Letter to the editor regarding the article “Kwon T‐R, Han SW, Yeo IK, et al. Biostimulatory effects of polydioxanone, poly‐d,l lactic acid, and polycaprolactone fillers in mouse model. J Cosmet Dermatol. 2019;18(4):1002‐1008.”

Dear Editor: We read with interest the article by Kwon et al1 entitled as “Biostimulatory effects of polydioxanone, poly-d,l lactic acid, and polycaprolactone fillers in mouse model,” which appeared in a recent issue of the Journal of Cosmetic Dermatology. The authors compared the biophysical characteristics, safety, and efficacy of three different stimulatory fillers, including poly-l-lactic acid (PLLA), polycaprolactone (PCL), and polydioxanone (PDO) fillers. This article provides us abundant valuable basic information about these three fillers. However, there was an inaccuracy in the article title and keywords, wherein “poly-d,l-lactic acid” (PDLLA) was used instead of the correct term “poly-l-lactic acid.” Both PDLLA and PLLA are subgroups of poly-lactic acid (PLA). Due to the chiral character of lactic acid, it has two enantiomers, l- and d-lactic acids. PLLA is a polymer that is completely composed of l-lactic acids; whereas PDLLA comprises various proportions of d- and l-lactic acids. PDLLA, PLLA, PCL, and PDO are all aliphatic polyesters that possess biodegradable, biocompatible, and biostimulatory properties. Calcium hydroxyapatite and polymethyl methacrylate also possess a biostimulatory property, and a recent animal study2 reported that hyaluronic acid acts not only as a tissue augmenter but also as a biostimulatory inducer. Poly-d,l-lactic acid filler (AestheFill; REGEN Biotech, Inc) is a new subdermal filler that was first approved by the Korean Food and Drug Administration in 2014.3 It consists of PDLLA microparticles and sodium carboxymethyl cellulose and is supplied as a lyophilized powder. Like the PLLA filler, the PDLLA filler must be reconstituted with sterile water before administration. PDLLA microparticles are spherical in shape with multiple micropores on the surface of and spongiform structures inside the microsphere (Figure 1). The size of the PDLLA microsphere ranges from 30 to 70 µm, which is large enough to prevent them from phagocytosis by various cells in the skin, but small enough to allow them to easily pass through an injection needle. Animal studies3, 4 conducted on the efficacy and safety of injecting the PDLLA filler have demonstrated that the injected volume could be maintained for 24 weeks. No abnormal findings were found around the injected site. PDLLA microspheres were localized to the injected layer without migration to the surrounding tissues and other distal organs. Inflammatory cells were observed at the 2nd week postinjection, but they exhibited a tendency to decrease at the 4th week. Formation of type I collagen and actin was also observed in the injected site, with a progressive increase from the 2nd to the 20th week postinjection. Due to the microporous feature of the PDLLA microspheres, the newly formed collagen and actin can be found not only between but also inside the microspheres. Clinical studies5 conducted by injecting the PDLLA filler for the correction of nasolabial folds with a 24-month long-term evaluation reported that there were no severe adverse effects related to the injection. The maximum improvement in the nasolabial fold wrinkle severity rating scale scores was observed at the 6th-month follow-up, and the scores were normalized at the 24th-month follow-up. In conclusion, the PDLLA filler is a new stimulatory subdermal filler. It possesses a few similar, as well as dissimilar, features compared with the PLLA filler. Dr Chen S-Y has no conflicts of interest to disclose. Dr Lin J-Y and Dr Lin C-Y are medical directors of REGEN Biotech.