Methods for the fabrication of polyelectrolyte capsules for different biomedical applications

Polyelectrolyte capsules (PEC) are hollow polymer particles fabricated by layer-by-layer (LbL) assembly of subsequently deposited polyelectrolytes of alternating charge. PECs, valued for their tunability and cargo encapsulation capabilities, are interesting for biomedical applications, underscoring the need for standardized fabrication and characterization techniques to optimize it for specific biomedical tasks. Here common protocols on how to synthesize and characterize such capsules are summarized. The fabrication of both, biodegradable and non-biodegradable capsules ranging in size from 800 nm to 5 μm is outlined. The entire preparation process-from the synthesis of sacrificial templates with diverse sizes and morphologies, to the controlled LbL deposition of polyelectrolyte shells and subsequent core dissolution is detailed. Here, calcium carbonate is selected as the sacrificial template of focus, owing to its high biocompatibility and loading capacity. Particular emphasis is placed on strategies for cargo loading, including co-precipitation and post-loading methods. Furthermore, the key characterization methods essential for confirming PEC formation-including size and zeta potential measurements (via dynamic light scattering), capsule concentration analysis (using optical or fluorescence microscopy), cargo encapsulation quantification (by UV-Vis spectroscopy or fluorescence analysis), and structural analysis (using transmission electron microscopy, TEM)-are highlighted and discussed. Finally, the review addresses current advantages and limitations in PEC fabrication, such as scalability and uniformity, and proposes future directions involving microfluidics, automation, and template design for the next generation of advanced biomedical applications.