Development of the chitosan tube prepared from crab tendon for nerve regeneration

Crystalline chitosan was successfully prepared from crab tendons with aligned chitin molecules. Chitosan obtained preserved the tube structure with a suitable size for nerve conduits (t-chitosan tube). The chitosan tubes were compounded with hydroxy apatite (HAp) using an alternate soaking method (t-chitosan/HAp tube) to enhance the strength of the tube walls. HAp crystals formed in the walls of the chitosan tubes, and their c-axis aligned well in parallel with the chitosan molecules. The growth of the HAp crystals was found to occur at the nucleation sites, most probably by forming complexes with amino groups on chitosan mediated by Ca ions. Furthermore, these tubes were treated at 120 °C to prevent from swelling. These treatments preserved well the hollow nature of the tubes. And the mechanical test showed that the force was significantly higher in the t-chitosan/HAp tube when compared to the circular or triangular t-chitosan tube at each strain.Bridge grafting (15 mm) into the sciatic nerve of SD rats was carried out using the t-chitosan tubes having either a circular or triangular cross-section as well as t-chitosan/HAp tubes (N=18 in each group). Specimens were taken after two, four, six and eight weeks for histology (N=3 in each group). And nerve regeneration was evaluated histologically after 12 weeks (N=6 in each group). The t-chitosan/HAp tubes, demonstrated preferable biodegradation and biocompatibility. In addition to the mechanical properties of the tubes, the results of histological findings suggest that a triangular shape of the tube's cross-section and HAp coating may benefit nerve regeneration.     

Cross-linked quaternary chitosan as an adsorbent for the removal of the reactive dye from aqueous solutions

Adsorption of reactive orange 16 by quaternary chitosan salt (QCS) was used as a model to demonstrate the removal of reactive dyes from textile effluents. The polymer was characterized by infrared (IR), energy dispersive X-ray spectrometry (EDXS) analyses and amount of quaternary ammonium groups. The adsorption experiments were conducted at different pH values and initial dye concentrations. Adsorption was shown to be independent of solution pH. Three kinetic adsorption models were tested: pseudo-first-order, pseudo-second-order and intraparticle diffusion. The experimental data best fitted the pseudo-second-order model, which provided a constant velocity, k₂, of 9.18 × 10⁻⁴ g mg⁻¹ min⁻¹ for a 500 mg L⁻¹ solution and a value of k₂, of 2.70 × 10⁻⁵ g mg⁻¹ min⁻¹ for a 1000 mg L⁻¹ solution. The adsorption rate was dependent on dye concentration at the surface of the adsorbent for each time period and on the amount of dye adsorbed. The Langmuir isotherm model provided the best fit to the equilibrium data in the concentration range investigated and from the isotherm linear equation, the maximum adsorption capacity determined was 1060 mg of reactive dye per gram of adsorbent, corresponding to 75% occupation of the adsorption sites. The results obtained demonstrate that the adsorbent material could be utilized to remove dyes from textile effluents independent of the pH of the aqueous medium.