The preferred technique for assessing the microstructure and porosity of the hybrid hydrogels, as well as for identifying embedded nano-objects is scanning electron microscopy (SEM), also including cryogenic SEM and field emission SEM. This technique allowed to observe that nano-objects can introduce surface roughness to an otherwise smooth matrix, confirming their presence (e.g., liposomes dispersed in HA, PPy NPs within PAA or an ALG/PAAm matrix ; PDA-modified HAP NPs in an ALG/Gel hydrogel , PEDOT NPs in a GelMA matrix ) and in some cases revealing their aggregation. For instance, the latter was observed on the walls of a CS-based hydrogel containing carbon nanotubes (Figure ) or poly(3-hydroxybutyrate-co-3hydroxyhexanoate) NPs, and when PEDOT NPs were dispersed in a poly (2-hydroxyethyl acrylate) matrix. In other examples, the use of SEM revealed an irregular and rough morphology in carboxymethylcellulose (CMC) hydrogels crosslinked using aminofunctionalized CoFe2O4 magnetic NPs. Similarly, cross sections of hybrid hydrogels made of PAA and PAAm-grafted CNCs and silica NPs dispersed within AAm or CS hydrogels exhibited uneven surfaces. It is interesting to note that the surface roughness introduced by Au NPs incorporated within an ALG matrix has proved advantageous for enhancing cell adhesion and consequently improving the biological functionality of the hybrid hydrogel, particularly in the context of repairing an infarcted area. Conversely, CS-based hybrid hydrogel beads exhibited a smoother surface as the concentration of CuO NPs increased (up to 1.5 mmol of CuCl2 content), which could be attributed to the interfacial interactions between CS chains and CuO NPs acting as crosslinkers. Such a crosslinking restricted the mobility of the CS chains, preventing the formation of pronounced wrinkles and numerous cavities upon drying of the beads. Bright dots in a Gel-based matrix (Figure ) and in a PNIPAAm hydrogel revealed the presences of liposomes and it was possible also to observe PDA NPs distributed along the surface of a HA hydrogel. Overall, this provided evidence of their successful integration into the matrix. TK/4-arm-PEG-SG hydrogels. Adapted with permission. Copyright 2022, Wiley-VCH.