6.3.3.1　Self-organizing nano-precipitation

Self-organizing nano-precipitation is a technique that takes advantage of the solubility difference of polymers and drug molecules in good and poor solvents to precipitate the polymers and drugs into NPs（Figure 6-3）.Firstly，the polymers and drugs are dissolved in a water-miscible organic solvent（the good solvent），then water（the poor solvent）is slowly added to induce the precipitation of both of them to form a nano-drug delivery system.In contrast to solution self-assembly，this method is applied for hydrophobic polymers（e.g.，PLA，PLGA，and PCL），and the obtained NPs are usually nano-spheres.The preparation conditions are mild（room temperature and atmospheric pressure）and the products are easy to be purified and no added additives.The size of NPs is closely related to the polymer and drug concentration.Particle size increases with the increase of polymer and drug concentration，and the NPs becomes less homogeneous.The encapsulation efficiency of drugs by using this method is also relatively low.Specific interactions between drug molecules and polymers can greatly improve the encapsulation efficiency.(https://www.daowen.com)