**3. Fabrication and characterization of PVA hydrogel**

The PVA polymeric powder (Mw = 60,000 g/mol, Merck Schuchardt OHG, Germany) with a degree of hydrolysis ≥98% was used for PVA solution. PVA hydrogels were fabricated by F-T cyclic process. First, the PVA polymer was dissolved in distilled water with a variation of weight compositions, namely 7.5, 10, 12.5, and 15 wt%. The solution was mixed and heated at 70–90°C to improve the solubility of the PVA polymer in water, as suggested in the previous papers [48, 50, 51]. Once the mixture was perfectly dissolved, indicated by a physical change from liquid to paste, it was then loaded into a cylindrical plastic mold followed by F-T process. The solution was cooled and kept at the frozen state at –10°C for 3 h. The process was continued by thawing at room temperature for 1 h. This F-T process was repeated to obtain PVA hydrogel samples up to five cycles. The PVA hydrogel samples were also prepared by varying the composition ratio of PVA and water as mentioned earlier.

The 1.5-T scanner (Signa Horizon; GE Medical Systems, Milwaukee, WI, USA) was used for the study of diffusion-weighted magnetic resonance imaging (DW-MRI). Apparent diffusion coefficient (ADC) value was obtained from MRI with diffusion-weighted imaging (DWI) method following Stejskal-Tanner sequence. The ADC value was calculated by Functool software (GE Medical Systems) for each sample. The characterization steps were similar to the previous reports [50, 51].

The consistency measurement was conducted using a penetrometer (Precision 73,515, Petroleum Analyzer Co., San Antonio, TX, USA) using a pressure sensor. The penetrometer was set under gravity force for 5 s, and the depth of penetration was measured in tenths of millimeters. The depth of penetration depended on the kinetic energy applied to the penetrometer and the sample resistance. The resistance data were collected to obtain the consistency value describing the required mechanical force to decelerate from its initial velocity to zero velocity.

#### **4. Preparation of Fe3 O4 nanoparticles from iron sand**

stability of the ferrogels [43]. As for the mechanical properties of the PVA-Fe<sup>3</sup>

ticle having average size less than 10 nm [47, 48].

F-T cyclic process.

162 Hydrogels

previous reports [50, 51].

has been shown that the deflection and elongation parameters are dependent on the Fe<sup>3</sup>

concentration and external magnetic field strength [40] and the deformation is independent on the shape of ferrogels [44]. Experimentally, the magnetodeformation of the ferrogels with highly concentrated particles (approximately above 30%) is due to the effect of short range order and magnetic interaction among the particles [45, 46]. Furthermore, the structural and magnetic behavior of ferrogels has been intensively studied with the dispersed magnetic par-

Sunaryono et al. have shown that the hydrogels owing the threshold PVA concentration of

centration has been found to be responsible for a weak magnetic response due to the increase of particle free volume and the decrease of interaction energy between magnetic nanoparticles and the cross-linked PVA hydrogel [48]. However, Sunaryono et al. [48, 49] stated a crucial problem is related to the durability of the PVA hydrogels and ferrogels prepared by

In this chapter, at first, we provide a study of PVA hydrogel application in tissue engineering. Then, it is continued by investigation of the durability of ferrogels prepared by F-T cyclic pro-

The PVA polymeric powder (Mw = 60,000 g/mol, Merck Schuchardt OHG, Germany) with a degree of hydrolysis ≥98% was used for PVA solution. PVA hydrogels were fabricated by F-T cyclic process. First, the PVA polymer was dissolved in distilled water with a variation of weight compositions, namely 7.5, 10, 12.5, and 15 wt%. The solution was mixed and heated at 70–90°C to improve the solubility of the PVA polymer in water, as suggested in the previous papers [48, 50, 51]. Once the mixture was perfectly dissolved, indicated by a physical change from liquid to paste, it was then loaded into a cylindrical plastic mold followed by F-T process. The solution was cooled and kept at the frozen state at –10°C for 3 h. The process was continued by thawing at room temperature for 1 h. This F-T process was repeated to obtain PVA hydrogel samples up to five cycles. The PVA hydrogel samples were also prepared by

The 1.5-T scanner (Signa Horizon; GE Medical Systems, Milwaukee, WI, USA) was used for the study of diffusion-weighted magnetic resonance imaging (DW-MRI). Apparent diffusion coefficient (ADC) value was obtained from MRI with diffusion-weighted imaging (DWI) method following Stejskal-Tanner sequence. The ADC value was calculated by Functool software (GE Medical Systems) for each sample. The characterization steps were similar to the

The consistency measurement was conducted using a penetrometer (Precision 73,515, Petroleum Analyzer Co., San Antonio, TX, USA) using a pressure sensor. The penetrometer

cess. Finally, the structural and magnetic properties of ferrogels are discussed briefly.

**3. Fabrication and characterization of PVA hydrogel**

varying the composition ratio of PVA and water as mentioned earlier.

23% in water content have the best mechanical properties [49]. Moreover, the lower Fe<sup>3</sup>

O4

ferrogels, it

O4 con-

O4

Fe3 O4 nanoparticles were prepared by coprecipitation method employing natural iron sand as a raw material. The preparation was the same as explained in the former papers [48, 52]. First, iron sand was extracted by permanent magnet several times to obtain microsized Fe<sup>3</sup> O4 powders. HCl and NH<sup>4</sup> OH were used as dissolving and precipitating agents, respectively. Fe3 O4 nanoparticles produced by the coprecipitation method were based on the following chemical reaction [52, 53].

$$\text{Fe}\_3\text{O}\_4 + 8\text{HCl} \rightarrow 2\text{FeCl}\_3 + \text{FeCl}\_2 + 4\text{H}\_2\text{O} \tag{1}$$

$$2\,\text{FeCl}\_3 + \text{FeCl}\_2 + 8\text{NH}\_4\,\text{OH} \rightarrow \text{Fe}\_3\text{O}\_4 + 8\text{NH}\_4\,\text{Cl} + 4\text{H}\_2\text{O} \tag{2}$$

Both reactions were maintained at room temperature. A complete reaction was indicated by the color change of the solution and the formation of black precipitation. Finally, the precipitated powders were rinsed several times using distilled water and then dried at 100°C for 1 h for ferrogel fabrication.

#### **5. Fabrication and characterization of PVA/Fe3 O4 hydrogel (Ferrogel) based on iron sand**

Ferrogel was fabricated by distributing the prepared Fe3 O4 nanoparticles in the PVA hydrogel paste solution, and then, they were stirred to obtain a uniform gel. Furthermore, the mixture gel was placed into a cylindrical mold to perform the similar F-T cyclic process as in the PVA hydrogels fabrication. The ferrogel samples were prepared by varying the concentration of PVA and Fe3 O4 nanoparticles, as well as the number of F-T cycles.

Basic characterizations using X-ray diffractometer (XRD) and transmission electron microscopy (TEM) were conducted to analyze the crystal structure and particle morphology of Fe3 O4 nanoparticles and ferrogels, respectively. Vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements were taken to investigate the magnetic properties of the PVA ferrogels. Particle size and the distribution of Fe<sup>3</sup> O4 nanoparticles in the PVA hydrogels were analyzed using small-angle X-ray scattering (SAXS) instrument as in the reported paper [48].

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 universal mechanical tester.

**Figure 1** displays the ADC values of the PVA hydrogels measured from DW-MRI with b = 1000

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 indi-

**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

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

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

having low ADC value indicates lower consistency or harder than the tissue having high ADC

/s and the higher b-value results in the lower ADC value. A tissue having low ADC

cated that the linearity of the ADC value as a function of F-T cycles at b = 3000 s/mm<sup>2</sup>

in **Table 1**. It is shown that the average value of ADC at b = 3000 s/mm<sup>2</sup>

0.92—0.99), so that it can assess the abnormal tissue consistency [51].

from the DW-MRI images at b-value of 1000 and 3000 s/mm<sup>2</sup>

**Figure 1.** ADC value of PVA hydrogels on the DW-MRI at b-value of 1000 s/mm<sup>2</sup>

(opened symbols) as a function of the number of F-T cycles and PVA concentration.

value. The ADC measurement using b = 1000 s/mm<sup>2</sup>

as a function of F-T cycles and different PVA concentration. It has been found

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

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

. This result is in a good agreement with the former result [55].

. The data have a good correlation (correlation number of

is better

165

is good and slightly

. They also found that the tissue

(closed symbols) and 3000 s/mm2

can distinguish the harder tissue with the

and 3000 s/mm2

0.75 mm<sup>2</sup>

than that at b = 1000 s/mm<sup>2</sup>

smaller than that at b = 1000 s/mm<sup>2</sup>
