Ang Lu

Intermolecular Interaction and the Extended Wormlike Chain Conformation of Chitin in NaOH/Urea Aqueous Solution

The intra- and intermolecular interactions of chitin in NaOH/urea aqueous system were studied by a combination of NMR measurements (including (13)C NMR, (23)Na NMR, and (15)N NMR) and differential scanning calorimetry. The results revealed that the NaOH and chitin formed a hydrogen-bonded complex that was surrounded by the urea hydrates to form a sheath-like structure, leading to the good dissolution. The optimal concentration range, in which chitin was molecularly dispersed in NaOH/urea aqueous, was found to investigate the chain conformation in the dilute solution with a combination of static and dynamic light scattering. The weight-average molecular weight (Mw), radii of gyration (⟨Rg⟩z), and hydrodynamic radii (⟨Rh⟩z) values of chitin were determined, and the structure-sensitive parameter (ρ) and persistent length (Lp) were calculated to be >2.0 and ∼30 nm, respectively, suggesting an extended wormlike chain conformation. The visualized images from TEM, cryo-TEM, and AFM indicated that, chitin nanofibers were fabricated from the parallel aggregation of chitin chains in NaOH/urea system. This work would provide a theoretical guidance for constructing novel chitin-based nanomaterials via bottom-up method at the molecular level.

Effects of Chitin Whiskers on Physical Properties and Osteoblast Culture of Alginate Based Nanocomposite Hydrogels

Novel nanocomposite hydrogels composed of polyelectrolytes alginate and chitin whiskers with biocompatibility were successfully fabricated based on the pH-induced charge shifting behavior of chitin whiskers. The chitin whiskers with mean length and width of 300 and 20 nm were uniformly dispersed in negatively charged sodium alginate aqueous solution, leading to the formation of the homogeneous nanocomposite hydrogels. The experimental results indicated that their mechanical properties were significantly improved compared to alginate hydrogel and the swelling trends were inhibited as a result of the strong electrostatic interactions between the chitin whiskers and alginate. The nanocomposite hydrogels exhibited certain crystallinity and hierarchical structure with nanoscale chitin whiskers, similar to the structure of the native extracellular matrix. Moreover, the nanocomposite hydrogels were successfully applied as bone scaffolds for MC3T3-E1 osteoblast cells, showing their excellent biocompatibility and low cytotoxicity. The results of fluorescent micrographs and scanning electronic microscope (SEM) images revealed that the addition of chitin whiskers into the nanocomposite hydrogels markedly promoted the cell adhesion and proliferation of the osteoblast cells. The biocompatible nanocomposite hydrogels have potential application in bone tissue engineering.

Dissolution of cellulose from different sources in an NaOH/urea aqueous system at low temperature

AbstractThe dissolution of different cellulose pulps from different sources such as wood, bamboo and ramie pulp in 7xa0wt% NaOH/12xa0wt% urea aqueous solution was investigated in the present article, as well as the structure and properties of the resultant regenerated films. All of the cellulose samples with molecular weight below 1.2xa0×xa0105 could be quickly and completely dissolved in NaOH/urea aqueous solution precooled to −12.5xa0°C in 2xa0min, regardless of the cellulose source, indicating the universality of cellulose dissolution in NaOH/urea solvent. The resultant cellulose solutions exhibited similar rheological behaviors, indicating a similar solution procedure of cellulose in NaOH/urea. These regenerated cellulose films exhibited similar structures and morphologies according to the results of the scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy analyses, indicating a microporous structure with a pore diameter ranging from 100 to 300xa0nm, as well as a complete transition from cellulose I to cellulose II after the dissolution and regeneration process. Furthermore, all of the films had good mechanical properties and light transmittance as a result of the homogeneous structure. In view of the results mentioned above, the NaOH/urea solvent system displayed a strong cellulose dissolving capacity, exhibiting great potential for the further development and comprehensive utilization of cellulose from agricultural and forestry wastes. It is capable of increasing the applications of cellulose and has potential for further development.n

Characterization of new sorbent constructed from Fe 3 O 4 /chitin magnetic beads for the dynamic adsorption of Cd 2+ ions

Novel magnetic chitin (CM) beads were successfully prepared by in situ synthesis of Fe3O4 nanoparticles in regenerated chitin beads (Ch beads) for the packing fixed-bed columns. The interpenetrated porous structure in the regenerated Ch beads at the swollen state served as templates for the inorganic nanoparticle preparation. The morphology and structure of the hybrid nanomaterials were characterized with scanning transmission electron microscopy, transmission electron microscopy, thermal gravimetry analysis, X-ray diffraction, and Fourier transform infrared spectroscopy, and the Cd2+ ion adsorption capacity of the CM beads was determined by UV–Vis spectrophotometry. The results revealed that the CM beads exhibited efficient adsorption of Cd2+ ions in the aqueous solution, as a result of the microporous structure, large surface area, and affinity for metal ions. The equilibrium process of this fixed-bed column was well described by Thomas and Bohart–Adams model, indicating that the external mass transfer was the rate-limiting process at the beginning of adsorption. The adsorption equilibrium was better described by the bed depth–service time model, indicating that the Cd2+ uptake could be controlled by external mass transfer at the beginning and intraparticle diffusion at a later stage of the adsorption. The CM beads loaded with the Cd2+ could be regenerated and reused easily. The CM beads should have potential applications in the chromatography packing and adsorbent both at the laboratory and industrial scales.

Rheological behaviors and miscibility of mixture solution of polyaniline and cellulose dissolved in an aqueous system.

In our previous work, supramolecular films composed of hydrophilic cellulose and hydrophobic polyaniline (PANI) dissolved in NaOH/urea aqueous solution at low temperature through rearrangement of hydrogen bonds have been constructed. To further understand the miscibility and processability of the complex solution, the dynamic rheological behaviors of the PANI/cellulose complex solution were investigated, for the first time, in the present work. Transmission electron microscope (TEM) results demonstrated that the inclusion complexes consisted of PANI and cellulose, existed in the aqueous solution, showing a good miscibility. Time-temperatures superposition (tTs) results indicated that the PANI/cellulose solution exhibited a homogeneous system, and the complex solution was more stable than the cellulose solution in the temperature range from 5 to 25 °C. Winter-Chambon theory was proved to be capable of describing the gelation behavior of the PANI/cellulose complex solution. The relaxation exponent at the gel point was calculated to be 0.74, lower than the cellulose solution, indicating strong interactions between PANI and cellulose chains. Relatively larger flow activation energy of the PANI/cellulose solution suggested the formation and rupture of linkages in junction zones during the gelation processes. Furthermore, PANI/cellulose gels could form at elevated temperature as a result of the physical cross-linking and chain entanglement, and it was a thermoirreversible process. Moreover, the PANI/cellulose solution remained a liquid state for a long time at the temperature range from 0 to 8 °C, which is important for the industry process.

Swelling behaviors of superabsorbent chitin/ carboxymethylcellulose hydrogels

Novel superabsorbent chitin/carboxymethylcellulose (CMC) hydrogels were successfully prepared from mixture of CMC and chitin solution dissolved in 8xa0wt% NaOH/4xa0wt% urea aqueous system at low temperature by crosslinking with epichlorohydrin. The morphology and structure of the resultant composite hydrogels were investigated by scanning electron microscope, thermogravimetry, and Fourier transform infrared spectroscopy. The results indicated that the stiff chains of chitin are as a strong backbone in the hydrogel to support the pore wall, whereas the CMC contributed to water absorption. The maximum swelling ratio in water reached an exciting level of 1300 as the hydrogels still kept an intact appearance. Moreover, the hydrogels exhibited smart swelling and shrinking behaviors in NaCl and CaCl2 aqueous solution, showing salt-responsive adsorption behaviors in different media. This work provided a “green” pathway to prepare chitin-based superabsorbent hydrogels, which would be potential for the application in the biodegradable water-absorbent material field.

Gelation behavior of cellulose in NaOH/urea aqueous system via cross-linking

Sol–gel transition of cellulose solution in NaOH/urea aqueous solution with the addition of epichlorohydrin (ECH) was investigated by rheological means. The gelation was controlled by a synergy of chemical and physical cross-linking processes, namely, the etherification reaction between cellulose and ECH as well as the self-association and entanglement of cellulose chains via hydrogen bonding re-construction in NaOH/urea. The results revealed that the cross-linker concentration, cellulose concentration and temperature played important roles in the gelation behavior. The gel time decreased with increasing either ECH or cellulose concentration, and the gel temperature dropped from 38 to 28xa0°C with an increase of cellulose concentration from 4 to 6xa0wt%, i. e. easier gelation was reached with higher cross-linker concentration, cellulose concentration or temperature, since higher cross-linker or cellulose concentration led to more network junctions via chemical or physical cross-linking, while higher temperature was favorable to both the etherification reaction and re-construction of cellulose hydrogen bonds. The compressive modulus of cellulose/ECH hydrogels was improved a lot by increasing either cellulose or ECH concentration, indicating the chemical cross-linking obviously improved the mechanical property, on the other hand, the swelling property could be tunable by changing the gelation parameter. This work supplied useful information to the control and optimization of the structure and properties of cellulose based hydrogels.

Stability of inclusion complex formed by cellulose in NaOH/urea aqueous solution at low temperature

Cellulose has been demonstrated to be dissolved in 7 wt% NaOH/12 wt% urea aqueous solution pre-cooled to -12 °C, as a result of the formation of inclusion complexes (ICs) associated with cellulose, urea and NaOH. However, this cellulose solution is meta-stable, and IC aggregate could form. In this work, the influences of solvent composition and temperature on the stability of the cellulose ICs in NaOH/urea aqueous solvent system were investigated by dynamic and static light scattering. The stability of cellulose ICs in NaOH/urea aqueous solvent system was firstly enhanced and then lessened with NaOH concentration increasing. The addition of urea slightly enhanced the stability of ICs. Furthermore, the solvent composition had been optimized to reduce the aggregation phenomenon of ICs. The proportion of single cellulose ICs in 9 wt% NaOH/13 wt% urea system increased to 0.96, indicating a stable and better dispersion system of the cellulose ICs. Moreover, temperature exhibited great effect on the IC stability. The molecular weight of cellulose in 9 wt% NaOH/13 wt% urea system at 10 °C reached a low value about 7.6×10(4) g/mol and the single cellulose ICs were predominant species in this case. This work provided a better pathway to characterize the dilute cellulose in NaOH/urea aqueous solution, in which the single cellulose ICs were predominant species.

Construction of blood compatible lysine-immobilized chitin/carbon nanotube microspheres and potential applications for blood purified therapy

Excess bilirubin often evokes hepatobiliary system dysfunction. In the present work, we developed an efficient, safe and blood compatible adsorbent for bilirubin removal from human blood. In view of the highly effective adsorption of carbon nanotubes (CNTs) on bilirubin but with many side effects, and good biocompatibility of chitin but with low efficiency for bilirubin removal, new chitin/carbon nanotube (Ch/CNT) nanofibrous microspheres were constructed from chitin solution in NaOH/urea aqueous system by blending with CNTs. The results of AFM, SEM, and TEM demonstrated that the CNTs were dispersed well in the chitin matrix, and the chitin nanofibers intertwined with CNTs to form hybrid chitin/CNT nanofibers and then weaved into a 3D interconnected network architecture. Moreover, lysine (Lys), a highly specific ligand for bilirubin, was immobilized tightly to the hybrid microspheres to obtain Ch/CNT/Lys. The resultant microspheres possessed large surface area and hierarchical pores including mesopores and micropores, which could allow bilirubin to enter easily and store, leading to highly efficient adsorption. The Ch/CNT/Lys microspheres exhibited excellent bilirubin adsorption property (107.2 mg g-1) and efficient bilirubin clearance rate from real hyperbilirubinemia plasma competing with protein, as well as good cell affinity and blood compatibility, as a result of the combination of the high adsorption of CNTs and inherent biocompatibility of chitin and lysine. Therefore, an effective strategy to develop a novel biocompatible and blood compatible bilirubin adsorbent is provided, showing potential applications for hemoperfusion in blood purified therapy.

Biocompatible chitin/carbon nanotubes composite hydrogels as neuronal growth substrates

In the past decades, extensive studies have demonstrated that carbon nanotubes (CNTs) could promote cell adhesion, proliferation and differentiation of neuronal cells. However, the potential cytotoxicity in biological systems severely restricted the utilization of CNTs as substrates for neural growth. In this study, biocompatible chitin/carbon nanotubes (Ch/CNT) composite hydrogels were developed via blending modified CNTs with chitin solution in 11wt% NaOH/4wt% urea aqueous system, and subsequently regenerating in ethanol. As the CNTs were dispersed homogeneously in chitin matrix and combined with chitin nanofibers to form a compact and neat Ch/CNT nanofibrous network through intermolecular interactions, such as electrostatic interactions, hydrogen bonding and amphiphilic interaction, etc. The tensile strength and elongation at break of the Ch/CNT composite hydrogels were obviously enhanced, and the swelling ratio decreased. In addition, the Ch/CNT hydrogels exhibited good hemocompatibility, biodegradation in vitro and biocompatibility without cytotoxicity and neurotoxicity nature to neuronal and Schwann cells (PC12 cells and RSC96 cells). Especially, the Ch/CNT3 composite hydrogels exhibited significant enhancement of the neuronal cell adhesion, proliferation and neurite outgrowth of neuronal cells with a great increase in both the percentage and the length of neurites. Therefore, we provide a simple and efficient approach to construct the novel Ch/CNT hydrogels as neuronal growth substrates for the potential application in nerve regeneration.