129 ImprovedPROVED AVB PhotostabilityOTOSTABILITY UsingING NLCs
hydration and elasticity.6–8. Through the generation of singlet oxygen, UVA radiation can
induce the expression of matrix metalloproteinases that destroy connective tissue.9 In this
context, the availability of sunscreens with broader protection is an increasing consumer
concern. Although most available commercial formulations have a variety of UVB filters,
the number of UVB filters that are also effective UVA absorbers are rare, and they often
present poor performance or are not photostable.
In 2019, the American Regulatory Agency Food and Drug Administration published
regulations for products containing sunscreens, providing for their classification regarding
the safety of filters that are marketed in the USA, classifying them as totally safe, unsafe,
and requiring additional research.10 Among those that require further research is butyl
methoxydibenzoylmethane, also known as avobenzone (AVB).10 AVB is a chemical UV
filter associated with UVA protection. It is presented as a mixture of two tautomeric forms:
enol and keto.11 Chemical equilibrium between the two isoforms favors the enol form
in almost all media due to its ability to form hydrogen bonds. The enol form absorbs in
the UVA spectrum and is responsible for the UVA protection effect. Under irradiation,
the enol form in solution photoisomerizes to the keto form, causing a large decrease in
absorption. The keto form mainly absorbs in the UVC spectrum region, losing its UVA
protective effect.11,12
Photostabilization is critical to the development of sunscreen formulations. Studies have
shown that the use of nanotechnology in photoprotective formulations can improve the
photo stability of some filters.13,14 Formulations of lipid nanoparticles containing AVB have
been evaluated for their ability to absorb UV radiation and their UVA protection factor
after irradiation.14 Type, physical properties, and chemical nature of lipid-based excipients
may influence the physicochemical properties and stability of the lipid carriers,15,16 as well
as their interaction with biological systems.17,18 Therefore, the screening of the excipients
has been described to ensure the development of safe, stable, and efficient lipid-based
formulations.19,20 In this study, we used thermogravimetry (TG/DTG), differential thermal
analysis (DTA), and Fourier-transform infrared spectroscopy (FTIR) techniques to evaluate
the interaction between AVB and lipid excipients and to select the most suitable components
for a rational nanostructured lipid carrier (NLC) design.
In the development of photoprotective formulations minimal skin permeation is required,
since the exposure to many organic sunscreens has been associated with several adverse
effects, such as endocrine21 and metabolic disruption.22,23 Besides the safety concern, the
search for sunscreens that are stable, and thus maintain the photoprotective ability of the
formulation, mobilizes the investigation of new applications, methods, and technologies
applied to photoprotective formulations. In this work, we designed a NLC formulation
encapsulating AVB, and evaluated its photostability against UV radiation and its ability to
reduce the cutaneous penetration of AVB, favoring its retention on the skin surface.
MATERIALS
Avobenzone was purchased from Symrise AG (Holzminden, Germany). Avobenzone
standard was purchased from Sigma-Aldrich (Missouri, USA). Beeswax, carnauba wax,
isopropyl myristate, sorbitan monoleate (Span 80) and trioleate sorbitan (Span 85) were of
cosmetic grade and purchased from Sigma-Aldrich (Missouri, USA). Oleic acid of cosmetic
grade was acquired from Labsynth Products Laboratories (Diadema, Brazil), Polysorbate 20

130 JOURNAL OF COSMETIC SCIENCE
(Tween 20) of cosmetic grade was acquired from Vetec Quimica Fina (Brazil), Polysorbate 80
(Tween 80) of cosmetic grade was acquired from Vetec Quimica Fina (Brazil), and glyceryl
monostearate and sesame oil, both of cosmetic grade, were acquired from Croda (Campinas,
Brazil). Capric and caprylic acid triglycerides (Captex, cosmetic grade) were purchased from
ABITEC Corporation (Ohio, USA). Mineral oil of cosmetic grade was purchased from
Penreco (Indiana, USA), and Poloxamer 188 of cosmetic grade was purchased from BASF
(Germany).
AVB QUANTIFICATION METHOD
The chromatographic method was adapted from Abid et al.,24 considering the recommended
criteria from the International Council for Harmonization of Technical Requirements
for Pharmaceuticals for Human Use (ICH) for validation of chromatographic methods
regarding linearity, precision, accuracy, and limits of detection and quantification (ICH
Q6B). Specifications: test procedures and acceptance criteria for biotechnological/biological
products—scientific guideline. The chromatographic parameters used were: Zorbax
Eclipse (Agilent) XDB – C18 column 150mm × 4.6mm, 3.5 µm, with precolumn C18
12.5 × 4.6 mm, 3.5 µm (Agilent), maintained at 30°C. Detection was carried out using a
photodiode array at 360 nm. The mobile phase was composed of acetonitrile (ACN) and
water (90:10 v/v), at a 1 mL/min−1 flow. The injection volume was 10 µL.
SELECTION OF EXCIPIENTS FOR NLC DEVELOPMENT
AVB SOLUBILITY
The solubility of AVB was evaluated in liquid lipids: oleic acid, sesame oil, mineral oil,
isopropyl myristate, capric acid triglycerides, and caprylic acid triglycerides. Excess amount
of AVB was weighed (150 mg) and transferred to amber glass bottles, where 1 mL of each oil
was added. Each oil was tested in triplicates. The samples were each vortexed for 1 minute
and then placed in an orbital shaker (KS 4000, IKA®, Germany) at a speed of 150 rpm,
at 37°C, for 24 hours. The samples were then filtered through 0.45 µm polyvinylidene
fluoride (PVDF) microfiltration membranes, were diluted with 10 mL ACN, and AVB
solubility was then quantified by high-performance liquid chromatography (HPLC).
THERMOGRAVIMETRY AND DIFFERENTIAL THERMAL ANALYSIS
The thermal evaluation of AVB and raw lipid excipients, as well as the AVB:excipients physical
mixture (1:1 m/m), was carried out in a DTG-60 thermobalance (Shimadzu, Kyoto, Japan),
with simultaneous measurement of mass loss (TG/DTG) and melting events (DTA), under a
nitrogen atmosphere (50 mL/min−1), with a heating rate of 10 °C.min−1, and a temperature
range of 25–500°C. Platinum crucibles were used for the analysis of 5 mg of each sample.
FOURIER TRANSFORM INFRARED SPECTROSCOPY
Attenuated total reflectance Fourier transform infrared spectra were obtained on a
Varian 640-IR (Varian Medical Systems Inc., Jundiaí, Brazil). AVB, lipid excipients, and