New CBD Nano-emulsions Remain Stable For More Than a Year, Say Scientists

Lipophilic compounds like CBD are insoluble in water, have poor physical stability, and erratic gastrointestinal tract bioavailability¹. Subsequently, the pharmacokinetic profile of CBD can be highly variable. A potential improvement path depends on making the substance more shelf stable and water soluble by converting it into emulsions or nano-emulsions.   

CBD can be converted into water-miscible nano-dispersions using different dispersion methods. It is anticipated that both stability and pharmacokinetic properties will be highly associated with dispersion size. Thus, a method that minimizes the use of chemical additives to produce fine nano-dispersions is of practical importance to pharmaceuticals.

High-pressure homogenization uses high velocity discharge to shear immiscible phases (typically oil and water) into dispersions. The strongest factor influencing dispersion size is homogenization pressure. Below 200 nanometers (nm) dispersion size, gravitational effect become weak and density driven instability is no longer an issue. Significantly increased bioavailability of lipophilic compounds encapsulated in nano-emulsions is known to correlate with oil droplet size reduction^2,3. Specifically, the intestinal absorption of CBD is markedly increased when delivered as an oral nano-emulsion where oil droplet size is extremely small⁴. 

Earlier this year, Pressure BioSciences tested if higher homogenization pressures could yield smaller, more stable nano-emulsions. These tests were conducted on a unique homogenizing system capable of 45,000 psi. This pressure is over ten times the pressure used to homogenize milk. The system uses a non-traditional approach to fluid pressure delivery and shear valve construction.

Our results showed that these nano-dispersions are characterized by small, monodisperse oil droplets and are stable at room temperature for more than a year. We also confirmed that up to 45,000 psi, higher pressure produced smaller oil droplets⁵.  

Results show that oil droplet size is a function of both formulation (the relative hydrophobicity and concentrations of bioactive, oil, and surfactant) and the method of physical shear used to prepare nano-emulsions. Progressively smaller particle sizes are produced by the intense fluid shear forces generated when course emulsions are expelled through a nanoscale valve at high pressure. Oil droplet size reduction over two orders of magnitude following a single pass through a self-throttle annular nanoscale valve has been reported⁵.

Homogenization at 45,000 psi produced nano-emulsions where the mean hydrodynamic diameter of CBD-encapsulated oil droplets ranged between 40-60 nm, depending on whether the oil phase was hemp seed oil or mixed triglycerides. Hemp seed oil produced smaller oil droplets than when using medium chain triglycerides as the oil phase. Unlike oil tinctures, these oil-in-water nano-emulsions contained less than 10 percent weight for weight oil. Oil droplets are stabilized by the absorption of surfactants on their surface, which increases intermolecular repulsion between the oil droplets and prevents their coalescence.

Stability studies of these CBD nano-emulsions showed no measurable change in oil droplet size, coalescence, or phase separation for at least 14 months when stored at room temperature and at least 18 months when stored under refrigeration. Accelerated aging studies at elevated temperatures could not be performed, because the formulations contained thermolabile polysorbates.

CBD nano-emulsions were also shown to be stable following repeated freeze-thaw cycling, suggesting that, when stored frozen, these nano-emulsions might be stable for years. 

Because the encapsulated CBD particles are so small, they do not scatter light and thus appear as clear light-yellow liquids that disperse freely in water or other clear beverages. When diluted several hundred times in water, nano-emulsions were stable for at least three months, suggesting that they could be infused in bottled water or canned beverage for reliable CBD dosing. For example, a teaspoon of CBD nano-emulsion added to a beverage could conveniently provide a 100 mg CBD dose without changing the organoleptic properties of the beverage.

In summary, the long-term stability of CBD is significantly increased when encapsulated in extremely small oil droplets of narrow size distribution. CBD nano-emulsions formed by 45,000 psi fluid shear were stable for at least 18 months. These are anticipated to have higher bioactivity.