Depending on the nature of ionic interactions, hydrogel properties may change with polymer concentration, degree of ionization of the charged groups, pH, ionic strength and temperature, such as in the case of chitosan-based networks. The natural polysaccharide chitosan (CS) carries positively charged ammonium groups (pK a ∼ 6.5), which can interact with negatively charged polymers or organic polyanions such as sodium triphosphate or sodium phytate to form crosslinked networks. Polyampholytes are polymers with a statistical distribution of cationic and anionic pendant side groups and have become an attractive material for the fabrication of tough hydrogels. Representative monomers with cationic side groups are 3-(methacryloylamino)propyltrimethylammonium chloride (MPTC) or dimethylaminoethyl acrylate hydrochloride (DMAEA-Q), while popular anionic monomers include sodium acrylate or sodium p-styrenesulphonate (NaSS). The random distribution of ionic groups within the polymer backbone leads to ionic interactions of various strengths, where stronger ones may act as persistent cross-links, while weaker ones are more dynamic serving as sacrificial bonds within the network. Consequently, ionic interactions have been used in various ways to mediate reversible cross-linking for the fabrication of tough hydrogels. Hydrogen bonding is a short-range electrostatic interaction between a hydrogen atom (covalently bound to an electronegative atom X), and a second electronegative atom Y, bearing a lone pair of electrons, thus, forming a hydrogenbonded dimer denoted as X-H• • • Y (Figure ). Hydrogen bonding is essential in many biological systems, for example to stabilize three-dimensional assemblies of nucleic acids and proteins. Hydrogen bonds are substantially weaker (2-15 kcal/mol) than covalent bonds, and relatively weak compared to other non-covalent interactions. Often, individual molecules are connected by more than one hydrogen bond, as in the case of the monomers acrylamide or acrylic acid. In both instances, each hydrogen is interacting with the complementary carbonyl oxygen forming dimers. This strategy has been adapted for a number of hydrogen bond motifs, for instance, the quadruple hydrogen bonding motif ureidopyrimidinone (UPy) with an acceptor-acceptor-donordonor array, which has been used in hydrogels, too. For the synthesis of tough hydrogels, however, most networks have exploited rather small monomers capable of (i) straight-forward (co)polymerization, (ii) multiple hydrogen bond formation per monomer, and (iii) synergistic strenghening through multivalent binding within the network. In this regard, the selected hydrogen bonding monomers include acrylamide (AAm), N,N'-dimethylacrylamide (DMAAm) in combination with acrylic acid (AAc), , vinyl imidazole (VIm), custom designed monomers, such as N-acryloyl glycinamide (NAGA), and Nacryloylsemicarbazide (NASC), as well as other hydrogen bond promoting systems. Microphase separation refers to the spontaneous separation of (chemically) incompatible components in a system to form separated phases in the microscopic regions of the material (Figure ). Historically, the phenomenon originates from block copolymers and polymer blends, where individual blocks pack into regular arrangements to maximize attractive interactions and to minimize repulsive ones as well as the total free energy of the system. The phase-separated domains can have different chemical or physical properties, such as refractive index, elasticity, or surface energy, offering interesting opportunities for the synthesis of materials. Besides the bulk phase, microphase separation has been observed in solutions, gels and even cells, as has been shown recently. For the sake of data representation in this review, we associate microcrystallization and salting-out effects to the phenomenon of microphase separation.