Polylactic acid is a polycondensate of lactic acid, which is hydrolyzed into lactic acid in human tissues. Lactic acid is a metabolite of human body and can be further decomposed into carbon dioxide and water. Therefore, polylactic acid is non-toxic and has good degradability, and can be made into many different kinds. Medical materials for use, such as: degradable surgical sutures, fracture internal fixation, tissue repair materials, and filling materials for treating retinal detachment. In addition, since polylactic acid itself is metabolically safe and easy to form a film, it can be used as an ideal material for sustained drug delivery, and is widely used in a sustained release/controlled release system of a pharmaceutical.