Selection of the nanoemulsion compositions
Composition for nanoemulsion formulations with 5% surfactant and oil phase at 10%, 20% and 30% (w/w) were selected for fabrication of nanoemulsions system. The disperse phase comprises skin active ingredient such as tocotrienol. The continuous phase comprises components other than water including but not limited to thickener, anti-microbial and humectant to impart an increased benefit to the skin tissues.
Preparation of emulsions
Emulsions were prepared using ultrasonic (UP400S Hielscher Sonifier, Germany) of 400 W nominal powers and a frequency of 24 kHz equipped with a 22 mm sonotrode tip. This was placed in a custom-built cooling jacket. Chilled water at 3°C was continuously passed through the jacket. Emulsions were prepared where both oil and aqueous phases were separately warmed up to 70 ± 5°C. Xanthan gum was dispersed in deionized water at 0.8% (w/w). An emulsion sample (100 mL) was prepared and homogenized at 6000 rpm for 5 min with a Polytron homogenizer (Kinematica GmbH, Germany) rotor stator. The temperature was lowered to 40°C. At 40°C, the active ingredients and preservative were added. The emulsions were further homogenized using ultrasonic cavitation for 5 min. The sonifier tip horn was adjusted to 2 cm below the surface of a 100 mL sample. Sonication was performed at acoustic amplitude of 20% and 0.5 cycles.
Sedimentation behavior
The stability of the emulsion was examined with an optical centrifuge, LUMiFuge® 116 particle separation analyzer (L.U.M. GmbH, Germany). LUMiFuge® 116 particle separation analyzer technologies, based on optical centrifuge detect includes near IR optics. The instrument simulates comprehensive emulsion processes due to gravitation forces [7]. The instrument presents a typical graph for each process: creaming, sedimentation and phase separation. The data are integrated by the computer and the integration graph shows the percentage of light absorbance per hour – the “creaming rate”.
The rate is correlated to the stability of the emulsions whereby higher creaming rate indicates lower stability. The samples in the LUMiFuge® 116 particle separation analyzer were centrifuged at 3000 rpm for 15 h at 32°C. Sample volume of 2 cm3 was used. A light source (NIRLED) is radiated to the cells during centrifugation and its transmission through the sample was measured. The obtained transmission profiles measured between the top and bottom of the measurement cell enabled quantification of the dispersion quality. Quantitative data were available by integration of the transmission profiles. The profile was used to calculate the sedimentation or flotation velocity. In general, as more stable the dispersion, means the dispersibility, the smaller the sedimentation and clarification rate.
Rheology
A rotational/ oscillatory viscometer, Kinexus Rheometer (Malvern Instrument, UK) was used. All measurements were performed with a stainless steel cone-plate sensor at 25.0 ± 0.1°C with 4°/40 mm.
Strain sweep measurements at 1 Hz were made with all samples to determine strain amplitude within the linear viscoelastic range. Subsequent oscillatory measurements were performed at a frequency range of 0.001 to 100 Hz. Storage modulus G’ (Pa), loss modulus G” (Pa), loss tangent and tan δ were evaluated.
Selection of the nanoemulsion compositions
Composition for nanoemulsion formulations with 5% surfactant and oil phase at 10%, 20% and 30% (w/w) were selected for fabrication of nanoemulsions system. The disperse phase comprises skin active ingredient such as tocotrienol. The continuous phase comprises components other than water including but not limited to thickener, anti-microbial and humectant to impart an increased benefit to the skin tissues.
Preparation of emulsions
Emulsions were prepared using ultrasonic (UP400S Hielscher Sonifier, Germany) of 400 W nominal powers and a frequency of 24 kHz equipped with a 22 mm sonotrode tip. This was placed in a custom-built cooling jacket. Chilled water at 3°C was continuously passed through the jacket. Emulsions were prepared where both oil and aqueous phases were separately warmed up to 70 ± 5°C. Xanthan gum was dispersed in deionized water at 0.8% (w/w). An emulsion sample (100 mL) was prepared and homogenized at 6000 rpm for 5 min with a Polytron homogenizer (Kinematica GmbH, Germany) rotor stator. The temperature was lowered to 40°C. At 40°C, the active ingredients and preservative were added. The emulsions were further homogenized using ultrasonic cavitation for 5 min. The sonifier tip horn was adjusted to 2 cm below the surface of a 100 mL sample. Sonication was performed at acoustic amplitude of 20% and 0.5 cycles.
Sedimentation behavior
The stability of the emulsion was examined with an optical centrifuge, LUMiFuge® 116 particle separation analyzer (L.U.M. GmbH, Germany). LUMiFuge® 116 particle separation analyzer technologies, based on optical centrifuge detect includes near IR optics. The instrument simulates comprehensive emulsion processes due to gravitation forces [7]. The instrument presents a typical graph for each process: creaming, sedimentation and phase separation. The data are integrated by the computer and the integration graph shows the percentage of light absorbance per hour – the “creaming rate”.
The rate is correlated to the stability of the emulsions whereby higher creaming rate indicates lower stability. The samples in the LUMiFuge® 116 particle separation analyzer were centrifuged at 3000 rpm for 15 h at 32°C. Sample volume of 2 cm3 was used. A light source (NIRLED) is radiated to the cells during centrifugation and its transmission through the sample was measured. The obtained transmission profiles measured between the top and bottom of the measurement cell enabled quantification of the dispersion quality. Quantitative data were available by integration of the transmission profiles. The profile was used to calculate the sedimentation or flotation velocity. In general, as more stable the dispersion, means the dispersibility, the smaller the sedimentation and clarification rate.
Rheology
A rotational/ oscillatory viscometer, Kinexus Rheometer (Malvern Instrument, UK) was used. All measurements were performed with a stainless steel cone-plate sensor at 25.0 ± 0.1°C with 4°/40 mm.
Strain sweep measurements at 1 Hz were made with all samples to determine strain amplitude within the linear viscoelastic range. Subsequent oscillatory measurements were performed at a frequency range of 0.001 to 100 Hz. Storage modulus G’ (Pa), loss modulus G” (Pa), loss tangent and tan δ were evaluated.
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