*2.6. G1Phy Quantification*

The amount of G1Phy ionically crosslinked in the membranes was quantified measuring the P content using ICP-OES (Perkin-Elmer, MA, US). Polymeric membranes were dried at 60 ◦C after their incubation in G1Phy solution until constant weight. Afterwards, membranes were digested in nitric acid, 65% (*v*/*v*) at 60 ◦C for 24 h. Then, samples were diluted with Milli-Q water to 5% nitric acid concentration in order to be compatible for ICP-OES analysis. A blank solution was prepared with only nitric acid at 5% in Milli-Q water. All measurements were performed in triplicate. A standard calibration curve of P with concentration from 0–1000 mg/L was used. Three measurements were made for each sample. Data were expressed as mean ± SD.

### *2.7. Swelling*

Dry membranes with a diameter of 12 mm were soaked in 10 mL of PBS (pH = 7.4) at 37 ◦C. The swollen membranes were removed at different periods of time. After removing the attached excess of water on the surface with filter paper, the membranes were weighed. The water uptake was calculated as described in Equation (2):

$$\text{Swelling} \left( \% \right) = \left[ (\text{W}\_{W} - \text{W}\_{0}) / \text{W}\_{0} \right] \times 100 \tag{2}$$

where W<sup>w</sup> and W<sup>0</sup> are the weight of the swollen membrane at time t, and the initial dried weight of the membrane, respectively. For each period of time and sample, a minimum of four replicates were measured and averaged. Data were expressed as mean ± SD.

### *2.8. Degradation*

Dry membranes (12 mm diameter and 0.2 mm thickness) were weighed and then placed in 10 mL of PBS (pH 7.4) at 37 ◦C. The membranes were retrieved at predetermined time point and washed with

Milli-Q water to remove any remaining salts. The membranes were then dried at 60 ◦C until constant weight. The percentage of weight loss was calculated following the Equation (3):

$$\text{Weight loss (\%)} = [(\text{W}\_W - \text{W}\_t)/\text{W}\_0] \times 100\tag{3}$$

where W<sup>0</sup> and W<sup>t</sup> are the weight of the initial dry membrane and the dried membrane at time t after incubation in PBS, respectively. For each period of time and sample, a minimum of four replicates were measured and averaged. Data were expressed as mean ± SD.
