MICROGELS FOR THE DELIVERY OF COSMETIC ACTIVE ORGANIC SUBSTANCES

Abstract

The present invention deals with organic cosmetic active molecules encapsulation into temperature-responsive and pH-responsive oligo(ethylene glycol)-based biocompatible microgels that are incorporated into cosmetic compositions for controlled delivery on skin or hair.

Claims

1. Microgels for pH-triggered, temperature-triggered and/or solvent-triggered delivery of a cosmetic active organic substance, which substance is entrapped in a at least one crosslinked poly(ethylene glycol) methyl ether methacrylate polymer, wherein the weight ratio of cosmetically active organic substance to crosslinked polymer in the microgel is from 250 microgram/mg to 10 mg/mg and wherein the crosslinked polymer comprises copolymer chains having diethylene glycol methacrylate monomeric units, oligoethylene glycol methacrylate monomeric units comprising from 6 to 10 ethylene glycol moieties, methacrylic acid monomeric units, and crosslinks.

2. Microgels according to claim 1, wherein the copolymer chains are linked with crosslinks each having di(meth)acrylate end groups and a moiety selected in the group consisting of (CH.sub.2-CH2O).sub.nCH.sub.2-CH.sub.2 where n is from 0 to 6 and preferably from 4 to 5, NHCH.sub.2NHand mixtures thereof.

3. Microgels according to claim 1, wherein the molar fraction of diethylene glycol methacrylate monomeric units is from 80 mol .% to 90 mol .%, preferably from 82 mol .% to 86 mol .%, the molar fraction of oligoethylene glycol methacrylate monomeric units is from 5 mol .% to 15 mol .%, preferably from 7 mol .% to 11 mol .%, the molar fraction of (meth)acrylic acid monomeric units is from 2 mol .% to 8 mol .%, preferably from 3 mol .% to 7 mol .%, and the molar fraction of the crosslinks is from 1 to 3 mol .%, molar fractions being the molar fractions in the crosslinked polymer.

4. Microgels according to claim 1, in the form of an aqueous dispersion or in the form of a film having a thickness being from 10 to 500 microns.

5. Microgels according to claim 1, wherein the weight ratio of cosmetic active organic substance to crosslinked polymer is lower than 10 mg/mg and higher than a lower limit selected in the group consisting of 250 microgram/mg, 350 microgram/mg, 400 microgram/mg, 450 microgram/mg, 500 microgram/mg, 550 microgram/mg, 600 microgram/mg, 650 microgram/mg, 700 microgram/mg, 750 microgram/mg, 800 microgram/mg, 850 microgram/mg, 900 microgram/mg and 1 mg/mg.

6. Microgels according to claim 1, wherein the cosmetic active organic substance is selected from the group consisting of octyl salicylate, hyaluronic acid, diethylamino hydroxybenzoyl hexyl benzoate, benzophenone-4, citronellol and salicylic acid.

7. Microgels according to claim 1, wherein the cosmetic active organic substance that is comprised in the microgels, goes out of the microgels into a release medium in an amount corresponding to a release percentage that is lower than 100% and higher than a value selected in the group consisting of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 90% and 95%, at the end of a period that is at least a number of hours selected from the group consisting of at least 6 hours, at least 12 hours, at least 24 hours and at least 48 hours, after that the microgels are put into contact with the release medium, and when the release medium has a pH being from 4.5 to 7.4, a ionic force being from 1 mM to 20 mM, and/or a temperature being 25 C. or 37 C.

8. A cosmetic composition comprising microgels according to claim 1, wherein the composition is in the form of a make-up product, a skin care product or a UV protecting product, and wherein the composition comprises a compound selected from the group consisting of oils, surfactants, pigments and dyes, said composition having a ionic strength being from 1 mM to 20 mM.

9. Cosmetic treatment method comprising a step of applying on skin, nails, lips or hair of a person, microgels according to claim 1.

10. Process for the preparation of microgels according to claim 1, said process comprising a step of preparing a feeding solution of the cosmetic active organic substance in a solvent, a step of preparing an aqueous dispersion of unloaded microgel particles, a step of mixing the solution and the aqueous dispersion under stirring so as to entrap the substance into the unloaded microgel particles, and a step of recovering the microgels.

11. Process for the preparation of microgels in the form of a film comprising the steps of preparing a feeding solution of the cosmetic active organic substance in a solvent, a step of preparing a film of unloaded microgel particles, a step of immersing the film in the feeding solution so as to cause swelling of the film and diffusion of the active substance into the film, and a step of recovering the microgels.

12. Process according to claim 10, wherein the entrapment efficiency EE % of the cosmetic active organic substance is higher than a upper limit selected from the group consisting of 50%, 60%, 70%, 80%, 90%, 95% when the amount of the active substance in the feeding substance is from 500 microgram/(mg unloaded microgel particles) to 10 mg/(mg unloaded microgel particles).

13. Cosmetic treatment method comprising a step of applying on skin, nails, lips or hair of a person, a cosmetic composition according to claim 8.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0123] FIG. 1 presents Uvinul-A encapsulated amount as a function of Uvinul-A feeding solution concentration with OEGDA microgel.

[0124] FIG. 2 presents Escalol encapsulated amount as a function of Escalol feeding solution concentration with OEGDA microgel.

[0125] FIG. 3 and FIG. 4 displays encapsulated amounts of Uvinul-A and Salicylic Acid as a function of feeding solution concentration for OEGDA microgel, EGDMA microgel and MBA microgel.

[0126] FIG. 5 displays encapsulated amounts of Citronellol and Hyaluronic acid active molecules as a function of feeding solution concentration with OEGDA microgel.

[0127] FIG. 6 displays encapsulated amounts of Benzophenone-4 as a function of feeding solution concentration for OEGDA microgel.

[0128] FIG. 7 displays encapsulated amount of Salicylic Acid as a function of feeding solution concentration for OEGDA microgel.

[0129] FIG. 8 provides with encapsulated amount of Uvinul-A as a function of feeding solution concentration for OEGDA self-assembled microgel film.

[0130] FIG. 9 displays encapsulated amount of Escalol as a function of feeding solution concentration for OEGDA self-assembled microgel film.

[0131] FIG. 10 displays encapsulated amount of Benzophenone-4 as a function of feeding solution concentration for OEGDA self-assembled microgel film.

[0132] FIG. 11 displays encapsulated amount of Salicylic Acid as a function of feeding solution concentration for OEGDA self-assembled microgel film.

[0133] FIG. 12 displays Salicylic Acid time release as a function of microgel microstructure depending on crosslinker type.

[0134] FIG. 13 displays Uvinul-A time release as a function of cross-linker type.

[0135] FIG. 14 is the time release curve of Benzophenone-4 as a function of temperature at pH 4.5.

[0136] FIG. 15 is the release curve of Salicylic Acid as a function of temperature at pH 4.5.

[0137] FIG. 16, FIG. 17, FIG. 18a and FIG. 18b are time release profiles of Salicylic acid, Benzophenone-4, Escalol and Uvinul-A as a function of ethanol content in the release medium.

[0138] FIG. 19a, FIG. 19b, FIG. 19c and FIG. 19d respectively present Uvinul-A, Escalol, Benzophenone-4 and Salicylic acid release with time as a function of release medium pH.

[0139] FIG. 20a, FIG. 20b, FIG. 20c and FIG. 20d respectively present Uvinul-A, Escalol, Benzophenone-4 and Salicylic acid time release profiles as a function of microgel dispersion pH and release medium pH.

[0140] FIG. 21a, FIG. 21b, FIG. 21c and FIG. 21d respectively present Uvinul-A, Escalol, Salicylic acid and Benzophenon-4 acid time release profiles in different receiving solutions.

EXAMPLES

[0141] Materials

[0142] Di(ethylene glycol) methyl ether methacrylate (MeO.sub.2MA 95%, Aldrich), oligo(ethylene glycol) methyl ether methacrylate (OEGMA, monomethyl terminated with 8 EG repeat units, number average weight Mn=475 g mol.sup.1, Aldrich), N,N-methylenebisacrylamide (MBA, Aldrich), (ethylene glycol)dimethacrylate (EGDMA, Aldrich), methacrylic acid (MAA, Aldrich), oligo(ethylene glycol) diacrylate (OEGDA, number average weight Mn=250 g mol.sup.1, Aldrich), potassium persulfate (KPS 99%, ABCR), and ethanol (VWR Chemicals) were used as received. Hydrochloric acid (HCl, 36 w/w, ABCR) and potassium hydroxide (KOH, Aldrich) were used to control the pH of dispersions. Citric acid (Sigma-Aldrich) and sodium phosphate dibasic (Na.sub.2HPO4, Sigma-Aldrich) were used to prepare the buffers.

Example 1

[0143] Encapsulation of Cosmetic Active Molecules into Bare Microgel Dispersion

[0144] Synthesis of Bare Microgel Dispersion

[0145] 83.90 mmol of MeO.sub.2MA, 9.36 mmol of OEGMA, 1.92 mmol of a cross-linker and 930 g of Milli-Q grade water were placed into a 2 L jacketed glass reactor. The cross-linker can be OEGDA, MBA or EGDMA. The reactor content was stirred at 150 rpm and purged with nitrogen for 45 min to remove oxygen at room temperature. Then, 5 mmol of MM dissolved in 30 mL of Milli-Q grade water were added to the jacketed glass reactor and the mixture was heated up to 70 C. After adding the initiator (0.89 mmol of KPS dissolved in 40 mL of degassed water), the polymerization reaction was allowed to continue under nitrogen atmosphere while stirring for 6 h. The reaction mixture was subsequently cooled to 25 C. maintaining the stirring, and the final dispersion was purified by centrifugation/redispersion cycles (10,000 rpm, 30 min) with Milli-Q grade water. A OEGDA-microgel dispersion, a MBA-microgel dispersion or a EGDMA-microgel dispersion is obtained.

[0146] Encapsulation Process

[0147] A cosmetic active substance was loaded into a OEGDA-microgel dispersion, a MBA microgel dispersion or a EGDMA-microgel dispersion prepared as described above.

[0148] The active substance could be diethylamino hydroxybenzoyl hexyl benzoate (Uvinul A also named Uvinul-A in the present description), octyl salicylate (Escalol 587 also named Escalol in the present description), benzophenone-4, hyaluronic acid, citronellol or salicylic acid .

[0149] a-Encapsulation process for Uvinul A, octyl salicylate, salicylic acid, benzophenone-4 and citronellol

[0150] A OEGDA-microgel dispersion, a MBA-microgel dispersion or a EGDMA-microgel dispersion (1 mg/L) was heated to and incubated at 50 C. (above the volume phase transition temperature VPTT) for 30 min. To this microgel dispersion different preheated concentrations of the active molecules in ethanol (0.5-2.5 mM) were added under magnetic stirring.

[0151] The mixture was stirred for 30 min at 50 C. (above the VPTT) or at 20 C. (below the VPTT). After that, the mixed dispersion was stirred overnight at 50 C. to remove the organic solvent.

[0152] Dispersion was filtered to remove the unloaded active molecule precipitate and the filter was washed with ethanol twice, obtaining a solution containing unloaded Uvinul-A, unloaded salicylic acid or unloaded Benzophenone-4. Unloaded active molecules amounts were determined by UV-Vis.

[0153] For all other compounds, samples were centrifuged during 30 min at 10,000 rpm after overnight incubation to recover the aqueous supernatant.

[0154] In the case of octyl salicylate, the aqueous supernatant was evaporated using a rotavap and the free octyl salicylate molecules were dissolved in ethanol to determine non-encapsulated amount by UV-Vis.

[0155] In the case of citronellol, aqueous supernatant containing free citronellol molecules was analyzed by 1H NMR.

[0156] b-Encapsulation Process for Hyaluronic Acid:

[0157] Microgel particles were lyophilized and suspended in different solutions of hyaluronic acid in water at particle concentration of 1 mg/mL. Then, the microgel particles were allowed to rehydrate for 12 h at room temperature while shaking. Microgel particles were separated from the aqueous medium containing by centrifugation and the equilibrium active molecule concentration was determined by ATR/FTIR.

[0158] Measurement of Microgel VPTT

[0159] Loaded microgels were prepared according to the above protocole at 20 C.

[0160] VPTT of loaded OEGDA-microgel dispersions were different depending on the type of encapsulated cosmetic active molecule (see Table 1). VPTT values were lower for encapsulated Uvinul-A and Escalol.

TABLE-US-00001 TABLE 1 VPTT values for bare and loaded-microgel particles Sample VPTT ( C.) Bare microgel 37.4 Uvinul-A-loaded microgel 35.0 Escalol-loaded microgel 35.1 Benzophenone-4-loaded 39.9 microgel Salicylic acid-loaded microgel 39.9

[0161] These results are very interesting from the point of view of cosmetic applications since, thanks to the thermal behavior of loaded-microgel particles as a function of pH, the release of different active molecules can be controlled by medium temperature and pH, confirming the results discussed above.

[0162] From the point of view of cosmetic applications one of the most interesting properties of oligo(ethylene glycol)-based microgels is their pH-sensitive thermal behavior.

[0163] Encapsulation Efficiency of Uvinul-A and Escalol into OEGDA-Microgel Dispersions

[0164] Uvinul-A-loaded OEGDA-microgels and Escalol-loaded microgels were prepared according to the above protocole at 20 C. and at 50 C.

[0165] Encapsulated amount of UvinulA increases as the feeding substance amount increases until 3.000 g/mg microgel, whatever the encapsulation temperature may be (above or under VPTT of the bare microgels). E.E. % is higher than 70% when the feeding substance amount is lower than 1,500 g/mg microgel. E.E. % is higher than 50% when the feeding substance amount is between 1,500 and 3,000 g/mg microgel (see FIG. 1).

[0166] The encapsulated amount increases as the Escalol concentration increases, does not depend on the encapsulation temperature. E.E. values are above 90% in all cases (see FIG. 2). Moreover, E.E. values above 70% were obtained independently of the type of hydrophobic active molecule and encapsulation temperature used.

[0167] This behavior was different to that observed for different hydrophobic drugs by Qiao et al., J. Control. Release, 152, (2011), 57-66. They observed that loading temperature, being higher above the VPTT of the nanogels, influenced encapsulation efficiency.

[0168] The driving force to encapsulate Uvinul-A and Escalol molecules into P(MeO.sub.2MA-OEGMA-MAA) microgel particles could be the hydrophobic interactions as well as the interactions by H-bonding between the OH groups of both cosmetic active molecules and the ether oxygen of the ethylene glycol units of microgel.

[0169] Comparison of OEGDA-Microgel, MBA-Microgel and EGDMA-Microgel Dispersions with Regard to Encapsulation of Uvinul-A and Salicylic Acid

[0170] Uvinul-A and Salicylic Acid were encapsulated into a OEGDA-microgel dispersion, a MBA-microgel dispersion or a EGDMA-microgel dispersion at 20 C. (see FIG. 3 and FIG. 4).

[0171] In the case of hydrophobic Uvinul-A, the inner morphology of microgel particles has an effect on encapsulation efficiency being the E.E. the lowest one in the case of hydrophilic MBA and highly cross-linked shell that could hinder the entering of Uvinul-A molecules.

[0172] In the case of Salicylic Acid encapsulation, taking account the experimental error of these measurements (-10%), it can be concluded that there is no effect of microgel microstructure on active molecules encapsulation.

[0173] Encapsulation Efficiency of Citronellol and Hyaluronic Acid into OEGDA-Microgel Dispersions

[0174] Encapsulation of Citronellol and Hyaluronic acid into homogeneously cross-linked (using OEGDA cross-linker) microgel particles was studied. Citronellol is a natural acyclic monoterpenoid (without aromatic ring and therefore having no hydrophobic interactions with the crosslinked polymer) and Hyaluronic acid is a hydrophilic polysaccharide (macromolecule) which structure contains repeating units of D-glucuronic acid and N-acetyl-D-glucosamine.

[0175] The encapsulated amounts of both molecules increased linearly with their concentration (see FIG. 5).

[0176] In the case of Citronellol it seems that hydrogen bonds were enough to obtain a good encapsulation of it (E.E. >70%).

[0177] In the case of Hyaluronic acid the E.E. values were lower than those observed in the case of small cosmetic active molecules (Uvinul-A, Salicylic acid, and Citronellol). At pH 6 (encapsulation pH), hyaluronic acid molecules were negatively charged (pKa=3) as were homogeneously cross-linked microgel particles; therefore, this could lead in an electrostatic repulsion between hyaluronic acid molecules and microgel particles causing a more difficult encapsulation. This together with the larger size of this macromolecule could be the reasons of 50% E.E. values at 600 microgram/mg.

[0178] However, the total amount of macromolecule loaded was much higher to that observed in the case of using other polymeric delivery systems to encapsulate macromolecules. For example, Cun et al. (Eur. J. Pharm. Biopharm., 2011, 77, 26) studied the encapsulation of siRNA molecules into poly(DL-lactide-co-glycolide acid) (PLGA) nanoparticles obtaining E.E. values of 70% and siRNA encapsulated amounts of around 2 microgram/mg.

[0179] Encapsulation Efficiency of Benzophenone-4 and Salicylic Acid into OEGDA-Microgel Dispersions [0180] Benzophenone

[0181] Ethanol is used in the encapsulation process as described before, at 20 C. and at 50 C. Loaded microgel dispersion was centrifuged and the supernatant was analyzed by UV-Vis.

[0182] As benzophenone-4 is water soluble, part of the non-encapsulated Benzophenone-4 could be soluble in water phase. In order to quantify non- encapsulated benzophenone and water solubilized active molecule amount, encapsulation amounts were calculated before the centrifugation step and after the centrifugation step. The encapsulation process was performed.

[0183] As can be observed, part of the non-encapsulated Benzophenone-4 is in the water phase: therefore, the encapsulated amount (see FIG. 6) and E.E. values are lower after centrifugation than before centrifugation. It is necessary to perform the centrifugation step in order to quantify the total non-encapsulated Benzophenone-4 amount.

[0184] The encapsulated amounts increased linearly with the active molecule concentration and E.E. values were higher than 80%, in all the cases as long as the feeding substance amount is lower than 1 mg/(mg unloaded microgels) (see FIG. 6). [0185] Salicylic acid

[0186] The same study has been performed with salicylic acid as the cosmetic active substance.

[0187] In FIG. 7, increasing the concentration of Salicylic Acid, the E.E. value and the encapsulated amount of it increase. In addition, as in the case of Benzophenone-4, centrifugation step is necessary in order to quantify the total non-encapsulated Salicylic Acid amount.

Example 2

[0188] Encapsulation of Cosmetic Active Molecules into Bare Microgel Films

[0189] Preparation of the Bare Microgel Films

[0190] Films composed of multilayer of self-assembled microgel were formed as follows: 30 mL of an aqueous OEGDA-microgel dispersion as prepared above (presence of water soluble polymers or not) and having different solid content (such as 1.4 wt%) was introduced into inert plastic mold and dried for 48 h at 35 C. (3 C.) at atmospheric pressure.

[0191] Ability of unloaded microgel particles to self-assemble and to form cohesive films has been demonstrated at different pHs and in presence of different types of salts (citric/sodium phosphate dibasic at pH 4.5, at pH 6 and at pH 7; potassium carbonate at pH 9). Cohesive films can be formed from aqueous dispersion of bare microgels aqueous dispersions having different pH and ionic strength.

[0192] Film stability in hydrated state was studied through the immersion of self-assembled microgel films into aqueous solution at room temperature for 24 h. Swelling of the film is observed instead of redispersion of microgels. Furthermore, self-assembled microgel films present a reversible swelling-deswelling process without losing its form. The reason could be the existence of elastic forces between the oligo(ethylene glycol) polymer chains preserving the cohesion between microgel particles.

[0193] Different medium conditions were prepared in order to evaluate swelling behavior of films. Hydrophobicity (water/ethanol and water/isopropanol), temperature, pH, and purification of water soluble polymer obtained as a by-product of the microgel particles preparation were medium criteria. Above the VPTT, swelling ability of the film in hydrophobic medium is higher than in hydrophilic one. However, swelling ratio is lower in the case of the films formed in presence of water soluble polymer by product that create osmotic pressure.

[0194] Encapsulation of Uvinul-A, Escalol, Salicylic Acid and Benzophenone-4 Molecules into Bare Microgel Films

[0195] Uvinul A, Escalol, salicylic acid and benzophenone-4 molecules were separately encapsulated into unloaded films composed of multilayer of self-assembled unloaded microgel as previously prepared.

[0196] A solution containing one of the four active substances in a water/ethanol (75/25) mixture was prepared, and the films were immersed in this feeding solution allowing the film to rehydrate for a 24 h period of time.

[0197] Salicylic acid loading into self-assembled microgel films was studied in media having different pH. Self-assembled microgel films were rehydrated in buffered media containing different concentrations of active molecules during 24 hours.

[0198] Encapsulated amount of the active substance in the films was evaluated by UV-Vis characterization or ATR-FTIR characterization recorded on a Spectrum One (PerkinElmer) spectrometer.

[0199] Transmittance data of loaded-films were collected using Shimadzu UV-2101 spectrometer from 300 to 500 nm. Loaded-films were enough sticky to hold themselves to sample holder and therefore, air was used as reference. Four scans were made for each measurement and all spectra were recorded at 25 C. and atmospheric pressure.

[0200] Above VPTT, short-distance hydrophobic interactions between self-assembled microgel film and Uvinul A (or Escalol) became more intense. Opposite is observed with Salicylic acid or Benzophenone-4.

[0201] Encapsulation efficiencies (E.E.) were above 70% in all cases. Entrapment efficiency is about 80% for every Benzophenone-4 concentration.

[0202] Independently of the type of active molecule used, encapsulated amount increases as the concentration of active molecule increases.

[0203] As can be seen in FIG. 11, encapsulated amount and E.E increase as the concentration of Salicylic Acid increases at both pHs. The same behavior was observed in the case of using microgel particles. In addition, it seems that there is no influence of the pH of the medium on the active molecule loading.

Example 3

[0204] In Vitro Release of Cosmetic Active Molecules from Loaded Microgels

[0205] The study of active molecules release kinetics was carried out by a dialysis method in order to verify that no microgel diffusion occur in dialysate medium (that may also be called release medium), and in order to observe the cosmetic active molecule release profile against time.

[0206] For that, active molecules-loaded microgel particle dispersions (1 mg/mg microgel) were dialyzed against a dialysate medium. Diffusion of the cosmetic active molecule from the loaded-microgel dispersion medium to the dialysate medium is observed, until an equilibrium concentration is reached between both media.

[0207] In vitro cosmetic active molecule percentage release results are represented in the form of curves as a function of time in FIGS. 12 through to 21.

[0208] If not mentioned otherwise in the examples, loaded microgel dispersions are loaded OEGDA-microgel dispersion (meaning that the crosslinker that is used to prepare the bare microgel particles is OEGDA).

[0209] Methods

[0210] i) In vitro release by a dialysis method

[0211] Loaded-microgel particles comprising an active molecule in an amount of 1 mg/(mg unloaded microgel) were placed inside a dialysis tube and dialyzed in different buffered dialysate media (having different pH, having different temperature, containing a solvent and/or containing a surfactant). The buffered dialysate medium can contain ethanol, citric acid, sodium phosphate dibasic or/and polyoxyethylene monooleate sorbitan (also named Polysorbate 80, Tween 80 or INCI Sorbitan oleate). Active substance concentration in the dialysate medium was determined by UV-Vis.

[0212] ii) In vitro release by real-time ATR/FTIR spectroscopy

[0213] In vitro release can alternatively be followed by real-time ATR/FTIR spectroscopy. In this case, no dialysis membrane is placed in the dispersion.

[0214] Loaded-microgel particles comprising 1 mg active molecule/(mg unloaded microgels) were placed in a buffered medium at pH 6 and 25 C. In situ ATR/FTIR monitoring was performed using a ReactIR 15 with a diamond attenuated total reflection DiComp probe and equipped with a liquid nitrogen cooled MCT detector. Spectra were collected directly in the release medium at different incubation times.

[0215] Effect of Microgel Microstructure on Cosmetic Active Molecule Time Release Profile

[0216] a) Salicylic acid

[0217] Three different microgel dispersions loaded with an active molecule were used: a salicylic acid loaded OEGDA-microgel dispersion (homogeneous crosslinked particles), a salicylic acid loaded MBA-microgel dispersion (loosely cross-linked core and highly cross-linked shell) and a salicylic acid loaded EGDMA-microgel dispersion (highly cross-linked core and loosely cross-linked shell). AS explained before, a OEGDA-microgel dispersion means that bare microgel particles have been prepared with a OEGDA crosslinker.

[0218] The homogeneous distribution of the cross-linker (OEGDA) inside microgel particles promoted a faster release of Salicylic acid between T0 and T40H. After T160H the same amount of active molecule was released in all three cases (see FIG. 12). Therefore, it seems that the microstructure of the microgels has an effect of Salicylic Acid release kinetics but not in the amount released.

[0219] b) Uvinul-A

[0220] Three different microgel dispersions loaded at a 1 mg active molecule/(mg microgel) concentration were used: a Uvinul-A loaded OEGDA-microgel dispersion, a Uvinul-A loaded MBA-microgel dispersion and a Uvinul-A loaded EGDMA-microgel dispersion.

[0221] In vitro Uvinul-A release was followed by real-time ATR-FTIR spectroscopy. The spectra were collected directly in the release medium (25 C. and pH 6) at different incubation times (see FIG. 13).

[0222] Effect of Temperature on Time Release Profile

[0223] The effect of temperature on the release kinetics of active molecules was investigated with the dialysate method maintaining pH of the dialysate medium constant at 4.5. The in vitro release was studied at two different temperatures: 25 C. (below the VPTT) and 37 C. (above the VPTT).

[0224] In the case of Benzophenone-4, it seems that the temperature has no effect on the release kinetics.

[0225] On the other hand, in the case of Salicylic Acid, the release is higher at 25 C. (being microgel hydrophilic) than that at 37 C. (being microgel hydrophobic).

[0226] The results are presented in FIG. 14 and in FIG. 15.

[0227] Effect of Hydrophobicity of the Release Medium on Time Release Profile

[0228] Four different active molecules loaded-microgel dispersion were tested: salicylic acid, benzophenone-4, Escalol and Uvinul-A.

[0229] Hydrophobicity of the dialysate medium was varied according to the dialysis method. By adding different amounts of ethanol (0%, 25%, 35% or 50% ethanol) in the dialysate medium maintaining the pH and the temperature constant (pH 6 and 25 C.).

[0230] The complete release of Salicylic acid is obtained increasing the ethanol percentage from 0 to 25% (see FIG. 16). By contrast, in the case of Benzophenone-4, the effect of the ethanol percentage on release kinetics is lower and the complete release of it is not achieved, in any case. In addition, the Benzophenone-4 release is higher at 35% of ethanol than that at 50% (see FIG. 17).

[0231] The active molecules release of hydrophobic molecules Uvinul-A and Escalol increases with an increasing ethanol percentage, in all the cases. These results are expected since increasing ethanol percentage causes hydrophobicity of the dialysate medium to increase, thereby enhancing the release of hydrophobic active molecules.

[0232] At an ethanol percentage of 35% and a 168 h incubation time, active molecule release increases from 20% to 40% for Uvinul-A, and from 10% to 100% for Escalol. In the case of Escalol the release is not sustained since 100% is released in the first 6 hours of incubation (see FIG. 18a and FIG. 18b).

[0233] Effect of Release Medium pH on Active Substance Time Release Profile

[0234] a) With the aim of studying pH effect on in vitro active molecule release, loaded microgel particles (1mg/mg microgel) were placed into different buffered dialysate media (1 mM at pH 4.5 or at pH 6) at 25 C. Several active molecules were studied. pH of the loaded-microgel dispersion was not varied.

[0235] In FIG. 19a, a plateau is reached at all pHs. It seems that the equilibrium between Uvinul-A loaded-microgel particles and dialysate medium is reached. Noteworthy, at pH 6 the release amount is higher than that at pH 4.5. The reason could be the hydrophobic character of Uvinul-A. At pH 4.5 the microgel is collapsed being more hydrophobic and therefore, Uvinul-A would prefer to be inside the microgel instead of going out to the buffered medium. In contrast at pH 6, the microgel is swollen (being hydrophilic) enhancing Uvinul-A release.

[0236] On the other hand, in the case of Escalol (FIG. 19b) the release values are under 5%. The reason could be the strong interactions between the active molecule and the microgel (that was confirmed by DOSY-NMR).

[0237] In FIG. 19c and FIG. 19d, the in vitro release of hydrophilic active molecules (Benzophenone-4 and Salicylic Acid) as a function of pH is shown. At pH 4.5 the release percentages of release is higher than those at pH 6 for both active molecules. At pH 4.5 the microgel tend to be hydrophobic meaning that there is less affinity between hydrophilic active molecules and microgel particles, so that Benzophenone-4 and Salicylic Acid prefer to move outside microgel particles (which explains the highest values of release, compared to those obtained in the case of pH 6). In addition at pH 6 microgel particles are negatively charged (deprotonation of carboxylic groups). At pH 6, Benzophenone-4 and Salicylic Acid are also negatively charged and thus, this could lead in an electrostatic repulsion between the active molecules and microgel particles. However, it seems that there is no electrostatic repulsion between microgel particles and hydrophilic active molecules. Therefore, these results suggest that hydrophobic/hydrophilic interactions are predominant in release kinetics.

[0238] b) As discussed previously, the in vitro release of different cosmetic active molecules was studied placing dialysis tubes into different dialysate buffered media (outside the dialyse tube). However, the pH of loaded-microgel dispersion was not varied. Therefore, the next step was to vary also the pH of loaded-microgel particles (dispersion placed into the dialysis tube). For that, after the encapsulation of different active molecules at a concentration of 1 mg/(mg microgel) the pH of loaded-microgel dispersion was adjusted to 4.5 using HCl and NaOH solutions.

[0239] In FIGS. 20a and 20b, the in vitro hydrophobic active molecules (Uvinul-A and Escalol) release with time is shown. As can be seen, the release values are too low, in all the cases. In addition, no difference is observed controlling the pH of loaded-microgel particles maybe because at pH 4.5 microgel particles are collapsed.

[0240] In FIGS. 20c and 20d, the in vitro release of hydrophilic active molecules (benzophenone-4 and salicylic acid) with time is shown. As can be observed, after adjusting the pH of loaded-microgel dispersion the released kinetics of active molecules is slower.

[0241] c) The effect of pH dialysate media composition on four active molecule release profile was studied again in other conditions.

[0242] Different dialysate medium solutions were used at 25 C.: i) buffered pH 6, ii) buffered pH 7.4, iii) 0.5% Tween 80 and buffered pH 7.4, and iv) 2.5% Tween 80 and buffered pH 7.4. A mixture of 0.1% sodium azide and PBS buffer was used for pH 7.4 (at this pH, loaded-microgel particles are swollen).

[0243] Released amount of Uvinul-A is the highest for pH 6 in the dialysate medium. The reason could be the low solubility of Uvinul-A in this medium provoking its precipitation and therefore, the lower release from dialysis tube. In the case of Escalol, although it is not soluble in the receiving solution a continuous and almost a complete release is obtained. In addition, the more concentration of Tween 80 increases, the faster the release of Escalol is. It seems that Tween 80 enhances the release of Escalol from microgel particles (see FIGS. 21a and 21b).

[0244] In the case of hydrophilic active molecules (benzophenone-4 and salicylic acid) there is no difference between pH 6 release kinetics and pH 7.4 release kinetics. However, the complete release is not obtained using the receiving solution. Therefore, the main conclusion of this part is that the complete release of all cosmetic active molecules is obtained using a water/ethanol mixture as a release medium (see FIGS. 21c and 21d).