Long-term efficacy of poly(L-lactide-co-ε-caprolactone) threads with hyaluronic acid nanoparticles: an <i>in vivo</i> skin remodeling study

BACKGROUND: Modern thread-lifting techniques aim to achieve an immediate mechanical lifting effect and provide a prolonged biostimulatory action directed at remodeling dermal structures. AIM: This study aimed to perform a histomorphological evaluation of the effects of monofilament P(LA/CL)-HA-nano threads on skin remodeling in a biomedical experiment and compare their outcomes with those of P(LA/CL)-HA threads and intact skin. METHODS: The study included five clinically healthy female Large White pigs aged 4 months weighing 40 ± 1.2 kg on average. Each animal underwent implantation of two types of threads: P(LA/CL)-HA and P(LA/CL)-HA-nano. Euthanasia of the animals and histomorphological analysis were performed on days 7, 21, 30, 90, and 180. Intact skin was considered the control. The following parameters were assessed: dermal thickness, content of type I and type III collagen fibers, and elastin levels. Histological staining included hematoxylin and eosin, Weigert–Van Gieson, and Picrosirius Red with polarized light analysis. Statistical analysis was conducted using the Wilcoxon signed-rank test. Differences were considered significant at p 0.05. RESULTS: P(LA/CL)-HA-nano thread implantation resulted in significantly increased dermal thickness (day 180, p = 0.0431), increased type I collagen density in the dermis (day 90, p = 0.0431) and hypodermis (all time points, p 0.05), and enhanced type III collagen synthesis in the hypodermis from day 21 (p = 0.0431). A significant increase in elastin levels in the dermis was observed on days 90 and 180 (p = 0.0431). Distinct kinetics of tissue remodeling were noted compared with non-modified P(LA/CL)-HA threads. CONCLUSION: P(LA/CL)-HA-nano threads exhibit pronounced bioactive properties, promoting structural remodeling of skin tissues.