Development of <i>Protium heptaphyllum</i> essential oil-loaded nanocapsules: experimental design and biological activity

Poly(ε-caprolactone) nanocapsules containing breu branco ( Protium heptaphyllum ) essential oil were successfully prepared by nanoprecipitation and optimized using a Box–Behnken design. Spherical nanosystems were obtained, with a mean particle size of 172.10 ± 0.90 nm, a polydispersity index of 0.14 ± 0.04, a zeta potential of −25.49 ± 1.08 mV and an encapsulation efficiency above 99%, in addition to long-term colloidal stability. Cell viability assays in HaCaT cells showed high biocompatibility, with cell viability above 70% up to 6 mg/mL and only moderate toxicity at 12 mg/mL. In antimicrobial assays, the free oil had no inhibitory effect against Staphylococcus aureus , while the nanocapsules exhibited a minimum inhibitory concentration of 0.55 mg/mL, indicating enhanced antibacterial activity. Wound-healing assays further demonstrated improved keratinocyte migration compared to serum-free controls. Additionally, cytokine profiling by cytometric bead array indicated an anti-inflammatory profile, with strong suppression of IL-6 and selective increases in IL-2, IL-4, and TNF-α at higher doses (6 mg/mL) in nanocapsule-treated fibroblasts. Overall, these findings demonstrate that nanoencapsulation not only stabilizes breu branco essential oil but also enhances its antimicrobial, regenerative, and immunomodulatory effects, while fostering the sustainable valorization of Amazonian biodiversity.