Superparamagnetic Hybrid Micelles, Based on Iron Oxide

Jul 23, 2009 - Department of Mechanical and Manufacturing Engineering, University of Cyprus, P.O. Box 20537,. 1678 Nicosia, Cyprus, Division of ...
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Biomacromolecules 2009, 10, 2662–2671

Superparamagnetic Hybrid Micelles, Based on Iron Oxide Nanoparticles and Well-Defined Diblock Copolymers Possessing β-Ketoester Functionalities Petri Papaphilippou,† Louiza Loizou,‡ Nicolae C. Popa,§ Adelina Han,| Ladislau Vekas,§ Andreani Odysseos,*,‡ and Theodora Krasia-Christoforou*,† Department of Mechanical and Manufacturing Engineering, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus, Division of Biomedical Research, EPOS-Iasis R&D, 5 Karyatidon Street, 2028 Nicosia, Cyprus, Center for Fundamental and Advanced Technical Research, Romanian Academy, Timisoara Branch, Bd. Mihai Viteazul, No. 24, 300223 Timisoara, Romania, and National Center for Engineering of Systems with Complex Fluids, University Politechnica Timisoara, Bd. Mihai Viteazul 1 RO-1900 Timisoara, Romania Received May 26, 2009; Revised Manuscript Received June 29, 2009

The quality of surface coating of magnetic nanoparticles destined as nanoprobes in clinical applications is of utmost significance for their colloidal stability and biocompatibility. A novel approach for the fabrication of such a coating involves the synthesis of well-defined diblock copolymers based on 2-(acetoacetoxy)ethyl methacrylate (chelating) and poly(ethylene glycol)methyl ether methacrylate (water-soluble, thermoresponsive), prepared by reversible addition-fragmentation chain transfer polymerization. Fabrication of magneto-responsive micelles was accomplished via chemical coprecipitation of Fe(III)/Fe(II) in the presence of diblock copolymers. Further to the characterization of micellar morphologies, optical and thermal properties, assessment of magnetic characteristics disclosed superparamagnetic behavior. The hybrid micelles did not compromise cell viability in cultures, while in vitro uptake by macrophage cells was significantly lower in comparison to that of the clinically applicable contrast agent Resovist, suggesting that these systems can evade rapid uptake by the reticuloendothelial system and be useful agents for in vivo applications.

Introduction The combination of metallic species with polymeric materials is a research area receiving much attention nowadays, due to the possibility of preparing complex, well-defined materials and devices in which novel photonic, electronic, magnetic, and structural properties may be combined.1 This in turn may lead to new materials that could be potentially used in a wide range of applications such as catalysis,2 wastewater treatment,3 information storage,4 biomedicine,5 semiconductor technologies,6 and nanolithography.7 Most polymeric materials are characterized by low surface energies; therefore, in order for a polymer to be able to adhere efficiently onto a metallic surface, the development of specific polymer-metal interactions is required. Such interactions include, among others, hydrogen or covalent bonding and dipolar and electrostatic interactions and require the presence of specific functional sites on the polymer backbone. The resulting organic-inorganic hybrid materials are of particular interest because they inherit properties of (a) the polymers, such as good mechanical performance and well-defined nanomorphologies, and (b) the metallic compounds, including magnetic, catalytic, and optical properties. In particular, the use of amphiphilic block copolymer micelles as nanoreactors for the preparation of ordered nanoparticle arrays has been an area of great scientific * To whom correspondence should be addressed. Tel.: +357 22892288 (T.K.-C.); +357 22894502 (A.O.). Fax: +357 22892254. E-mail: krasia@ ucy.ac.cy (T.K.-C.); [email protected] (A.O.). † University of Cyprus. ‡ EPOS-Iasis. § Romanian Academy. | University Politechnica Timisoara.

interest due to their broad range of applications.8-11 Of major significance is their use as nanoprobes for magnetic resonance imaging (MRI)12 when combined with magnetoactive inorganic materials. Superparamagnetic iron oxide nanoparticles (SPIONs) have been used in a wide range of applications including nanoscale electronic devices13 and magnetic storage.14 SPIONs are currently used as contrast enhancement agents in MRI15 and are being investigated for in vivo drug delivery.16 Such clinical applications require that the SPIONs remain stably dispersed in aqueous media. At a nanoscale level, this is a difficult target because the nanoparticles are characterized by large surfaceto-volume ratios, hence, presenting the tendency to aggregate to reduce their surface energies. Furthermore, additional magnetic dipole-dipole attractive forces between the nanoparticles enhance agglomeration.17 Considering the above-mentioned, the nature of the “coat” of superparamagnetic iron oxide nanoparticles is of paramount significance.18 Primarily, it influences the stability and surface properties of their colloidal dispersions. For their stabilization in aqueous media, electrostatic and steric stabilizing agents such as organic surfactants and polymers have been incorporated into inorganic colloidal dispersions.19-21 Particularly, functionalized water-soluble block copolymers are capable of providing solubility in water (via the hydrophilic block segment) and simultaneously bind onto magnetic nanoparticles (via the functionalized segment), providing effective nanoparticle stabilization in solution.22,23 Major parameters considered in the selection and design of coating materials for SPIONs include (a) their in vivo kinetics and biodistribution and (b) the potential to target them to specific tissues or molecules of interest by conjugation with affinity

10.1021/bm9005936 CCC: $40.75  2009 American Chemical Society Published on Web 07/23/2009

Superparamagnetic Hybrid Micelles

probes (peptides, antibodies, aptamers, small molecules).24-26,18b Intense efforts are currently directed toward targeted (functionalized) nanoparticles which are expected to reach the clinic in the foreseeable future.26,27 Current MRI applications involve mainly dextran- and carboxydextran-coated SPIONs that have been already approved in clinical use, such as Endorem or Feridex IV (generic name: ferumoxides, 100-250 nm diameter) and Resovist (generic name: ferucarbotran, ∼60 nm diameter).28 These dextran-based agents are readily and nonspecifically taken up by phagocytic cells and accumulate in the reticuloendothelial system (RES) such as lymph nodes, spleen and the Kupffer cells of the liver. Thus they are commonly used as contrast agents for liver MRI.28a Furthermore, such dextran-based SPIONs are used in clinical MRI to assist accurate cancer imaging, nodal staging and detection of metastases.28b-2930 A significant drawback of polysaccharide coatings is that they present structural instability in highly acidic environments.31 Furthermore, in dextran-coated nanoparticles, dextran is not strongly associated with the iron oxide core and can be easily detached from the surface of the iron oxide particles, leading to their aggregation and eventually their precipitation under physiological conditions.26 To minimize the nonspecific uptake of the nanoparticles by macrophages32-35 and achieve longer circulating times and wider delivery time-windows, numerous significant attempts have been made toward (a) decreasing particle size ( 0.05). Further comparison of M1 or M2 with H2O by paired Student’s t-test failed to yield any statistically significant differences in cell viability (Pv ) 0.22 and 0.26, respectively), providing substantial evidence that these systems are biocompatible in cell cultures and thus safe for further studies. Similar in vitro biocompatibility data have

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Figure 13. In vitro uptake of hybrid micelles by macrophages determined by Prussian Blue staining after incubation for 2 h with the indicated agent at a concentration equivalent of 0.15 mg Fe/mL in complete media: (A) Resovist, (B) hybrid micelle M1, (C) hybrid micelle M2, (D) untreated control. The presence of Prussian Blue precipitate arising from the formation of potassium ferrous ferricyanide reveals the accumulation of the Fe-based agent into the cells.

been provided by Lee et al. for a comparable poly-PEGMAbased SPION,32 which has been safely applied in preclinical studies. In Vitro Macrophage Uptake. Lowering the uptake of SPIONs by RES, such as macrophages, for the magnetic nanoparticles to circulate long enough and be accumulated into the tumor by the enhanced permeability and retention (EPR) effect remains a key consideration for the in vivo use of SPIONs for in vivo imaging of cancer. To assess this property in vitro, cell uptake experiments were conducted using the RAW264.7 macrophage cell line. The uptake of both M1 and M2 was compared to that of the clinically approved dextran-based agent Resovist, which is of comparable size and has well-established uptake by macrophages.64 The incorporation of M1, M2, and Resovist into the cells was determined by Prussian Blue staining, following a 2 h incubation with the macrophages (Figure 13). Interestingly, most of the cells retained a blue staining as a result of high uptake in the samples treated with Resovist (Figure 13A), whereas both M1 and M2 showed significantly lower uptake (Figure 13B,C). These data strongly suggest that the coating layer with (AEMA36-b-PEGMA292) in these systems minimizes pronouncedly the recognition and phagocytosis of the hybrid micelles by macrophages.

Conclusions Conclusively, we have presented that the PEGMAx-b-AEMAy diblock copolymers enable stabilization of iron oxide magnetic nanoparticles in water via encapsulation within the AEMA ligating core, resulting in novel biocompatible superparamagnetic hybrid micelles. The tunable superparamagnetic behavior exhibited by these materials depending on the amount of iron oxide loaded inside the micellar core contributes effectively to their efficacy as potential nanomagnets, while their thermoresponsive properties may allow for their future exploitation as potential drug delivery agents. In vitro biocompatibility at Fe concentrations up to 100 µg/mL provide strong grounds for upcoming in vivo investigations. These hybrid micelles exhibited macrophage exclusion, superior to those of the tested dextran-based magnetic contrast agent. These properties which are directly associated to the wellcharacterized PEGMAx-b-AEMAy outer shell are expected to

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endow these novel superparamagnetic hybrid self-assemblies with distinct and valuable biodistribution characteristics that would enable their potential application as magnetic contrast agents. Acknowledgment. This work was financially supported by the Cyprus and Romania Research Promotion Foundations (bilateral collaboration program, KY-POY/0407/09) and the project NANOMA-FP7-ICT-2007-2. We are grateful to Profs. C. S. Patrickios and P. Koutentis for useful comments and for providing access to the DLS, DSC, turbidimetry, and TGA apparati. We also thank Ms. M. Ioannou and Dr. T. Kyratsi for the XRD measurements and Ms. A. Heilig (Max-Planck Institute of Colloids and Interfaces, Potsdam) for the AFM measurements. We are deeply indebted to Dr I. Seimenis for stimulating discussions and valuable information on the MRI clinical applicability of SPIONs.

References and Notes (1) Grubbs, R. B. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 4323– 4336. (2) Muller, C.; Nijkamp, M. G.; Vogt, D. Eur. J. Inorg. Chem. 2005, 20, 4011–4021. (3) Savage, N.; Diallo, M. S. J. Nanopart. Res. 2005, 7, 331–342. (4) Pyun, J. Polym. ReV. 2007, 47, 231–263. (5) (a) Harris, L. A.; Goff, J. D.; Carmichael, A. Y.; Riffle, J. S.; Harburn, J. J.; St. Pierre, T. G.; Saunders, M. Chem. Mater. 2003, 15, 1367– 1377. (b) Leary, S. P.; Liu, C. Y.; Apuzzo, M. L. I. Neurosurgery 2006, 58, 1009–1025. (6) (a) Zhao, H.; Douglas, E. P.; Harrison, B. S.; Schanze, K. S. Langmuir 2001, 17, 8428–8433. (b) Cheng-Chien, W.; An-Liu, C.; I-Han, C. J. Colloid Interface Sci. 2006, 293, 421–429. (c) Black, C. T.; Ruiz, R.; Breyta, G.; Cheng, J. Y.; Colburn, M. E.; Guarini, K. W.; Kim, H.C.; Zhang, Y. IBM J. Res. DeV. 2007, 51, 605–633. (7) (a) Chai, J.; Wang, D.; Fan, X. N.; Buriak, J. M. Nat. Nanotechnol. 2007, 2, 500–506. (b) Krishnamoorthy, S.; Hinderling, C.; Heinzelmann, H. Mater. Today 2006, 9, 40–47. (8) (a) Ka¨stle, G.; Boyen, H.-G.; Weigl, F.; Lengl, G.; Herzog, T.; Ziemann, P.; Riethmu¨ller, S.; Mayer, O.; Hartmann, C.; Spatz, J. P.; Mo¨ller, M.; Ozawa, M.; Banhart, F.; Garnier, M. G.; Oelhafen, P. AdV. Funct. Mater. 2003, 13, 853–861. (b) Bro¨nstein, L.; Kramer, E.; Berton, B.; Burger, C.; Fo¨rster, S.; Antoniett, M. Chem. Mater. 1999, 11, 1402–1405. (c) Lohmueller, T.; Bock, E.; Spatz, J. P. AdV. Mater. 2008, 20, 2297–2302. (d) Abraham, S.; Ha, C. S.; Batt, C. A.; Kim, I. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 3570–3579. (9) (a) Bruinink, C. M.; Peter, M.; Maury, P. A.; De Boer, M.; Kuipers, L.; Huskens, J.; Reinhoudt, D. N. AdV. Funct. Mater. 2006, 16, 1555– 1565. (b) Aizawa, M.; Buriak, J. M. J. Am. Chem. Soc. 2006, 128, 5877–5886. (c) Yun, S.-H.; Sohn, B.-H.; Jung, J. C.; Zin, W.-C.; Lee, J.-K.; Song, O. Langmuir 2005, 21, 6548–6552. (d) Bennett, R. D.; Miller, A. C.; Kohen, N. T.; Hammond, P. T.; Irvine, D. J.; Cohen, R. E. Macromolecules 2005, 38, 10728–1073. (10) (a) Hou, W. B.; Dehm, N. A.; Scott, R. W. J. J. Catal. 2008, 253, 22–27. (b) Li, D. J.; Dunlap, J. R.; Zhao, B. Langmuir 2008, 24, 5911– 5918. (c) Bergbreiter, D. E. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 2351–2363. (11) (a) Park, I. S.; Jung, K.; Kim, D.; Kim, S. M.; Kim, K. J. MRS Bull. 2008, 33, 190–195. (b) He, S.; Iacono, S. T.; Budy, S. M.; Dennis, A. E.; Smith, D. W.; Smith, R. C. J. Mater. Chem. 2008, 18, 1970– 1976. (c) Caliendo, C.; Fratoddi, I.; Russo, M. V.; Sterzo, C. L. J. Appl. Phys. 2003, 93, 10071–10077. (12) (a) Lee, J.; Yang, J.; Seo, S.-B.; Ko, H.-J.; Suh, J.-S.; Yong-Min Huh, Y.-M.; Haam, S. Nanotechnology 2008, 19, 1–9. (b) Qin, J.; Laurent, S.; Jo, Y. S.; Roch, A.; Mikhaylova, M.; Bhujwalla, Z. M.; Muller, R. N.; Muhammed, M. AdV. Mater. 2007, 19, 1874–1878. (13) Murray, C. B.; Kagan, C. R.; Wendi, M. G. Science 1995, 270, 1335– 1338. (14) Chakraborty, A. J. Magn. Magn. Mater. 1999, 204, 57–60. (15) Berry, C. C.; Curtis, A. S. G. J. Phys. D 2003, 36, R198-R206. (16) Roullin, V. G.; Deverre, J.-R.; Lemaire, L.; Hindre´, F.; Venier-Julienne, M.-C.; Vienet, R.; Benoit, J.-P. Eur. J. Pharm. Biopharm. 2002, 53, 293–299. (17) Vekas, L.; Avdeev, M. V. Bica, D. In Nanoscience in Biomedicine; Donglu S., Ed.; Springer, New York, 2009.

Papaphilippou et al. (18) (a) Gupta, A. K.; Gupta, M. Biomaterials 2005, 26, 3995–4021. (b) Gupta, A. K.; Naregalkar, R. R.; Vaidya, V. D.; Gupta, M. Nanomedicine 2007, 2, 23–39. (19) Shen, L.; Laibinis, P. E.; Hatton, T. A. Langmuir 1999, 15, 447–453. (20) Wormuth, K. J. Colloid Interface Sci. 2001, 241, 366–377. (21) Harris, L. A.; Goff, J. D.; Carmichael, A. Y.; Riffle, J. S.; Harburn, J. J.; St. Pierre, T. G.; Saunders, M. Chem. Mater. 2003, 68, 1367– 1377. (22) (a) Wan, S.; Zheng, Y.; Liu, Y.; Yan, H.; Liu, K. J. Mater. Chem. 2005, 15, 3424–3430. (b) Wan, S.; Huang, J.; Liu, Y.; Yan, H.; Liu, K. J. Mater. Chem. 2006, 16, 298–303. (23) Bronstein, L. M.; Kostylev, M.; Shtykova, E.; Vlahu, T.; Huang, X.; Stein, B. D.; Bykov, A.; Remmes, N. B.; Baxter, D. V.; Svergun, D. I. Langmuir 2008, 24, 12618–12626. (24) Bulte, J. W.; Kraitchman, D. L. NMR Biomed. 2004, 17, 484–499. (25) Neves, A. A.; Brindle, K. M. Biochim. Biophys. Acta 2006, 1766, 242–261. (26) McCarthy, J. R.; Weissleder, R. AdV. Drug DeliVery ReV. 2008, 60, 1241–1251. (27) Peng, X. H.; Qian, X.; Mao, H.; Wang, A. Y.; Chen, Z. G.; Nie, S.; Shin, D. M. Int. J. Nanomed. 2008, 3, 311–321. (28) (a) Reimer, P.; Tombach, B. Eur. Radiol. 1998, 8, 1198–1204. (b) Reimer, P.; Balzer, T. Eur. Radiol. 2003, 13, 1266–1276. (29) Tanimoto, A.; Kuribayashi, S. Eur. J. Radiol. 2006, 58, 200–216. (30) Harisinghani, M. G.; Barentsz, J.; Hahn, P. F.; Deserno, W. M.; Tabatabaei, S.; Van de Kaa, C. H.; De la Rosette, J.; Weissleder, R. N. Engl. J. Med. 2003, 348, 2491–2499. (31) Leslie-Pelecky, D. L.; Labhasetwar, V.; Kraus, R. H. In AdVanced Magnetic Nanostructures; Sellmyer, D. J., Skomski, R., Ed.; Springer: New York, 2006. (32) Lee, H.; Lee, E.; Kim Do, K.; Jang, N. K.; Jeong, Y. Y.; Jon, S. J. Am. Chem. Soc. 2006, 128, 7383–7389. (33) Zhang, Y.; Kohler, N.; Zhang, M. Biomaterials 2002, 23, 1553–1561. (34) Rogers, W. J.; Basu, P. Atherosclerosis 2005, 178, 67–73. (35) Leuschner, C.; Kumar, C. S.; Hansel, W.; Soboyelo, W.; Zhou, J.; Hormes, J. Breast Cancer Res. Treat. 2006, 99, 163–176. (36) Saini, S.; Sharma, R.; Baron, R. L.; Turner, D. A.; Ros, P. R.; Hahn, P. F.; Small, W. C.; Delange, E. E.; Stillman, A. E.; Edelman, R. R.; Runge, V. M.; Outwater, E. K. Clin. Radiol. 2000, 55, 690– 695. (37) Bulte, J. W.; Douglas, T.; Witwer, B.; Zhang, S. C.; Strable, E.; Lewis, B. K.; Zywicke, H.; Miller, B.; Van Gelderen, P.; Moskowitz, B. M.; Duncan, I. D.; Frank, J. A. Nat. Biotechnol. 2001, 19, 1141–1147. (38) Shi, X.; Thomas, T. P.; Myc, L. A.; Kotlyar, A.; Baker, J. R. Phys. Chem. Chem. Phys. 2007, 9, 5712–5720. (39) Illum, L.; Church, A. E.; Butterworth, M. D.; Arien, A.; Whetstone, J.; Davis, S. S. Pharm. Res. 2001, 18, 640–645. (40) Kohler, N.; Fryxell, G. E.; Zhang, M. J. Am. Chem. Soc. 2004, 126, 7206–7211. (41) Hu, F. X.; Neoh, K. G.; Cen, L.; Kang, E.-T. Biomacromolecules 2006, 7, 809–816. (42) Lutz, J.-F.; Stiller, S.; Hoth, A.; Kaufner, L.; Pison, U.; Cartier, R. Biomacromolecules 2006, 7, 3132–3138. (43) Kumar, A.; Sahoo, B.; Montpetit, A.; Behera, S.; Lockey, R. F.; Mohapatra, S. S. Nanomedicine 2007, 3, 132–137. (44) Wan, S. R.; Huang, J. S.; Guo, M.; Zhang, H.; Cao, Y.; Yan, H.; Liu, K. J. Biomed. Mater. Res. 2007, 80A, 946–954. (45) (a) Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S. H. Macromolecules 1998, 31, 5559–5562. (b) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2005, 58, 379– 410. (c) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2006, 59, 669–692. (46) Lutz, J. F. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 3459– 3470. (47) Mehrotra, R. C.; Bohra, B.; Gaur, D. P. Metal β-Diketonates and Allied DeriVatiVes; Academic Press: New York, 1978. (48) Le, T. P. T.; Moad, G.; Rizzardo, E.; Thang, S. H. PCT. Int. Appl. WO 9801478 A1 980115. (49) Massart, R. IEEE Trans. Magn. 1981, 17 (2), 1247–1248. (50) Mosmann, T. J. Immunol. Methods 1983, 65, 55–63. (51) Krasia, T.; Soula, R.; Bo¨rner, H. G.; Schlaad, H. Chem. Commun. 2003, 4, 538–539. (52) Neuberger, T.; Scho¨pf, B.; Hofmann, H.; Hofmann, M.; Von Rechenberg, B. J. Magn. Magn. Mater. 2005, 293, 483–486. (53) DiMarco, G.; Lanza, M.; Pieruccini, M. Solid State Ionics 1996, 89, 117–125.

Superparamagnetic Hybrid Micelles (54) (a) Lutz, J.-F.; Akdemir, O.; Hoth, A. J. Am. Chem. Soc. 2006, 128, 13046–13047. (b) Lutz, J.-F.; Hoth, A. Macromolecules 2006, 39, 893– 896. (c) Zhao, B.; Li, D.; Hua, F.; Green, D. R. Macromolecules 2005, 38, 9509–9517. (55) Maeda, Y.; Kubota, T.; Yamauchi, H.; Nakaji, T.; Kitano, H. Langmuir 2007, 23, 11259–11265. (56) Chen, S.; Li, Y.; Guo, C.; Wang, J.; Ma, J.; Liang, X.; Yang, L.-R.; Liu, H.-Z. Langmuir 2007, 23, 12669–12676. (57) (a) Hanabusa, K.; Suzuki, T.; Koyama, T.; Shirai, H. Makromol. Chem. 1992, 193, 2149–2161. (b) Dell’Anna, M. M.; Mastrorilli, P.; Rizzuti, A.; Suranna, G. P.; Nobile, C. F. Inorg. Chim. Acta 2000, 304, 21– 25. (c) Dell’Anna, M. M.; Gagliardi, M.; Mastrorilli, P.; Suranna, G. P.; Nobile, C. F. J. Mol. Catal. A 2000, 158, 515–520. (d) KrasiaT.; Schlaad, H. In Metal Containing and Metallo-supramolecular Polymers and Materials; Newkome, G. R., Manners, I., Schubert, U. S., Eds.; ACS Symposium Series 928; American Chemical Society: Washington, DC, 2006; p 157.

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(58) (a) Pich, A.; Bhattacharya, S.; Lu, Y.; Boyko, V.; Adler, H.-J. P. Langmuir 2004, 20, 10706–10711. (b) Bhattacharya, S.; Eckert, F.; Boyko, V.; Pich, A. Small 2007, 3, 650–657. (59) Suriano, F.; Coulembier, O.; Dege´e, P.; Dubois, P. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 3662–3672. (60) Jiang, L. M.; Sun, W. L.; Kim, J. Mater. Chem. Phys. 2007, 101, 291– 296. (61) Wan, S.; Zheng, Y.; Liu, Y.; Yan, H.; Liu, K. J. Mater. Chem. 2005, 15, 3424–3430. (62) Li, L. C.; Jiang, J.; Xu, F. Mater. Lett. 2007, 61, 1091–1096. (63) Reddy, K. R.; Lee, K.-P.; Gopalan, A. I. J. Appl. Polym. Sci. 2007, 106, 1181–1191. (64) Metz, S.; Bonaterra, G.; Rudelius, M.; Settles, M.; Rummeny, E. J.; Daldrup Link, H. E. Eur. Radiol. 2004, 14, 1851–1858.

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