*2.8. Hydrolytic Degradation of the Samples*

The samples with a dimension of 3 cm × 3 cm were cut, dried and placed in the glass vials of PBS and distilled water (pH = 7.4 ± 0.2). They were then placed in an incubator at 25 ◦C (room temperature) and 40 ◦C for three weeks. After the selected immersion periods, the selected samples were collected and rinsed with distilled water several times. Afterward, the rinsed samples were put into the oven to dry. This hydrolytic degradation was assessed in the neutral pH; the hydrolytic degradation in acidic and alkaline mediums were also investigated. To this end, the net weight of samples before and after hydrolytic degradation was measured.

The samples with the same dimensions were placed into the glass vials of NaOH solution (pH = 13). They were taken out at specific time intervals, rinsed with distilled water just like the previous step and placed in an oven at 70 ◦C for 3 h. Thus, hydrolytic degradation was investigated at the water bath at temperatures of 23 ◦C and 40 ◦C for three weeks. The sample weights were then measured precisely and an acid environment was created with hydrochloric acid. Afterward, hydrolytic degradation was analyzed according to alkaline and acid environments.

The residual weight after hydrolytic degradation (Q) was calculated based on Equation (3) as follows:

$$\mathbf{Q} = \frac{\mathbf{W\_t}}{\mathbf{W\_0}} \times 100\tag{3}$$

W<sup>0</sup> and W<sup>t</sup> represent the samples' initial weight (g) and the samples' weight (g) after being degraded at each specific time, respectively.

To make a better understanding of the samples' hydrolytic degradation, the hydrolytic degradation (R, %h) was defined according to the following Equation (4):

$$\mathbf{R} = \begin{array}{c} \mathbf{Q}\_0 \ - \mathbf{Q}\_t \\ \mathbf{t} \end{array} \tag{4}$$

Q<sup>0</sup> and Q<sup>t</sup> represent the weight of the samples before and after degradation at specific time periods.
