Polystyrene particles of 50 nm and 500 nm in size adhere to model cell membranes through hydrophobic interactions and van der Waals forces, but do not penetrate these membranes in the absence of cellular machinery, demonstrating that passive penetration into living cells requires active cellular processes beyond simple membrane partitioning.

Tiny plastic particles stick to cell membranes because they are oily and naturally attract to the fatty parts of the membrane. They can slip directly inside the cell without help from the cell, or the cell can actively pull them in using special machinery. Once inside, the particles end up in waste compartments called lysosomes, which then either dump them back out by fusing with the membrane or the particles leak back out on their own through the fatty layer of the membrane.