Study on the homeostasis mechanism of in vivo degradation of PCL microsphere fillers

Polycaprolactone (PCL) has been widely applied in the fields of medical aesthetics and clinical filling due to its excellent biocompatibility, controllable degradability, and favorable mechanical properties. However, the high crystallinity and hydrophobicity result in a longer degradation period, making it more suitable for long-term and sustained filling treatments. Yet it is difficult to observe the degradation endpoint in a short period of time, which poses a challenge for the safety and efficacy evaluation of the product before its market launch. At present, the differences in in vivo behavior among various PCL microspheres and their clinical implications remain incompletely understood. In this study, a subcutaneous implantation model in rabbits was employed to investigate the in vivo degradation patterns of two types of PCL microsphere fillers and the material-tissue interactions contributing to the establishment of bodily homeostasis. The results demonstrated that PCL microsphere fillers achieve a homeostasis of safety at 12 months through a sequential process involving "surface erosion-cellular involvement-collagen encapsulation." Furthermore, they maintain a homeostasis of efficacy for at least 30 months via a collagen remodeling strategy characterized by "initial reinforcement, subsequent shaping, and eventual equilibration," thereby forming a predictable dynamic filler construct. These findings provide a mechanistic basis for individualized clinical application and quality evaluation.