Efficacy and safety of poly-D,L-lactic acid microspheres as subdermal fillers in animals

Aim: This animal study aims to examine the efficacy and safety of poly-D,L-lactic acid (PDLLA) microspheres as subdermal fillers.Methods: Thirty 2-week-old male Sprague Dawley rats were used as test animals, and 0.5 mL filler solutions were injected into the subdermal tissues on their backs. Groups of five rats were randomly selected and sacrificed for examination on the 2nd, 4th, 8th, 12th, 16th, and 20th weeks after injection. Clinical and histological examinations were performed via the hematoxyline-eosin and immunohistochemical (IHC) staining of injected sites after collecting the injected masses. The body weights of the rats were measured, and the presence of filler substance in other organs was determined.Results: Injected volumes were stable from the 2nd to the 20th week after injection, and no abnormalities were observed around the injection sites. The injected substance did not migrate to the surrounding tissues. In IHC staining experiments, myofibroblasts were observed from the 2nd week, and collagen was detected from the 4th week. Myofibroblast was observed in the spaces between and inside the microspheres in the 8th week after injection, whereas type I collagen was found between and inside the microspheres at 8th and 12th weeks, respectively.Conclusion: The animal experiments confirm the efficacy and safety of injectable PDLLA as a subdermal filler