Ultraviolet (UV) radiation from the sun is the most harmful factor for human skin, causing sunburn, melasma, freckles, blemishes, and skin cancer. Sunscreens play a key role in blocking UV absorption on the skin. This study focused on the synthesis of hollow polydopamine (h-PDA), whose structure mimics the naturally occurring melanin in humans, for use as an active ingredient in sunscreens by means of a hard-template-based method. The reactions involve a spontaneous polymerization of a dopamine monomer in the presence of tris­(hydroxymethyl)­aminomethane (Tris) as a catalyst onto a polystyrene (PS) core template. Different sizes of the PS core (about 280 and 450 nm) and weight ratios of PS/DA were applied to elucidate the effect of the hollow diameter and thickness of the shell on the morphology and absorbance of the synthesized h-PDA. From UV absorption results, it was observed that the synthesized h-PDA particles with a larger core diameter (about 450 nm) and a thin shell thickness (about 57 nm) presented high UV absorption. We found that the structure of the synthesized h-PDA is mainly composed of a mixture of 5,6-dihydroxyindole and indole-5,6-quinone precursors covalently linked together. After blending the h-PDA particles with the base cream, the formulation containing h-PDA with a large void diameter of about 450 nm showed the highest sun protection factor (SPF) of up to 7.43, which is related to % booster of 234.7%. In addition, the h-PDA particles exhibited biocompatibility and cellular uptake in keratinocyte HaCaT cells after 24 h of incubation, indicating the potential to mimic natural melanin in preventing UV-induced DNA damage, which could be safely used as an alternative sunscreen.

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.

127I-modified mIBG was successfully synthesized and grafted covalently to the surface of carboxylated PEG-GNPs. The particles were not toxic to the normal fibroblast cells while specifically internalized into neuroblastoma cells line via NET.