**3.1 Synthesis of microgels in homogeneous phase**

The first approach is based on the investigations of Staudinger [45], who prepared inter- and intramolecularly cross-linked microgels by free radical cross-linking copolymerization of monomers in dilute solutions. However, the resulting internal structure of microgels was not well established, but investigations performed on these systems were key step to understand the process of gel formation [46].

Other techniques include coacervation and desolvation. In both techniques phase separation of readily formed polymers takes place, resulting in micro-/nanoparticles which are then cross-linked. **Figure 1** represents typical steps involved in coacervation method. Phase separation is usually induced by changing temperature, adding salt, nonsolvent addition, non-compatible polymer addition, or polymer-polymer interaction. The resulting coacervate (polymer droplet) is then solidified and stabilized forming microgel particle. This technique is usually employed in synthesis of microgels from biopolymers such as (modified) gelatin or chitosan. For example, pHresponsive chitosan nanoparticles were synthesized by complex coacervation [47] and two-step desolvation route was involved in synthesis of gelatin nanoparticles [48].
