Advances in porous chitosan-based composite hydrogels: Synthesis and applications

Chitosan (CS) as the only polycation coming from renewable resources is endowed with intrinsic valuable properties, such as: biocompatibility, biodegradability, low cost, easy availability, and high reactivity due to plenty of the reactive functional groups (-NH2 and -OH). Therefore, CS and its derivatives have been involved in numerous applications, either alone or as components in composite materials. This review aims to present an overview on the most recently published information on the preparation of porous CS based composite hydrogels such as: porous chitosan/synthetic polymer as beads and monoliths, CS/inorganic particles, porous semi- and full-IPN hydrogels, and on their applications either as very efficient composite sorbents for heavy metals and dyes, or as hemostats, smart drug delivery systems, wound dressings. The techniques currently applied to prepare porous CS-based composites, including ice-templating (cryogelation), freeze-thawing, freeze-drying (lyophilization), and imprinting/leaching will be especially highlighted. Using cryogelation in tandem with IPN strategy led to composite cryogels with high mechanical properties and high performances in separation processes of ionic species. Main factors which control the separations of dyes and heavy metal ions by porous CS-based composite sorbents are discussed based on the recently published articles and own results.