Nanoparticle network hydrogels (NNHs) in which nanoparticles are used as a key building block to build the gel network have attracted significant interest given their potential to leverage the favorable properties of both hydrogels (e.g., hydrophilicity, tunable pore sizes, mechanics, etc.) and a variety of different nanoparticles (e.g., high surface area, chemical activity, independently tunable porosity, mechanics) to create new functional materials. Herein, recent progress in the design and use of NNHs is comprehensively reviewed, with an emphasis on defining the typical gel morphologies/architectures that can be achieved with NNHs, the typical crosslinking approaches used to fabricate NNHs, the fundamental properties and functional benefits of NNHs, and the reported applications of NNHs in electronics (flexible electronics, sensors), environmental (sorbents, separations), agriculture, self‐cleaning‐materials, and biomedical (drug delivery, tissue engineering) applications. In particular, the way in which the NNH structure is applied to improve the performance of the hydrogel in each application is emphasized, with the aim to develop a set of principles that can be used to rationally design NNHs for future uses.

While photopolymerization has been broadly used to fabricate hydrogels, the kinetics of the structural evolution of such hydrogels during photopolymerization and how the kinetics relate to ultimate hydrogel properties are not well-understood. Herein, small-amplitude oscillatory shear rheology (bulk scale) and time-resolved very small-angle neutron scattering (vSANS, microscale) are used in tandem to investigate the kinetics of the photopolymerization of methacrylated starch building blocks with different concentrations, charges (cationic (+), anionic (−), or neutral (0)), and morphologies (soluble branched starch, starch nanoparticles, or combinations thereof). Starch nanoparticles (SNPs) enabled the fabrication of much denser hydrogels than soluble starch but took longer to gel due to the reduced conformational mobility of the polymerizable methacrylate groups on the SNPs. The addition of charge (cationic or anionic) increases the bulk gelation time while significantly reducing the observed changes in the fluid scale and correlation length, suggesting less covalent crosslinking and inherent SNP deformation during photogelation; indeed, the fluid exponent analysis suggests that charged SNPs deswell upon crosslinking, consistent with the behavior of microgels in colloidal crystals, while uncharged SNPs swell due to competition between inter-and intraparticle crosslinking. The combination of shear rheology and vSANS measurements can thus inform the design of new photopolymerizable hydrogels with targeted comprehensive properties.