1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussions
  6. Conclusions
  7. Acknowledgments
  8. References

The coencapsulation of two UV filters, butyl-methoxydibenzoylmethane (BMDBM) and octocrylene (OCT), into lipid nanocarriers was explored to develop stable cosmetic formulations with broad-spectrum photoprotection and slow release properties. Different types of nanocarriers in various concentrations of the two UV filters were tested to find the combination with the best absorption and release properties. Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) have been the two types of lipid nanocarriers used. The NLCs were based on either medium chain triglycerides (MCT) or squalene (Sq). The following physicochemical properties of the nanocarriers have been evaluated: particle size, morphology, zeta potential (ZP), entrapment efficiency, loading capacity, and thermal behavior. The nanocarriers have been formulated into creams containing low amounts of UV filters (2.5% BMDBM and 1% OCT). The best photoprotection results were obtained with the cream based on NLCs prepared with MCT, having a sun protection factor (SPF) of 17.2 and an erythemal UVA protection factor (EUVA–PF) of 50.8. The photostability of the encapsulated BMDBM filter was confirmed by subjecting the nanocarriers-based creams to in vitro irradiation. The prolonged UV-protection efficacy was coupled with a slow in vitro release of the synthetic UV filters, which followed the Higuchi release model.


  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussions
  6. Conclusions
  7. Acknowledgments
  8. References

The skin exposure to UV radiation induces a broad range of adverse effects, such as sunburn, photoaging, photoimmunosuppression and photocarcinogenesis [1-3]. To protect the skin against the deleterious effects of UV rays, different types of sunscreens were developed. The application of sunscreens on large areas of skin determines significant amounts of organic UV filters to penetrate into the skin [4] being further metabolized in the body and bioaccumulated [5, 6], thus causing various adverse health effects. Over the last years, the side effects of UV filters contained in the market sunscreen products, such as contact dermatitis, allergies, phototoxicity [7, 8] and estrogenic activity [9, 10], have been intensively discussed. Although the performance of sunscreens is usually associated with the physicochemical properties of the UV filters, it is also stated that it is influenced by the carrier systems used to deliver them [11]. As a result, the development of sunscreen products based on new safer delivery systems for human use has been promoted to remove the disadvantages of conventional sunscreen formulations.

Among the colloidal systems, the lipid nanoparticles (LNs) used as carriers for UV filters have been studied [12-15] and their advantages [e.g. enhancement of chemical stability of active compounds [16, 17] and UV attenuation by both absorption and scattering [18]] were underlined, making solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) suitable systems as carriers for sunscreen formulations.

SLNs consist of a matrix composed of entirely solid lipids, whereas NLCs contain a mixture of solid and liquid lipids [19, 20]. Both of them remain solid at room and body temperatures and are highly suitable for carrying lipophilic compounds [21-23].

In a previous study of the authors [24], butyl-methoxydibenzoylmethane (BMDBM), one of the most widely used filters against the harmful UVA radiation [25], was encapsulated into lipid nanoparticles. However, BMDBM suffers from substantial decomposition under sunlight exposure leading to a decrease in the photoprotective efficacy of the cosmetic formulations that use it [26, 27]. The cream formulations with lipid nanoparticles based on a low amount of BMDBM exhibit an improved UVA protective effect than that of the conventional cream, but their photoprotective properties after irradiation remain efficient only for the cosmetic formulation with BMDBM loaded into nanostructured lipid carriers based on MCT (medium chain triglycerides) and Squalene (Sq).

Furthermore, having in view that the commercially available products should protect against both UVA and UVB rays, the utilization of a UVB filter together with the UVA filter has to be performed. In this context, octocrylene (OCT) is a UVB filter that acts as an efficient photostabilizer for BMDBM [7, 28]. The coencapsulation of multiple UV filters could lead to improve in vitro absorptive properties. The coencapsulation approach was previously studied by Xia et al., loading the both types of UVA and UVB filters into lipid nanoparticles prepared with carnauba wax, thus obtaining a significantly improved protection in comparison with the nanoemulsion [29]. Some encouraging results have been revealed in this study, but no sun protection and erythemal UVA protection factors have been determined to assess the performance of the developed nanoparticles. An interesting study led by Scalia has demonstrated that by coloading of BMDBM and OCT into lipid microparticles, a slight decrease in BMDBM photodegradation was obtained comparing to single BMDBM microencapsulation [30]. 2 years ago, Montenegro et al. [31] investigated by differential scanning calorimetry the interactions between SLNs components and loaded UV filters, BMDBM and octylmethoxycinnamate (OMC). When the two UV filters were coloaded into SLNs based on ceteth-20 as main surfactant, the UV filters were stable but their loading capacity has been decreased.

Starting from the results stated above, the aim of this study was to develop nanocarriers-based formulations, which are, first and foremost, stable, show improved UVA and UVB efficacy, and lead to minimal skin side effects caused by the UV filters. Lipid nanocarriers coencapsulated with UV filters were prepared by melt emulsification method coupled with high shear homogenization, using Tween 20 as main nonionic surfactant and two solid lipids (cetyl palmitate and emulgade) together with MCT or Sq. It is worth to be noted that no research has reported the encapsulation of both BMDBM and OCT in the same NLCs or SLNs formulation. Furthermore, no studies were done on the multiple in vitro releases of both UVA and UVB filters from the lipid nanocarriers.

The physicochemical properties of the lipid nanoparticles, such as particle size, morphology, zeta potential (ZP), entrapment efficiency, loading capacity and thermal analysis (crystallinity), were in detail investigated. The optimized formulations in terms of UV absorptive properties were further formulated into a cream and in vitro sun protection factor (SPF) and erythemal UVA protection factor (EUVA–PF) were assessed. In addition in vitro studies were performed on cream formulations to evaluate the photostability of sensitive BMDBM after two irradiation stages. The multiple in vitro release study of BMDBM and OCT from the same lipid nanocarriers was comparatively performed using vertical Franz diffusion cell.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussions
  6. Conclusions
  7. Acknowledgments
  8. References


The two UV filters, BMDBM (Merck, Germany) and OCT, have been purchased from Sigma Aldrich. The surfactants used for the preparation of all formulations were as follows: Tween 20 (Polyoxyethylenesorbitan monolaurate; Merck, Germany) as main nonionic surfactant; Synperonic PE/F68 (Poloxamer 188, block copolymer of polyethylene and polypropylene glycol); and L-α-Phosphatidylcholine (Lecithin) obtained from Sigma Aldrich Chemie GmbH (Munich, Germany). The solid lipids used were: n-Hexadecyl Palmitate – CP (Acros Organics) and Emulgade SE/PF – Em (Glyceryl Stearate, Ceteareth-20, Ceteareth-12, Cetearyl Alcohol, Cetyl Palmitate from Cognis GmbH, Dusseldorf, Germany) provided by Elmiplant S.A. (Romania). The NLCs were prepared with Myritol 812 MCT or Sq purchased from Merck. The base cream (which contains stearats, glycerin, fatty alcohols, emulsifier, emollients and an antioxidant – butylhydroxyanisole) was provided by Elmiplant S.A. All other chemicals used were of analytical grade.

Preparation of UV filters coencapsulated into LNs

Both types of lipid nanoparticles (SLNs and NLCs) were prepared using melt emulsification method coupled with high shear homogenization. The method is similar to that described in a previous work of the authors [32]. The lipid phase, consisting in solid lipids, CP, and Em, (for SLNs preparation) or a mixture of solid lipids, CP and Em, and oils, MCT or Sq, (for NLCs preparation), was heated under stirring at 85°C. BMDBM and OCT were added into the lipid phase and stirred until forming a clear molten solution. The lipid phase was gradually added into the aqueous phase consisting in 3.5% surfactant mixture and continuous stirred for 1 h at 85°C. The formed preemulsion was subjected to an external mechanical energy by high shear homogenization (High-Shear Homogenizer PRO250 type; 0~8765 g; power of 300 W, Germany), by applying 6987 g for 10 min. The nanoparticle dispersions were lyophilized, using an Alpha 1–2 LD Freeze Drying System Germany. Table 1 gives an overview of the formulations produced. For comparative purpose, some nanoemulsions were produced in the same manner as solid nanoparticles, except that the lipid phase was entirely composed of oils, MCT or Sq.

Table 1. Composition of UV filters coencapsulated into lipid nanoparticles
Oil typeMCTSqualene
  1. All LNs were prepared with 3.5% (w/w) surfactants (Lecithin:Synperonic F68:Tween 20 in a ratio of 1:1:4.66), and 10% (w/w) lipid mixtures, in a ratio of Em:PC:MCT/Sq = 49:21:30 for NLC and in a ratio of Em:PC = 70:30 for SLN.

Composition of LNs dispersionsBMDBM % w/w0.
OCT % w/w0.
Composition of LNs lyophilizedBMDBM % w/w553.5253.52
OCT % w/w223.5523.55

Particle size and zeta potential analysis

Particle size (Zave), polydispersity index (PdI), and zeta potential (ZP) of lipid nanoparticles were analyzed by dynamic light scattering (DLS; Zetasizer Nano ZS, Malvern Instruments Ltd., UK). The ZP was determined by measuring the electrophoretic mobility of the nanoparticles in an electric field using the appropriate accessory of the Zetasizer Nano ZS. Before measurements, the dispersions were diluted with deionized water to an adequate scattering intensity. All measurements were performed at 25°C and data were given as average of three individual measurements.

Nanoparticle morphology

The morphology of lipid nanoparticles loaded with BMDBM and OCT (selected sample was NLC4) was investigated using a transmission electron microscope (TEM; Tecnai G2 F30 S-TWIN equipped with STEM with HAADF detector, EDX, EELS) running at an acceleration voltage of 300 kV. The nanoparticle dispersions were diluted with water and three drops were placed onto a carbon-coated copper grid and allowed to dry at room temperature for 24 h before examination.

Entrapment efficiency and loading capacity

The entrapment efficiencies (EE%) and drug loading (DL%) of BMDBM and OCT into SLNs and NLCs were determined by measuring the concentration of free BMDBM and OCT in the dispersion medium [33, 34]. The nanoparticle dispersion was uniformly mixed with ethanol and then centrifuged for 20 min at 25 155 g. The supernatant was filtered using a membrane filter (0.45 μm, Sartorius Stedim Biotech). The filtrate was collected, diluted with ethanol and measured spectrophotometric at λmax 356.5 nm for BMDBM and at λmax 303 nm for OCT using a UV–Vis–NIR spectrophotometer type V670, Jasco (Japan). The percentage of entrapment efficiency and drug loading of UV filter, BMDBM/OCT, were calculated as follows [Eqs. (1) and (2)] [33]:

  • display math(1)
  • display math(2)

Differential scanning calorimetry analysis

The analysis was performed by DSC Jupiter, STA 449C (Netzsch, Germany). Lipid nanoparticles with or without UV filters and the corresponding bulk materials were heated from 5°C to 85°C, at a scanning rate of 10°C/min. The samples (10 mg) were weighed into standard alumina pan using an empty pan as reference.

In vitro UV absorptive properties

The nanostructured lipid carriers, either in dispersion or lyophilized, loaded with BMDBM and OCT (2 mg cm−2) were evenly applied onto a quartz plate covered with the Transpore™ tape (3M Health Care) [35, 36]. The absorption spectra of the samples were registered from 290 to 400 nm with UV–Vis V670 Spectrophotometer equipped with integrated sphere and using a Transpore™ tape without sample as reference support. The absorption spectrum of each sample was obtained from measurements in six different points.

In vitro SPF and EUVA–PF measurements

The method was conducted according to Diffey–Robson methodology [37] and it is based on the measurement of the transmission radiation intensity transmitted through the substrate of the applied sample, by recording the photocurrent in 5 nm steps from 290 to 400 nm. Each sample, consisting into a cream formed by adding lyophilized lipid nanoparticles loaded with UV filters into a base cream, was spectrophotometric registered in six different points and the average values were used to calculate the SPF and the EUVA–PF. The EUVA–PF was calculated following the SPF equation and considering the UVA wavelength ranging between 320 and 400 nm [Eqs. (3) and (4)] [38, 39]:

  • display math(3)
  • display math(4)

Photostability studies

Cream formulations containing BMDBM (2.5%, w/w) and OCT (1%, w/w), or their equivalent amounts encapsulated into SLN2, NLC4, and NLC8 were subjected to irradiation. The irradiation was performed with the BioSun irradiation system (Vilver Lourmat, France), at two wavelengths, one at 365 nm (UVA) and the other at 312 nm (UVB) with energy of 19.5 J/cm2 [40]. The cream formulations were subjected to two irradiation intervals: a short interval, 1 h 30 min on UVA and 2 h 30 min UVB, irradiation I, and a long interval, 3 h on UVA and 5 h UV-B, irradiation II. The SPF and EUVA–PF of the samples were determined after each interval of irradiation.

In vitro release study

The BMDBM and OCT release from the lipid nanoparticles in dispersion was performed using vertical Franz diffusion cell (25 mm in diameter; Hanson Reasearch Corporation). The 6 mL receptor chamber was loaded with phosphate-buffered saline (pH 5.5)/ethanol, 70:30 (v/v). The nanoparticles (200 μL) were placed in the donor chamber on the cellulose nitrate membrane filter (0.1 μm; Whatman, Germany). The membrane was hydrated in ethanol buffer solution for 1 h before using it. The receptor medium was continuously stirred at 400 rpm and maintained at 37°C. At fixed time intervals (0.5, 1–24 h), 500 μL of the samples was withdrawn and replaced by an equal volume of fresh receptor medium. After dilution with ethanol, the samples were analyzed spectrophotometric at λmax 356.5 and 303 nm for BMDBM and OCT respectively. The release medium was maintained constant in the receptor chamber throughout the study. The release kinetics of BMDBM and OCT from lipid nanoparticles was compared with their release from nanoemulsion by using the following mathematical models equations [Eqs. (5)-(9)] [41, 42]:

  • display math(5)
  • display math(6)
  • display math(7)
  • display math(8)
  • display math(9)

where, %R is percent of UV filter release at time t; k0, k1, k2, k3, and k4 are the rate constants for zero order, first order, Higuchi, Korsmeyer–Peppas, and Hixson–Crowell respectively; n is the release exponent. The criterion for selecting the most appropriate model was based on a goodness-of-fit test.

Results and Discussions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussions
  6. Conclusions
  7. Acknowledgments
  8. References

Characterization and stability of lipid nanoparticles

The mean particle size and the PdI of SLNs and NLCs have been evaluated immediately after their production by DLS. The results are presented in Fig. 1. All the tested formulations showed a mean particle diameter in the range of 104–130 nm and PdI values between 0.183 and 0.233, indicating a relatively narrow particle size distribution. The particle sizes of both NLCs systems prepared with MCT or Sq are larger than those of SLNs. Usually, by adding oil to the solid lipid core of nanoparticles, the size of the resulted nanoparticles is reduced because of the viscosity reduction, and consequently of the surface tension reduction, determining the formation of particles with smaller and smoother surface [43]. The total amount of lipid phase was kept constant in all nanoparticles (10%, w/w) and the percentage of oil, MCT or Sq, in the lipid matrix of the NLCs was 30% of lipid phase. Thus, the concentration of emulgade in NLCs is reduced to 49% (w/w) from 70% (w/w) in the lipid matrix of SLNs. Emulgade is a self-emulsifying base, having Ceteareth-20 and Ceteareth-12 in composition, and by its concentration reduction, there are less surfactant molecules which could diminish the interfacial tension. Zave of loaded SLNs with 1% UV filters (SLN2) is 112 nm, and of the corresponding NLCs with MCT and Sq (NLC4 and NLC8) is 117 and 118 nm respectively. By adding the UV filters into LNs, the particle sizes increase as compared with those of unloaded LNs. Comparing the influence of the oils in the lipid matrix of NLCs, the use of MCT forms great imperfections in the crystal lattice determining the formation of smaller nanoparticles, by approximately 15 nm, than those with Sq.


Figure 1. Physicochemical characterization, particle size (Zave) and polydispersity index (PdI) of lipid nanoparticles coloaded with butyl-methoxydibenzoylmethane and OCT.

Download figure to PowerPoint

Initially, the physical stability of the colloidal system was assessed by the magnitude of the ZP value. The ZP values of the lipid nanoparticles were around −25 mV (Fig. 2). These results indicate that all SLNs and NLCs systems are relatively stable, with no significant tendency of the lipid particles to interact and to aggregate [44].


Figure 2. The evaluation of Zeta potential of lipid nanoparticles coloaded with butyl-methoxydibenzoylmethane and OCT.

Download figure to PowerPoint

To obtain more information about the lipid nanocarriers morphology, the particle size and stability in time, a TEM analysis was also performed 2 months after their preparation. The transmission electron micrographs of NLCs based on MCT coloaded with 0.7% BMDBM and 0.3% OCT (Fig. 3) showed spherical particles with diameters around 200 nm and no obvious sign of aggregation. The larger particle size of NLC4 obtained by TEM than that determined by DLS could be due to the different sample preparation utilized by these methods.


Figure 3. Transmission electron microscopy photographs of MCT-based NLC (NLC4) coloaded with butyl-methoxydibenzoylmethane and OCT.

Download figure to PowerPoint

Entrapment efficiency and drug loading

The percentage of BMDBM and OCT coencapsulated into nanoparticles and their loading in the lipid matrix were represented in Fig. 4. The highest entrapment efficiency of the UV filters was found in NLC4 prepared with MCT and with a ratio of BMDBM:OCT/7:3 (82.9% for OCT and 81.2% for BMDBM). The presence of carrier oils improved the capacity of the nanostructured lipid carriers to encapsulated BMDBM and OCT comparing with that of solid lipid nanoparticles (76.4% OCT and 71.3% BMDBM for SLN2), as the solubility of UV filters is greater in oils than in solid lipids alone. Furthermore, for lipid mixtures with different molecular structures, as in case of MCT, the number of imperfections resulted inside the crystal lattice is greater than for highly purified drug, such as Sq, offering more space inside the lipid matrix for the UV filters [14, 24, 40]. Thus, the entrapment efficiency values are greater for MCT-based NLCs than for Sq-based NLCs (77.33% OCT and 75.68% BMDBM for NLC8 with Sq). It can be observed that EE values of UV filters coencapsulated into all lipid nanoparticles are bigger for OCT than for BMDBM. This is due to the fact that OCT (logKow 6.9) is more lipophilic than BMDBM (logKow 6.1) [45].


Figure 4. The percent of entrapment efficiency (% EE) (a) and drug loading (% DL) (b) of lipid nanoparticles loaded with different amounts of butyl-methoxydibenzoylmethane and OCT.

Download figure to PowerPoint

Despite the advantages of SLNs and NLCs, they could exhibit some difficulties associated with the low loading capacity of UV filters which is limited to 10% of the amount of lipid [46]. The loading capacity obtained in this study was between 4.76% and 5.38% for BMDBM–LNs prepared with 7% BMDBM (w/lipid w) and between 2.24% and 2.43% for OCT–LNs prepared with 3% OCT (w/lipid w).

Thermal analysis

The thermal analysis was used to investigate the physical state of the lipid matrix of nanoparticles [31, 47]. The crystalline arrangements of both SLN and NLC cores have been comparatively evaluated on free and loaded lipid nanoparticles with a ratio of BMDBM:OCT/7:3. In Fig. 5, the thermograms of SLNs and selected MCT–NLCs, and Sq–NLCs are compared with their corresponding bulk lipids. Table 2 shows the DSC parameters (melting point, Tm and melting enthalpy) of the selected lipid nanoparticles. It can be observed that the melting points of the lipid core of SLNs/NLCs are at a lower temperature than those of their corresponding bulk lipids. Also, the lipid nanoparticles show a narrow melting range and a decrease in the melting enthalpy than its bulk lipid. These findings are attributed to the presence of surfactants which confers an ordered arrangement of the lipid matrix [32] and to the smaller particle size which determines an increase of the specific surface area [48].

Table 2. The melting points (Tm, °C) and enthalpies measured by DSC of the lipid mixtures and of the lipid nanoparticles unloaded or loaded with UV filters
Physical mixture/Enthalpy (J/g)Em:PC (−200.9)Em:PC:MCT (−119.5)Em:PC:Sq (−135.1)
Tm (°C)39.451.846.143.451.1
LN/Enthalpy (J/g)SLN1 (−142.4)NLC3 (−86.32)NLC7 (−111.3)
Tm (°C)48.1 44.844.250
LN/Enthalpy (J/g)SLN2 (−135)NLC4 (−88.8)NLC8 (−86.87)
Tm (°C)48.6 45.343.248.3

Figure 5. The thermal behavior of SLNs and MCT-based NLCs (a) and Sq-NLCs (b) unloaded and coloaded with butyl-methoxydibenzoylmethane and OCT.

Download figure to PowerPoint

BMDBM has a melting temperature in the range of 81°C–84°C. The absence of its melting event can be due to a supercooled melted state, amorphous or molecular dispersed state of BMDBM in the lipid matrix [49]. Thus, the formation lipid nanoparticles coloaded with BMDBM and OCT with the lipid matrix in the nanometer size and with the melting temperatures above body temperature is confirmed. It is well known that the presence of the liquid lipid into nanostructured lipid carriers determines a less ordered lipid matrix, as compared to that of SLNs, fact confirmed by the DSC curves from Fig. 5a, where a decrease in the endotherm peak intensity and melting temperature of NLCs is observed (Tm 45.3°C for NLC4 and 48.6°C for SLN2).

By incorporating the organic UV filters into the lipid matrix of the nanoparticles, the thermal behavior of the loaded nanoparticles vary as function of the lipid nanoparticles type and oil type. According to literature data, when melting temperature shifts toward lower temperatures, a decrease in the particle size of the nanoparticles could be associated [50], and a reduction in the melting enthalpy could determine a disorder in the crystalline arrangement of the lipid matrix [51]. Thus, the UV filters loaded SLNs (Tm 48.6°C) show bigger particle sizes, fact confirmed by DLS, and a more disorder crystal lattice (enthalpy 135 J/g) than for unloaded SLNs (Tm 48.1°C, enthalpy 142.4 J/g).

In case of lipid nanocarriers prepared with MCT (NLC3 and 4), the DSC profile did not show a significant crystalline modification after BMDBM and OCT coencapsulation. Only a slight increase in the melting temperature, with 0.5°C above that of the unloaded NLCs, and melting enthalpy can be observed. For loaded NLCs based on Sq, a significant decrease in the melting point and enthalpy has been revealed as compared with the unloaded NLCs (Fig. 5b). It could be presumed that an efficient rearrangement of the solid and liquid lipids, associated with a more homogeneous lipid core, has occurred after BMDBM and OCT coencapsulation. Even though, the long tail of Sq structure does not allow the best accommodation of UV filters inside the lipid core, fact confirmed by comparing the previous entrapment efficiency results of NLC4 and 8. This will determine (as will be seen in 'In vitro release study') a higher release of BMDBM and OCT from nanocarriers based on Sq than those based on MCT.

In vitro UV absorptive properties

The UV absorption of lipid nanocarriers was investigated in aqueous dispersions using Transpore® tape. A wavelength scan from 290 to 400 nm was carried out to cover the UVA and UVB range. The investigated lipid nanocarriers contain the UV filters in a concentration of 1% (w/w). Figure 6 shows the absorption profiles of various ratios of BMDBM–OCT loaded into NLCs based on MCT and on Sq. By increasing the BMDBM concentration from 0.3% to 0.7%, the UV absorption of both types of NLCs is strongly increased in the UVA domain by approximately twice, whereas the concentration increase in OCT slightly influences the UVB absorption. This could be explained by the photoprotective properties of the individual UV filters, OCT having a moderate absorptive capacity as compared to BMDBM [29], and by the drug loading capacity of NLCs. The NLCs formulations with the highest UV absorption profiles are those composed with 0.7% BMDBM and 0.3% OCT, whatever was the type of the lipid core.


Figure 6. The electronic spectra of butyl-methoxydibenzoylmethane –OCT loaded into MCT-based NLCs dispersions and NE (a) and Squalene-based NLCs dispersions and NE (b) using Transpore® tape1.

Download figure to PowerPoint

Among lipid nanoparticle dispersions loaded with UV filters, the NLCs based on MCT (NLC4) present a shift to higher UV absorption values than those of NLCs based on Sq (NLC8). These UV blocking properties of the developed NLCs could be assigned to the loading capacity of nanoparticles. Furthermore, an improved UVA and UVB protection of the lipid nanoparticle formulations in comparison to nanoemulsion was observed, fact also confirmed by previous studies [14]. The NLCs based on MCT (NLC4) presents the highest absorption profile, with a twice increase in the absorbance (at 356.5 nm) as compared to that of the reference nanoemuslsion with the same amount of UV filters. This is due to the solid core of NLCs which are able to scatter and reflect incoming UV radiation more than liquid droplets from nanoemulsion [30].

The UV absorption profiles of lyophilized lipid nanoparticles loaded with 5% BMDBM and 2% OCT are shown in Fig. 7. In the UVA range, the lipid nanocarriers present different absorption intensities, the NLCs based on MCT (NLC4) having the highest absorption profile. A different behavior has been observed for the lyophilized lipid nanoparticles in the UVB range, all types of lipid nanocarriers with 2% OCT presenting the same absorption profile.


Figure 7. The electronic spectra of lyophilized lipid nanocarriers loaded with 5% butyl-methoxydibenzoylmethane and 2% OCT using Transpore® tape.

Download figure to PowerPoint

Photostability studies

The photostability evaluation of the UV filters loaded into lipid nanoparticles is a prerequisite to develop efficient and safer sunscreen formulations. The cream formulations based on lipid nanoparticles coloaded with 2.5% BMDBM and 1% OCT were subjected to a photochemical UV irradiation at a low energy that simulates the solar energy during the middle of the day. The SPFs and EUVA–PFs of the creams exposed to irradiation stages are shown in Fig. 8. All the developed cream formulations based on lipid nanoparticles presents increased photoprotective properties as compared to those of the reference cream.


Figure 8. The effect of irradiation on SPFs (a) and EUVA–PFs (b) of different creams based on lipid nanoparticles and on reference cream, which contain 2.5% butyl-methoxydibenzoylmethane and 1% OCT.

Download figure to PowerPoint

The increased photoprotective properties of creams based on lipid nanoparticles vs conventional cream are described in many studies [24, 32, 36, 40] being attributed to the synergistic effect of the UV protective properties of the lipid matrix and of the UV filters loaded into lipid nanoparticles. Before irradiation, the best photoprotection was obtained for NLC–MCT, with a EUVA–PF of 50.8 and a SPF of 17.2 (NLC4), followed by NLCs based on Sq (EUVA–PF 34.4, SPF 12.7 for NLC8) and by SLNs (EUVA–PF 32.2, SPF 12.6 for SLN2). The unloaded lipid nanoparticles did not manifest photoprotective properties, having EUVA–PF and SPF around 1 (data not shown). A twice increase in EUVA–PF of NLCs based on MCT, 50.8 has been obtained as compared to the conventional cream, 23.

All the creams offer a high protection in the UVA range but only the cream based on NLC–MCT provides a medium UVB protection, the other ones offering a rather low UVB protection, according to legislation [52]. The SPF values of creams based on the lipid nanoparticles were slightly increased as compared to those of the reference cream. It is known that SPF mainly indicates the protection on UVB domain, thus the slightly increased of SPF suggesting the possibility of OCT distribution into the shell structure of the SLNs/NLCs.

After irradiation, the creams containing SLNs and NLCs coloaded with BMDBM and OCT have kept their photoprotective effect, while the reference cream was not (EUVA–PF initial was 23 and after irradiation II was 16, SPF initial was 10.2 and after irradiation II was 8). There is a difference in the irradiation behavior on the UVA and UVB domains of creams based on lipid nanoparticles. The SPF values were maintained constant through the irradiation process, while the EUVA–PF values were increased. The increase is more evident for the cream prepared with BMDBM and OCT loaded into SLN2 followed by Sq-based NLCs (NLC8). This could be explained by the more ordered lipid lattice of SLNs than that of NLCs, which could lead to a greater BMDBM expulsion from the lipid matrix of SLN2 into the base cream during irradiation. All these assumptions are based on the previous DSC results and by the in vitro release study. Regarding the stability of the UVB filter OCT throughout the irradiation, the SPF values were negligibly varied suggesting a high stability of OCT under exposure to UV radiation.

In vitro release study

The in vitro release study has been achieved for optimized lipid nanoparticles (e.g. SLN2, NLC4, and NLC8) using the vertical Franz diffusion cells. To evaluate the release behavior of the solid core of the lipid nanoparticles, a nanoemulsion prepared with MCT has been subjected to the same release study. The both encapsulated UV filters, BMDBM (Fig. 9a) and OCT (Fig. 9b), showed an initial burst release in the first 0.5 h, followed by a sustained release for the next 8 h. After 8 h of release, a plateau was obtained for both UV filters.


Figure 9. The release profiles of butyl-methoxydibenzoylmethane (a) and OCT (b) from lipid nanoparticles (SLNs, NLCs) in comparison with NE, in release medium PBS (pH 5.5): ethanol/70:30. The percentage of cumulative amounts released was plotted against time.

Download figure to PowerPoint

The initial burst release in the first 0.5 h of the UV filters from the lipid nanoparticles could be explained by the presence of free BMDBM/OCT localized in the outer surfactant shell evidenced by the UV filter entrapment efficiency study. This burst release could be related to the experimental conditions used to prepare the lipid nanoparticles. The preparation of lipid nanoparticles at high temperature determines a slight solubility of the active compounds in the aqueous phase. Next, during the solidification at low temperature, the solid lipid matrix crystallizes and the solubility of the active compounds in the aqueous phase has decreased. Because the solid lipid matrix has been already formed, the UV filters are partitioning into the surfactant outer shell. According to literature data, the partition of the UV filters is correlated with the drug-enriched shell model [53].

The slow release for the next 24 h of the UV filters from the lipid matrices could be explained by their low solubility in the released medium. Different studies [36, 49] stated that a slow release profile of the drug suggests a homogeneous entrapment of the drug throughout the carrier. Consequently, the higher entrapment efficiency of BMDBM/OCT into lipid nanoparticles is correlated with slower release rates.

The release data obtained from 0.5 to 8 h were fitted into various kinetic models, including zero order, first order, Higuchi, Korsmeyer–Peppas and Hixon–Crowell. The correlation coefficients (R2), the rate constants (k) and the release exponent (n) were collected in Table 3. For all the tested nanoparticles, the data best fitted the Higuchi model having a good correlation coefficient (R2 from 0.9889 to 0.9931). The Higuchi drug release model describes a Fickian diffusion process of BMDBM and OCT from the SLNs, NLCs, and NE.

Table 3. Release kinetic parameters of BMDBM and OCT
UV filterSampleZero orderFirst orderHiguchiPeppas–KorsmeyerHixon–Crowell
R 2 k 0 R 2 k 1 R 2 k 2 R 2 k 3 n R 2 k 4

The release profile of the both UV filters in phosphate-buffered saline/ethanol (7/3 v/v) increased in the order MCT-NLC4 < MCT-NE < Sq-NLC8 < SLN2. The bigger release after 24 h was obtained for SLN2 (11.8% for BMDBM and 36% for OCT) and the smallest for MCT-based NLC (NLC4 with 7.56% BMDBM and 26.8% for OCT). Instead, the rate constants of the Higuchi model, k2, increased in the order MCT-NLC4 < Sq-NLC8 < SLN2 < MCT-NE. The difference between the release profile and the constant rates of the nanoparticles comes from the initial burst release. In the first 0.5 h, the UV filters are more easily released out of SLNs than from the NLCs and NE, the UV filters having a better solubility in liquid lipids than in solid lipids. The initial release of BMDBM from MCT-based NE (5%) is smaller than from NLCs and SLNs because BMDBM is homogenously dissolved inside the liquid MCT nanoparticles. For the next 8 h, a faster release of BMDBM was observed from NE (k2 = 7.88) than from SLNs (k2 = 7.54) and NLCs (k2 = 6.3 for NLC4 and k2 = 7.46 for NLC8), BMDBM being less tightly incorporated in the liquid droplets. The release of OCT followed the same profile as BMDBM, but with higher rates, which could be due to the encapsulation of OCT at the surface of the lipid matrix.


  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussions
  6. Conclusions
  7. Acknowledgments
  8. References

The results described in this study have demonstrated that the coencapsulation of the BMDBM and OCT into lipid nanocarriers by the high shear homogenization method has been successfully performed. All the formulations exhibit a mean particle size of 110 nm–130 nm with a narrow size distribution (PdI < 0.23) and a good physical stability indicated by the ZP (greater than −25 mv). The presence of oil inside the solid lipid matrix has led to a less ordered structure within the particles, assuring an appropriate loading capacity of UV filters, particularly for NLCs prepared with MCT, confirmed by DSC and by in vitro release study.

By encapsulating BMDBM together with OCT, all the developed NLCs and SLNs systems provided a stabilizing effect of BMDBM under exposure to artificial UV radiation. The cream, which contains 2.5% BMDBM and 1% OCT based on MCT–NLCs, presents the best photoprotective efficacy by absorbing up to 98% of the hazardous short UVA radiation and 94% of the UVB radiation. Thus, a market broad-spectrum sunscreen could be developed with a significant decrease in the UV filters concentrations and an improved UV protection as compared to the conventional formulations with the same amount of UV filters. Furthermore, the in vitro release study has demonstrated that the encapsulation of the UV filters into lipid nanocarriers results in the reduction of the skin penetration leading to a high degree of safety.


  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussions
  6. Conclusions
  7. Acknowledgments
  8. References

The work has been funded by the Sectoral Operational Programme Human Resources Development 2007–2013 of the Romanian Ministry of Labour, Family and Social Protection through the Financial Agreements POSDRU/107/1.5/S/76909 and by the Partnership in priority domains program-PN II, with support from ANCS, CNDI – UEFISCDI, project no. PN-II-PT-PCCA-132/2012.

  1. 1

    [Correction added on 09 August 2013, after first online publication: Figure 6b has been added].


  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussions
  6. Conclusions
  7. Acknowledgments
  8. References
  • 1
    González, S., M. Fernández-Lorente and Y. Gilaberte-Calzada (2008) The latest on skin photoprotection. Clin. Dermatol. 26, 614626.
  • 2
    Chen, L., J. Y. Hu and S. Q. Wang (2012) The role of antioxidants in photoprotection: A critical review. J. Am. Acad. Dermatol. 67, 10131024.
  • 3
    Gasparro, F. P., M. Mitchnick and J. F. Nash (1998) A review of sunscreen safety and efficacy. Photochem. Photobiol. 68, 243256.
  • 4
    Serpone, N., D. Dondi and A. Albini (2007) Inorganic and organic UV filters: Their role and efficacy in sunscreens and suncare products. Inorg. Chim. Acta 360, 794802.
  • 5
    Vilela, F. M. P., Y. M. Fonseca, J. R. Jabor, F. T. M. C. Vicentini and M. J. V. Fonseca (2012) Effect of ultraviolet filters on skin superoxide dismutase activity in hairless mice after a single dose of ultraviolet radiation. Eur. J. Pharm. Biopharm. 80, 387392.
  • 6
    Chisvert, A., Z. León-González, I. Tarazona, A. Salvador and D. Giokas (2012) An overview of the analytical methods for the determination of organic ultraviolet filters in biological fluids and tissues. Anal. Chim. Acta 752, 1129.
  • 7
    Kockler, J., M. Oelgemöller, S. Robertson and B. D. Glass (2012) Photostability of sunscreens. J. Photochem. Photobiol., C 13, 91110.
  • 8
    Ou-Yang, H., J. Stanfield, C. Cole, Y. Appa and D. Rigel (2012) High-SPF sunscreens (SPF ≥ 70) may provide ultraviolet protection above minimal recommended levels by adequately compensating for lower sunscreen user application amounts. J. Am. Acad. Dermatol. 67, 12201227.
  • 9
    Díaz-Cruz, M. S., M. Llorca and D. Barceló (2008) Organic UV filters and their photodegradates, metabolites and disinfection by-products in the aquatic environment. TrAC, Trends Anal. Chem. 27, 873887.
  • 10
    Giokas, D. L., A. Salvador and A. Chisvert (2007) UV filters: From sunscreens to human body and the environment. TrAC, Trends Anal. Chem. 26, 360374.
  • 11
    Shi, L., J. Shan, Y. Ju, P. Aikens and R. K. Prud'homme (2012) Nanoparticles as delivery vehicles for sunscreen agents. Colloids Surf. A 396, 122129.
  • 12
    Wissing, S. A. and R. H. Müller (2002) The development of an improved carrier system for sunscreen formulations based on crystalline lipid nanoparticles. Int. J. Pharm. 242, 373375.
  • 13
    Müller, R. H., R. D. Petersen, A. Hommoss and J. Pardeike (2007) Nanostructured lipid carriers (NLC) in cosmetic dermal products. Adv. Drug Deliv. Rev. 59, 522530.
  • 14
    Nikolić, S., C. M. Keck, C. Anselmi and R. H. Müller (2011) Skin photoprotection improvement: Synergistic interaction between lipid nanoparticles and organic UV filters. Int. J. Pharm. 414, 276284.
  • 15
    Wissing, S. A. and R. H. Müller (2001) A novel sunscreen system based on tocopherol acetate incorporated into solid lipid nanoparticles. Int. J. Cosmet. Sci. 23, 233243.
  • 16
    Jee, J. P., S. J. Lim, J. S. Park and C. K. Kim (2006) Stabilization of all-trans retinol by loading lipophilic antioxidants in solid lipid nanoparticles. Eur. J. Pharm. Biopharm. 63, 134139.
  • 17
    Jenning, V., M. Schafer-Korting and S. Gohla (2000) Vitamin A-loaded solid lipid nanoparticles for topical use: Active release properties. J. Control. Release 66, 115126.
  • 18
    Wissing, S. A. and R. H. Müller (2002) Solid lipid nanoparticles as carrier for sunscreens: In vitro release and in vivo skin penetration. J. Control. Release 81, 225233.
  • 19
    Joshi, M. D. and R. H. Müller (2009) Lipid nanoparticles for parenteral delivery of actives. Eur. J. Pharm. Biopharm. 71, 161172.
  • 20
    Mehnert, W. and K. Mäder (2012) Solid lipid nanoparticles: Production, characterization and applications. Adv. Drug Deliv. Rev. 64, 83101.
  • 21
    Pardeike, J., A. Hommoss and R. H. Müller (2009) Lipid nanoparticles (SLN, NLC) in cosmetic and pharmaceutical dermal products. Int. J. Pharm. 366, 170184.
  • 22
    Müller, R. H., M. Radtke and S. A. Wissing (2002) Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) in cosmetic and dermatological preparations. Adv. Drug Deliv. Rev. 54, S131S155.
  • 23
    Souto, E. B. and R. H. Muller (2008) Cosmetic features and applications of lipid nanoparticles (SLN, NLC). Int. J. Cosmet. Sci. 30, 157165.
  • 24
    Niculae, G., I. Lacatusu, N. Badea and A. Meghea (2012) Lipid nanoparticles based on butyl-methoxydibenzoylmethane: in vitro UVA blocking effect. Nanotechnology 23, 315704.
  • 25
    Chatelain, E. and B. Gabard (2001) Photostabilization of butyl methoxydibenzoylmethane (avobenzone) and ethylhexyl methoxycinnamate by bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter. Photochem. Photobiol. 74, 401406.
  • 26
    Scalia, S. and M. Mezzena (2010) Photostabilization effect of quercetin on the UV filter combination, butyl methoxydibenzoylmethane–octyl methoxycinnamate. Photochem. Photobiol. 86, 273278.
  • 27
    Herzog, B., M. Wehrle and K. Quass (2009) Photostability of UV absorber systems in sunscreens. Photochem. Photobiol. 85, 869878.
  • 28
    Gaspar, L. R. and P. M. B. G. Maia Campos (2006) Evaluation of the photostability of different UV filter combinations in a sunscreen. Int. J. Pharm. 307, 123128.
  • 29
    Xia, Q., A. Saupe, R. H. Müller and E. B. Souto (2007) Nanostructured lipid carriers as novel carrier for sunscreen formulations. Int. J. Cosmet. Sci. 29, 473482.
  • 30
    Scalia, S. and M. Mezzena (2009) Incorporation in lipid microparticles of the UVA filter, butyl methoxydibenzoylmethane combined with the UVB filter, octocrylene: Effect on photostability. AAPS Pharm. Sci. Tech. 10, 384390.
  • 31
    Montenegro, L., M. G. Sarpietro, S. Ottimo, G. Puglisi and F. Castelli (2011) Differential scanning calorimetry studies on sunscreen loaded solid lipid nanoparticles prepared by the phase inversion temperature method. Int. J. Pharm. 415, 301306.
  • 32
    Lacatusu, I., N. Badea, A. Murariu and A. Meghea (2011) The encapsulation effect of UV molecular absorbers into biocompatible lipid nanoparticles. Nanoscale Res. Lett. 6, 73.
  • 33
    Singh Negi, J., P. Chattopadhyay, A. K. Sharma and V. Ram (2013) Development of solid lipid nanoparticles (SLNs) of lopinavir using hot self nano-emulsification (SNE) technique. Eur. J. Pharm. Sci. 48, 231239.
  • 34
    Lv, Q., A. Yu, Y. Xi, H. Li, Z. Song, J. Cui, F. Cao and G. Zhai (2009) Development and evaluation of penciclovir-loaded solid lipid nanoparticles for topical delivery. Int. J. Pharm. 372, 191198.
  • 35
    Tursilli, R., G. Piel, L. Delattre and S. Scalia (2007) Solid lipid microparticles containing the sunscreen agent, octyl-dimethylaminobenzoate: Effect of the vehicle. Eur. J. Pharm. Biopharm. 66, 483487.
  • 36
    Sanad, R. A., N. S. Abdel Malak and T. S. El-Bayoomy (2010) Formulation of a novel oxybenzone-loaded nanostructured lipid carriers (NLCs). AAPS Pharm. Sci. Tech. 11, 16841694.
  • 37
    Diffey, B. L. and J. J. Robson (1989) A new substrate to measure sunscreen protection factors throughout the ultraviolet spectrum. Soc. Cosmet. Chem. 40, 127133.
  • 38
    Garoli, D., M. Guglielmina Pelizzo, B. Bernardini, P. Nicolosi and M. Alaibac (2008) Sunscreen tests: Correspondence between in vitro data and values reported by the manufacturers. J. Dermatol. Sci. 52, 193204.
  • 39
    Villalobos-Hernández, R. and C. C. Müller-Goymann (2007) In vitro erythemal UV-A protection factors of inorganic sunscreens distributed in aqueous media using carnauba wax-decyl oleate nanoparticles. Eur. J. Pharm. Biopharm. 65, 122125.
  • 40
    Lacatusu, I., N. Badea, A. Murariu, D. Bojin and A. Meghea (2010) Effect of UV sunscreens loaded in solid lipid nanoparticles: A combinated SPF assay and photostability. Mol. Cryst. Liq. Cryst. 523, 247259.
  • 41
    Costa, P. and J. M. S. Lobo (2001) Modeling and comparison of dissolution profiles. Eur. J. Pharm. Sci. 13, 123133.
  • 42
    Kumbhar, D. D. and V. B. Pokharkar (2013) Engineering of a nanostructured lipid carrier for the poorly water-soluble drug, bicalutamide: Physicochemical investigations. Colloids Surf. A 416, 3242.
  • 43
    Villalobos-Hernández, J. R. and C. C Müller-Goymann (2005) Novel nanoparticulate carrier system based on carnauba wax and decyl oleate for the dispersion of inorganic sunscreens in aqueous media. Eur. J. Pharm. Biopharm. 60, 113122.
  • 44
    Hu, F. Q., S. P. Jiang, Y. Z. Du, H. Yuan, Y. Q. Ye and S. Zeng (2005) Preparation and characterization of stearic acid nanostructured lipid carriers by solvent diffusion method in an aqueous system. Colloids Surf. B 45, 167173.
  • 45
    Kaiser, D., A. Sieratowicz, H. Zielke, M. Oetken, H. Hollert and J. Oehlmann (2012) Ecotoxicological effect characterisation of widely used organic UV filters. Environ. Pollut. 163, 8490.
  • 46
    Schäfer-Korting, M., W. Mehnert and H. C. Korting (2007) Lipid nanoparticles for improved topical application of drugs for skin diseases. Adv. Drug Deliv. Rev. 59, 427443.
  • 47
    de Almeida, A. E., A. L. R. Souza, D. L. Cassimiro, M. P. D. Gremião, C. A. Ribeiro and M. S. Crespi (2012) Thermal characterization of solid lipid nanoparticles containing praziquantel. J. Therm. Anal. Calorim. 108, 333339.
  • 48
    Sanna, V., G. Caria and A. Mariani (2010) Effect of lipid nanoparticles containing fatty alcohols having different chain length on the ex vivo skin permeability of Econazole nitrate. Powder Technol. 201, 3236.
  • 49
    Teeranachaideekul, V., E. B. Souto, V. B. Junyaprasert and R. H. Müller (2007) Cetyl palmitate-based NLC for topical delivery of Coenzyme Q10 – Development, physicochemical characterization and in vitro release studies. Eur. J. Pharm. Biopharm. 67, 141148.
  • 50
    Lacatusu, I., N. Badea, O. Ovidiu, D. Bojin and A. Meghea (2012) Highly antioxidant carotene-lipid nanocarriers: Synthesis and antibacterial activity. J. Nanopart. Res. 14, 902.
  • 51
    Kovacevic, A., S. Savic, G. Vuleta, R. H. Müller and C. M. Keck (2011) Polyhydroxy surfactants for the formulation of lipid nanoparticles (SLN and NLC): Effects on size, physical stability and particle matrix structure. Int. J. Pharm. 406, 163172.
  • 52
    Hexsel, C. L., S. D. Bangert, A. A. Hebert and H. W. Lim (2008) Current sunscreen issues: 2007 Food and Drug Administration sunscreen labeling recommendations and combination sunscreen/insect repellent products. J. Am. Acad. Dermatol. 59, 316323.
  • 53
    Bose, S., Y. Du, P. Takhistov and B. Michniak-Kohn (2013) Formulation optimization and topical delivery of quercetin from solid lipid based nanosystems. Int. J. Pharm. 441, 5666.