**6. Applications of PVA hydrogels for tissue engineering**

PVA hydrogels fabricated through a number of F-T cycle processes have the ability to mimic a complex structure of human body. In a normal condition, water can be diffused into organic tissue during body's metabolism. However, the diffusion of water can be disturbed if water molecules are passing through an abnormal tissue due to swelling of the tissue, for example in tumor tissue. Moreover, about two-thirds of the human body consist of water, in which water molecules have hydrogen atoms that allow for magnetic resonance imaging (MRI) observation. Diffusion-weighted MRI (DW-MRI) is a device with high sensitivity in detecting "Brownian motions." The diffusion of water molecules caused by heat energy associated with the temperature of the human body can be used for analyzing a variety of brain diseases including brain tumors [54]. Additionally, diffusion-weighted imaging (DWI) is a technique that can be used to measure diffusion of water molecules in biological tissue such as white matter in the brain. In the MRI observation, the value of apparent diffusion coefficient (ADC) is used widely for describing the diffusion coefficient of the material.

In order to investigate the diffusion properties and the consistencies of the fabricated PVA hydrogels applied for tissue replica, several PVA hydrogel samples have been produced by variation number of F-T cycles and PVA concentrations. ADC values of the PVA hydrogels were obtained by performing the DW-MRI measurement. Sari et al. [51] have shown the ADC values versus PVA concentration for PVA hydrogels with the F-T process of three to five cycles. It has been found that the increase of PVA concentration from 7.5 to 15 wt% decreases the ADC values corresponding to the diffusion coefficient of all PVA hydrogels.

The enlargement of the tumor cells causes a reduction in the volume of extracellular space, increases the intracellular viscosity, and then inhibits the movement of water molecules described by the decrease of ADC value. Moreover, for PVA hydrogel fabricated by cryogelation process, the decrease of ADC value is described by swelling indicated by the significant increase of crystallization of hydrogel with increasing the number of F-T cycles. ADC value helps to distinguish a tumor tissue from a nontumor tissue. However, the abnormal tissue of brain tumor has a variety of classifications depending on the location and type of tumor tissue. Therefore, in the application of DW-MRI, it is necessary to find the most aggressive area at first to identify the highest cellularity and the most restrictive for the movement of water molecules. The use of higher b-value is to obtain a brighter contrast and has the impact on the easiness of diffusion imaging. The higher b-value can produce images on the high value of signal-to-noise ratio (SNR). Otherwise, at 1.5 T or lower, a low b-value may produce a poor image quality and lower value of SNR [55].

**Figure 1** displays the ADC values of the PVA hydrogels measured from DW-MRI with b = 1000 and 3000 s/mm2 as a function of F-T cycles and different PVA concentration. It has been found that the greater the concentration and number of cycles, the lower the diffusion coefficient of the PVA hydrogels. The crystallization, the degree of the physically cross-linked network, and the stiffness of hydrogel increase with the increase of the F-T cycle [15, 56]. The increase of crystallization indicates that the diffusion of water may be inhibited, so that the value of diffusion coefficient, described by ADC value, decreases. This is general diffusion behavior of a hydrogel, in which the diffusivity of a hydrogel decreases as cross-linking density increases and as the volume fraction of water within the hydrogel decreases [57]. It has also been indicated that the linearity of the ADC value as a function of F-T cycles at b = 3000 s/mm<sup>2</sup> is better than that at b = 1000 s/mm<sup>2</sup> . This result is in a good agreement with the former result [55].

The ferrogels were exposed to the external magnetic field of an electromagnet apparatus, which is able to generate a magnetic field up to 460 mT. The response of the ferrogel was measured by the extent of deflection and elongation. The top end of a ferrogel sample was fixed, whereas the lower end was free to deflect and elongate during the application of the external magnetic field. Variation in the magnetic field was obtained by changing the electric current of the electromagnetic apparatus. The Young's modulus was measured using a uni-

PVA hydrogels fabricated through a number of F-T cycle processes have the ability to mimic a complex structure of human body. In a normal condition, water can be diffused into organic tissue during body's metabolism. However, the diffusion of water can be disturbed if water molecules are passing through an abnormal tissue due to swelling of the tissue, for example in tumor tissue. Moreover, about two-thirds of the human body consist of water, in which water molecules have hydrogen atoms that allow for magnetic resonance imaging (MRI) observation. Diffusion-weighted MRI (DW-MRI) is a device with high sensitivity in detecting "Brownian motions." The diffusion of water molecules caused by heat energy associated with the temperature of the human body can be used for analyzing a variety of brain diseases including brain tumors [54]. Additionally, diffusion-weighted imaging (DWI) is a technique that can be used to measure diffusion of water molecules in biological tissue such as white matter in the brain. In the MRI observation, the value of apparent diffusion coefficient (ADC)

In order to investigate the diffusion properties and the consistencies of the fabricated PVA hydrogels applied for tissue replica, several PVA hydrogel samples have been produced by variation number of F-T cycles and PVA concentrations. ADC values of the PVA hydrogels were obtained by performing the DW-MRI measurement. Sari et al. [51] have shown the ADC values versus PVA concentration for PVA hydrogels with the F-T process of three to five cycles. It has been found that the increase of PVA concentration from 7.5 to 15 wt% decreases

The enlargement of the tumor cells causes a reduction in the volume of extracellular space, increases the intracellular viscosity, and then inhibits the movement of water molecules described by the decrease of ADC value. Moreover, for PVA hydrogel fabricated by cryogelation process, the decrease of ADC value is described by swelling indicated by the significant increase of crystallization of hydrogel with increasing the number of F-T cycles. ADC value helps to distinguish a tumor tissue from a nontumor tissue. However, the abnormal tissue of brain tumor has a variety of classifications depending on the location and type of tumor tissue. Therefore, in the application of DW-MRI, it is necessary to find the most aggressive area at first to identify the highest cellularity and the most restrictive for the movement of water molecules. The use of higher b-value is to obtain a brighter contrast and has the impact on the easiness of diffusion imaging. The higher b-value can produce images on the high value of signal-to-noise ratio (SNR). Otherwise, at 1.5 T

**6. Applications of PVA hydrogels for tissue engineering**

is used widely for describing the diffusion coefficient of the material.

the ADC values corresponding to the diffusion coefficient of all PVA hydrogels.

or lower, a low b-value may produce a poor image quality and lower value of SNR [55].

versal mechanical tester.

164 Hydrogels

**Figure 2** shows the consistency measurement as a function of F-T cycles and different PVA concentration. The data show that the higher PVA concentration and a number of F-T cycles cause the lower consistency and ADC value [50]. These results are consistent with the former paper [58]. The Pearson correlation method was used to correlate the data and are presented in **Table 1**. It is shown that the average value of ADC at b = 3000 s/mm<sup>2</sup> is good and slightly smaller than that at b = 1000 s/mm<sup>2</sup> . The data have a good correlation (correlation number of 0.92—0.99), so that it can assess the abnormal tissue consistency [51].

Generally, ADC values of the human brain for both normal and abnormal cases are different significantly. In the DW-MRI analysis, ADC value in the normal human brain is about 0.75 mm<sup>2</sup> /s and the higher b-value results in the lower ADC value. A tissue having low ADC value eliminates signals faster than that on the tissue having higher ADC value, and therefore, the contrast should increase. Sari et al. [51] have analyzed some cases for human brain tumor from the DW-MRI images at b-value of 1000 and 3000 s/mm<sup>2</sup> . They also found that the tissue having low ADC value indicates lower consistency or harder than the tissue having high ADC value. The ADC measurement using b = 1000 s/mm<sup>2</sup> can distinguish the harder tissue with the

**Figure 1.** ADC value of PVA hydrogels on the DW-MRI at b-value of 1000 s/mm<sup>2</sup> (closed symbols) and 3000 s/mm2 (opened symbols) as a function of the number of F-T cycles and PVA concentration.

**7. Stability and durability of PVA-Fe<sup>3</sup>**

**No. Ratio of PVA and water Fe3**

and water ratio.

**O4**

In order to study the stability and durability of ferrogel, a number of ferrogel samples have been

a number of F-T cycles. The stability was investigated by observing the increase of the required external magnetic field to elongate and deflect the ferrogels until a certain length and distance over a particular time. The observations were conducted from the first day since the ferrogels fabricated until the fifth day. The ferrogels can be called relatively stable if the change of required magnetic field is considerably small over the time to get the same deformation condition.

**Table 2** shows ferrogel samples with a variation of PVA and water ratio together with their elasticity moduli. It can be seen from the elasticity properties that the stiffness of ferrogel depends on the PVA concentration in water. Higher PVA concentration causes the increase of stiffness. The stability of ferrogels is shown in **Figure 3**. **Figure 3** demonstrates the time dependence of the required external magnetic field to elongate ferrogel up to 1 mm. It indicates that

fabricated with a variation of PVA and water ratio, the concentration of Fe3

**O4**

 13:100 10 4 PA.13 67.18 18:100 10 4 PA.18 69.96 23:100 10 4 PA.23 61.23 28:100 10 4 PA.28 119.10 33:100 10 4 PA.33 221.20

**Table 2.** Ferrogel samples prepared with different PVA and water ratio, together with the modulus elasticity.

**Figure 3.** Required magnetic field to elongate ferrogel up to 1 mm as a function of time for ferrogels with different PVA

 **hydrogels (Ferrogels)**

Development of PVA/Fe3O4 as Smart Magnetic Hydrogels for Biomedical Applications

 **(wt%) Number of F-T cycles Sample code Modulus elasticity (Pa)**

O4

http://dx.doi.org/10.5772/intechopen.71964

nanoparticles, and

167

**Figure 2.** Consistency measurement using digital penetrometer as a function of the number of F-T cycles and PVA concentration.

normal one and provides a clearer image, although the ratio of normal and abnormal tissue is not as high as the use of b = 3000 s/mm<sup>2</sup> . A better value of correlation with the physical parameters gives a suggestion that the use of DW-MRI 1.5 T with b = 1000 s/mm<sup>2</sup> provides a better image and the use of penetrometer is necessary for additional information for determining surgery. Otherwise, the use of DW-MRI 1.5 T with b-value higher than 1000 s/mm<sup>2</sup> is more preferred to examine the swelling that occurs around the area of the abnormal tissue because it provides more contrast image.


**Table 1.** The Pearson correlation result for both data of PVA hydrogels with different F-T cycle and PVA concentration.

#### **7. Stability and durability of PVA-Fe<sup>3</sup> O4 hydrogels (Ferrogels)**

In order to study the stability and durability of ferrogel, a number of ferrogel samples have been fabricated with a variation of PVA and water ratio, the concentration of Fe3 O4 nanoparticles, and a number of F-T cycles. The stability was investigated by observing the increase of the required external magnetic field to elongate and deflect the ferrogels until a certain length and distance over a particular time. The observations were conducted from the first day since the ferrogels fabricated until the fifth day. The ferrogels can be called relatively stable if the change of required magnetic field is considerably small over the time to get the same deformation condition.

**Table 2** shows ferrogel samples with a variation of PVA and water ratio together with their elasticity moduli. It can be seen from the elasticity properties that the stiffness of ferrogel depends on the PVA concentration in water. Higher PVA concentration causes the increase of stiffness. The stability of ferrogels is shown in **Figure 3**. **Figure 3** demonstrates the time dependence of the required external magnetic field to elongate ferrogel up to 1 mm. It indicates that


**Table 2.** Ferrogel samples prepared with different PVA and water ratio, together with the modulus elasticity.

normal one and provides a clearer image, although the ratio of normal and abnormal tissue is

**Figure 2.** Consistency measurement using digital penetrometer as a function of the number of F-T cycles and PVA

image and the use of penetrometer is necessary for additional information for determining

preferred to examine the swelling that occurs around the area of the abnormal tissue because

surgery. Otherwise, the use of DW-MRI 1.5 T with b-value higher than 1000 s/mm<sup>2</sup>

Two cycles 0.96 0.77 Three cycles 0.96 0.99 Four cycles 0.99 0.96 Five cycles 0.96 0.97

7.5 wt% 0.98 0.93 10 wt% 0.99 0.99 12.5 wt% 0.94 0.99 15 wt% 0.92 0.98

**Table 1.** The Pearson correlation result for both data of PVA hydrogels with different F-T cycle and PVA concentration.

eters gives a suggestion that the use of DW-MRI 1.5 T with b = 1000 s/mm<sup>2</sup>

**PVA hydrogels with different F-T cycle at constant PVA concentration of 10 wt% Data (s/mm2**

PVA hydrogels with different PVA concentration at constant F-T cycle for three

. A better value of correlation with the physical param-

provides a better

**) b = 1000 b = 3000**

) b = 1000 b = 3000

Data (s/mm<sup>2</sup>

is more

not as high as the use of b = 3000 s/mm<sup>2</sup>

it provides more contrast image.

concentration.

166 Hydrogels

times

**Figure 3.** Required magnetic field to elongate ferrogel up to 1 mm as a function of time for ferrogels with different PVA and water ratio.

ferrogel becomes stiffer with the passage of time due to the decrease of water content. The ferrogel with PVA and water ratio of 23:100 (PA.23) shows a relatively small change of the required magnetic field up to five days indicating a relative stability compared to the others. This stability relates to the optimum portion of water inclusion binding in the PVA hydrogel.

**Figure 4** presents magnetic field dependence of ferrogel deflection with different PVA and water ratio. **Figure 4** displays interesting hysteresis loop in which the deflection increases with increasing magnetic field and returns to its original length through a different path, thereby decreasing the magnetic field. These noncontinuous deflection behaviors have also been observed by Zrínyi et al. [59] and modeled by Snyder et al. [60]. The hysteresis loops tend to shift day by day, indicating a rigid gel character due to the

O4

presented in **Table 3**. It appears that there is no significant change in the modulus of elasticity

former report [40], in which the obtained elastic modulus was in the range of 0.17–0.75 MPa for a magnetoactive elastomer. **Figure 5** shows the stability characteristic of the ferrogels

ferrogel up to the same length for each day, indicating the decrease of water content and

10 wt%, the trapped magnetic particles in the PVA chain were less and therefore the distribution was inhomogeneous, creating more spaces which were filled with water. According to the structural model of hydrogel described by Goiti et al. [43], the trapped, free and linked water molecules attached to the PVA chain may cause a soft ferrogel and dry quickly due

solids and liquid, resulting in a good cross-linked hydrogel and then the trapped water can

**Figure 6** shows magnetic field dependence of ferrogel deflection with different concentra-

that the hysteresis behavior observed in ferrogel is not consequences from the magnetic

significant change in the hysteresis loops up to the fifth day. The change and the distortion

O4

O4

to rapid evaporation of the water. On the other hand, for ferrogels with Fe<sup>3</sup>

erately stable compared to the others. For the ferrogels with Fe<sup>3</sup>

more than 10 wt%, there might be a space filled by Fe<sup>3</sup>

O4

O4

**Table 3.** Ferrogel samples prepared with different Fe<sup>3</sup>

particles [59]. It appears that ferrogels with Fe<sup>3</sup>

**O4**

 23:100 5 4 FE.5 60.54 23:100 7.5 4 FE.7 60.94 23:100 10 4 FE.10 61.23 23:100 12.5 4 FE.12 61.59

O4

O4

maintain flexibility of the gel.

**No Ratio of PVA and water Fe3**

nanoparticles and the modulus elasticity are

http://dx.doi.org/10.5772/intechopen.71964

169

concentration from 5 to 12.5 wt%. This result is consistent with the

Development of PVA/Fe3O4 as Smart Magnetic Hydrogels for Biomedical Applications

concentration of 10 wt% (FP.10) appears to be mod-

O4

concentration less than

concentration

O4

nanoparticles so that the water is

concentrations of 10 and 12.5 wt% have no

concentrations associated with **Table 3**. It implies that the increase of

O4

concentration of 10 wt%, it is expected to have a proportional amount of

nanoparticles. The hysteresis behavior of the deflection curves depends on the

nanoparticles could directly coincide with the polymer chain. For the

nanoparticles and the elasticity of ferrogel itself. It should be noted

 **(wt%) Number of F-T cycles Sample code Modulus elasticity (Pa)**

concentrations, together with the modulus elasticity.

concentration tends to decrease the required magnetic field to elongate

decrease of water content.

with the increase of Fe3

with various Fe3

suppressed. The Fe<sup>3</sup>

O4

concentration of Fe3

ferrogel with Fe3

tion of Fe3

nano-sized Fe3

Ferrogels with different concentration of Fe<sup>3</sup>

O4

O4

stiffer ferrogels. Ferrogel with Fe<sup>3</sup>

O4

**Figure 4.** Hysteresis curves of the deflection behavior of ferrogels with PVA and water ratio: (a) 13:100, (b) 18:100, (c) 23:100, (d) 28:100, and (e) 33:100.

**Figure 4** presents magnetic field dependence of ferrogel deflection with different PVA and water ratio. **Figure 4** displays interesting hysteresis loop in which the deflection increases with increasing magnetic field and returns to its original length through a different path, thereby decreasing the magnetic field. These noncontinuous deflection behaviors have also been observed by Zrínyi et al. [59] and modeled by Snyder et al. [60]. The hysteresis loops tend to shift day by day, indicating a rigid gel character due to the decrease of water content.

ferrogel becomes stiffer with the passage of time due to the decrease of water content. The ferrogel with PVA and water ratio of 23:100 (PA.23) shows a relatively small change of the required magnetic field up to five days indicating a relative stability compared to the others. This stability relates to the optimum portion of water inclusion binding in the PVA hydrogel.

**Figure 4.** Hysteresis curves of the deflection behavior of ferrogels with PVA and water ratio: (a) 13:100, (b) 18:100,

(c) 23:100, (d) 28:100, and (e) 33:100.

168 Hydrogels

Ferrogels with different concentration of Fe<sup>3</sup> O4 nanoparticles and the modulus elasticity are presented in **Table 3**. It appears that there is no significant change in the modulus of elasticity with the increase of Fe3 O4 concentration from 5 to 12.5 wt%. This result is consistent with the former report [40], in which the obtained elastic modulus was in the range of 0.17–0.75 MPa for a magnetoactive elastomer. **Figure 5** shows the stability characteristic of the ferrogels with various Fe3 O4 concentrations associated with **Table 3**. It implies that the increase of nano-sized Fe3 O4 concentration tends to decrease the required magnetic field to elongate ferrogel up to the same length for each day, indicating the decrease of water content and stiffer ferrogels. Ferrogel with Fe<sup>3</sup> O4 concentration of 10 wt% (FP.10) appears to be moderately stable compared to the others. For the ferrogels with Fe<sup>3</sup> O4 concentration less than 10 wt%, the trapped magnetic particles in the PVA chain were less and therefore the distribution was inhomogeneous, creating more spaces which were filled with water. According to the structural model of hydrogel described by Goiti et al. [43], the trapped, free and linked water molecules attached to the PVA chain may cause a soft ferrogel and dry quickly due to rapid evaporation of the water. On the other hand, for ferrogels with Fe<sup>3</sup> O4 concentration more than 10 wt%, there might be a space filled by Fe<sup>3</sup> O4 nanoparticles so that the water is suppressed. The Fe<sup>3</sup> O4 nanoparticles could directly coincide with the polymer chain. For the ferrogel with Fe3 O4 concentration of 10 wt%, it is expected to have a proportional amount of solids and liquid, resulting in a good cross-linked hydrogel and then the trapped water can maintain flexibility of the gel.

**Figure 6** shows magnetic field dependence of ferrogel deflection with different concentration of Fe3 O4 nanoparticles. The hysteresis behavior of the deflection curves depends on the concentration of Fe3 O4 nanoparticles and the elasticity of ferrogel itself. It should be noted that the hysteresis behavior observed in ferrogel is not consequences from the magnetic particles [59]. It appears that ferrogels with Fe<sup>3</sup> O4 concentrations of 10 and 12.5 wt% have no significant change in the hysteresis loops up to the fifth day. The change and the distortion


**Table 3.** Ferrogel samples prepared with different Fe<sup>3</sup> O4 concentrations, together with the modulus elasticity.

of hysteresis shape are influenced by magnetostatic and magnetostriction mechanisms in the ferrogel [61]. Sample geometry may also be one parameter for determining the mechanical behaviors (elongation, deflection, etc.) of the ferrogel in the external magnetic field [60]. The modulus elasticity of ferrogels with a different number of F-T cycles was also investigated as shown in **Table 4**. In general, the greater the number of F-T cycles, the more rigid ferrogels will be obtained due to the evaporation of water. **Figure 7** shows the durability of ferrogels produced by 4, 8, and 12 times F-T cycles. It is also clear that ferrogel produced by four times F-T cycles has better stability as indicated by relatively small changes of the external magnetic field required to elongate ferrogel up to the same length until the fifth day. The stability of the ferrogels can also be studied by observing the hysteresis loop of elongation as shown in **Figure 8**. Ferrogels fabricated by more than four cycles are generally unstable, implying that there is a reduction of water in the ferrogels during F-T cycle processes. This result is consistent with the previous papers [34, 49]. Through the F-T cycles, crystallites will be formed and act as the cross-linking points in the polymer matrix. The amount and size of these crystallites depend on the number of F-T cycles, as well as composition and concentration of the initial

**Figure 7.** Required magnetic field to elongate ferrogel up to 1 mm as a function of time for ferrogels with a different

**Table 4.** Ferrogel samples prepared with a different number of F-T cycles, together with the modulus elasticity.

 **(wt%) Number of F-T cycles Sample code Modulus elasticity (Pa)**

Development of PVA/Fe3O4 as Smart Magnetic Hydrogels for Biomedical Applications

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171

solution [15].

number of F-T cycles.

**No Ratio of PVA and water Fe3**

**O4**

1 23:100 10 4 FT.4 61.23 2 23:100 10 8 FT.8 535.2 3 23:100 10 12 FT.12 267.0

**Figure 5.** Required magnetic field to elongate ferrogel up to 1 mm as a function of time for ferrogels with different Fe<sup>3</sup> O4 concentrations.

**Figure 6.** Hysteresis curves of the deflection behavior of ferrogels with Fe<sup>3</sup> O4 concentration of: (a) 5 wt%, (b) 7 wt%, (c) 10 wt%, and (d) 12 wt%.


**Table 4.** Ferrogel samples prepared with a different number of F-T cycles, together with the modulus elasticity.

**Figure 5.** Required magnetic field to elongate ferrogel up to 1 mm as a function of time for ferrogels with different Fe<sup>3</sup>

**Figure 6.** Hysteresis curves of the deflection behavior of ferrogels with Fe<sup>3</sup>

(c) 10 wt%, and (d) 12 wt%.

O4

concentration of: (a) 5 wt%, (b) 7 wt%,

concentrations.

170 Hydrogels

O4

of hysteresis shape are influenced by magnetostatic and magnetostriction mechanisms in the ferrogel [61]. Sample geometry may also be one parameter for determining the mechanical behaviors (elongation, deflection, etc.) of the ferrogel in the external magnetic field [60].

The modulus elasticity of ferrogels with a different number of F-T cycles was also investigated as shown in **Table 4**. In general, the greater the number of F-T cycles, the more rigid ferrogels will be obtained due to the evaporation of water. **Figure 7** shows the durability of ferrogels produced by 4, 8, and 12 times F-T cycles. It is also clear that ferrogel produced by four times F-T cycles has better stability as indicated by relatively small changes of the external magnetic field required to elongate ferrogel up to the same length until the fifth day. The stability of the ferrogels can also be studied by observing the hysteresis loop of elongation as shown in **Figure 8**. Ferrogels fabricated by more than four cycles are generally unstable, implying that there is a reduction of water in the ferrogels during F-T cycle processes. This result is consistent with the previous papers [34, 49]. Through the F-T cycles, crystallites will be formed and act as the cross-linking points in the polymer matrix. The amount and size of these crystallites depend on the number of F-T cycles, as well as composition and concentration of the initial solution [15].

**Figure 7.** Required magnetic field to elongate ferrogel up to 1 mm as a function of time for ferrogels with a different number of F-T cycles.

Ferrogel has potential application for an artificial muscle or a soft actuator due to the combined properties of good elasticity and flexibility from PVA hydrogel and specific magnetic behavior from the magnetic particles. Ramanujan et al. [40] have proposed two possible approaches of an artificial finger synthesized from PVA hydrogel and microsized iron oxide. First, they found that the deflection of ferrogel can be controlled by adjusting the concentration of magnetic particles. The second one is by coating manipulation of ferrogel. They demonstrated a finger-like motion based on instantaneous elongation and defection under

As mentioned previously, in order to apply the ferrogel as an artificial tissue, one should understand the behavior of magnetoelastic properties. Based on numerous references [40, 48], the magnetoelasticity of ferrogel basically depends on the particle size and concentration of the magnetic particles in the polymeric matrix. Due to the particle size effect, the magnetiza-

one. This may affect the threshold value of the magnetic field which is the minimum magnetic field required to start a large and instantaneous elongation or deflection of ferrogel. **Figure 9**

This result is consistent with the former report [40]. This result implies that the ferrogels

**Figure 9** reflects the magnetic response for both variation of ferrogels, in which the ferrogel

gel with microsized filler is more sensitive to deform ferrogel under external magnetic field. This result can be explained by the lower threshold value of the magnetic field as illustrated in **Figure 9**. **Figure 11** shows the magnetoelastic hysteresis loops for ferrogels with different

O4

threshold magnetic field tends to decrease with increasing concentration of Fe<sup>3</sup>

are more sensitive to the external magnetic field with the increase of Fe<sup>3</sup>

particles in the ferrogel is generally higher than that of the nano-sized

Development of PVA/Fe3O4 as Smart Magnetic Hydrogels for Biomedical Applications

particles has smaller threshold value than the ferrogel with nano-sized

concentration dependence of elongation and deflection behaviors

O4

concentration on the threshold magnetic field for both elonga-

O4

particles. It is found that the

O4

http://dx.doi.org/10.5772/intechopen.71964

fillers for ferrogels during (a) elongation

particles as fillers. It indicates that ferro-

O4

particles.

173

concentration.

external magnetic field.

tion of microsized Fe3

with microsized Fe3

**Figure 10** displays the Fe3

Fe3 O4

shows the dependence of Fe3

O4

O4

O4

**Figure 9.** The threshold of magnetic field versus micro- and nano-sized Fe<sup>3</sup>

and (b) deflection. The solid lines are for the eye guidance.

for both ferrogels with micro- and nano-sized Fe3

O4

tion and deflection of ferrogels with micro- and nano-sized Fe<sup>3</sup>

particles as a consequence of the higher magnetization.

**Figure 8.** Hysteresis curves of the deflection behavior of ferrogels with the number of F-T cycles for: (a) 4, (b) 8, and (c) 12 times.

#### **8. Structural and magnetic properties of Ferrogels**

In addition to the substantial biomedical and biomechanical applications of PVA hydrogels and ferrogels, respectively, a basic study of structural and dynamical properties of ferrogel has to be investigated in detail. Structural studies using small-angle X-ray scattering (SAXS) measurement of PVA hydrogel and ferrogel have been reported by Puspitasari et al. [62] and Sunaryono et al. [48], respectively. Puspitasari et al. have confirmed that the crystallization of PVA hydrogel has a radius of approximately 2.9–3.3 nm and an average distance between polymer crystallites of 15–17.5 nm [62]. This result is consistent with the recent paper [48]. Moreover, Sunaryono et al. have illustrated the size distribution of Fe<sup>3</sup> O4 nanoparticles in the PVA hydrogel obtained by F-T cyclic process [48]. They have found that there are so-called primary particles (approximately 3 nm) and secondary particles as well as the clusters of magnetic nanoparticles in ferrogel observed by the synchrotron radiation (SAXS technique) with global fitting analysis data. The cluster size of the Fe<sup>3</sup> O4 in the ferrogel system was observed to be significantly reduced with decreasing concentration of the magnetic nanoparticles.

Ferrogel has potential application for an artificial muscle or a soft actuator due to the combined properties of good elasticity and flexibility from PVA hydrogel and specific magnetic behavior from the magnetic particles. Ramanujan et al. [40] have proposed two possible approaches of an artificial finger synthesized from PVA hydrogel and microsized iron oxide. First, they found that the deflection of ferrogel can be controlled by adjusting the concentration of magnetic particles. The second one is by coating manipulation of ferrogel. They demonstrated a finger-like motion based on instantaneous elongation and defection under external magnetic field.

As mentioned previously, in order to apply the ferrogel as an artificial tissue, one should understand the behavior of magnetoelastic properties. Based on numerous references [40, 48], the magnetoelasticity of ferrogel basically depends on the particle size and concentration of the magnetic particles in the polymeric matrix. Due to the particle size effect, the magnetization of microsized Fe3 O4 particles in the ferrogel is generally higher than that of the nano-sized one. This may affect the threshold value of the magnetic field which is the minimum magnetic field required to start a large and instantaneous elongation or deflection of ferrogel. **Figure 9** shows the dependence of Fe3 O4 concentration on the threshold magnetic field for both elongation and deflection of ferrogels with micro- and nano-sized Fe<sup>3</sup> O4 particles. It is found that the threshold magnetic field tends to decrease with increasing concentration of Fe<sup>3</sup> O4 particles. This result is consistent with the former report [40]. This result implies that the ferrogels are more sensitive to the external magnetic field with the increase of Fe<sup>3</sup> O4 concentration. **Figure 9** reflects the magnetic response for both variation of ferrogels, in which the ferrogel with microsized Fe3 O4 particles has smaller threshold value than the ferrogel with nano-sized Fe3 O4 particles as a consequence of the higher magnetization.

**Figure 10** displays the Fe3 O4 concentration dependence of elongation and deflection behaviors for both ferrogels with micro- and nano-sized Fe3 O4 particles as fillers. It indicates that ferrogel with microsized filler is more sensitive to deform ferrogel under external magnetic field. This result can be explained by the lower threshold value of the magnetic field as illustrated in **Figure 9**. **Figure 11** shows the magnetoelastic hysteresis loops for ferrogels with different

**8. Structural and magnetic properties of Ferrogels**

(c) 12 times.

172 Hydrogels

Moreover, Sunaryono et al. have illustrated the size distribution of Fe<sup>3</sup>

global fitting analysis data. The cluster size of the Fe<sup>3</sup>

In addition to the substantial biomedical and biomechanical applications of PVA hydrogels and ferrogels, respectively, a basic study of structural and dynamical properties of ferrogel has to be investigated in detail. Structural studies using small-angle X-ray scattering (SAXS) measurement of PVA hydrogel and ferrogel have been reported by Puspitasari et al. [62] and Sunaryono et al. [48], respectively. Puspitasari et al. have confirmed that the crystallization of PVA hydrogel has a radius of approximately 2.9–3.3 nm and an average distance between polymer crystallites of 15–17.5 nm [62]. This result is consistent with the recent paper [48].

**Figure 8.** Hysteresis curves of the deflection behavior of ferrogels with the number of F-T cycles for: (a) 4, (b) 8, and

PVA hydrogel obtained by F-T cyclic process [48]. They have found that there are so-called primary particles (approximately 3 nm) and secondary particles as well as the clusters of magnetic nanoparticles in ferrogel observed by the synchrotron radiation (SAXS technique) with

be significantly reduced with decreasing concentration of the magnetic nanoparticles.

O4

O4

in the ferrogel system was observed to

nanoparticles in the

**Figure 9.** The threshold of magnetic field versus micro- and nano-sized Fe<sup>3</sup> O4 fillers for ferrogels during (a) elongation and (b) deflection. The solid lines are for the eye guidance.

**9. Conclusions**

as the following:

hydrogel.

**Author details**

Malik Anjelh Baqiya<sup>1</sup>

Yanurita Dwihapsari<sup>1</sup>

Malang, Malang, Indonesia

**Acknowledgements**

PVA hydrogel and ferrogels with Fe3

grading. The b-value of 1000 s/mm<sup>2</sup>

trast is recommended for brain tumor grading.

O4

successfully prepared by freezing-thawing (F-T) cyclic method. We can conclude the chapter

• In the biomedical application, a study of hydrogen (water molecules) diffusion behavior in the PVA hydrogel by analyzing the ADC value can be used as a parameter of brain tumor

• The time dependence of the elongation and deflection curves as a function of PVA concentration, particle concentration, and a number of F-T cycles can be used to determine the durability and performance of the ferrogel under certain external magnetic fields. It has been suggested that ferrogel with PVA and water ratio of 23:100 and four times F-T cycles, respectively, has the best elastic properties. Ferrogel fabricated by a F-T cyclic process has the best magnetoelastic response when it has a relatively large magnetic particle size as the filler with a concentration of 10–15 wt% in the PVA

This chapter is based on research funded by several schemes of research grants, provided by LPPM ITS, DP2M—Ministry of National Education, and DRPM—Ministry of Research,

, Sunaryono2

1 Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi

2 Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Negeri

3 Faculty of Engineering, Universitas Muhammadiyah Ponorogo, Ponorogo, Indonesia

, Munaji<sup>3</sup>

, Dita Puspita Sari<sup>1</sup>

,

Technology and Higher Education, Republic of Indonesia, 2006−2016.

\*

Sepuluh Nopember (ITS), Kampus ITS Keputih Sukolilo, Surabaya, Indonesia

, Ahmad Taufiq<sup>2</sup>

and Darminto<sup>1</sup>

\*Address all correspondence to: darminto@physics.its.ac.id

micro- and nano-sized particles as fillers have been

http://dx.doi.org/10.5772/intechopen.71964

175

Development of PVA/Fe3O4 as Smart Magnetic Hydrogels for Biomedical Applications

and higher providing a better image quality and con-

**Figure 10.** (a) Elongation and (b) deflection of ferrogels under 329 mT versus the concentration of micro- and nano-sized Fe3 O4 particles as fillers. The solid lines are for the eye guidance.

concentration of microsized Fe3 O4 particles from 2.5 to 15%. The hysteresis loops are found to be narrower and smaller with decreasing magnetic filler concentration. This is attributed to the different magnetic response of ferrogel to be deformed and returned to its original length and position. This behavior is also associated with a magnetic remnant of the ferrogels. A higher magnetic concentration leads to a higher ferrogel ability to deform even under a low external magnetic field. Moreover, a wider hysteresis loop for ferrogel with microsized filler was observed, indicating a stronger magnetic saturation. This is in a good agreement with the previous paper [27] that the ferrogel with large particle size has the best magnetosensitive effect, so it can be applied for drug release system.

**Figure 11.** Hysteresis loops of the deflection versus electric current (proportional to the magnetic field) for ferrogels with different concentrations of Fe<sup>3</sup> O4 microparticles: 2.5 wt%, 7.5 wt%, and 15 wt%.
