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. 2018 Dec 18;14:33–43. doi: 10.2147/IJN.S187470

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© 2019 Ahmed et al. This work is published and licensed by Dove Medical Press Limited

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Three-dimensional response surface plots showing the effects of the independent variables X₁ and X₂ at midpoint of X₃ on the investigated dependent variables Y₁ (A and B), Y₂ (C), and Y₃ (D–F).

Notes: X₁: ALA in TPGS; X₂: citral concentration; X₃: PG concentration; Y₁: elongation percent; Y₂: initial permeation after 2 hours; and Y₃: cumulative permeation after 24 hours.

Abbreviations: ALA, alpha lipoic acid; PG, propylene glycol; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate; VNP, vinpocetine.