Dynamic chitosan-hyaluronic acid hydrogels for extrusion printing: Combined effects of polymer molecular weight and carbon nanofillers

Despite the increasing interest on self-healing hydrogels in the fabrication of customized scaffolds for tissue engineering applications, their optimal printability is still a challenge due to the weak mechanical stability of dynamic networks. This work presents the first successful extrusion-based 3D-printing of N-succinyl chitosan (S-CHI) and oxidized hyaluronic acid (A-HA). The dynamic hydrogels based on imine bonds formation between S-CHI and A-HA were reinforced with graphene oxide (GO), amino-functionalized GO (GO-NH₂), carboxyl-functionalized carbon nanotubes (CNT-COOH), and amino-functionalized CNTs (CNT-NH₂) in order to study their effect on the 3D-printability, mechanical, rheological and self-healing properties of the gels. Compression tests, strain sweeps tests and the geometry of the printed scaffolds shown that non-aminolized GO and CNTs strengthen the networks, and improve printability but cause a detrimental effect on the self-recovery capability, unlike amino-functionalized fillers that enhance self-repairing but weaken mechanical strength and printability. The presence of the fillers also delays gelation, particularly in the case of amino functionalized particles. However, electrochemical impedance spectroscopy confirmed that the incorporation of the fillers did not affect the electrical conductivity of the hydrogels. Besides, this study analyses the role of the molecular weight of S-CHI units on the aforementioned properties.