4. Results and discussion

Initial investigations were aimed at determining the spinnability and the physical characteristics of potential dopes to ensure they were in the range required for fiber formation.

#### 4.1. Spinnability vs. concentration

Spinnability can be defined as the ability of a material of being suitable for spinning or the capability of being spun. In the context of wet-spinning, spinnability could be referred to the ability of a solution to form fibrillar arrangements via injection into a non-solvent medium which makes it precipitate, so-called a coagulation bath [16]. The spinnability of a polymer solution depends on many parameters, including the rheological properties of a solution, size of nozzle, shear rate applied during injection through spinneret and mass transfer rate difference between the extruded solution and non-solvent. Several types of either suitable solvent or coagulant could be employed depending on the chemical structure of material. Often an upper and lower limit for polymer concentration during wet-spinning is considered facilitates spinning continuous length of fibers. The capillary break-up is widely understood as a surfacetension induced break-up of filaments into drops can occur at low concentrations of the polymer solution which determines the lower limit of spinnability. Spinnable concentrations have been reported for chitosan varying from 2 to 15% (w v<sup>1</sup> ). Here, we found that 2–5% (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 a concentration of below 2% (w v<sup>1</sup> ) would not generate a continuous fibrous structure via wet-spinning; increasing the alginate concentration from 2 to 4% (w v<sup>1</sup> ), the solution became highly spinnable [1]. Then again, at concentrations above 4% (w v<sup>1</sup> ), the solution became highly viscous which imped continuous flow through the needle, rendering the solution unspinnable. A concentration of 3% (w v<sup>1</sup> ) has been thus selected for both gel precursors due to the ease of spinnability, together with maintaining the suitable mechanical properties for coaxial wet-spinning [1].

#### 4.2. Rheology

) and

samples are named here as Chit-Alg (0.5), Chit-Alg (1) and Chit-Alg (2). Solutions were

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>

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

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

Initial investigations were aimed at determining the spinnability and the physical characteris-

Spinnability can be defined as the ability of a material of being suitable for spinning or the capability of being spun. In the context of wet-spinning, spinnability could be referred to the ability of a solution to form fibrillar arrangements via injection into a non-solvent medium which makes it precipitate, so-called a coagulation bath [16]. The spinnability of a polymer solution depends on many parameters, including the rheological properties of a solution, size of nozzle, shear rate applied during injection through spinneret and mass transfer rate difference between the extruded solution and non-solvent. Several types of either suitable solvent or coagulant could be employed depending on the chemical structure of material. Often an upper and lower limit for polymer concentration during wet-spinning is considered facilitates spinning continuous length of fibers. The capillary break-up is widely understood as a surfacetension induced break-up of filaments into drops can occur at low concentrations of the polymer solution which determines the lower limit of spinnability. Spinnable concentrations

tics of potential dopes to ensure they were in the range required for fiber formation.

constant. The percentage of released TB (%) was plotted versus time [11].

delivered at flow rates of 14 mL h<sup>1</sup> for chitosan and 25 mL h<sup>1</sup> for the sheath [11].

chitosan/TB solution as the core component [11].

3.2. Toluidine blue release measurement

128 Hydrogels

4. Results and discussion

4.1. Spinnability vs. concentration

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 determined from aqueous solutions of chitosan at 3% (w v<sup>1</sup> ) and alginate at 3% (w v<sup>1</sup> ). Spinning solutions of 3% (w v<sup>1</sup> ) chitosan resulted in a solution with a viscosity of 6.4 Pas. The viscosity of 3% (w v<sup>1</sup> ) sodium alginate solution was approximately 8.5 Pas. The viscosities of the two 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 Copyright 2015, Wiley-VCH.

solutions which resulted in a viscosity of 2.5 Pas for chitosan and 2.8 Pas for alginate solutions. These outcomes seem to be ideal for coaxial spinning [1].

4.4. Morphology of As-prepared fibers

are shown in Figure 8 in wet and dry-states.

The stereomicroscope images of wet-spun chitosan, alginate and core-sheath Chit/Alg fibers

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As can be seen in Figure 8 (a) and (b), the surface of the chitosan fiber seemed to be very smooth and soft, while some wrinkles can be noticed spreading on the surface of the alginate fiber which will be increased during the fiber drying process [1]. Moreover, one can see that the

Figure 8. Stereomicroscope images of side view of wet (a) alginate, (b) chitosan, (c) coaxial Chit-Alg (1) and (b) dry Chit-

Alg (1) fiber. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

#### 4.3. Continuous spinning of coaxial fibers

To produce continuous uniform fibers, chitosan with injection rate of 14 mL h<sup>1</sup> and alginate solution with rate of 25 mL h<sup>1</sup> have been simultaneously injected into the 2% (w v<sup>1</sup> ) aqueous CaCl2 coagulation bath through the ports built in the coaxial spinneret [11]. Using this method, an unlimited length of fibers could be obtained which was collected using a collector as shown in Figure 6. It is worth mention that the preparation of coaxial fibers without incorporating a certain amount of CaCl2 did not turn out to be successful when tried.

The woven structure of Chit-Alg fibers (containing TB) in dry and wet state were shown in Figure 7 (a) and (b), respectively. This capability provides the potential for these structures to be utilized as tissue scaffolds and drug delivery vehicle applications [11].

Figure 6. The capability of producing unlimited length of coaxial Chit-Alg (1) fibers as shown onto a collector. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

Figure 7. The photographs of scaffold structure woven by coaxial fibers; imaged in (a) dry state and (b) wet state. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

#### 4.4. Morphology of As-prepared fibers

solutions which resulted in a viscosity of 2.5 Pas for chitosan and 2.8 Pas for alginate

To produce continuous uniform fibers, chitosan with injection rate of 14 mL h<sup>1</sup> and alginate

CaCl2 coagulation bath through the ports built in the coaxial spinneret [11]. Using this method, an unlimited length of fibers could be obtained which was collected using a collector as shown in Figure 6. It is worth mention that the preparation of coaxial fibers without incorporating a

The woven structure of Chit-Alg fibers (containing TB) in dry and wet state were shown in Figure 7 (a) and (b), respectively. This capability provides the potential for these structures to

Figure 6. The capability of producing unlimited length of coaxial Chit-Alg (1) fibers as shown onto a collector. [11]

Figure 7. The photographs of scaffold structure woven by coaxial fibers; imaged in (a) dry state and (b) wet state. [11]

) aqueous

solution with rate of 25 mL h<sup>1</sup> have been simultaneously injected into the 2% (w v<sup>1</sup>

solutions. These outcomes seem to be ideal for coaxial spinning [1].

certain amount of CaCl2 did not turn out to be successful when tried.

be utilized as tissue scaffolds and drug delivery vehicle applications [11].

4.3. Continuous spinning of coaxial fibers

130 Hydrogels

Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

The stereomicroscope images of wet-spun chitosan, alginate and core-sheath Chit/Alg fibers are shown in Figure 8 in wet and dry-states.

As can be seen in Figure 8 (a) and (b), the surface of the chitosan fiber seemed to be very smooth and soft, while some wrinkles can be noticed spreading on the surface of the alginate fiber which will be increased during the fiber drying process [1]. Moreover, one can see that the

Figure 8. Stereomicroscope images of side view of wet (a) alginate, (b) chitosan, (c) coaxial Chit-Alg (1) and (b) dry Chit-Alg (1) fiber. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

core-sheath fibers are straight and smooth with a core loaded in the center of fibers. They have a uniform structure and diameter of ca. 220 μm and 136 μm for the sheath and core when wet, respectively (Figure 8(c)). However, the dried fibers hold the thickness of 140 10 μm (This average value was calculated after measuring the diameter under the stereomicroscope 10 times). In addition, some lines or longitudinal indentations can be observed running parallel with the fibers on totally dried core-sheath fiber as shown in Figure 8 (d). The chitosan core is 90 μm which is surrounded by a thin layer of alginate sheath of 8–12 μm. Still, the thicknesses of core and sheath materials are adjustable by changing solution feed rates and the drawing ratio (data, variables vs. dimensions). Considering two selected collection rates at angular velocities of 20 and 60 rpm (with the assumption of keeping the injection rates constant), it is possible to measure draw ratio upon increasing the collection rate from 20 to 60 rpm while having a constant collector [1].

The fiber diameter decreased as the drawing ratio increased. In general, the molecular orientation of fiber materials obtained through the drawing process governs their properties, particularly the mechanical properties. In addition, the thickness of the sheath would have a direct relationship with increasing its injection rate; the thickness of alginate increased as the shear rate increased while the feeding rate of core component was kept constant. However, while the application of shear is essential in obtaining orientation in the fiber, high shear rates develop beaded non-uniform fiber in the coagulation bath as a result of die swell (swelling of the free jet of solution upon injection from spinneret) and skin formation. Die swell occurs as a consequence of polymer relaxation due to its low entropy conformation after shear is applied during extrusion through the spinneret, where polymer molecules are oriented by the flow. The diameter of the jet then decreases as a result of drawing along the spinning path. A hard skin is also formed on the surface of the filament which results in the rate the jet diameter decreases. When the shear rate of chitosan increased to 20 mL h<sup>1</sup> , formation of the coaxial structure did not turn out to be successful. It seemed that the sheath components were not thick enough to hold the core material in place.

4.5. Mechanical properties of as-prepared fibers

permission. 158 Copyright 2015, Wiley-VCH.

) CaCl2.

modulus and ultimate stress compared to other coaxial fibers [11].

respectively [11].

more than 1% (w v<sup>1</sup>

fibers which contain 1% (w v<sup>1</sup>

The mechanical properties of alginate, chitosan and Chit-Alg coaxial fibers employing different concentrations of calcium chloride in chitosan core spinning dope are depicted in Figure 10. Ultimate stresses (MPa), ultimate strains (%), Young's moduli (MPa) and swelling ratios (%) were measured for alginate, chitosan, Chit-Alg (0.5), Chit-Alg (1) and Chit-Alg (2) fibers,

Figure 9. LV-SEM images of hydrated as-prepared (a) alginate, (b) chitosan and (c) Chit-Alg (1) cross-section in SBF, (d) chitosan core arrangement in cross-section (e) alginate sheath construction in the cross-section. [11] Reproduced with

Mechanical analysis results revealed that with addition of more calcium chloride to the coredope, the Young's modulus decreased. Increasing the amount of calcium chloride into fiber core will probably cause agglomerations which can lead to phase separation. Thus, there would be an upper threshold for the amount of CaCl2 in the core at which the optimum mechanical parameters could be achieved. As a result, the mechanical properties of asprepared fibers such as Young's modulus and ultimate stress were decreased by addition of

The results, which are presented in Table 1, also confirmed the reinforcing role played by the chitosan core in coaxial Chit-Alg fibers. Young's modulus was measured to be ca. 1.7 and 6.6 MPa for alginate and chitosan solid fibers, respectively. It has been also revealed that the

) CaCl2 resulted in the highest mechanical results due to their

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SEM images of cross-sections and the surfaces of solid and core-sheath fibers are illustrated in Figure 9 (a–e). They give valuable information about the morphology of the two polymers. Before imaging fibers were immersed in SBF and imaged with SEM in an attempt to capture structural information in the "wet state", since that is how they would be used in future possible applications [1].

Cross-sections of solid fibers fabricated showed the cylindrical shaped form of the hydrated chitosan and alginate solid fibers (Figure 9 (a) and (b)), respectively. Alginate fibers appeared to be permeable and spongy, while the cross-section of chitosan fibers appeared to be denser. In contrast, cross-sections of the coaxial fibers reveal slightly irregular, oval shaped fibers with a distinct separation between chitosan in the core and the outer alginate sheath as is indicated in Figure 9(c). In addition, both polymers showed an extensive porous structure in the coaxial structure. On the cross-section of chitosan, regular crystalline structures can be seen which are probably due to the presence of calcium chloride inside the core (Figure 9 (d), while alginate has a honeycomb structure (Figure 9 (e)). It is evident that the fiber is composed of two distinct areas of chitosan and alginate [1].

Figure 9. LV-SEM images of hydrated as-prepared (a) alginate, (b) chitosan and (c) Chit-Alg (1) cross-section in SBF, (d) chitosan core arrangement in cross-section (e) alginate sheath construction in the cross-section. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

#### 4.5. Mechanical properties of as-prepared fibers

core-sheath fibers are straight and smooth with a core loaded in the center of fibers. They have a uniform structure and diameter of ca. 220 μm and 136 μm for the sheath and core when wet, respectively (Figure 8(c)). However, the dried fibers hold the thickness of 140 10 μm (This average value was calculated after measuring the diameter under the stereomicroscope 10 times). In addition, some lines or longitudinal indentations can be observed running parallel with the fibers on totally dried core-sheath fiber as shown in Figure 8 (d). The chitosan core is 90 μm which is surrounded by a thin layer of alginate sheath of 8–12 μm. Still, the thicknesses of core and sheath materials are adjustable by changing solution feed rates and the drawing ratio (data, variables vs. dimensions). Considering two selected collection rates at angular velocities of 20 and 60 rpm (with the assumption of keeping the injection rates constant), it is possible to measure draw ratio upon increasing the collection rate from 20 to

The fiber diameter decreased as the drawing ratio increased. In general, the molecular orientation of fiber materials obtained through the drawing process governs their properties, particularly the mechanical properties. In addition, the thickness of the sheath would have a direct relationship with increasing its injection rate; the thickness of alginate increased as the shear rate increased while the feeding rate of core component was kept constant. However, while the application of shear is essential in obtaining orientation in the fiber, high shear rates develop beaded non-uniform fiber in the coagulation bath as a result of die swell (swelling of the free jet of solution upon injection from spinneret) and skin formation. Die swell occurs as a consequence of polymer relaxation due to its low entropy conformation after shear is applied during extrusion through the spinneret, where polymer molecules are oriented by the flow. The diameter of the jet then decreases as a result of drawing along the spinning path. A hard skin is also formed on the surface of the filament which results in the rate the jet diameter decreases.

not turn out to be successful. It seemed that the sheath components were not thick enough to

SEM images of cross-sections and the surfaces of solid and core-sheath fibers are illustrated in Figure 9 (a–e). They give valuable information about the morphology of the two polymers. Before imaging fibers were immersed in SBF and imaged with SEM in an attempt to capture structural information in the "wet state", since that is how they would be used in future

Cross-sections of solid fibers fabricated showed the cylindrical shaped form of the hydrated chitosan and alginate solid fibers (Figure 9 (a) and (b)), respectively. Alginate fibers appeared to be permeable and spongy, while the cross-section of chitosan fibers appeared to be denser. In contrast, cross-sections of the coaxial fibers reveal slightly irregular, oval shaped fibers with a distinct separation between chitosan in the core and the outer alginate sheath as is indicated in Figure 9(c). In addition, both polymers showed an extensive porous structure in the coaxial structure. On the cross-section of chitosan, regular crystalline structures can be seen which are probably due to the presence of calcium chloride inside the core (Figure 9 (d), while alginate has a honeycomb structure (Figure 9 (e)). It is evident that the fiber is composed of two distinct

, formation of the coaxial structure did

60 rpm while having a constant collector [1].

132 Hydrogels

When the shear rate of chitosan increased to 20 mL h<sup>1</sup>

hold the core material in place.

possible applications [1].

areas of chitosan and alginate [1].

The mechanical properties of alginate, chitosan and Chit-Alg coaxial fibers employing different concentrations of calcium chloride in chitosan core spinning dope are depicted in Figure 10. Ultimate stresses (MPa), ultimate strains (%), Young's moduli (MPa) and swelling ratios (%) were measured for alginate, chitosan, Chit-Alg (0.5), Chit-Alg (1) and Chit-Alg (2) fibers, respectively [11].

Mechanical analysis results revealed that with addition of more calcium chloride to the coredope, the Young's modulus decreased. Increasing the amount of calcium chloride into fiber core will probably cause agglomerations which can lead to phase separation. Thus, there would be an upper threshold for the amount of CaCl2 in the core at which the optimum mechanical parameters could be achieved. As a result, the mechanical properties of asprepared fibers such as Young's modulus and ultimate stress were decreased by addition of more than 1% (w v<sup>1</sup> ) CaCl2.

The results, which are presented in Table 1, also confirmed the reinforcing role played by the chitosan core in coaxial Chit-Alg fibers. Young's modulus was measured to be ca. 1.7 and 6.6 MPa for alginate and chitosan solid fibers, respectively. It has been also revealed that the fibers which contain 1% (w v<sup>1</sup> ) CaCl2 resulted in the highest mechanical results due to their modulus and ultimate stress compared to other coaxial fibers [11].

Figure 10. Stress-strain curves obtained from tensile tests of alginate sinzgle and chitosan/alginate coaxial fibers using different CaCl2 concentrations. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

It can be seen in Figure 11 that coaxial fibers containing 0.5% (w v<sup>1</sup>

shown the least amount of initial swelling, while fibers with 1% (w v<sup>1</sup>

sheaths which show less swelling [1].

with permission. 158 copyright 2015, Wiley-VCH.

4.7. In-vitro release measurement

core demonstrated the highest degree of swelling [1]. It seems that two simultaneous events are occurring by increasing the calcium chloride content in the core (from 0.5 to 2% (w v<sup>1</sup>

Figure 11. Swelling properties of coaxial wet-spun fibers in SBF as a function of the immersion time. [11] Reproduced

Increasing the number of ionic groups (Ca2+) in hydrogels is known to increase their swelling capacity [17]. This is mainly due to the simultaneous increase of the number of counterions inside the gel, which produces an additional osmotic pressure that swells the gel as described in Flory theory previously. Therefore, by adding more calcium chloride to the chitosan solution the degree of swelling increases. On the other hand, increasing the amount of Ca2+ ions also results in an increase in the ion exchange process within the sodium alginate. In fact, the ratio of calcium will increase in the alginate. The increase of the cross-linking agent concentration leads to the formation of a hydrogel with a greater 3D network density and so results in

The calibration curve was determined by monitoring the absorption of TB at its λmax (630 nm) in SBF with various concentrations of TB using UV-vis spectroscopy. The ability of the drug to release from the polymer matrix depend on a number of factors such as the solubility of the drug in the polymer matrix, the solubility of the drug in the medium, swelling and solubility of the polymer matrix in the medium and the diffusion of the drug from the polymer matrix to

) calcium chloride have

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

) calcium chloride in the

)).


Table 1. Comparison of mechanical properties of solid and coaxial biofibers [11]. Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

#### 4.6. Swelling properties in SBF

The swelling properties of the fibers were determined in SBF medium over a period of 48 hrs. Fiber diameters were measured at different time intervals. Results are shown in Figure 11 and listed in Table 1. Solid fibers have shown quite different degrees of swelling; while chitosan fibers showed only 90% calcium alginate fiber, the swelling of alginate fibers occur quite fast up to high ratios (until the fiber lose its fibrillar shape completely which make it almost impossible to be measured). This phenomenon is mostly due to the ionic exchange between the divalent cations and sodium in the environment.

Figure 11. Swelling properties of coaxial wet-spun fibers in SBF as a function of the immersion time. [11] Reproduced with permission. 158 copyright 2015, Wiley-VCH.

It can be seen in Figure 11 that coaxial fibers containing 0.5% (w v<sup>1</sup> ) calcium chloride have shown the least amount of initial swelling, while fibers with 1% (w v<sup>1</sup> ) calcium chloride in the core demonstrated the highest degree of swelling [1]. It seems that two simultaneous events are occurring by increasing the calcium chloride content in the core (from 0.5 to 2% (w v<sup>1</sup> )). Increasing the number of ionic groups (Ca2+) in hydrogels is known to increase their swelling capacity [17]. This is mainly due to the simultaneous increase of the number of counterions inside the gel, which produces an additional osmotic pressure that swells the gel as described in Flory theory previously. Therefore, by adding more calcium chloride to the chitosan solution the degree of swelling increases. On the other hand, increasing the amount of Ca2+ ions also results in an increase in the ion exchange process within the sodium alginate. In fact, the ratio of calcium will increase in the alginate. The increase of the cross-linking agent concentration leads to the formation of a hydrogel with a greater 3D network density and so results in sheaths which show less swelling [1].

#### 4.7. In-vitro release measurement

4.6. Swelling properties in SBF

Copyright 2015, Wiley-VCH.

134 Hydrogels

the divalent cations and sodium in the environment.

The swelling properties of the fibers were determined in SBF medium over a period of 48 hrs. Fiber diameters were measured at different time intervals. Results are shown in Figure 11 and listed in Table 1. Solid fibers have shown quite different degrees of swelling; while chitosan fibers showed only 90% calcium alginate fiber, the swelling of alginate fibers occur quite fast up to high ratios (until the fiber lose its fibrillar shape completely which make it almost impossible to be measured). This phenomenon is mostly due to the ionic exchange between

Table 1. Comparison of mechanical properties of solid and coaxial biofibers [11]. Reproduced with permission. 158

Figure 10. Stress-strain curves obtained from tensile tests of alginate sinzgle and chitosan/alginate coaxial fibers using

Sample Breaking stress (MPa) Strain at break (%) Young's modulus (GPa) Initial swelling ratio (%)

Alginate fiber 31 5 26 3 1.6 0.15 (Non-measurable)

different CaCl2 concentrations. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

Chitosan fiber 146 30 19 5.2 6.6 0.8 90 Chit-Alg (0.5) 30 5 22 8 0.6 0.1 360 Chit-Alg (1) 80 10 14 3 1.9 0.2 540 Chit-Alg (2) 28 5 37 5 0.55 0.1 385

> The calibration curve was determined by monitoring the absorption of TB at its λmax (630 nm) in SBF with various concentrations of TB using UV-vis spectroscopy. The ability of the drug to release from the polymer matrix depend on a number of factors such as the solubility of the drug in the polymer matrix, the solubility of the drug in the medium, swelling and solubility of the polymer matrix in the medium and the diffusion of the drug from the polymer matrix to

the medium [18]. The release profiles of TB from dye loaded coaxial fibers in SBF for up to 5 days were plotted vs. time and are demonstrated in Figure 12.

TB from coaxial fibers. TB is a hydrophilic molecule with a greater solubility in aqueous environment, so its drug diffusion rate through the polymeric matrix is highly dependent on the swelling of the polymeric fiber. Thus, according to the swelling ratio results, it is expected to obtain much

The development and fabrication of hydrogels fibers has been carried out to evaluate their performance for drug delivery systems. The production of coaxial hydrogels fibers were successfully developed for the first time using a wet-spinning method. The morphological, mechanical, thermal and swelling properties of these fibers are discussed [1]. Enhanced mechanical properties of 260% in ultimate stress and more than 300% in the Young's modulus

the cross-section of chitosan-alginate fibers clearly show the cylinder shaped monofilament form of the chitosan fiber covered with alginate. These biofibers as delivery platforms have demonstrated great potentials toward advancing current drug delivery systems. Hybrid Chit/ Alg fibers could likely be promising as a novel kind of 3D bioscaffolds in drug release studies

This work was supported by funding from the Australian Research Council under Discovery Early Career Researcher award (Javad Foroughi DE12010517). The authors would also like to

The authors declare that there is no conflict of interest; this chapter is wholly our own work unless otherwise referenced or acknowledged. The document has not been submitted for

thank Saber Mostafavian for 3D design of the wet-spinning process.

publication at any other publishing organization.

Acronyms and Abbreviations

3D three-dimensional ECM extracellular matrix

Chit chitosan Alg alginate

) CaCl2 into the chitosan core. SEM micrographs of

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faster release from alginate fibers than those of either chitosan or coaxial fibers [11].

5. Conclusion

or tissue engineering [1].

Acknowledgements

Conflict of interest

were observed by incorporating 1% (w v<sup>1</sup>

The whole release time period varied for different types of fibers including alginate, chitosan and the core-sheath fiber depending on the period over which they could resist the media before their structure fell apart [1]. As noted previously, calcium alginate could be easily degraded when used for in-vivo applications due to the ionic exchange between the divalent cations and sodium in the which are present in the body environment [11, 18]. Therefore, it is believed that the release of TB observed from alginate fibers was mainly due to the degradation of alginate fibers. On the other hand, wet-spinning of chitosan fiber is needed to be done in basic coagulation bath which is not an appropriate condition for most of loaded drugs. Coaxial fibers indicated a controlled manner of release more or less like chitosan fibers. However, with the help of coaxial spinning, their fabrication process via wet-spinning is performed in a neutral coagulation bath. These results provide the suitable condition to load any types of drugs into the wet-spun fibers for drug delivery applications. As can be seen in Figure 12, the coaxial fibers showed similar release behavior to that of the chitosan fibers. However, they could withstand the media for a shorter period of time without losing the initial structure.

In the initial period of 2 h, a fast release of TB from alginate fibers is observed at which more than 70% of TB is released. Either chitosan or Chit/Alg coaxial fibers showed approximately 30% burst release of TB followed by a sustained release within over 5 days. While alginate fiber could not withstand the media for more than 4 days, ca. 42 and 50% of the TB is released from chitosan and Chit/Alg fibers, respectively. Figure 12 shows a good sustained-release profile of

Figure 12. Time dependent TB releasing behavior of chitosan, alginate and Chit/Alg hydrogel fibers in SBF at 37C. Inset; burst release of coaxial fibers in the first 30 min. [11] Reproduced with permission. 158 Copyright 2015, Wiley-VCH.

TB from coaxial fibers. TB is a hydrophilic molecule with a greater solubility in aqueous environment, so its drug diffusion rate through the polymeric matrix is highly dependent on the swelling of the polymeric fiber. Thus, according to the swelling ratio results, it is expected to obtain much faster release from alginate fibers than those of either chitosan or coaxial fibers [11].
