Stiffness‐Gated Cytoplasmic mRNA Delivery Through Engineered Membrane Fusion for Breast Cancer Immunotherapy

ABSTRACT Traditional lipid nanoparticles (LNPs) suffer from low lysosomal escape efficiency (<4%) and off‐target toxicity, hindering mRNA therapy translation. While membrane fusion carriers bypass endosomal entrapment, their lack of cell specificity induces non‐target cytotoxicity. To overcome these limitations, we developed a stiffness‐gated mRNA delivery platform (PGC@FM). This system features a PLGA core loaded with G0‐C14 dendrimer/mRNA complexes and coated with an engineered, low‐stiffness tumor cell fusion membrane (FM). The membrane stiffness is strategically reduced via unsaturated fatty acid enrichment, enabling direct cytoplasmic delivery through selective fusion with low‐stiffness target cells. Conversely, encountering high‐stiffness non‐target cells, PGC@FM undergoes endocytosis and lysosomal degradation, minimizing off‐target effects. Compared to LNPs, this stiffness‐gated strategy enhanced EGFP‐mRNA transfection efficiency in 4T1 cells by 5.2‐fold and increased tumor‐specific p53‐mRNA delivery efficiency by 4.2‐fold, resulting in potent tumor suppression and immune activation. Crucially, non‐target cells rapidly degrade internalized PGC@FM in lysosomes, significantly reducing off‐target toxicity compared to conventional fusion carriers. These research results indicate that by leveraging the biophysical principle of membrane rigidity compatibility, highly selective mRNA delivery can be achieved, providing new ideas for the development of mRNA delivery carriers.