**1. Introduction**

Among the available biomaterials, hydrogels, three-dimensional polymeric networks capable of imbibing large amounts of water or biological fluids, have proved their value in diverse biomedical applications [1–3]. In addition to the swelling property of the hydrogels, their biocompatibility, good mechanical properties, tunable chemical structure, and three-dimensional physical structure have made them one of the promising class of materials for tissue engineering [4, 5], pharmaceutical applications [6, 7], and biomaterials science [8]. In recent years, with the advancements in technology, interest in microscopic (microgels) and nanoscopic hydrogels (nanogels) has increased [9, 10].

Microgels, hydrogel particles formed by physical or chemical cross-linking of polymer networks in microscale size [11], have exceptional properties like large surface area, tunable size from micrometers to nanometers, ease in synthesis, control over particle size, responsiveness to environmental factors, and an interior network for the incorporation of therapeutic agents [12, 13].
