Polydopamine-Based Nanoparticles for Safe Sunscreen Protection Factor Products with Enhanced Performance

Excessive exposure to ultraviolet light (UV) can damage skin cells and cause skin cancer. Applying sunscreen that blocks both UVA and UVB is recommended before going outside. An ideal sunscreen should not come off, penetrate the bloodstream, or cause health risks, while also remaining effective at blocking UV rays. Herein, we focused on sunscreen applications based on polydopamine (PDA) nanoparticles, an artificial melanin material. Various sizes of nanoparticles were fabricated using a spontaneous oxidation reaction with the dopamine monomer to sodium hydroxide (DA/NaOH) molar ratios of 1:0.2 to 1:1. The monodisperse and spherical PDA nanoparticles with sizes ranging from 59.5 to 659.1 nm showed monotonic broadband UV–vis absorption. PDA2 (molar ratio of DA/NaOH 1:0.8) presented the highest UVB absorption (290–320 nm) and a sun protection factor boosted by approximately 50% compared to that of the original base formulation. When the particle size was larger than 150 nm, the results from X-ray photoelectron spectroscopy and confocal spectroscopy showed that the surface functionality of the synthesized PDA nanoparticles that was dominated with hydroxyl groups induced their adherence to the stratum corneum after 24 h of incubation. The nanoparticles were biocompatible with human keratinocytes (HaCaT), that is, direct interactions between the PDA particles and HaCaT cells did not cause any cell damage. Results from in vitro photoprotection ability suggested that PDA nanoparticles could protect the cells from UVA irradiation in terms of membrane protection, reactive oxygen species reduction, and cell viability recovery. Interestingly, the results obtained from the bacterial reverse mutation and in vitro skin irritation tests indicated that the nanoparticles did not induce mutagenicity or irritate skin cells. Our findings provide a promising approach for the synthesis of PDA nanoparticles as a safe sunscreen component.