3. Materials and methods

#### 3.1. Wet-spinning of hydrogels fibers

Wet-spun chitosan fibers were produced in a coagulation bath consisting of 1 M sodium hydroxide (NaOH) using a rotary wet-spinning system. Uniform alginate fibers were spun in a 2% CaCl2 coagulation bath. Core-sheath fibers of chitosan-alginate (Chit-Alg) were successfully spun using a coaxial spinneret. The chitosan spinning solution (with different amounts of CaCl2) was injected as the core component and extruded through the center nozzle into the coagulation bath of calcium chloride [11]. Simultaneously, alginate was injected as sheath of the fiber, providing an outer casing for the core, by injection through port A. In this method, by using a blend of chitosan with various percentages of calcium chloride, it is possible that the alginate sheath can be coagulated from the inner chitosan core, while also creating the opportunity to react chitosan with sodium alginate at a much faster rate [1]. The setup is shown in Figure 4, previously. Therefore, as mentioned earlier chitosan solutions including 0.5, 1 and 2% (w v<sup>1</sup> ) CaCl2 were prepared for the core component of the fibers and alginate sheath. The samples are named here as Chit-Alg (0.5), Chit-Alg (1) and Chit-Alg (2). Solutions were delivered at flow rates of 14 mL h<sup>1</sup> for chitosan and 25 mL h<sup>1</sup> for the sheath [11].

have been reported for chitosan varying from 2 to 15% (w v<sup>1</sup>

wet-spinning; increasing the alginate concentration from 2 to 4% (w v<sup>1</sup>

highly spinnable [1]. Then again, at concentrations above 4% (w v<sup>1</sup>

a concentration of below 2% (w v<sup>1</sup>

for coaxial wet-spinning [1].

solutions of 3% (w v<sup>1</sup>

Copyright 2015, Wiley-VCH.

4.2. Rheology

of 3% (w v<sup>1</sup>

unspinnable. A concentration of 3% (w v<sup>1</sup>

mined from aqueous solutions of chitosan at 3% (w v<sup>1</sup>

) is the appropriate concentration range enabling wet-spinning of MMW chitosan into a coagulation bath of 1 M NaOH. Observations also indicated that aqueous alginate solutions at

highly viscous which imped continuous flow through the needle, rendering the solution

due to the ease of spinnability, together with maintaining the suitable mechanical properties

Viscosity is considered in the selection of suitable concentrations of chitosan and alginate solutions for fiber spinning. For coaxial spinning matching viscosities of the two components is also a consideration [1]. Figure 5 shows changes in viscosity versus shear rate was deter-

solutions became closer as the shear rate increased. Under shear, hydrogel chains are in a less expanded conformation and become less entangled causing the viscosity to drop. At the time of spinning, chitosan is injected with rate of 14 mL h<sup>1</sup> while is 25 mL h<sup>1</sup> for the alginate solution. The shear rates calculated to be about 97 s<sup>1</sup> for alginate and 75 s<sup>1</sup> for chitosan

Figure 5. Viscosities of spinning solutions of chitosan and sodium alginate [11]. Reproduced with permission. 158

(w v<sup>1</sup>

). Here, we found that 2–5%

http://dx.doi.org/10.5772/intechopen.74188

), the solution became

Hydrogels Fibers

129

), the solution became

). Spinning

) would not generate a continuous fibrous structure via

) has been thus selected for both gel precursors

) and alginate at 3% (w v<sup>1</sup>

) chitosan resulted in a solution with a viscosity of 6.4 Pas. The viscosity

) sodium alginate solution was approximately 8.5 Pas. The viscosities of the two

Toluidine blue (TB) was used as an indicative dye incorporated into the coaxial fibers to track the release experiment. For the purpose of fiber preparation for release experiments, the dye was mixed with chitosan solution before spinning with the concentration of 0.1% (w v<sup>1</sup> ) and then injected as the core component. These solutions were then spun into the same coagulation baths which were previously used to make pristine fibers. Coaxial fibers containing TB were also fabricated using the method mentioned previously with the small difference of using chitosan/TB solution as the core component [11].

#### 3.2. Toluidine blue release measurement

The release kinetics of the prepared fibers for drug release applications was studied using TB as a model dye introduced into the fibers over a 5-day period. The amount of released TB was determined via UV-vis spectroscopy by monitoring the absorption of TB at its λmax 630 nm in simulated body fluid (SBF). To construct an absorbance calibration curve for sample analysis using a Shimadzu UV 1601 spectrophotometer, UV-vis spectra of SBF solutions containing TB with different concentrations were recorded between 200 nm and 1100 nm. Approximately 5 cm of each dried sample (in triplicate) was placed in a 2 mL Eppendorf tube and 1 mL of SBF was added into it. The release medium was taken by micro-pipette at specific time points over 5 days and replaced with the same volume of fresh SBF solution to maintain the total volume constant. The percentage of released TB (%) was plotted versus time [11].
