Alginate/Chitosan Complex Fibers Reinforcement and Their Mechanical Transition Continuum With Water Uptake Increasing.

Living tissues span a remarkable spectrum of modulus ranging from the level of Pa to GPa in a water-rich environment. Constructing soft and hard materials that match the mechanics of tissues and researching mechanical transition in water, are beneficial for their biological applications. Here, using polyelectrolyte complex fiber as a model system and reinforcing the fiber by stepwisely introducing additional coordination and covalent bonds, this investigated that the water effect on mechanical transition behaviors. Alginate/chitosan fiber (AC fiber) has a single electrostatic bond and shows continuous mechanical transition containing a glassy state, rubbery state, and terminal relaxation (initial modulus lower than 10 MPa) in aqueous solution. Alginate/chitosan/calcium fiber (ACC fiber) has both electrostatic and coordination bonds, which shows the behavior of hard rubber (initial modulus 100 MPa) when water reaches equilibrium. Alginate/chitosan/calcium/polydopamine fiber (ACCP fiber) with triple bonds, including electrostatic, coordination, and covalent bonds, exhibits the behavior like ductile plastics in aqueous solution (initial modulus 1000 MPa). This work not only provides important insight into the toughening mechanism of polyelectrolyte complexes in water but also contributes to the preparation of tissue adaptive implantations.