 3 days. Herein, we also propose a novel pathway-specific binding constant (PSBC) that describes the strong interaction between Ca2+ ions and poly(acrylic acid), in connection with their stoichiometric ratio. Overall, these microcapsules hold promise for multiple fast-moving consumer goods, where maximizing the mechanical strength of microcapsules for encapsulation of valuable functional actives is paramount; this includes but is not limited to energy storage, household, agrochemical, personal care, and healthcare applications.