Preparation of magnetic hydrogel by in-Situ coprecipitation process - Ngoc Uyen Nguyen Thai

Vietnam Journal of Science and Technology 56 (1A) (2018) 167-173 PREPARATION OF MAGNETIC HYDROGEL BY IN-SITU COPRECIPITATION PROCESS Ngoc Uyen Nguyen-Thai 1, * , Chi Nhan Ha Thuc 1 , Thi Vi Vi Do 1 , Nang An Vu 1 , Tien Trung Vu 1 , Thi Ngoc Mai Tran 2 1 Faculty of Materials Science and Technology, University of Science-VNU-HCM City, 227 Nguyen Van Cu, District 5, Ho Chi Minh City 2 Bio-Food Technology and Environment Department, Hutech University of Technology, 475A Dien Bien Phu, Binh Thanh District, Ho Chi Minh City * Email: ntnuyen@hcmus.edu.vn Received: 15 August 2017; Accepted for publication: 25 February 2018 ABSTRACT This study describes a preparation of magnetite nanoparticle by co-precipitation of Fe(II) and Fe(III) in alginate hydrogel matrix. This simple process is sufficient for producing a superparamagnetic, well dispersible magnetite nanoparticle in polymer hydrogel matrix. Two approaches for iron ions loadings are induced. The first approach includes two steps, the hydrogel beads are formed before the iron ions are being diffused into the hydrogel matrix. The second approach is the simultaneous forming of hydrogel containing iron ions. The ions loaded hydrogel is then coprecipitated in the presence of ammonium hydroxide to afford iron oxide magnetite nanoparticles in alginate hydrogel matrix. The composition and characteristics of the hydrogel containing magnetite nanoparticle were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM). The results showed that the particles size of magnetic nanoparticles prepared by in-situ coprecipitation method is around ~ 6 nm and smaller than that produced by normal coprecipitation method. The magnetic hydrogel exhibits superparamagnetic properties with the saturation magnetization of about 25 emu/g, the ratio of Mr/Ms about 0.8 ×10 -3 . Possessing the biocompatibility as well as superparamagnetism, the magnetite hydrogel is a promising materials for environmental and biomedical applications. Keywords: hydrogel, magnetic nanoparticles, coprecipitation. 1. INTRODUCTION Magnetite (Fe3O4) is a ferrite material with inverse spinel structure in the nature. When a size of Fe3O4 decreases to nanoscopic scale about 5 – 15 nm [1], it has superparamagnetism behavior. In addition, magnetite nanoparticles have high surface areas which increase in bonding with various organic or inorganic molecules for promising applications in biomedical and biotechnological engineering. In contrast, the nanometer scale of nanoparticles make them tend Ngoc Uyen Nguyen-Thai, et al. 168 to agglomerate and thus negate the advantages in the properties of nanoparticles. By incorporation with polymer, especially with biopolymers, ones can combine the special properties of magnetite nanoparticle (MNP) and the remarkable properties of (bio)polymer such as the ease in fabrication of flexible films or hydrogel materials, the biocompatibility, biodgegradable and low toxicity properties. Alginate is one of the most common biopolymer for environmental and biomedical materials such as pharmaceutical, wound dressing and tissue regeneration materials [2 - 4] due to their ability of forming hydrogel by coordinating with ion calcium. The incorporations of magnetic nanoparticles in alginate for biomedical application were reported [5]. Generally, MNP was synthesized by coprecipitation and then loaded into alginate hydrogel [6, 7] or by in-situ coprecipitation of Fe(II) and Fe (III) in the sodium- or calcium-alginate matrix [5, 8]. Briefly, the particle sizes in the previous reports were varied from 5 to over 100 nm. Concerning the biomedical applications, the quick removable of nanoparticles out of the body after used is neccesary. In detail, the particle size is smaller than 5.5 nm, MNP can be quickly removed through the renal system [7]. However, only several reports successfully synthesized MNP at this size [5, 8, 9]. Therefore, we studied the synthesis of iron nanoparticle which was trapped in alginate hydrogel matrix to reduce the size of iron nanoparticle and subsequently produce the magnetic hydrogel. 2. EXPERIMENTAL 2.1. Materials Ferrous chloride (FeCl2.4H2O, 99.5 %), ferric chloride (FeCl3.6H2O, 99 %), ammonia solution (NH4OH, 25 %) and sodium-alginate were purchased from Merck, Germany. Calcium chloride originated from China was used as received. 2.2. Synthesis of pure Fe3O4 nanoparticles (T30) by co-precipitation method Fe3O4 nanoparticles were synthesized by co-precipitation method with 40 mL ferrous chloride (0.1257 M) and 40 mL ferric chloride (0.2515 M). The solution mixture of Fe 2+ and Fe 3+ were degassed. Ammonia solution (13 mL, 25 %) was slowly dropped into the mixture at room temperature, approximately of 30 C. The solution was continued to stir for about 1 h and the black precipitate was obtained by magnet. The nanoparticles were filtered and washed several times with distilled water and dried in vacuum at 50°C. 2.3. Synthesis of alginate Fe3O4 hydrogel in two step (H1) in-situ co-precipitation method In this process, the alginate hydrogel was first prepared by dropping 2 wt% sodium alginate solution into 0.5 wt% CaCl2 and washing with water (white beads in Figure 1). The calcium- alginate hydrogel beads were then immersed in iron ion solution containing [FeCl2]:[FeCl3] 1:2, [FeCl2] = 0.2 M for 30 minutes (the brown beads in Figure 1), washed and then immersed into the solution of NH4OH and stirred for 30 minutes (the black beads in Figure 1). The magnetic hydrogel was then obtained, washed with distilled water several times. 2.4. Synthesis of alginate Fe3O4 hydrogel in one step (H2) in-situ co-precipitation method Preparation of magnetic hydrogel by in-situ coprecipitation process 169 In this process, the alginate hydrogel incorporated with iron ions were prepared simultaneously by dropping sodium alginate solution into the solution containing CaCl2, FeCl2, FeCl3. The brown hydrogel was obtained, washed with distilled water and then immersed into base solution for 30 minutes. After washing, the magnetic hydrogel (H2) was obtained. Figure 1. Digital pictures of alginate hydrogel (white beads), alginate-iron ion hydrogel (brown beads) and alginate iron nanoparticles (black beads) prepared in two step process (H1). 2.5. Characterizations Fourier transform infrared spectroscopy (FT-IR) spectra were recorded in range of 400- 4000 cm -1 on Bruker Tensor 27 FT-IR. X-ray diffraction (XRD) patterns were obtained with 2 from 10 to 70°, scan speed of 0.03°/0.7s using 8D-ADVANCE diffractometer with Cu-Kα radiation (λ=1.54184 Å) at 40 kV and 40 mA. Magnetic property of iron oxide nanoparticles was measured on vibration sample magnetometer (VSM), EV11-VSM, Microsense LLC. Transmission electron microscope (TEM), JEM-1400 (JEOL, USA) was used. 3. RESULTS AND DISCUSSION 3.1. Chemical structure of materials characterized by FT-IR spectroscopy 4000 3500 3000 2500 2000 1500 1000 500 C=O , OH CH ~ 2920, 2680 cm -1 OH Fe-O T ra n s m it ta n c e ( a .u .) Wavenumber (cm -1 ) T30 H1 H2 CA OH ~ 3400 cm -1 Fe-O Figure 2. Fourier transform infrared spectra of Fe3O4 nanoparticles (T30), calcium-alginate (CA) and magnetic hydrogel (H1, H2). Ngoc Uyen Nguyen-Thai, et al. 170 The interaction of alginate with iron oxide was determined through FT-IR spectra. Representative FT-IR spectra of calcium-alginate (CA), iron oxide nanoparticles (T30) and magnetic hydrogel were presented in Figure 2. FT-IR spectrum of iron oxide (T30) exhibits characteristic vibrations in low frequency region (1000-500 cm -1 ) [6]. Two absorption bands appear at 580, 450 cm -1 attributed to the stretching vibration mode of Fe-O bonds in the tetrahedral and octahedral sites in Fe3O4, respectively. The OH stretching and bending vibration of absorbed water is appeared at 3390 and 1625 cm -1 , respectively. The characteristic vibrations of CA are observed on IR spectrum which is 5 times magnification for clarification. The broad peaks in the region of 3750-3000 cm -1 are attributed for the stretching vibration of OH stretching vibration. The band at 2920 and 2860 cm -1 are due to stretching vibration mode of –CH2 and –CH3 in the backbone of CA. The absorption band at ~ 1630 cm -1 are due to stretching vibration of C=O groups on alginate combine with O-H bending vibrations. In magnetic hydrogel (H1, H2) spectra, the characteristic vibration of CA and T30 were all appear indicating the formation of iron nanoparticle in calcium alginate matrix. 3.2. Crystal structure of materials characterized by XRD and TEM microscopy The crystal structure and the morphology of magnetic hydrogel were determined using XRD (Figure 3) and TEM (Figure 4). X-ray diffraction patterns of T30 and H1, H2 exhibited the typical crystal structure of spinel ferrite at diffraction peaks at 30.4° (220) , 35.5° (311), 43.5° (400), 57.1° (511), 62.9° (440) [6] indicating the successful formation of iron oxide magnetic particles. However, the presence of alginate caused the peaks of (200), (400), (511), (440) are broad. 10 15 20 25 30 35 40 45 50 55 60 65 70 In te n s it y 2 ( ) T30 H1 H2 220 311 400 511 440 Figure 3. Powder X-ray diffraction patterns of Fe3O4 nanoparticles (T30) and magnetic hydrogel (H1, H2). Since the (311) peak is the most prominent peak for all samples, the average grain sizes of Fe3O4 nanoparticles were calculated based on the Scherrer equation for the (311) peaks. The Preparation of magnetic hydrogel by in-situ coprecipitation process 171 results were presented in Table 1. It could be observed that the average grain sizes of T30, H1 and H2 were of 8.5, 5.4 and 5.6 nm, respectively. The smaller iron oxide particles of H1 and H2 than T30 proved the efficient in decreasing the size of iron oxide magnetic particles by alginate hydrogel. Table 1. Iron oxide nanoparticles size calculated by Scherrer equation. Sample FHMW Particle size (nm) T30 0.98 8.5 H1 1.55 5.4 H2 1.45 5.6 Figure 4 showed the representative TEM images of magnetic hydrogel, H1. It can be seen that the particle sizes are distributed in a broad range with the most abundance particle size lower than 6 nm. It is also observed that the very small particles (the circles in Figure 4) appeared which may be the results of iron oxide nanoparticle trapped inside the alginate matrix. Figure 4. TEM images of magnetic hydrogel H1. Compared with the previous reports, the size of H1, H2 are of equivalent to the smallest sizes of MNPs [5, 8, 9]. The decrease of MNP size can be attributed to the limit of the crystal growth since the Fe (II) and Fe (III) ions are trapped inside the hydrogel matrix. 3.3. Magnetization properties The magnetism of samples were showed via magnetization curves presented in Figure 5 and Table 2. According to vibrating sample magnetometer results, Fe3O4-CA nanoparticles exhibit superparamagnetism behavior with significantly lower Hc and Mr/Ms (Table 2, Figure 5) than that of T30. Although the saturation magnetization (Ms) of Fe3O4 was 70.83 emu/g, which is higher than those of H1, H2, the magnetizations of the hydrogels are high enough for biomedical application. In addition, the Mr/Ms values of H1 and H2 are significantly lower than T30 and the previous studies [8, 9]. In the limit of the authors’ knowledge, this is the lowest Mr/Ms has been reported. The low Mr/Ms value means no remanence exists in the sample after removing the external magnetic field that is suitable for applications in the biomedical fields. The significantly drop of Mr and Mr/Ms value are still unclear, it may attributed to the Ngoc Uyen Nguyen-Thai, et al. 172 significantly small size of MNP (Figure 4). At this nanometer size, the MNP exists as single domain, therefore, the remanence closes to zero value at room temperature. Table 2. The magnetic parameters obtained from magnetization curves. Sample Ms (emu/g) Mr (×10 -3 emu/g) Hc(Oe) Mr/Ms (×10 -3 ) T30 70.8 5044 54.8 71.2 H1 13.0 11 1.1 0.8 H2 24.9 148 2.7 5.9 -15000 -10000 -5000 0 5000 10000 15000 -80 -60 -40 -20 0 20 40 60 80 M ( e m u /g ) H (Oe) T30 H1 H2 -70 0 70 -5 0 5 Figure 5. Magnetization curves of Fe3O4 nanoparticles (T30) and magnetic hydrogels (H1, H2). Inset is a magnified magnetization curves. 4. CONCLUSIONS We synthesized magnetic hydrogel by the in-situ co-precipitation method. Two in-situ co- precipitations were performed. The process that involved the initial formation of calcium alginate hydrogel before incorporation with iron ion and co-precipitation to afford in-situ magnetic nanoparticles in alginate hydrogel showed the most efficient method. Magnetic nanoparticles produced by this two steps possesses the typical spinel structure and exhibit significantly low remanence magnetization (Mr) and (Mr/Ms) of 1.1 Oe and 0.8 10 -3 , respectively. The particle size of H1 is also small and about 5.4 nm. The present study presented a facile, efficient way to synthesis significantly small iron oxide nanoparticles in-situ in the alginate hydrogel. The combination of magnetic nanoparticles in hydrogel matrix promises the efficient applications in biomedical such as controlled release drug substance and improved the drug delivery systems. Acknowledgements. Authors would like to acknowledge the support from University of Science, VNU-HCM city under Grant number T2016-19. Preparation of magnetic hydrogel by in-situ coprecipitation process 173 REFERENCES 1. Philippova O., Barabanova A., Molchanov V., Khokhlov A. - Magnetic polymer beads: Recent trends and developments in synthetic design and applications, European polymer journal 47 (2011), 542-559. 2. Lee K. Y., Mooney D. J. - Alginate: properties and biomedical applications, Progress in polymer science 37 (1) (2012) 106-126. 3. Pawar S. N., Edgar K. J. - Alginate derivatization: a review of chemistry, properties and applications, Biomaterials 33 (11) (2012) 3279-3305. 4. Pasparakis G., Bouropoulos N. - Swelling studies and in vitro release of verapamil from calcium alginate and calcium alginate-chitosan beads, International journal of pharmaceutics 323 (2006) 34-42. 5. Liao S. H., Liu C. H., Bastakoti B. P., Suzuki N., Chang Y., Yamauchi Y., Lin F. H., Wu, K. C. - Functionalized magnetic iron oxide/alginate core-shell nanoparticles for targeting hyperthermia, International journal of nanomedicine 10 (2015) 3315-3327. 6. Ma H. L., Qi X. R., Maitani Y., Nagai T. - Preparation and characterization of superparamagnetic iron oxide nanoparticles stabilized by alginate, International journal of pharmaceutics 333 (1-2) (2007) 177-186. 7. Cuong, N.D., Thu, T.T.A., Trinh, H.T.H., Anh, N.D.M. - A study on the synthesis of alginate coated magnetite nanoparticles, Journal of Science and Education, Hue university's college of education 1 (2011) 43-48. 8. Morales M. A., Finotelli P. V., Coaquira J. A. H., Rocha-Leão M. H. M., Diaz-Aguila C., Baggio-Saitovitch E. M., Rossi A. M. - In situ synthesis and magnetic studies of iron oxide nanoparticles in calcium-alginate matrix for biomedical applications, Materials science and engineering: C 28 (2008) 253-257. 9. Kroll E., Winnik F. M., Ziolo R. F. - In situ preparation of nanocrystalline γ-Fe2O3 in iron(II) cross-linked Alginate gels, Chemistry of materials 8 (1996) 1594-1596. 10. Li Y., Huang G., Zhang X., Li B., Chen Y., Lu T., Lu T. J., Xu F. - Magnetic hydrogels and their potential biomedical applications, Advanced Functional Materials 23 (2013) 660-672.