Designable synthetic complex coacervates enabling protein delivery to cells

Biomolecular condensates offer a versatile platform for the accumulation of biomacromolecules, particularly proteins. This study investigated synthetic complex coacervates as a model of biomolecular condensates and developed a novel tool for the intracellular delivery of proteins to overcome the issues of cytotoxicity and poor cellular uptake. By optimizing preparation conditions and chemical structures and developing a simple pre-coating method, we achieved an improvement in the interaction and internalization of coacervates for HeLa and Jurkat cells and the reduction of cytotoxicity. Furthermore, the use of charge-density reduced polymers enabled the effective encapsulation and intracellular delivery of various proteins. The mechanism of cellular internalization was also investigated, and macropinocytosis was concluded to be a primary internalization pathway. These findings provide a foundation for future advancements in biomaterials. Complex coacervates (CCs) are a promising platform for protein encapsulation obtained via simple mixing of some components. Using the novel precoating treatment of living cells, the cellular internalization of CCs was greatly enhanced. Besides, upon using the side-chain modified aniomers for CC fabrication, a wide variety of proteins were successfully encapsulated, which can expand the future biomedical application of CCs.