Morphological characterization of encapsulated fish oil with β-cyclodextrin and polycaprolactone

The present study characterized the morphology of fish oil β-cyclodextrin (β-CD) complex or fish oil encapsulated with polycaprolactone (PCL) by transmission electron microscopy (TEM) observation using low or high voltage with or without phosphotungstic acid (PTA) staining. Emulsion–diffusion or self-assembly aggregation methods were used to encapsulate fish oil in PCL or β-CD. PCL spheres averaged 200 nm in diameter. However, β-CD spheres were significantly larger and dependent on host:guest mixing ratio (w:w), being approximately 300 nm and 600 nm at ratios of 10:1 and 10:10, respectively. TEM enabled the visual distinction of core and wall materials, and revealed that fish oil was encapsulated with a different structure depending on whether the self-resembling aggregation of β-CD or emulsion–diffusion method with PCL was used. Hexagonal-type β-CD aggregates were evident at a mixing ratio 10:1 between β-CD and fish oil. The hexagonal arrangement of β-CD enveloped the fish oil with a thick (100–150 nm) membrane. Incorporation of β-CD with fish oil at a 10:10 mixing ratio produced a worm-type of β-CD. It is suggested that the fish oil might be physically blended without wrapping with β-CD. For the PCL formulation, the lower voltage TEM operating condition better enabled the observation of the thin PCL layer (1–2 nm) encapsulating the fish oil. Nanosizer® and TEM yielded comparable measurements.