Compositions of injectable poly-d,l-lactic acid and injectable poly-l-lactic acid.

Injectable poly‐l‐lactic acid (PLLA) was first available in Europe in 1999. In 2004, it was approved by the US Food and Drug Administration (FDA) for facial filling of patients with lipoatrophy resulting from human immunodeficiency virus, under the name of Sculptra (Dermik Laboratories, Bridgewater, NJ, USA), and in 2009, the use of injectable PLLA was further expanded to facial cosmetic application.1 Injectable poly‐d,l‐lactic acid (PDLLA) is a new subdermal filler (AestheFill; REGEN Biotech, Inc., Seoul, South Korea), which was first approved by the Korean FDA in 2014.2

Clinical trials of injectable PDLLA were performed in Korea by Hyun et  al., and the study was published in Clinical and Experimental Dermatology under the title ‘Efficacy and safety of injection with poly‐L‐lactic acid compared with hyaluronic acid for correction of nasolabial fold: a randomized, evaluator‐blinded, comparative study’.3 This study provides us with valuable information that injectable PDLLA is safe and has noninferior efficacy compared with hyaluronic acid 6 months after being used to treat moderate to severe nasolabial folds. However, there was an inaccuracy in this article, with ‘poly‐l‐lactic acid’ used instead of the accurate ‘poly‐d,l‐lactic acid’.

Lactic acid is a natural product of starch fermentation, and can also be produced by chemical synthesis. Poly‐lactic acid (PLA) is synthesized by direct polycondensation of lactic acid or by ring‐opening polymerization of the lactide dimer. Because of the chiral character of lactic acid, there are two enantiomers: l‐ and d‐lactic acids. These two enantiomers can produce four distinct PLA substances: poly‐d‐lactic acid (PDLA), PLLA, PDLLA and meso‐PLA. As PDLLA and PLLA both belong to the PLA group, both are endowed with the biocompatible, biodegradable and biostimulatory properties of PLA. However, some differences between PDLLA and PLLA exist. PLLA is hemicrystalline and has a regular chain structure, whereas PDLLA is amorphous and has an irregular chain with random distribution of l‐ and d‐lactic acids. The glass transition temperature, melting temperature and tensile strength of PDLLA are all lower than those of PLLA, and the degradation time of PDLLA is faster than that of PLLA.4, 5

Injectable PLLA is supplied as a lyophilized powder. A vial of injectable PLLA contains 150 mg of PLLA microparticles, 90 mg of carboxymethyl cellulose (CMC) and 127.5 mg of nonpyrogenic mannitol. The PLLA microparticles are solid, irregular in shape, and between 40 and 63 µm in diameter.1 Injectable PDLLA is also supplied as a lyophilized powder. A vial of injectable PDLLA contains 154 mg of PDLLA microparticles and 46 mg of CMC. The PDLLA microparticles are spherical in shape with multiple pores on the surface, and have a diameter of 30–70 µm.2 The microparticle size of both PDLLA and PLLA make them small enough to pass through an injection needle, but large enough to protect them from phagocytosis. Both injectable PDLLA and PLLA must be reconstituted with sterile water before injection. The component CMC in both products plays an important role in reconstitution.

In conclusion, the two products are both biocompatible, biodegradable and biostimulatory, but there are some differences in composition between injectable PDLLA and injectable PLLA.