Many experiments show that the strong polycationic PEI should be sheltered with activated PEI in order to protect the cell from toxic effect. The activated PEG can associate with PEI to form an amphiphilic structure, and this assemblies inverted micelles with the addition of PDNA. The inverted micelles is therefore can enter the cell actively, while PEG which is covalently bound with PEI reduces the PEI toxic effect dramatically on cells.
