Thermo-/pH-responsive chitosan-cellulose nanocrystals based hydrogel with tunable mechanical properties for tissue regeneration applications

Abstract

In this study, we developed and characterized an injectable hydrogel with physical and mechanical properties that can mimic the bone microenvironment and promote bone regeneration. The injectable hydrogel was prepared with thermogelling biopolymers, chitosan and cellulose nanofibers/nanocrystals (CNFs/CNCs)). The chitosan solution can undergo sol-gel transition at body temperature, and CNFs/CNCs were used as an additive nanomaterial to enhance the mechanical properties of the chitosan gel and mimic bone tissue properties. Cellulose nanocrystals (CNCs) can significantly improve the gelation kinetics (from ~24 s to 7 s) and mechanical properties of the injectable chitosan hydrogel (from ~28 kPa to ~379 kPa). An increase in percent gel fraction corresponding to the weight percent of CNCs incorporated in the hydrogel demonstrated that the incorporated CNCs were completely reacted into the chitosan network, resulting in a high density of crosslinked network as shown by SEM imaging. Fourier-transform infrared spectroscopy (FTIR) analysis used to probe the reinforcement effect of CNCs showed an increase of hydrogen bonding due to the presence of CNCs within the chitosan networks. The hydrogel formulations were biocompatible as demonstrated by high cell viability in the LIVE-DEAD cell staining analysis. Presence of CNCs in the chitosan gel altered cell morphology by inducing spreading morphology due to higher mechanical sensing from the CNCs. The versatility of this formulation to exhibit strong mechanical properties combined with its ability to support cell encapsulation makes it attractive as a biomaterial for bone regeneration. Statement of significanceBone grafting has increasingly been used in surgery with more than two million times per year worldwide to promote bone regeneration. However, bone grafting failures remain the main constraints in this treatment option. In the past decade, the use of cell-based biomaterials has been extensively investigated as alternatives for bone grafting procedures. Yet, biomaterials that can effectively promote bone fracture healing with a minimally invasive procedure remain in high demand. Herein we describe a novel injectable tunable biomaterial using cellulose nanocrystals-hybridized chitosan-based hydrogel that can safely encapsulate pre-osteoblast cells and can potentially use as an injectable bone graft substitute. This research will establish a novel concept for the use of cell-based biomaterials in bone tissue engineering and other regenerative medicines.