*3.9. Stability Studies*

The long-term stability of the two optimized rivastigmine-loaded NLC formulations (i.e., the one with the best CQAs produced by the ultrasound technique and the one with the best CQAs produced by HPH method) was assessed according to ICH (Q1A) guidelines [87]. For the studies, formulations were stored at room temperature (20.0 ± 0.5 ◦C) and in the refrigerator (4.0 ± 0.5 ◦C), and the particle size (Z-Ave, D50, D90), PDI, ZP, and EE were evaluated after 90 days of storage. The results were presented as mean values of three replicates (*n* = 3) ± SD.
