141 ImprovedPROVED AVB PhotostabilityOTOSTABILITY UsingING NLCs
In addition to photostability, the increase in the photoprotective properties of creams based
on lipid nanoparticles versus conventional creams has already been described.36,37 Liposomes
and lipid nanoparticles have increased AVB photoprotection by 40%.38 The increased UV
protection is attributed to the synergistic effect of the lipid matrix. Isopropyl myristate has
been shown to be the most appropriate lipid-excipient for ensuring AVB photostability.30
Similarly, the entrapment of avobenzone in lipid microparticles have been demonstrated as
an effective strategy to reduce the photo-instability of AVO after irradiation.39 Normally
nanoparticles act as UV physical filters, due to their efficient light scattering properties,
which promotes a synergistic UV protection effect with the encapsulated UV chemical
filter. Additionally, depending on their composition, lipid components may present
antioxidant activity and add to the photostabilisation effect of the encapsulated material.39
Understanding photodegradation pathways when using photosensitive filters is a crucial
step in the design of photoprotective formulations. The combination of several strategies,
including encapsulation, antioxidants, photostabilizing substances, and suppressors can be
used as effective tools for photoprotection.39-41
SKIN RETENTION AND PERMEATION
Recently, the Food and Drug Administration has evidenced that various UV filters
can diffuse into systemic circulation and cause harm.42 The lipophilic character and
permeability properties of AVB, such as its lipophilicity, could favor its diffusion through
biological membranes. AVB pKa is between 9.60–9.80. At both physiological pH values
and cutaneous pH, there will be a clear dominance of AVB in the nonionized state, which
is predictive of high permeation across biological barriers.43,44
The effectiveness of a sunscreen depends on its ability to keep UV filter molecules in the
outermost region of the skin. The ideal sunscreen should have low permeation properties
and high accumulation capacity in this region.39 Here, we demonstrated that encapsulation
in NLCs promoted greater skin retention of AVB, showing a significantly (p 0.05) higher
retention on the skin surface when compared to the concentration that penetrated the
stratum corneum (Figure 8).
Figure 7. Photostability of free and NLC-encapsulated AVO (F3). Samples were exposed for 24h and subjected
to UVA radiation (3,025 mW/cm²) for 24h in a photostability chamber.

142 JOURNAL OF COSMETIC SCIENCE
The structure of the nanocarriers has also been shown to influence penetration through
the skin. Semisolid formulations containing nanocapsules provided greater retention in
the stratum corneum compared to semisolids containing benzophenone-3 in.the free
form.21 Gels containing oxybenzone nanoencapsulated in solid-lipid nanoparticles, and
confocal microscopy was used to assess the localization of the formulations on the skin.
The authors demonstrated that there was a reduction in the penetration of sunscreen
when nanoencapsulated.22 Cutaneous retentions of AVB entrapped in cyclodextrin was
investigated. In their work, the authors demonstrated that the stratum corneum contained
most of the absorbed UV filter.45,46 The proportion of the applied dose that was diffused
into the stratum corneum for the sunscreen cream with nonencapsulated sunscreen agents
was about 30.3% for AVB. The cream with microencapsulated UV filters reduced in vivo
skin penetration by a statistically significant amount. In the deeper stratum corneum layers,
the lipid microparticles inhibitory effect on permeability was more pronounced (45–56.3%
decrease).39
Together, the results show the advantages of encapsulating AVB in NLCs. In the pathway to
incorporating AVB-NLCs in a cosmetic base to develop a commercially available product,
the AVB release, stability of the nanocarriers once incorporated in a cosmetic base stability,
long-term stability of the formulation, and scaling-up should be investigated.
CONCLUSION
Based on the results of the active and excipient interaction studies using DTA and TG/DTG
and FTIR, it was possible to rationally select the components for the preparation of NLCs.
Carnauba wax, isopropyl myristate, Span 85, and Tween 80 were tested for the preparation
of NLCs and encapsulation of AVB. NLCs prepared with carnauba wax showed less loss of
active content in the face of exposure to UVA radiation (maximum 5%, compared to 50% of
loss of AVB in ACN) and greater retention on the skin surface, when compared to the AVB
that penetrated the stratum corneum. These results demonstrate that the incorporation of
this type of active in lipid nanoparticles can contribute both to improve the efficiency of
sunscreen activity and to reduce the permeation of these molecules in the skin.
Figure 8. Amount of AVB-NLC (F3) retained in the cutaneous surface and permeated through the skin
after 24h of the experiment. The pig ear skin model was used in Franz-type static flow cells. Medium was
maintained at 300 rpm, 37°C. The diffusion area was 1.86 cm2. The receiving compartment contained PBS
buffer solution (pH: 7.4) with 5% Tween 20, with 1 mL samples being collected at each time point.