Rubbery Chitosan/Carrageenan Hydrogels Constructed through an Electroneutrality System and Their Potential Application as Cartilage Scaffolds

In the present work, the bulk and homogeneous composite hydrogels were successfully constructed from positively charged chitosan (CS) and negatively charged carrageenan (CG) in alkali/urea aqueous solution via a simple one-step approach for the first time. An electroneutral CS solution was achieved in alkali/urea, leading to a homogeneous solution blended by CS and CG, which could not be realized in acidic medium because of the agglomeration caused by polycation and polyanion. Subsequently, the CS/CG composite hydrogels with multiple cross-linked networks were prepared from blend solution by using epichlorohydrin (ECH) as the cross-linking agent. The composite hydrogels exhibited hierarchically porous architecture, excellent mechanical properties as well as pH- and salt-responsiveness. Importantly, the composite hydrogels were successfully applied for spreading ATDC5 cell's, showing high attachment and proliferation of cells. The results of fluorescent micrographs and scanning electronic microscope images revealed that the CS/CG composite hydrogels enhanced the adhesion and viability of ATDC5 cells. The alcian blue staining, glycosaminoglycan quantification, and real-time PCR analysis proved that the CS/CG composite hydrogels could induce chondrogenic differentiation of ATDC5 cells in vitro, exhibiting great potential for application in cartilage repair. This work provides a facile and fast fabrication pathway for the construction of ampholytic hydrogel from polycation and polyanion in an electroneutrality system.