Encapsulation of Magnetic Nanoparticles with Biopolymer for Biomedical Application Suk Fun Chin, Mohamed Makha, Colin L Raston School of Biomedical, Biomolecular and Chemical Sciences The University of Western Australia, Crawley, Western Australia 6009 Email:
[email protected] Telephone: (618) 64881572, Fax: (618) 64881005 nanoparticles will not only improve the biocompatibility of magnetite nanoparticles but also provides amino and hydroxyl groups for interplay with biomolecules. Furthermore, chitosan can be produced by deacetylation of chitin. Chitin is the main component of exoskeleton of crustaceans and is the second most abundant natural polymer after cellulose, and therefore is a cheap, renewable biopolymer [7].
Abstract—Magnetite nanoparticles were synthesized by coprecipitation of Fe2+ and Fe3+ with NH4OH using Spinning Disc Processing (SDP). Chitosan was then coated on the surface of magnetite nanoparticles using SDP. FTIR study and zeta potential measurement confirmed the absorption of chitosan unto the surface of magnetite nanoparticles. Transmission electron microscope (TEM) image showed that the particle sizes are in the range 10 – 200 nm.
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A) Synthesis of magnetite nanoparticles
Keywords-magnetite, nanoparticles; chitosan; coating
I.
Magnetite nanoparticles were prepared by coprecipitation of ferric and ferrous chlorides (1:2) with aqueous ammonia solution. Both solutions were purged with argon gas for at least 15 minutes and then continuously fed into the SDP at feeding rate of 0.5 ml/s. The disk spinning rate was 2000 rpm. The synthesis was carried out under an argon atmosphere. The conical flask contained the resulting magnetite was placed on a permanent magnet, the supernatant solution was discarded. Deoxygenated ultra pure deionized water was added to wash the magnetite nanoparticles. This process was repeated for several times until the pH of the suspension was nearly neutral. The magnetite nanoparticles were then re-dispersed in deoxygenated deionized water.
INTRODUCTION
Magnetic nanoparticles have been extensively studied because of their potential applications as contrast agents in magnetic resonance imaging (MRI) of tumors, cell and DNA separation, magnetically guided drug delivery, tumor hyperthermia etc. [1-3]. Among the magnetic oxides, magnetite nanoparticles are most suitable due to their low toxicity and good magnetic properties. Magnetite is a ferromagnetic iron oxide, Fe3O4 with an inverse spinel crystalline structure in which part of the iron atoms are octahedrally coordinated to oxygen and the rest are tetrahedrally coordinated to oxygen [4]. However, magnetite tends to aggregate due to strong magnetic dipole-dipole attractions between particles combined with inherently large surface energy.
B) Coating of magnetite nanoparticles with chitosan
In order to successfully prepare stable magnetite dispersions, any attractive forces between the nanoparticles must be overcome. Stabilizers or surfactants have been used to prevent sedimentation of these nanoparticles. The choice of stabilizer relates to its ability to interact with magnetite particles via functional groups and form a tightly bonded monomolecular layer around the particles. Another possible way of stabilizing iron oxide nanoparticles in aqueous solution is to encapsulate them with polymeric materials. The polymer coatings serve as a steric barrier which reduces magnetic attractions between the particles. Besides these, coatings on magnetite nanoparticles can also improve chemical stability by protecting the particles surface from oxidation.
Chitosan solution was prepared by dissolved various amount of chitosan in 1% of acetic acid. Chitosan coated magnetite nanoparticles were prepared by mixing the preformed magnetite nanoparticles with chitosan solution using SDP at feeding rate of 0.5 ml/s and at 1500 rpm disk spinning rate. The chitosan coated magnetite nanoparticles were then washed several times with deionized water to remove the excess chitosan in the suspension. C) Characterization The FTIR spectra of the samples were recorded on a Perkin Elmer FTIR Spectrometer at 4 cm-1 resolution. Samples were ground-blended with KBr and the compressed to form pellet. All the spectra were recorded at the range of 400 – 4000 cm-1.
In this study, encapsulation of magnetite nanoparticles using chitosan coupled with Spinning Disk Processing (SDP) technique is reported. As a natural biopolymer, chitosan is a hydrophilic, biocompatible, biodegradable and non-toxic polymer, making it attractive for biomedical applications [5-6]. The presence of a shell of this biopolymer around magnetite
1-4244-0453-3/06/$20.00 2006 IEEE
MATERIALS AND METHOD
Zeta potentials of uncoated magnetite and chitosan coated magnetite as a function of pH were determined using a Zetasizer Nano ZS series (Malvern Instruments Ltd., UK).
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A Philips 410 transmission electron microscope (TEM) was used to investigate the particle size and morphology of chitosan coated magnetite nanoparticles. The applied operating voltage was 80 kV. III.
chitosan. As observed in Figure 2, the IEP of chitosan coated magnetite is shifted from pH 6.3 to 8.6. As the reported IEP of chitosan is at pH 8.7 [10], this shift of IEP can be explained by the formation of chitosan on the surface of magnetite nanoparticles.
RESULT AND DISCUSSION
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The FTIR spectra of chitosan, chitosan coated magnetite and uncoated magnetite are shown in Figure 1. Both the chitosan and chitosan coated magnetite exhibited the characteristics peaks of chitosan. The absorption peak observed at 3436 cm-1 is due to the hydroxyl (OH-) group and the peak at 1637 cm-1 is due to the amine group (-NH2). The absorption peak at around 1072 cm-1 relates to C-C and C-O stretching modes of polysaccharides backbone, and the bending vibration of –CH2 group is at 1400 cm-1 [8] . The characteristic peaks of magnetite at 582 cm-1 and 565 cm-1 were also observed in the spectra of magnetite and chitosan coated magnetite. These spectra confirmed that the chitosan has coated onto the surface of magnetite. However, the spectra of chitosan coated magnetite nanoparticles showed very little difference from the pure chitosan indicating weak interactions between chitosan and magnetite nanoparticles.
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Figure 2. Zeta potential of magnetite nanoparticles and chitosan coated magnetite nanoparticles as a function of pH value.
TEM imaging of chitosan coated magnetite nanoparticles is shown in Figure 3. The image indicated that the particle sizes range from 10 – 200 nm. The broad size distribution may be due to the formation of aggregation of the magnetite. It can be seen from the image that the magnetite nanoparticles are surrounded by the chitosan.
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Figure 1. FTIR spectra of chitosan, chitosan coated magnetite and magnetite.
The zeta potential of magnetite nanoparticles with and without chitosan coating as a function of pH value is highlighted in Figure 2. The surface charge potential of iron oxides in water at various pH values could be explained by surface hydroxyl groups of iron oxides (FeOH) [9]. In a basic environment, the surface of iron oxide shows negative charge potential due to the dissociation of FeOH to form FeO-. In contrast, in an acidic environment, the positive surface charge is due to the formation of FeOH2+. The measured isoelectric point (IEP) of uncoated magnetite is at ~pH 6.3. This value is very close to the reported value of magnetite which is at about pH 6 [9]. After coated with chitosan, the zeta potential of the magnetite are more positive below the IEP and less negative above the IEP. The coating of chitosan not only reduced the number of negative surface sites but also induced positive surface sites due to the protonization of –NH2 groups of
Figure 3.
TEM image of chitosan coated magnetite nanoparticles
CONCLUSION In conclusion, we have successfully coated chitosan onto the surface of magnetite by SDP. Future work will focus on optimizing the synthesis conditions for preparation of stable chitosan derivative coated magnetite nanoparticles with desirable particles size, surface and magnetic properties for biomedical applications.
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[4]
R.M. Cornell, U. Schwertmann. The Iron Oxides; VCH: New York, 1996. [5] Z.Ma, H.H, Yeoh, L.Y. Lim. “Formulation pH modulates the interaction of insulin with chitosan nanoparticles” J. Pharm Sc. Vol.91, No.6, pp1396 -1404, 2002. [6] T. Chandy, CP, Sharma. “Chitosan beads and granules for oral sustained delivery of nifedipine: In vitro studies. Biomaterials. Vol.13, pp 949952, 1992. [7] Q. Li, E.T. Dunn, E.W. Grandmaison, M.F. Goosen. “Application and Properties of chitosan. In Applications of chitin and Chitosan; M.F. Goosen, Ed., Technomic Publishing: Lancaster, P.A, pp 3 -29, 1997. [8] J.Brugnetto, J. Lizardi, F.M. Goycoolea, W. Argulles-Monal, J. Desbrieres, M. Rinaudo. “An infrared investigation in relation with chitin and chitosan characterization. Polymer. Vol.42, pp 3569 -3580, 2001. [9] Z.X. Sun, F.W.Su, W. Forsling, P.O. Samskorg. “ Surface characteristics of magnetite in aqueous suspension”. Vol. 197, pp 151 – 157, 1998. [10] C.Huang, Y. Chen. “Coagulation of colloidal particles in water by chitosan”. J. Chem. Tech. Biotechnology. Vol 66, pp227 – 232, 1996.
ACKNOWLEDGMENT The authors would like to gratefully acknowledge University of Malaysia Sarawak and The University of Western Australia for the support of this work. REFERENCES [1]
[2]
[3]
D.C.F. Chan, D.B. Kirpotin, P.A. Bunn. “ Synthesis and evaluation of colloidal magnetic iron oxides for the site-specific radiofrequencyinduced hyperthermia of cancer. J. Magn. Magn. Mater. Vol.122, pp 374 – 378, 1993, H. Chen, R. Langer. “Magnetically-responsive polymerized limposomes as potential oral delivery vehichles” Pharm. Res. Vol. 14, pp 537 – 540, 1997. D.K. Kim, , Y.Zhang, J. Kehr, Klason, T, B. Bjelke, M. Muhammed. “ Characterization and MRI study of surfacted-coated superparamagnetic nanoparticles into the rat brain”. J. Magn. Magn. Mater. Vol 225, pp 256 -261, 2001.
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