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The development of non-cellularized composites of chitosan (CHI) hydrogels, filled with cellulose nanofibers (CNFs) of the type nanofibrillated cellulose, was proposed for the repair and regeneration of the intervertebral disc (IVD) annulus fibrosus (AF) tissue. With the achievement of CNF-filled CHI hydrogels, biomaterial-based implants were designed to restore damaged/degenerated discs. The structural, mechanical and biological properties of the developed hydrogel composites were investigated. The neutralization of weakly acidic aqueous CNF/CHI viscous suspensions in NaOH yielded composites of physical hydrogels in which the cellulose nanofibers reinforced the CHI matrix, as investigated by means of microtensile testing under controlled humidity. We assessed the suitability of the achieved biomaterials for intervertebral disc tissue engineering in ex vivo experiments using spine pig models. Cellulose nanofiber-filled chitosan hydrogels can be used as implants in AF tissue defects to restore IVD biomechanics and constitute contention patches against disc nucleus protrusion while serving as support for IVD regeneration.

SYNOPSISThe adsorption of mercuric ions by chitosan was investigated. The study of the adsorption kinetics shows that the rate of adsorption of mercuric ions on chitosan can be interpreted in terms of intraparticle diffusion as the rate-limiting step. The experimental data of adsorption equilibrium from mercuric chloride solutions correlate well with the Langmuir isotherm equation, although at high-solute concentrations, a multilayer type of adsorption with the subsequent increase in the uptake is observed. Column experiment confirms the ability of chitosan for the removal of mercuric ions from solutions in the absence of a high concentration of chlorides.

The heterogeneous hydrolysis of fully deacetylated chitosan solid samples was carried out with concentrated HCl. The hydrolysis kinetics was studied at different temperatures and HCl concentrations. From 5 to 50 degrees C in the hydrolysis time range up to 50 h, a monomodal distribution of molecular weights was observed connected to the only degradation of amorphous domains. Between 70 and 90 degrees C and for the hydrolysis longest times, a multimodal distribution appeared with the additional hydrolysis of the crystalline phase. The crystallinity index increased from 57 to 73% with the elimination and partial recrystallization of amorphous regions. X-ray diffraction patterns revealed the presence of the anhydrous polymorph, absent in the starting materials only containing the hydrated polymorph. The apparent crystallite width (from the Scherrer equation) of both the anhydrous and hydrated allomorphs did not vary significantly with time despite the increase in the fraction of anhydrous allomorph. Therefore, the hydrolysis in the solid state was complex, revealing several regimes. The activation energy parameters were deduced, and the mechanisms were discussed.

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