3.4.4. Assessment of Encapsulation Parameters

The effectiveness of lipid nanoparticles for drug incorporation can be assessed by calculating the encapsulation efficiency (EE) and loading capacity (LC). High EE and LC values suggest that lipid nanoparticles can encapsulate and delivery the desired therapeutic amount of drug, reducing adverse effects and frequency of administration [18].

EE and LC were determined indirectly by calculating the amount of free rivastigmine (non-encapsulated) in the aqueous phase of NLC dispersions according to the following equations [72]:

$$\text{EE } (\%) = \frac{\text{Total amount of rivastigmine} - \text{amount of free rivastigmine}}{\text{Total amount of rivastigmine}} \times 100\tag{1}$$

$$\text{LCC (\%)} = \frac{\text{Total amount of rivastigmine} - \text{Amount of free rivastigine}}{\text{Total amount of rivastigine} - (\text{Amount of free rivastigine} + \text{Total amount of liquid})} \times 100\tag{2}$$

Briefly, 1 mL of each sample was diluted with purified water and placed in an Amicon® Ultracel-50K (Millipore Corporation, Ireland) centrifugal filter device and centrifuged at 3450 rpm for 1 h. Afterwards, the filtrate was collected, diluted in acetonitrile, and analyzed by HPLC. The tests were performed on the production day for 10 different batches of NLC formulations (*n* = 10) [72].
