*2.5. Patches Preparation*

The hybrid ZnAl-KET was formulated in patches by casting method [22] starting from the hydrogel composition optimized in previous work [23]:

ZnAl-KET: 1% *wt.*/*wt*. NaCMC: 2% *wt.*/*wt*. Glycerol: 10% *wt.*/*wt*. Water (CO2 free): 87% *wt.*/*wt*.

The hybrid was mixed with NaCMC powder by mortar and pestle and then wetted with glycerol. The water, free from CO2 in order to avoid KET deintercalation, was added slowly until complete hydrogel formation. In order to remove the air incorporated during the mixing, the hydrogel was degassed in a conditioning planetary mixer (Thinky mixer ARE-250, Intertronics, Kidlington, England) at 2000 rpm for 10 min. The patches were prepared by casting 3.5 g of the hydrogel in circular silicon molds (diameter 3 cm) and then placed in a ventilated oven at 37 ◦C for 24 h.

## *2.6. Patches Characterization*

#### 2.6.1. Weight and Thickness Measurement

Patches (circles, area: 7.065 cm2) were weighted by a Mettler-Toledo weighing balance, model XS205 (Milano, Italy). The thickness was measured in three different points of the patch by an electronic micrometer (QuantuMike IP 65 Coolant Proof, Mitutoyo, Takatsu-ku, Japan).

## 2.6.2. Mechanical Characterization

The tensile tests were performed by using a digital microprocessor instrument Llyod LR30K (Lloyd instruments, Bognor Regis, UK). The patches were cut in portions 100 × 10 mm (UNI ISO 527) to have a useful length of 50 mm. The experiment was performed at 5 mm/min, cell load 50 N. The two ends of the patch were fixed with clamps to the dynamometer. The sample was subjected to tensile stress until deformation and break. Maximum stress (σ*max*), deformation at the break for maximum stress (ε *at* <sup>σ</sup>*max*), and elastic modulus (*EYoung*) values were calculated from the stress-strain curves. Before the test, the patches were equilibrated for 1 week under silica gel (relative humidity, RH 30%). The results were an average of five measurements (n = 5).
