Physical hydrogels based on natural polymers

Physical hydrogels have gained significant attention in recent years, with their applications ranging from biomedicine to soft electronics. Developing physical hydrogels based on natural polymers is an effective way to improve the biocompatibility of materials, which may improve their performances and broaden their applications. In this review, we describe four main types of physical interactions used to cross-link with natural polymers, that is, ionic interactions, crystallization, hydrophobic association, and hydrogen bonding, respectively. Meanwhile, natural polymers used to prepare physical hydrogels, such as chitosan, alginate, poly(γ-glutamic acid), and cellulose are briefly introduced. Finally, we conclude with the characteristic advantages and provide an insight into the remaining challenges and future perspectives of physical hydrogels based on natural polymers.