2.8. Ex Vivo Evaluation (Skin Permeation Study)

Rate skin is regarded as the best choice for implementing a skin permeation study because of its great structural similarity to human skin, it is handled easily and low cost. Using an electric clipper, the dorsal hair skin of male Wistar rats was removed. Afterwards, animals were sacrificed and the skin were excised and the adipose tissue was removed then the skin, hydrated with phosphate buffer (pH 7.4) and stored at 4 °C overnight [33].

An ex vivo permeation study of Cur from all preparations on male Wistar rat skin was implemented using modified Franz diffusion cells developed in our lab [25,34,35]. The skin membranes were mounted in the diffusion cell, with the upside facing the drug-loaded formulation and the dermis facing the receptor media containing 100 mL phosphate buffer (pH 7.4) and 0.02% sodium azide at 37 ± 0.5 °C. Next, 1 g of the formulation (that is equivalent to 1 mg Cur) was applied to the donor area that was attached to the glass tubes and covered with skin membranes. The tubes were suspended into the dissolution apparatus, shielded with Parafilm (Bemis, Oshkosh, WI, USA) to prevent water evaporation and stirred at 100 rpm [33]. Certain parameters correlated with the ex vivo permeation study of Cur across the rat skin were estimated for all formulations including steady state transdermal flux (SSTF) and the enhancement ratio (ER). These parameters were calculated as follow:

SSTF = amount of permeated drug / (area × time);

ER = SSTF from test / SSTF from control.