6.3.6　Layer-by-layer self-assembly technology

Polymer layer-by-layer self-assembly technology refers to the technology of alternating deposition of two or more kinds of polymers and drugs onto the substrate and controlling the structure and function of nano-drug carriers at the nanometer level.It is a new nanotechnology with great development prospects.The nano-drug carriers can be prepared by layer-by-layer self-assembly technology with NPs as substrate cores.The preparation condition of this method is mild.It is easy to prepare multifunctional carriers and the structure of the nano-drug carriers is precisely controlled.This method has unique advantages in the aspects of sustained release，controlled release，especially programmed release，which makes it have great prospects in the field of cancer treatment.The adsorption forces during layer-by-layer self-assembly deposition are mainly electrostatic interaction，hydrogen bond，covalent bond，hydrophobic interaction，etc.Layer-by-layer self-assembly of polyelectrolytes via electrostatic interaction has been most widely studied.Natural biological macromolecules，such as polypeptides，proteins，nucleic acids and most polysaccharide molecules，carry a large amount of electric charge in the solution.As a result，they are easily adsorbed by electrostatic interaction.Water-soluble drug molecules with charges can be loaded into the carriers by means of adsorption with high drug loading.Hydrophobic drug molecules are prior to be loaded into the substrate cores，such as charged surface of polymer NPs/capsules，micelles，and mesoporous silica.The nano-drug carriers obtained by this technology can load different drugs in different microdomain.For example，Ramasamy et al.prepared a nano-drug carrier through layer-by-layer self-assembly of poly（ethylene glycol）and polylysine with liposome micelles as the substrate cores.Moreover，the doxorubicin was loaded in core and mitoxantrone was loaded within multilayer films.(https://www.daowen.com)