*2.5. Characterization*

Fourier transform infrared (FTIR) spectra of samples were performed on a spectrometer (Vertex 70, Bruker, Ettlingen, Germany). 1H NMR spectra were recorded on a NMR spectrometer (Ascend TM 600 MHz, Bruker, Rheinstetten, Germany). The weight percentage of POL in ALG–POL copolymers was determined using an elemental analyzer (Vario EL III, Elementar, Hanau, Germany). The morphology of BG NPs was viewed with a transmission electron microscope (TEM, Tecnai G2, FEI, Hillsboro, OR, USA). Hydrodynamic size and zeta (ζ) potential of BG NPs were measured using a dynamic light scattering (DLS) instrument (Nano-ZS90, Malvern Instruments, Worcestershire, UK). A mass of BG NPs (100–150 mg) were dried for 12 h at 120 ◦C and degassed for 24 h at 200 ◦C under vacuum. The volume of nitrogen adsorbed and desorbed at different relative gas pressures was measured using a surface area and pore size analyzer (ASAP 2020 Plus, Micromeritics, Norcross, GA, USA), and it was then utilized to construct adsorption–desorption isotherms. The specific surface area was determined with the Brunauer–Emmett–Teller (BET) method. The pore volume and the mean pore size were derived from the adsorption branches of the isotherms using the Barrett–Joyner–Halanda (BJH) method. The porous cross-section structure of dry gels was examined by scanning electron microscopy (SEM, Quanta 200, FEI, Eindhoven, Netherlands). Dry gel samples with known weight (*W*d, g) were immersed in PBS at 37 ◦C till they attained equilibrium, and their wet weight (Ws, g) was measured after removal of excess surface water with filter paper. Swelling index (SI) of gels was calculated using the following formula:

$$\text{SI} \, (\text{g/g}) = (\text{W}\_{\text{s}} - \text{W}\_{\text{d}}) / \text{W}\_{\text{d}} \tag{2}$$
