(M1030-07-40) Drug Release Rate Characterization of Double Nanoemulsions (W1/O/W)

Purpose: The goal of this work is to develop a quick screening method that yields drug release profiles from complex nanoformulations, such as double nanoemulsions. Water-in Oil-in Water emulsions (W1/O/W) can be used to deliver a combination of hydrophobic and hydrophilic drugs by employing semipermeable water compartments within oil particles [1, 2]. Encapsulation efficiency and release rates are important characteristics of the formulation for delivery, stability, stealthiness, and storage life. These studies were designed to identify the major factors that affect the release characteristics of formulations. While elaborate methods to determine delivery rates exist, quick screening is a useful tool that helps with the selection of ingredients in the development phase of the formulation. A significant reduction in resources may be obtainable, including materials, synthesis time and testing, and project costs.

Methods: Two small molecule drugs were used in this work: (1) C1, a hydrophilic drug with water solubility 95 mg/ml, and (2) C2, a hydrophobic drug, with water solubility < 1mg/ml. Certain formulations contained only C1 in the core W1 phase, while others contained C2 in the O phase. Both formulation types contained surfactant(s) in both water phases, W1 and W2. A small amount of water-soluble green dye was added to W1 to visualize phase interactions. Soybean oil was the main ingredient of the O phase. Commonly used surfactants for injectable formulations were used, including Tween 80 and egg phospholipids in the W1 and W phases. The W phase consisted of either di-ionized water, saline solution, or di-ionized water with glycerin. The fraction of W1/O was 35-39% of the total emulsion. A rotor-stator mixer and a high pressure homogenizer equipped with Delphi’s Dual Feed Impinging Jet Reactor were used to create the double emulsions. These were produced in two steps, first by forming the W1/O emulsion and then by emulsifying it again to form the W1/O/W emulsion. For the transfer experiments, only the first step was completed. A measured amount of W phase, was placed into a tube and W1/O was placed on top, which stayed there because of its lower density. The two phases interacted for certain periods of time during which drugs, C1 and/or C2, transferred to phase W, Figure 1. Physical separation and/or filtration through a 0.22 micron PTFE filter was used to separate W1/O from W. Ultracentrifuge was used to break the W1/O/W emulsion. The drug concentration in W was determined using HPLC, while the average particle size of the W1/O/W emulsions were measured using Dynamic Light Scattering. Several aspects of the mass transfer technique were examined, including the measured time profile for the amount of drug transferred, the effect of specific ingredients in the formulations, and the initial location of the drug. The results were compared with mass transport models that are applicable for analyses of this experimental set-up [3].

Results: The average particle size of the various W1/O/W batches were in the range of 140-200 nm and that remained unchanged for at least one month. While the 140-185 nm batches filtered readily, batches with higher particle size did not. Using filtration, the particles of batches with 185-200 nm size were trapped on the filter, while the W phase passed through, without breaking the emulsions. HPLC analysis of the W phase determined the amount of the drug transferred between the phases. The composition of the O phase highly affected the flux of C1, which decreased over time, Figure 2a. The transfer of hydrophobic C2 from the O was much lower than that of the hydrophilic C1 from W1. This was both in terms of flux and percentage of encapsulated drug. For example, when only C2 was present, less than 1% of it was transferred and when only C1 was present, 5-40% of it was transferred, under similar conditions, depending on the formulation of the O phase and interaction time, Figure 2b. Additionally, the W composition affected the mass transfer, with di-ionized water allowing the transfer of almost twice the amount of C1 than saline or glycerin solutions. This was true for either surfactant used in W1, Figure 3. The W1/O/W emulsions were separated after 48 hrs from production. The range for the amount of drug transferred was 20-32% for the filtered (unbroken) emulsion, Figure 2b. These results are in good agreement with the transfer experiments. For the broken emulsions, over 70% of C1 was transferred.

Conclusion: As proposed, these transfer emulsion results do identify the effect of key variables sought after, including surfactant types, drug properties and location in the emulsion, and other excipients in the W1, O and W phases. The results were compared well with mass transport models that are applicable for analyses of this experimental set-up. The parameter fitting protocol has provided robust predictive capabilities for reformulation studies and more advanced experimental designs.

References: 1. Shukai Dinga, Christophe A. Serrab, Thierry F. Vandammec, Wei Yub, Nicolas Anton, “Double emulsions prepared by two–step emulsification: History, state-of the- art and perspective”, Journal of Controlled Release, https://doi.org/10.1016/j.jconrel.2018.12.037, 2018.
2. Nico Leister and Heike P. Karbstein, “Evaluating the Stability of Double Emulsions—A Review of the Measurement Techniques for the Systematic Investigation of Instability Mechanisms”, Colloids Interfaces 2020, 4, 8; doi:10.3390/colloids4010008.
3. Crank J. “The Mathematics of Diffusion,” Oxford University Press, London, UK (1956).

Acknowledgements: The authors would like to thank Mr. Jonathan Doughty for helping us with the production of the emulsions. The work was funded internally by Delphi Scientific, LLC and Avantgarde Molecular, LLC. The authors declare that they have no conflicts of interest.

Figure 1. Mass transfer testing of hydrophilic drug, C1, from W1 to W phase: (a) Time = 0, and (b) Time = 20 hrs.
Green dye was added to the W1 phase to visualize the mass transfer.


Figure 2. (a) Time resolved flux of C1 hydrophilic drug from formulations with two different O phase
compositions, and (b) % of C1 or C2 transferred to W during transfer experiments and from the W1/O/W
emulsion separation. The bulk water phase, W, consisted of di-ionized water.


Figure 3. Percentage of hydrophilic compound, C1, transfer from W2 to W phases after 20 hrs,
for various W phase compositions and W1 phase surfactants