Chitin, Chitosan, and Alginate Fibers

Keywords

Metal sorption • Catalysis support • Tubular scaffold • Nerve tissue engineering

Hollow chitosan fibers (Fig. 27.1) were fabricated by removing unprecipitated chitosan through air and water flow [01Vin, 08Ara]. These hollow fibers have been used for various applications. For instance, hollow chitosan fibers were used to extract Cr(VI) with aliquot 336 by assembling the hollow fibers into a module and circulating the metal ion solution and extract inside the hollow lumen. It was observed that Cr(VI) ions were sorbed on the fiber and also by solvent which flowed through the fiber. Reacetylation of the fiber maintained the efficiency of extraction and also increased the mechanical and chemical resistance [01Vin]. Hollow chitosan fibers supported with palladium were also used to degrade nitrophenol found in industrial waste waters [04Vin]. A sodium formate system and a hydrogen system were used, and the former was found to be more efficient. Experimental parameters such as residence time, recycling, and concentration of the chemicals were reported to determine the efficiency of degradation. Similarly, palladium — supported chitosan fibers were also used as a catalytic system for hydrogenation of nitrotoluene [08Blo]. The diffusion of biological agents such as tryptophan, chlor­amphenicol, amoxicillin, and vitamin B12 through hollow chitosan fibers was investigated to understand the potential of using the fibers as nerve guide channels [08Pei]. pH of the permeant was found to have the most significant impact on permeability with the permeability coefficient decreasing with the molecular weight of the permeant. These fibers were considered suitable for catalysis and support for biological molecules or enzymes or for controlled drug release and enzyme immobilization [08Pei]. Hollow chitosan/cellulose acetate fibers were produced by wet spinning for use as absorptive membranes for affinity-based separations [05Liu]. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) studies showed interactions between cellulose acetate and chitosan. Blend fibers had good tensile properties and showed high surface absorption for copper

ions and bovine serum albumin [05Liu]. Absorption of copper up to 30 mg/g of chitosan and 8 mg/g of bovine serum albumin was obtained.

Porous chitosan tubular scaffolds for nerve tissue engineering were developed by knitting and lyophilizing. Chitosan fibers were knitted into tubes into which mandrels (acupuncture needles) were inserted, and the assembly was later dipped in a chitosan solution and lyophilized. The freeze-dried samples were immersed in NaOH solution and then neutralized with acetic acid, and the mandrels were then removed to obtain the hollow structures [06Wan]. Figure 27.2 shows a digital image of the hollow tubular scaffolds produced, and Fig. 27.3 shows the SEM image of the highly porous matrix with axially oriented microchannels. Scaffolds developed had an average porosity of 68.8 %, and the total pores were 0.031 m2/g. It was also found that the inner surface of the scaffold was about 30 times higher than that of the hollow tubes. Neuro-2a cells cocultured on the scaffolds showed confluent cell growth, 5 days after incubation. Extensive growth of the cells oriented along the scaffold in the channel and bridging between the cells was observed as seen in Fig. 27.3. In a continuation of this work, porous fiber-reinforced nerve conduits were fabricated from chitosan yarns using braiding, casting, and lyophilization. Conduits developed were permeable to glucose (180 Da) and to bovine serum albumin (66,200 Da) and had tensile strength of about 3.4 MPa

(0.03 g/den). In vitro and in vivo studies showed that the conduits were compatible with the tissues and suitable for medical applications [07Wan].

Composite fibers composed of chitosan (2 x 105 Mw; 76 % deacetylation), and carbon nanotubes were developed via wet spinning. CNTs (0.7-1.3 nm in diameter and several micrometers in length) dispersed in chitosan solution were extruded into an ethanol-NaOH coagulation bath. Fibers obtained were cross-linked with 25 % glutaraldehyde to improve performance properties [06Spi]. Fibers obtained after centrifuging did not show any aggregation of the CNTs and resulted in fibers with smooth surfaces. CNT-reinforced fibers had considerably low elongation of 10-14 % compared to 24 % for the neat chitosan fibers. However, the CNT-containing fibers had a modulus of 77 g/den compared to 32 g/den for the neat chitosan fibers. In the swollen state, the CNT-reinforced fibers showed higher elongation but lower strength compared to their properties in the dry state. The swollen microfiber gel was reported to have strength of 0.4 g/den similar to that of the pure chitosan fibers.

References

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