Droplet-Based Microgels: Attractive Materials for Drug Delivery Systems

A microgel as defined by IUPAC is “particle of gel of any shape with an equivalent diameter of approximately 0.1 to 100μm”. Baker’s group was one of the first that studied microgels, and “micro” refers to the size and “gel” refers to the structure of the particle [1]. Thus, microgels are cross-linked polymer chains and are similar to macrogels, but they are in the micro-scale. Because of their micro-scale size, microgels have advantages over macrogels, and some of them are mentioned here. i) Microgel suspensions are free-flowing liquids which depend upon volume fraction of swollen particles and cross-linking properties. ii) Microgels respond to changing environment very rapidly, much faster than macrogels, because they have a high surface to volume ratio which transports mass to-and-from the microgels. iii) Exotic microgel morphologies can be used to fine-tune properties. iv) Microgels are considered as colloidal dispersions, and several colloidal science techniques including dynamic light scattering and small range light can provide structural information for microgels. On the other hand, these techniques cannot be used in the case of macrogels. v) Microgels can be assembled into useful larger objects such as 2D assemblies of the air-water and oil-water interfaces [2]. Examples of the 3D structure are colloidal crystals, environmentally sensitive optical properties, and layer-by-layer assemblies. These kinds of assemblies are not feasible when using macrogels.