Bio-based lignin/polyhydroxybutyrate nanoparticles for encapsulation of ethylhexyl methoxycinnamate toward...

In this study, a safer and more sustainable sunscreen system was developed using polyhydroxybutyrate (PHB) and lignin, selected for their intrinsic UV-shielding properties and biocompatibility. To enhance photoprotective performance, 2-ethylhexyl 4-methoxycinnamate (EHMC) was encapsulated within PHB/lignin nanoparticles. EHMC-loaded PHB/lignin nanoparticles were successfully fabricated and optimized using Response Surface Methodology (RSM). The optimal formulation consisted of 0.625% (w/v) total polymer concentration, a PHB:lignin ratio of 1:2, and 0.69% (w/v) EHMC. Under these conditions, the nanoparticles achieved an encapsulation efficiency of 80.2 ± 1.0%, loading capacity of 76.0 ± 3.3%, and a sun protection factor (SPF) of 44.2 ± 0.9. The nanoparticles had an average diameter of 474.6 ± 2.5 nm and a zeta potential of -39.7 ± 0.1 mV, indicating good colloidal stability. The nanoparticles exhibited sustained-release behavior, with only 5% cumulative EHMC release after 24 h in phosphate buffer solution pH 5.5 and pH 7.4, suggesting reduced risk of systemic transdermal absorption. The system also demonstrated antioxidant activity and anti-acne effects against Staphylococcus epidermidis MSCU0484. Cytotoxicity assays using human keratinocyte (PSVK1) cells confirmed excellent biocompatibility. Furthermore, the PHB/lignin matrix effectively protected encapsulated EHMC from UV and thermal degradation, retaining 92.0 ± 6.9% after 90 days. The optimized nanoparticles were incorporated into a cream base, achieving homogeneous dispersion and an SPF of 28.8 ± 3.3 at 10% (w/w) loading. Overall, PHB/lignin nanoparticles represent a promising bio-based, photostable, and multifunctional sunscreen additive for environmentally sustainable formulations.