Hydrogels differentiated by length scales: A review of biopolymer-based hydrogel preparation methods, characterization techniques, and targeted applications

Hydrogels, a 3D network structure of polymer chains with significant water content, can be formed of either natural or synthetic polymers; biopolymers are highly preferred for their biocompatibility, biodegradability, and cell response. For targeted applications such as wound dressing, 3D printing, packaging, implants, drug delivery, cell imaging and targeting, biopolymer hydrogels can be formed across multiple scales of macro to nano size. To achieve the desired gel utility at any scale, the properties can be controlled by modifying the structural characteristics such as crosslink density, mesh size, polymer conformation, and microstructure. This review aspires to give a perspective assessment of the preparation methods, characterization techniques, and targeted applications of biopolymer-based hydrogels at macro and micro/nano scales. Additionally innovative coupling of characterization modes can provide both quantitative and qualitative insight into gel structure, property, and functionality.