RESUMEN
Hydrogels have been studied as promising materials in different biomedical applications such as cell culture in tissue engineering or in wound healing. In this work, we synthesized different nanocellulose-alginate hydrogels containing cellulose nanocrystals, TEMPO-oxidized cellulose nanocrystals (CNCTs), cellulose nanofibers or TEMPO-oxidized cellulose nanofibers (CNFTs). The hydrogels were freeze-dried and named as gels. The nanocelluloses and the gels were characterized by different techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA), while the biological features were characterized by cytotoxicity and cell growth assays. The addition of CNCTs or CNFTs in alginate gels contributed to the formation of porous structure (diameter of pores in the range between 40 and 150 µm). TEMPO-oxidized cellulose nanofibers have proven to play a crucial role in improving the dimensional stability of the samples when compared to the pure alginate gels, mainly after a thermal post-treatment of these gels containing 50 wt % of CNFT, which significantly increased the Ca2+ crosslinking density in the gel structure. The morphological characteristics, the mechanical properties, and the non-cytotoxic behavior of the CNFT-alginate gels improved bioadhesion, growth, and proliferation of the cells onto the gels. Thus, the alginate-nanocellulose gels might find applications in tissue engineering field, as for instance, in tissue repair or wound healing applications.
RESUMEN
The colloidal stability together with the tunable aggregation and viscoelastic properties of thermoresponsive polymer-grafted cellulose nanocrystals (CNCs) were investigated. TEMPO oxidation of CNCs followed by peptidic coupling in water were used to covalently graft thermosensitive Jeffamine polyetheramine M2005 chains onto the surface of CNCs. The resulting polymer-decorated particles (M2005-g-CNCs) exhibited new colloidal properties, by their ability to perfectly redisperse in water and organic solvents such as toluene, dichloromethane or DMF after freeze-drying. In addition, they presented an enhanced thermal stability when compared to that of sulfated or TEMPO-oxidized CNCs. Dynamic light scattering experiments were used to demonstrate that the thermally induced aggregation of M2005-g-CNCs was fully reversible and reproducible over many temperature cycles and that, most interestingly, the aggregation number could be tuned by varying the ionic strength and/or the pH of the medium, making the suspension multiresponsive. This property arises from the variations of the sign (attractive or repulsive) and the range of the different types (entropic, electrostatic, hydrophobic) of interaction forces between the thermosensitive polymer-decorated nanoparticles. The variation of the viscoelastic properties of M2005-g-CNCs suspensions as a function of temperature, probed by oscillatory rheology measurements of more concentrated suspensions, revealed a reversible temperature-triggered liquid-to-gel transition. Such enhanced functionalities pave the way to the design of advanced CNC-based materials benefiting both from the intrinsic characteristics of these biosourced particles and the new properties imparted by the stimuli-sensitive grafted chains.
