Study of Cellulose Nanocrystals and Zinc Nitrate Hexahydrate Addition in Chitosan Hydrogels

Abstract

In this study, chitosan hydrogels were produced with 0, 2, 4 and 6 wt% of cellulose nanocrystals (CNC) using hexahydrate zinc nitrate (Zn(NO 3) 2 .6H 2 O) as a catalyst for chitosan crosslinking reaction. CNC´s size was estimated by dynamic light scattering (DLS) and surface charge by zeta potential. Hydrogels were characterized by rotational rheometer, swelling test, uniaxial compression test, in vitro degradation, scanning electron microscopy (SEM) and microtomography. Results showed that zinc nitrate and CNC addition did not influence mechanical properties, degradation, and morphology of the hydrogels. However, zinc nitrate decreased 36.54% of the gel time and 41.37% of the swelling degree, and increased the crosslinking degree of the chitosan hydrogels, proving not only its catalytic effect but also its participation in the crosslinking reaction. Porosity was slightly reduced after addition of zinc nitrate and incorporation of CNC. In the mechanism of crosslinking reaction, a competition between CNC and zinc nitrate was observed.

Chitosan Hydrogels Crosslinked by Genipin and Reinforced with Cellulose Nanocrystals: Production and Characterization

“…The porosity values of hydrogels with 0, 2, and 4 wt % CNC were about 69, 79, and 77, respectively. These values are similar to those reported for chitosan hydrogels with different crosslinkers and for hydrogels resulting from a combination of chitosan with other polymers [8,[33][34][35]. For example, Carvalho and Mansur [35] reported porosity values of 69% to 88% for methacrylamide-chitosan hydrogels.…”

“…Therefore, the simultaneous crosslinking processes, one from the reaction between genipin and chitosan and the other from the ionic interaction with CNC, resulted in the lower porosity. In the work of Ferreira et al [8], the effect of CNC addition was less drastic since the chitosan hydrogel analyzed by them was obtained through crosslinking reaction with glutaraldehyde, which is known to be a more efficient crosslinker than genipin. Therefore, in their samples, there was lower availability of protonated amino groups of chitosan to interact with CNC.…”

“…Thus, although no statistical difference was observed for this value compared to the others, a tendency of decreasing porosity is observed with increasing CNC content. It is well known that the addition of nanofillers to a hydrogel may decrease the porosity [1,8,33]. Montanheiro et al [1] reported a decrease of ~20% in the poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) scaffolds porosity due to the addition of 3% (wt %) of CNC.…”

“…Montanheiro et al [1] reported a decrease of ~20% in the poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) scaffolds porosity due to the addition of 3% (wt %) of CNC. Ferreira et al [8] showed a decrease in chitosan hydrogel porosity from 88% to 82.4% upon the addition of 6% (wt %) of CNC. Herein, a similar ratio of chitosan to CNC resulted in a more significant decrease of porosity.…”

“…Hydrogels may be produced from synthetic polymers such as polyacrylamide (PAM) [7] or natural polymers, such as chitosan, among others [8][9][10][11]. The great advantage in the use of natural polymers is the ability to interact with cells and cellular enzymes and to be remodeled and/or degraded to provide a place for tissue growth [12].…”