Protection of Retinol in Organosilica Microparticles

May 1, 2011 | Contact Author | By: Kim S. Finnie, PhD; and Chris Barbé, PhD, Ceramisphere Pty., Ltd.
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Title: Protection of Retinol in Organosilica Microparticles
retinolx microparticlex encapsulationx stabilityx organosilicax
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Keywords: retinol | microparticle | encapsulation | stability | organosilica

Abstract: In this article, retinol encapsulated in organosilica microparticles (12–14% w/w) having an average particle size of 0.3 micron are shown in a 40-day test period to exhibit enhanced stability to oxidation when compared with similar commercial stabilized retinol products.

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KS Finnie and Barbé, Protection of Retinol in Oranosilica Microparticles, Cosm & Toil 126(5) 362 (2011)

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Vitamin A in the form of all-trans retinol is a popular component of cosmetic anti-aging creams due to its effects in rejuvenating skin, smoothing wrinkles and enhancing elasticity. Although retinol aids in the creation of stronger, healthier skin,1, 2 its incorporation into dermal creams is problematic due to the highly fragile nature of the molecule. Retinol is a naturally occurring hydrophobic compound with a polyolefinic structure that is subject to facile isomerization to cis-isomers, with lowered biological activity,3 upon exposure to light. Moreover, the photo-sensitive molecule is also rapidly degraded by oxygen and elevated temperatures. Chemists handling retinol in the laboratory employ inert atmosphere, e.g., nitrogen or argon, in the absence of light since significant degradation occurs after several hours of exposure to air.4 Derivatives such as retinyl acetate, propionate and palmitate esters are less susceptible to decomposition but are also less active, requiring an additional hydrolysis step to release retinol in the skin.2

For practical handling purposes, it would therefore be advantageous to stabilize retinol by encapsulating it in a carrier, which is also beneficial in that it would allow for the incorporation of stabilizers such as butylated hydroxytoluene (BHT) and vitamins E and C, widely used as antioxidants. Furthermore, the use of a carrier could help to address the limited aqueous solubility of retinol. Indeed, there has been considerable research interest in developing methods for stabilizing retinol in a range of host materials. Examples include liposomes,5 polymers,6 solid lipid nanoparticles,7 chitosan8 and silica microparticles9—even a combination of materials to give a multiply stabilized system.10

Clearly, however, the necessity to protect retinol from the surrounding environment must be balanced with the ease by which the molecule can later be released from the host matrix. There is considerable evidence for improved stability in the encapsulated form, as evidenced by the number of stabilized retinol/carrier products that are available commercially. In response, the author’s company has developed a process for encapsulating retinol as part of a wider technology for the encapsulation of hydrophobic molecules into organosilica microparticles. The synthetic procedures employed are sol-gel based and conducted at an ambient temperature and benign pH to form ceramic particles in which the active molecules are fully encapsulated. This technology minimizes the release of the active in aqueous conditions but rapidly releases it under lipophilic conditions.

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Figure 1. UV/visible diffuse reflectance spectra of retinol-doped and undoped phenylsiloxane particles

Figure 1. UV/visible diffuse reflectance spectra of retinol-doped and undoped phenylsiloxane particles

UV/visible spectra of both retinol doped and undoped phenysiloxane particles dispersed in PTFE powder, 10% w/w, are shown in Figure 1.

Figure 2. SEM images of a) vinylsiloxane and b) phenylsiloxane particles; size bars = 5 µm

Figure 2. SEM images of a) vinylsiloxane and b) phenylsiloxane particles; size bars = 5 µm

Also, SEM images (see Figure 2) showed that the particles are spherical and, in the case of the vinylsiloxane sample (see top in Figure 2), the majority of particles had a size ~250 nm, with some larger micron-sized particles also present.

Figure 3. Size distributions for a) vinylsiloxane and b) phenylsiloxane particles

Figure 3. Size distributions for a) vinylsiloxane and b) phenylsiloxane particles

Particle size distributions (see Figure 3) showed that the average particle size for the samples was ~250–300 nm.

Figure 4. Free retinol dissolved in ethanol, a) freshly dissolved retinol at 7 mg/mL and b) retinol exposed to air for 2 hr then dissolved at 14 mg/mL

Figure 4. Free retinol dissolved in ethanol, a) freshly dissolved retinol at 7 mg/mL  and b) retinol exposed to air for 2 hr then dissolved at 14 mg/mL

The spectra of retinol in ethanol solutions are shown in Figure 4.

Figure 5. Absorbance of retinol extracted from commercial 2 exposed to air for: a) 1 day, b) 3 days, c) 10 days, d) 18 days, e) 25 days and f) 32 days

Figure 5. Absorbance of retinol extracted from commercial 2 exposed to air for:  a) 1 day, b) 3 days, c) 10 days, d) 18 days, e) 25 days and f) 32 days

Figure 5 shows the spectra obtained, in units of AU/mg, for the solid commercial sample (commercial 2) dried in air and exposed to air up for 32 days.

Figure 6. After 1 day and 40 days, blue and red curves, respectively, exposure to air for phenylsiloxane, a) dried in air and b) dried in nitrogen

Figure 6. After 1 day and 40 days, blue and red curves, respectively, exposure to air for phenylsiloxane, a) dried in air and b) dried in nitrogen

Figure 6 shows the spectra of the phenylsiloxane samples after 1 day and 40 days, respectively, of exposure to air.

Figure 7. Change in activity as % of original for stabilized retinol samples, a) dried in air, and b) dried 1 day in nitrogen, then exposed to air

Figure 7. Change in activity as % of original for stabilized retinol samples, a) dried in air, and b) dried 1 day in nitrogen, then exposed to air

CT1105+Finnie+Figure+7+Key

Footnotes (CT1105 Finnie)

a The solid retinol and BHT used for this study were obtained from Sigma Aldrich.
b The HPLC system used for this study is manufactured by Waters Corp.
cThe Cary 500 spectrometer equipped with a Biconical accessory is manufactured by Varian.
d The Neoscope JCM-5000 benchtop SEM is manufactured by Jeol.
e The Mastersizer 2000 Static Light Scattering instrument is manufactured by Malvern.
f The Cary 50 spectrometer is manufactured by Varian.

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