Safety and efficacy of polycaprolactone copolymer nanosphere hydrogel injected into the scalp dermal tissue of rats

ABSTRACT

BACKGROUND: Currently, dermal fillers need to be 25 µm or larger to reduce in vivo degradation by macrophages. However, the large size of fillers may cause side effects, including interruption of blood flow and nodule formation. Therefore, using rats, we tested a polycaprolactone copolymer hydrogel with nanoscale particles that could maintain a low in vivo degradation rate. METHODS: Thirty-six 6-week-old Sprague-Dawley rats were divided into group A (normal saline), group B (polycaprolactone microsphere filler), and group C (polycaprolactone copolymer nanosphere hydrogel). The corresponding materials were injected into the dermal layer of the scalp of the rats. At 4, 8, and 12 weeks after injection, blood biochemical and kidney and liver histological analyses were performed. Tissues were examined using hematoxylin-eosin staining to observe tissue infiltration of materials. Collagen formation in the dermal tissue of the scalp was observed with Masson trichrome staining and the collagen content was quantified using a soluble collagen assay kit. RESULTS: The histologic examination for organ infiltration showed no abnormal findings. All blood test results were within the normal ranges. The amount of collagen at 12 weeks increased by 1.22 mg/g in group C and by 0.6 mg/g in group B. CONCLUSIONS: The results reveal that the nanosphere complex near the injection site induced collagen formation. Regardless of the sphere size, aggregation of the copolymer prevented macrophage phagocytosis. The polycaprolactone copolymer nanosphere hydrogel was effective for more than 3 months when injected in the scalp dermal tissue of Sprague-Dawley rats and can be used safely.