The article by Gao, Shi, and Freund explores the mechanics of receptor-mediated endocytosis, focusing on how the size of a bioparticle affects its entry into animal cells. The authors develop a model to explain how a cell membrane with diffusive mobile receptors wraps around a ligand-coated cylindrical or spherical particle. They show that particles in the range of tens to hundreds of nanometers can enter or exit cells via wrapping, even without clathrin or caveolin coats, and that there is an optimal particle size for the smallest wrapping time. The model is extended to include the effect of clathrin coats and shows broad agreement with experimental observations. The study highlights the importance of particle size in receptor-mediated endocytosis, suggesting that an optimal particle size exists for efficient entry. This finding has implications for understanding the mechanisms of virus entry and the design of targeted drug delivery systems.The article by Gao, Shi, and Freund explores the mechanics of receptor-mediated endocytosis, focusing on how the size of a bioparticle affects its entry into animal cells. The authors develop a model to explain how a cell membrane with diffusive mobile receptors wraps around a ligand-coated cylindrical or spherical particle. They show that particles in the range of tens to hundreds of nanometers can enter or exit cells via wrapping, even without clathrin or caveolin coats, and that there is an optimal particle size for the smallest wrapping time. The model is extended to include the effect of clathrin coats and shows broad agreement with experimental observations. The study highlights the importance of particle size in receptor-mediated endocytosis, suggesting that an optimal particle size exists for efficient entry. This finding has implications for understanding the mechanisms of virus entry and the design of targeted drug delivery systems.