This brief overview will focus on making cannabis nanoemulsions via ultrasonication so that others may start or find useful such information. Initially, response surface methodology (RSM) was performed to optimize the formulation variables of oil-in-water (o/w) emulsions induced by ultrasound. The optimal formulation variables, as predicted by RSM, resulted in improved physical characteristics of nanoemulsions formulated with cannabis by minimizing their droplet size, polydispersity index, and viscosity. Moreover, the cannabis nanoemulsions exhibited excellent stability over long periods of time (1 year) under different storage conditions (cold / hot).
Cannabis Sativa L. and Olive Oil were chosen as the dispersed phase (oil) for oil-in-water (o/w) emulsion. The cannabis oil has been produced via ultrasound-assisted extraction (UAE) from fresh frozen cannabis inflorescences (Le Herbe). The olive oil has been produced via traditional cold press (Berkeley Olive Grove). For reducing the interfacial tension between oil and water, two types of emulsifying agents have been selected based on previous data and their HLB value. Tween 80 (HLB = 15) and Span 80 (HLB = 4.3) (Sigma-Aldrich Co.) were used as emulsifying agents because of their Generally Recognized As Safe (GRAS) status. Q700 (Qsonica) was used for generating the ultrasound with a maximum power input of 700 W and a frequency of 20 kHz. These experiments were conducted in batches using 500 ml jacketed reaction beaker (Kimble Chase) connected to a compact recirculating chiller (Qsonica) operating at a temperature of less than 25 °C. After each ultrasonication, the mean droplet size (MDS) was measured using dynamic light scattering by a Zetasizer Nano ZS (Malvern Instruments). Deionized water was used for the preparation of all formulations (Thermo Fisher). The pH of the suspensions was measured by a micro-pH 2000 (Crison Instruments)
Nanoemulsions were formulated using oil, a mixture of non-ionic surfactants, water and ultrasonication. The dispersed phase (cannabis/olive oil containing Span 80) was heated up to 110 °C and allowed to cool (24 hrs) in a nitrogen atmosphere for a complete dissolution of surfactant, decarboxylation of cannabinoids and protection from degradation. The continuous phase (water containing Tween 80) was also heated up to 45 °C and allowed to cool (24 hrs) for complete dissolution. The emulsification was carried out using a two-step homogenization process. The first step is to produce a coarse o/w emulsion. The dispersed phase was added drop-by-drop in the continuous phase using a magnetic stirrer (500 rpm for 5 min.) at ambient temperature (25 °C). The second step is to immediately take the coarse emulsion an apply ultrasonication. The high-frequency voltage output of the generator (Q700) was transferred into mechanical vibrations by piezoelectric transducers into a standard horn with a tip diameter of 1/2" (12.7 mm), placed at the center of the beaker and to a depth of 3 cm. The amount of amplitude (as a percentage of the maximum amplitude 120 μm) was kept constant by the control electronics of the generator. Ultrasonic exposure was applied in a continuous process. The same experiment was repeated with varying sonication times (min), surfactant fractions, oil fractions, high-power amplitudes and different hydrophilic lipophilic balance (HLB) values.
In the first published set of experiments, hydrophilic lipophilic balance (HLB) concept shows the amphiphilicity for non-ionic surfactants. The desired HLB was obtained by mixing Tween 80 and Span 80 at desired ratios. The prepared samples were diluted and then analyzed to determine particle size distribution. FIG 1 shows, except HLB 9, an increase in HLB led to a decrease in particle size and optical density, but beyond HLB 13 the droplet size remained constant. Surfactant(s) with low HLB <7 gives water-in-oil w/o emulsions whereas high HLB >7 gives oil-in-water emulsions (o/w). Generally, mixed-surfactant systems are more effective than a single-type surfactant in retarding the particle aggregation. Simultaneous application of lipophilic and hydrophilic surfactants facilitate the formation of small particles using high-power ultrasonication. After optimization of HLB value, the effect of surfactant volume fractions in the range of 0.02 to 0.14 was investigated.
In the next set of experiments, surfactant(s) are required to decrease the interfacial tension and hence the shear forces required to break up the droplets into smaller droplets. The optimum surfactant volume fraction was found at 0.08, which was highly stable with the least amount of surfactants. The oil fraction was held constant from previous data at 0.10, which was found to be optimum as the emulsion exhibited lower droplet size and high stability after 5 minutes. As the surfactant concentration increases, the appearance of emulsion becomes translucent from white color, which indicates the formation of nanoemulsion at high-power amplitude. After optimization of surfactant volume fraction, the effect of sonication time 1, 2, 3, 4, 5, 6, 7, 8 min was investigated.
In the final published set of experiments, emulsions were prepared by varying sonication times at high-power amplitudes of 60% - 70%. The optimum HLB value of 12, oil fraction of 0.10 and surfactant fraction 0.08 were chosen from FIG 1 & 2. There was a significant decrease in the MDS with an increase in sonication time from 1 to 5 min. Sonication time of 7.5 min was found optimum as further increase in time had little effect on the MDS reduction. Careful control of the temperature should be carried out during ultrasonication. After 5 min of sonication, the emulsion appeared translucent and very stable. 5 minutes via a continuous process may be selected in order to avoid overheating, which can degrade sensitive bioactive compounds such as cannabinoids, terpenoids and flavonoids.
Lab or bench scale units are necessary to reduce costs and risks while identifying optimal parameters before scaling up to make cannabis nanoemulsions with ultrasonic technology. Flow-through cells that incorporate multiple horns are effective at providing uniform delivery of ultrasound to large volumes of material. Since Le Herbe is primarily a cannabis beverage company, we specialize in nanoemulsions, scaled-up units and have vast technical experience with batch sizes of 4,500 + gallons / processing rates of 2 metric tons/hr. Ultrasonication is now readily available and can be customized for a range of cannabis applications like beverages, tinctures, gel caps, etc.
The present experiment briefly reports on cannabis nanoemulsions stabilized by Span 80 and Tween 80 at different operating conditions. Please do not use Tween and Span for commercial production. Effects of various operating parameters such as HLB value, surfactant fraction, oil fraction, sonication times and high-power amplitude were investigated and optimized on the basis of droplet size and stability of nanoemulsions. The ability of ultrasound to produce unique, high-value products with improved functionality, while reducing chemical and energy consumption in cannabis nanoemulsions is revolutionary. It is envisioned that the continual development of this technology will lead to gradual industrial uptake of ultrasonics and eventually its mainstream adoption for the production of valuable Consumer Packaged Goods (CPG) like cannabis beverages and water soluble cannabinoids.
Le Herbe would like to acknowledge Qsonica for their insights on sonication technology. Please click on the logo(s) below to find out more information.