The presence of nano-objects can also affect the porosity of the hydrogel. As the observations are made after sample freeze-drying, the inclusion of nano-objects in form of aqueous dispersions can lead to hydrogels displaying an even distribution of pores, in contrast to the irregular structure of bare gel. As an example, void spaces and a multitude of homogeneous pores were created in a CS/HA hydrogel containing a dispersion of lipid nanocarriers after complete water removal. Similarly, the dispersion of nanosilicates into a CS hydrogel resulted in uniform porosity with stable pores that were less likely to collapse during freezedrying compared to those of the pure hydrogel. Concerning pore size, the accumulation of nano-objects in the hydrogel can interfere with the matrix structure and create greater distances between hydrogel constituents. The result is a decrease in connectivity and formation of larger pores as observed, for instance, when Au NPs were incorporated into CS-based hydrogels and after dispersion of bare iron oxide NPs in Gel. This effect is often concentration dependent. The introduction in a starch gel of increasing concentration of silica-coated Cu NPs (up to 1.27 mmol Cu per gram of hydrogel) resulted in the collapse of the starch structure and the formation of larger and fewer pores compared to the gel without NPs (Figure ). In the case of carboxyl-modified MSNs, the incorporation of a small amount into GelMA (e.g., Si concentrations < 1 mg mL -1 ) caused a gradual enlargement of pore sizes. This may relate to increased interactions between the NPs and the polymer, which condense locally and create larger voids. A further increase in Si concentration (> 1 mg mL -1 ) led to a reduction in pore size, probably due to the increase in crosslinking density. A similar trend was observed in hybrid hydrogels made of catecholmodified HA (HA-DA) and reduced graphene oxide (rGO) wherein the higher the mass ratio of rGO, the smaller the hydrogel pore size. For rGO/HA-DA weight ratios from 0 to 3 and 5% the pore size ranged from 88 to 58 and 45 µm, respectively.