Swellable, Nanoporous Organosilica for Extended and Triggered Release

Oct 1, 2013 | Contact Author | By: Paul L. Edmiston, PhD, ABS Materials Inc.
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Title: Swellable, Nanoporous Organosilica for Extended and Triggered Release
encapsulationx fragrancesx activesx stimulated releasex
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Keywords: encapsulation | fragrances | actives | stimulated release

Abstract: Nanoporous organosilica particles were developed to swell upon the addition of organic solvents. These are evaluated here for encapsulating and controlling the release of fragrance. Slower, continuous release was observed, suggesting their ability to extend sensory benefits. In addition, the stimulated release of encapsulated lidocaine was studied, and results implicate their use to deliver cosmetic actives.

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PL Edmiston, Swellable, Nanoporous Organosilica for Extended and Triggered Release, Cosm & Toil 128(10) 754 (2013)

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Prolonging the degradation and volatilization of fragrances is key to creating personal care products with extended and balanced sensory stimuli. Encapsulation is a widely used approach for controlling the delivery of sensory compounds and other active ingredients. In addition to altering the rate of fragrance vaporization, encapsulation can be beneficial for formulations where the volatile compound(s) are insoluble in a suitable solvent system.

Various encapsulation technologies have been developed, including entrapment within polymer systems, molecular inclusion in a host such as cyclodextrin, absorption into silica microspheres and co-addition to various emulsified fluids prepared via coacervation. Another is the loading of active ingredients into polymers via interfacial polymerization or in situ polymerization. The fundamental principle of delivery is to limit the rate of fragrance diffusion through hindered mass transport. Binding the fragrance to a surface or host may also play an important role in reducing volatility and extending the sensory characteristics of the product; this has been explored by some. Regardless of the approach, fragrances must be chemically inert to be encapsulated by most mechanisms, especially those that use active polymerization routes to entrap solutes.

The stimulated release and increase in delivery of fragrances during physiological or environmental changes is also a mechanism of interest. In relation, chemistries have been developed that link pro-fragrance molecules to a solid support through a liable covalent bond. Without a stimulus, the pro-fragrance is incapable of being volatized by the covalent bond linkage; however, bond breakage and volatilization of the fragment can be induced by light, heat, hydrolysis, changes in pH or the activity of enzymes. A drawback to chemical bond cleavage and delivery is the limited number of mild reactions and pro-fragrances that are available. Also, careful packaging is necessary to extend shelf-life of the inherent reactive pro-fragrance systems. Further research is needed to optimize delivery systems, increase the number of simultaneously released fragrances, and reduce the need for expensive raw material stocks.

Other options for potential fragrance delivery are animated materials that can change their physical properties as a function of a stimulus. Hydrogels, which can swell with water, are the most common example of such materials, changing their porosity to deliver an active ingredient. Through careful control of their chemistry, hydrogels can be made to be thermally reversible or pH-responsive. Silica-based solids typically are characterized as inelastic and not swellable, with only rare exceptions. For other materials, a modest degree of swelling has been reported, typically < 15% of their initial volume, based on some type of physical or chemical change; for example, a change in temperature or pH. Described here is a chemically inert nanoporous organosilica that is designed to rapidly (< 1 sec) swell up to four times its volume and eight times it mass with organic solvents. Here, the author evaluates its capabilities for the extended release of volatile fragrances and the stimulated release of active ingredients.

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Table 1. Relative first order rate constants for volatilization

Table 1. Relative first order rate constants for volatilization

Assuming volatilization followed the first order kinetics, the rate constant for menthol was 3.7–3.9 times less than for the glass beads and natural sponge (see Table 1).

Figure 1. Nanoporous organosilica swelling

Figure 1. Nanoporous organosilica swelling

Figure 1. (top, L to R) Nanoporous organosilica swelling at 0, 5 and 10 sec; (middle, L to R) SEM images of nanoporous organosilica matrix in the dry collapsed form, a partially swollen state, and fully expanded; and (bottom) schematic of the arrangement of the organosilica nanoparticles in the corresponding swollen states.

Figure 2. Log plot of relative headspace concentration of α-pinene, as measured by integrated peak area vs. time, for nanoporous organosilica (□), natural sponge (•) and glass beads (◊))

Figure 2. Log plot of relative headspace concentration of α-pinene, as measured by integrated peak area vs. time, for nanoporous organosilica (q), natural sponge (•) and glass beads ()

The amount of α-pinene was measured in the headspace over time for rose extracted loaded into the nanoporous organosilica, as compared to glass beads and natural sponge (see Figure 2).

Figure 3. Relative headspace concentration of menthol vs. time, as released from natural sponge (•) and nanoporous organosilica (□)

Figure 3. Relative headspace concentration of menthol vs. time, as released from natural sponge and nanoporous organosilica

The rate of release for all three compounds was measured at 25°C over a period of 24 days (see Figures 3-5).

Figure 4. Relative headspace concentration of hexanol vs. time, as released from natural sponge (•) and nanoporous organosilica (□)

Figure 4. Relative headspace concentration of hexanol vs. time, as released from natural sponge (•) and nanoporous organosilica (□)

The rate of release for all three compounds was measured at 25°C over a period of 24 days (see Figures 3-5).

Figure 5. Relative headspace concentration of dodecane (log chromatographic peak area) vs. time, as released from natural sponge (•) and nanoporous organosilica (□)

Figure 5. Relative headspace concentration of dodecane (log chromatographic peak area) vs. time, as released from natural sponge (•) and nanoporous organosilica (□)

The rate of release for all three compounds was measured at 25°C over a period of 24 days (see Figures 3-5).

Figure 6. Release of encapsulated lidocaine by repeated three-minute excursions of 5% v/v ethanol in flowing buffer; measured in real time by a liquid chromatography UV detector

Figure 6. Release of encapsulated lidocaine by repeated three-minute excursions of 5% v/v ethanol in flowing buffer; measured in real time by a liquid chromatography UV detector

The composition of the aqueous phase could be varied and the concentration of lidocaine measured in real-time using a downstream UV detector (see Figure 6).

Figure 7. Release of encapsulated lidocaine by three-minute excursions of ethanol in flowing buffer varying the ethanol concentration; measured in real time by a liquid chromatography UV detector

Figure 7. Release of encapsulated lidocaine by three-minute excursions of ethanol in flowing buffer varying the ethanol concentration; measured in real time by a liquid chromatography UV detector

As the concentration of the dissolved ethanol stimulus increased, a higher release of lidocaine was observed (see Figure 7).

Footnotes (CT1310 Edmiston)

a Osorb (INCI: not yet determined) is a product of ABS Materials, Inc., www.absmaterials.com.
b Bulgarian rose extract was purchased from Miracle Botanicals, www.miraclebotanicals.com.
c Other chemical reagents were obtained from Sigma-Aldrich, www.sigmaaldrich.com.
d The 6890 Series: 5973 Network Mass Selector Detector, and the 1100 HPLC system are manufactured by Agilent Technologies, www.chem.agilent.com.

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