Hydrogel–nanogel composite systems: Effect of nanogel loading and incorporation strategy

The incorporation of nanoscale structures within hydrogel matrices represents a promising strategy for modulating the structural and physicochemical properties of multiscale soft materials. In this study, polyethylene glycol (PEG)–Jeffamine nanogels were incorporated into a PEG–agarose–carbomer hydrogel matrix using different incorporation strategies and nanogel loadings in order to investigate their influence on hydrogel organization and bulk material behavior. In particular, nanogels were introduced either before microwave-assisted processing, immediately after microwave treatment, or during a later stage of hydrogel organization, while two different nanogel:hydrogel mass ratios (1:10 and 1:20) were evaluated. The obtained hydrogel–nanogel (HG–NG) composite systems were characterized in terms of structural, morphological, rheological, and swelling properties. FTIR analyses confirmed that nanogel incorporation did not significantly modify the chemical composition of the hydrogel matrix. However, scanning electron microscopy revealed differences in pore architecture and structural organization depending on the incorporation strategy, with pre-microwave incorporation resulting in greater structural heterogeneity and post-microwave incorporation leading to a more regular and continuous porous architecture. Despite these morphological differences, the overall pore size distribution remained largely comparable among the formulations. Rheological characterization showed that all formulations maintained a predominantly elastic behavior, although both nanogel loading and incorporation timing significantly affected the viscoelastic response of the systems. Overall, these findings demonstrate that nanogel incorporation can be effectively exploited as a processing-dependent strategy to modulate hydrogel network organization and bulk physicochemical behavior.