Research Progress of Poly-L-Lactic Acid Microspheres for Facial Rejuvenation: Degradation Behaviors, Collagen-Inducing Mechanisms and Composite Modification Strategies

Current dermal fillers for aesthetic applications commonly suffer from the trade-off between therapeutic efficacy and durability. Hyaluronic acid (HA) merely delivers short-term soft-tissue augmentation, whereas autologous collagen transplantation is limited by donor-site availability. It has been demonstrated that poly-L-lactic acid microparticles (PLLA) de novo induce the formation of autologous collagen. However, the continuous release of lactic acid, which accompanies the hydrolytic degradation of the material, can lead to erythema and subcutaneous nodules, and the collagen-stimulating potential of PLLA still awaits further improvement. Based on new evidence from domestic and international sources, this review outlines the cellular and molecular changes underlying skin aging, contrasts the behavior of the three polylactic acid stereoisomers—PLLA, PDLA, and PDLLA—and clarifies the mechanistic cascade through which PLLA microparticles drive collagen biosynthesis. The synergistic effects of combining PLLA with hyaluronic acid, bioactive glass, tranexamic acid (TXA), and native collagen are also systematically evaluated. Key challenges in microsphere production and multi-component mixing are highlighted, while substrate modification and multifunctional composite systems are proposed as promising directions for future research, thus serving as a reference point for the development of next-generation regenerative aesthetic fillers.