Programming Hierarchical Architectures in Biodegradable Microcapsules for Advanced Functions

Programming biomaterials at multiscale is critical in developing advanced technologies in addressing environmental issues. For instance, several industries have a compelling need to substitute open-used, non-degradable, intentionally added microplastics with biodegradable alternatives. Biopolymers extracted from natural products or food waste, such as regenerated silk fibroin, offer many merits. However, assembling biopolymers at multiscale remains challenging due to their complex compositions.<br/>To address this challenge, we present a biodegradable silk-based microencapsulation technique achieved by modulating the structural protein protonation and chain relaxation at the point of material assembly. It can sustain the release of soluble and insoluble payloads typically used in cosmetic and agriculture applications. Manufacturing through well-established fabrication techniques, such as spray drying, yields microcapsules with tunable morphology and degradation kinetics. As a proof-of-concept for agrochemicals delivery, a greenhouse trial demonstrated that a commonly used herbicide (i.e., Saflufenacil) delivered via silk microcapsules on corn plants reduced crop injury compared to the non-encapsulated version.<br/>Additionally, we introduce a synergistic assembly of biopolymer microparticles into hierarchical structures, such as spiny microcapsules and interconnected micro-network. We can tune the biopolymer type, geometry, structure, crystallinity, payload, and mechanical properties for different functions. For example, engineered multi-spines effectively improved the retention percentage of microcapsules on smooth spinach leaves after wash-off. Furthermore, the echinate micro-network can transfer and co-localize different fluorescent payloads in the micro-bridges. Our findings provide a platform for the advanced biopolymers assembly into functional structures, which is of great potential in agriculture, environmental remediation, and other applications that interact directly with the environment.