6.3.2　Solution self-assembly

In selective solvents，when the concentration of an amphiphilic block copolymer is above its critical micelle concentration（CMC），the block copolymer spontaneously aggregate into assemblies with hydrophobic chains as the core whereas hydrophilic chains as the corona.This process is known as solution self-assembly（Figure 6-2）.According to the block ratio of hydrophilic block to hydrophobic block，assemblies of various morphologies，including spherical micelles，vesicles，or other shaped micelles can be obtained.During the selfassembly process，hydrophobic drugs can be loaded in the core of the spherical micelles or the wall of vesicles，whereas hydrophilic drugs can be encapsulated inside vesicles or linked on the surface of carriers.Solution self-assembly is a robust and simple method，and the surface of carriers are hydrophilic polymer chains，which are conducive to the stability，targeting，circulation in vivo of nano-drug delivery system.Due to these advantages，solution self-assembly has become the mostly used method for the preparation of nano-drug delivery systems in the clinical research at present.One of the disadvantages of this method is that the encapsulation efficiency of drugs is relatively low.Besides，CMC are very low for most copolymers；therefore，it costs lots of solvents in fabrication.In recent years，a method combining polymerization and self-assembly，i.e.，polymerization induced selfassembly（PISA）is attracting increasing attention because of high concentration and tunable morphologies of assemblies（see extended reading 1）.(https://www.daowen.com)