NLC-Based Sunscreen Formulations with Optimized Proportion of Encapsulated and Free Filters Exhibit Enhanced UVA and UVB Photoprotection

Abstract

The topical use of sunscreens is recommended for avoiding the damaging effects of UV radiation. However, improvements are still needed in the existing products to enhance their photoprotection effectiveness and safety. This involves minimizing the use of chemical UV filters while providing enhanced and prolonged photoprotection. This work investigated novel sunscreen formulations and their UV protection effects by encapsulating Uvinul^® A, Tinosorb^® S, and Uvinul^® T150 into nanostructured lipid carriers (NLCs) based on bacuri butter and raspberry seed oil. First, the impact of critical formulation and process parameters on NLCs' particle size was evaluated using a 2² Face Centered Central Composite Design. Then, formulations were evaluated in terms of critical quality factors, in vitro skin permeation, and in vitro and in vivo photoprotection activities. The developed NLCs-containing formulations exhibited appropriate size (122-135 nm), PdI (<0.3), encapsulation efficiency (>90%), and drug content (>80%), which were preserved for at least 90 days under different stability conditions. Moreover, these NLCs-based formulations had equivalent skin permeation to emulsion-based controls, and the addition of NLCs into sunscreen cream bases in the optimum proportion of 20% (w/w) resulted in enhanced UVA and UVB photoprotection levels, despite a 10% reduction in the total filters content. Altogether, these results describe the application of nanoencapsulated organic UV filters in innovative sunscreen formulations to achieve superior photoprotection and cosmeceutical properties.

Keywords: in vitro photoprotection; in vivo photoprotection; industrial research; nanostructured lipid carrier; skin penetration; sunscreen.

Figure 1

(a) Scheme describing the interaction between UVR (UVA, UVB, and UVC) and the different layers of the skin structure (stratum corneum, epidermis, and dermis). (b) Depiction of different lipid-based nanoparticles applied to sunscreen formulations.

Figure 2

Design space (yellow region) of SC-NLC varying (a) Polysorbate 60:Polyglyceryl-3-dioleate ratio (b) and HPH parameters—pressure and time of processing.

Figure 3

(a) AFM image, where the color scale shows that the brighter spots represent regions that are more exposed (in a higher position), and the darker fraction indicates the sample background. The scale shown in the image as reference is 2 µm. The histogram is resultant from a sum of several AFM images, showing the size frequency (non-normalized) of the optimized SC-NLC; (b) UV-Vis light extinction spectra of the mixtures of Uvinul^® A Plus, Tinosorb^® S, and Uvinul^® T150 free and encapsulated in the SC-NLC, also of the mixture of the SC-NLC unloaded (no filters).

Figure 4

Evolution over time (in days) of SC-NLC’s (a) size (nm), PdI, (b) zeta potential (mV), and pH during three months under different incubation temperature conditions (4, 25, and 40 °C) and relative humidity of 75% (except for 4 °C). For the plot (a), the bars are referent to the particles’ hydrodynamic diameter (D_H), and the lines express the PdI trend.

Figure 5

Percentage of UV filter total load and encapsulation efficiency for Uvinul^® A Plus, Tinosorb^® S, and Uvinul^® T150 at relative humidity (RH) of 75% and temperature of (a) 4 °C (refrigerator stability condition—RH not controlled), (b) 25 °C (long term stability condition), (c) 40 °C (accelerated stability condition). For all graphs the bars are referent to the percentage of filter content found in the SC-NLCs sample, and the lines express the percentual of filters encapsulated into the NLCs.

Figure 6

Permeation of (a) Uvinul^® A Plus, (b) Tinosorb^® S, and (c) Uvinul^® T150 into the stratum corneum, epidermis, dermis, and receptor liquid. This data set was statistically evaluated by the Kruskal–Wallis test and a significance threshold of less than 0.05.

Figure 7

Photoprotection responses obtained in vivo tests assessing (a) SPF and (b) UVA-PF₀ of CBI-80%, CBI-80%/Emulsion-20%, and CBI-80%/SC-NLC-20%; (c) SPF and (d) UVA-PF₀ of CBII-80%, CBII-80%/Emulsion-20% and CBII-80%/SC-NLC-20%; and (e) SPF and (f) UVA-PF₀ of CBIII-80%, CBIII-80%/Emulsion-20% and CBIII-80%/SC-NLC-20%. The results of SPF and UVA-PF₀ are represented by their median, quartiles, and upper and bottom limits. The statistical difference was evaluated using the Brown–Forsythe and Welch ANOVA test followed by Dunnett’s T3 multiple comparisons test; it was considered significantly different when p < 0.05, and the symbols *, **, ***, and # indicate significant differences.