6.3.5　Spray drying method

Polymers and drug molecules are firstly dissolved in a volatile solvent，then the solution is sprayed into tiny droplets，followed by drying into a powder of NPs（Figure 6-5）.This method is suitable for both hydrophobic and hydrophilic nano-drug delivery systems，and no surfactant is needed.However，the preparation of nanoscale drug systems requires high quality and expensive equipment.Similar with the emulsion-solvent evaporation method，the size of the NPs obtained by spray drying method depends on the size of the droplets and their concentration.Compared with self-organizing nano-precipitation method，this method has a higher encapsulation efficiency.But this method generally requires the solvent in fogdrop to evaporate instantaneously under high temperature condition，which is not suitable for high temperature intolerant polymers and drugs.(https://www.daowen.com)