Materials Science and Engineering C 30 (2010) 583–589

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Materials Science and Engineering C

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A biocompatible approach to surface modification: Biodegradable polymerfunctionalized super-paramagnetic iron oxide nanoparticles

Lin Sun, Chi Huang, Tao Gong, Shaobing Zhou ⁎School of Materials Science and Engineering, Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, 610031, PR China

⁎ Corresponding author. Tel.: +86 28 87634023; fax:E-mail addresses: shaobingzhou@swjtu.edu.cn, shao

(S. Zhou).

0928-4931/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.msec.2010.02.009

a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 October 2009Received in revised form 27 December 2009Accepted 9 February 2010Available online 23 February 2010

Keywords:BiodegradationBiomedicalMicrocarriersTissue cell cultureViabilitySuper-paramagnetic

In the study, Fe3O4 nanoparticles with a size range of 10–20 nm were firstly prepared by the modifiedcontrolled chemical coprecipitation method from the solution of ferrous/ferric mixed salt-solution in alkalinemedium. Then, the super-paramagnetic iron oxide nanoparticles were covalently modified by biodegradablepolymers such as polyethylene glycol (PEG) and poly(ethylene glycol)-co-poly(d,l-lactide) (PELA). The sizeand its distribution of the nanoparticles were determined by dynamic light scattering measurements (DLS).The magnetic nanoparticles was characterized by X-ray powder diffraction (XRD), transmission electronmicroscopy (TEM), electron diffraction (ED), Fourier transform infrared spectroscopy (FT-IR) and UV–visiblespectrophotometry (UV). Magnetic properties were measured using a vibrating sample magnetometer. Andthe 5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide (MTT) assay was performed to evaluate thebiocompatibility of the magnetic nanoparticles. The results showed that the Fe3O4 nanoparticlesfunctionalized by PEG and PELA possessed a mean size of 43.2 and 79.3 nm, respectively, and exhibitedan excellent biocompatibility.

+86 28 87634649.bingzhou@hotmail.com

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© 2010 Elsevier B.V. All rights reserved.

1. Introduction

In the past decades, more researchers had paid attention to super-paramagnetic iron oxide nanoparticles. The magnetite nanoparticleswith a small size, narrow particle size distribution and highmagnetization values had been used widely in many biomedicalapplications, such as targeted drug delivery [1,2], contrast agents inmagnetic resonance imaging [3] and hyperthermia treatment ofcancers [4,5]. These applications also need distinct surface propertiesof the magnetic nanoparticles, such as biocompatibility and function-ality. Furthermore, magnetic nanoparticles have a large surface area/volume ratio and tend to agglomerate and adsorb plasma proteins.When the nanoparticles agglomerate or are covered with adsorbedplasma proteins, they will be quickly cleared by macrophages [6].Therefore, surface modification of magnetic nanoparticles wasrequired in biomedical application, which can stabilize magnetitenanoparticles in the physiological environment, and functionalizemagnetite nanoparticles that are responsive to physical stimuli. Bysurface modification, magnetic stimuli responsive of magnetitenanoparticles combined with other stimuli responsive to create amulti-stimuli-responsive system, such as magnetic-thermo-respon-sive [7,8].

Several methods have been developed to modify the magnetitenanoparticles. The most commonly used method was to encapsulate

magnetic nanoparticles in a polymeric matrix, such as polylactic acid(PLA) or polylactic-co-glycolic acid (PLGA) microspheres [9,10], whichcan be used as a targeted drug delivery system. Magnetic-thermo-responsive was achieved by using some temperature-responsivepolymers [11], such as poly(N-isopropylacrylamide) (poly(NIPPAm),poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)(F127) and so on. The disadvantage of this method was that manynanoparticles were encapsulated in polymeric matrix together, whichmade the nanoparticles agglomerate and limited the application inbiomedicine. This method is very flexible since it allows for thepreparation of magnetic nanoparticles carrying a wide variety ofstabilizers. Whereas, the polymer-encapsulated methods have somedrawbacks: (1) broad distributions of magnetic nanoparticles aregenerally synthesized through this method, together with irregularcrystallite shapes,mainly due to the uncontrolled rate of nucleation thatoccurs in aqueous solutions [12]; (2) functional magnetic nanoparticleswith thismethod are unstablewhen the external environment changed.The reason is attributed to the lack of strong chemical bonds betweenpolymer and magnetic nanoparticles. Another method was to graftpolymer chains with some functional groups on the magnetitenanoparticle surface [13]. The steric effect of polymer chains canstabilize the magnetite nanoparticle in the physiological environment.And the magnetite nanoparticles were given the new functionality bythe functional groups in the polymer chains.

Poly(ethylene glycol) (PEG) is non-toxic and non-immunogenic.Its uncharged hydrophilic residues and high surface mobility leadhigh steric exclusion to stabilize the surface in aqueous systems, and itis effective in preventing the adsorption of proteins and adhesion of

584 L. Sun et al. / Materials Science and Engineering C 30 (2010) 583–589

cells [14,15]. Therefore, covalently immobilizing PEG on the surface ofmagnetic nanoparticles is expected to improve the biocompatibilityand stabilization of the nanoparticles. Moreover, PEG chains withsome functional groups can be combined with some biopolymers tocreate biodegradable copolymers, such as PELA [16], PEG-PCL [17],and so on [18–20].

In this work, PEG-silane was first synthesized by reacting PEGdicarboxylic acid with 3-aminopropyl triethoxysilane (APS) in thepresence of N, N-dicyclohexylcarbodiimide (DCC) and N-hydroxy-succinimide (NHS) as shown in Fig. 1. And then, magnetic nanopar-ticles were modified by hydrolysis of PEG-silane in an acidenvironment. The magnetic nanoparticles (MNPs) modified by PELApolymer were synthesized by a polycondensation reaction betweenPEG carboxylic acid on the surface of MNPs and the terminal

Fig. 1. Illustration of the mod

hydroxyls of PLAwith lowmolecular weight. Finally, PELA copolymerswere grafted onto the surface of MNPs by Si–O groups. FT-IR was usedto characterize the immobilization of PEG and PELA on the nano-particle surface. XRD was carried out to characterize the crystalline ofmagnetite. TEM was performed to characterize the morphology anddispersion. MTT assay was performed to assess the cytotoxicity.Histochemistry analysis was also performed.

2. Experimental procedures

2.1. Materials

The divalent (FeCl2·4H2O), trivalent (FeCl3·6H2O) iron salts,aqueous ammonium hydroxide (25–28%, w/w), and oleic acid (OA)

ification route of MNPs.

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were purchased from Chengdu KeLong Chemical Reagent Company(Sichuan, China) and used as received. 3-aminopropyl triethoxysilane(APS) was purchased from Nanjing Lipai Chemical Company (JiangSu,China) and used as received. Polyethylene glycol (PEG, Mw 1000) waspurchased from Chengdu KeLong Chemical Reagent Company andused after purification. Polylactic acid (PLA, Mn 600) was synthesizedas our previous report [21]. The cells were obtained from the neonatalrat's mandibular osteoblasts.

2.2. Synthesis of Fe3O4 nanoparticles coated by OA (MNPs)

Fe3O4 nanoparticles were prepared by chemical co-precipitation,which was modified based on previous research [22]. Firstly, 5.41 gferric chloride hexahydrate (FeCl3·6H2ON99%) and 1.99 g ferrouschloride tetra-hydrate (FeCl2·4H2ON99%) was dissolved in 100 mLdistilled water in a three-necked flask. Then, 25 mL aqueous am-monium hydroxide (25–28%, w/w) was added with strong stirringunder the protection of dry nitrogen at 80 °C. After the solution colorchanged from light brown to black, 1 mL OA was dropped into thedispersion slowly under strong stirring in 1 h. After reaction, theprecipitate Fe3O4 nanoparticles were washed by repeated cycles ofcentrifugation and re-dispersion in distilled water. Washing wasperformed for five times in distilled water. Then, the final productswere dried in a vacuum oven at room temperature for 24 h, andthe Fe3O4 nanoparticles coated by OA were finally obtained.

2.3. Synthesis of PEG-silane

The synthesis of PEG-silane was divided into two steps. The firststep is as follows. Firstly, PEG dicarboxylic acid was synthesized usingsuccinic anhydride which formed ester bonds with terminal hydroxylgroups in PEG and converted to dicarboxylic acid [23]. Next, hydroxyl-terminated PEG (10 g, Mn 1000) was dissolved in chloroform(200 mL). Succinic anhydride (10 g) and pyridine (10 mL) wereadded to the chloroform solution, and the mixture was reacted at60 °C for 72 h. The solution was cooled, filtered, and concentrated todryness by rotary evaporation. The crude product was dissolved in30 mL of 1 N HCl, washed with diethyl ether, extracted withchloroform, and dried with anhydrous sodium sulfate. Finally, excesssolvents were removed under vacuum.

At the second step, carboxyl groups in PEG dicarboxylic acid werereacted with amino groups in APS via amidation reaction to obtainPEG-silane described previously [24]. In a three-necked flask, PEGdicarboxylic acid (2.5 g, 2.5 mmol) was dissolved in dichlormethane.And, N,N-dicyclohexylcarbodiimide (DCC, 1 g, 5 mmol) and N-hydro-xysuccinimide (NHS, 0.5 g, 5 mmol) were solubilized in CH2Cl2 understirring for 1 h. Then, amount of APS (250 μL, 1.25 mmol) was added.This reaction aroused under room temperature for 5 h. After reaction,the solution was filtered, to remove the white precipitate ofdicyclohexylurea. The mixture was dried in vacuum and stored in adesiccator.

2.4. Surface modification of MNPs with PEG-silane (MNPs–PEG)

Oleic acid on the surface of magnetite nanoparticles can beexchanged for PEG-silane by ligand exchange reaction. APS hydro-lyzes in the presence of water and in a subsequent reaction thesilanol groups condensate with metal hydroxyl groups on thenanoparticles' surface to form a strong M–O–Si covalent bond(M=metal ion). 1 g of magnetite-OA nanoparticles was added in100 mL of dichloromethane and dispersed well using a sonicator.Then, 2 g of PEG-silane was dissolved in dispersion system. Tocatalyze the hydrolysis and condensation of silane groups in thePEG-silane, 25 μL of acetic acid was added and the reaction systemwas kept stirring under nitrogen atmospher for 24 h at roomtemperature. After reaction, nanoparticles were precipitated by

adding ethyl ether until a turbid solution was observed. The pre-cipitate was washed for five times in acetone and dried in a vacuumoven at room temperature.

2.5. Surface modification of MNPs with PELA (MNPs–PELA)

Polylactic acid (PLA) was linked to the surface of Fe3O4 nano-particle by reacting with terminal hydroxyl of PEG chains, using N,N′-dicyclohexylcarbodiimide (DCC) in presence of 4-dimethylaminopyridine (DMAP) as catalyst. 0.5 g of Fe3O4-PEG nanoparticles wasadded in 20 mL of dichloromethane and ultrasonically dispersed.Then, 0.5 g of PLA was dissolved in this dispersion system. To catalyzethe esterification, DMAP (24 mg) was dissolved in this solutionand 0.45 g of DCC was added. The mixture was magnetically stirredfor 30 min at 0 °C and stirred for another 24 h at room temperature.After reaction, nanoparticles were precipitated by adding ethyl etheruntil a turbid solution was observed. The precipitate was washedfor five times in acetone and dried in a vacuum oven at roomtemperature.

2.6. Characterization

The morphology and size of the synthesized particles wereobserved using transmission electron microscope (TEM, HITACHI H-700H) at an accelerating voltage of 150 kV. Samples were prepared byplacing drops of diluted ethanol dispersed of nanocrystalline on thesurface of cooper grids, which were purchased commercially. Volumestatistics of particle sizes were determined by dynamic light scattering(DLS) (ZETA-SIZER, MALVERN Nano-ZS90). The Fe3O4 nanoparticleswere analyzed for phase composition using X-ray powder diffraction(XRD, Philips X'Pert PRO) over the 2θ range from 10–90° at rate of2.5°/min, using Cu-Kα radiation (λ=1.54060 Å) at room tempera-ture. Fourier transform infrared spectroscopy (FT-IR, Nicolet 5700)was performed to analyze the surface modification of magnetitenanoparticles. The magnetic properties of the resultant Fe3O4

nanoparticles were measured with a vibrating sample magnetometer(VSM, Quantum Design) at room temperature. Thermogravimetricanalysis (TGA) was performed on a TA instrument (Netzsch STA 449C,Bavaria, Germany), at a scan rate of 10 °C min−1, up to 700 °C undernitrogen atmosphere.

The decrease in UV/vis absorption of the MNPs solution as a resultof the magnetic nanoparticles precipitation was used to calculate theaverage absorption to determine the dispersion and solubility withUV–visible spectrophotometer (UV–2550, Shimadzu, Japan). Thespectra were collected within a range of 200–800 nm.

2.7. MTT assay and histochemistry analysis

To evaluate the cytotoxicity of Fe3O4 nanoparticles, the 5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide (MTT) assaywas performed. Osteoblasts were cultured in Dulbecco's modifiedEagle's medium (DMEM) supplemented with 10% fetal bovine serum(FBS) at 37 °C in a 5% CO2 incubator. For the cytotoxicity test,osteoblasts were seeded in a 24-well flat bottomed microassay platesand incubated for 24 hbefore the addition of Fe3O4 nanoparticles. After24 h, Fe3O4 nanoparticleswere added to the cells in triplicatewithfinala concentration of 30 μg/mL and incubated for 72 h. The cells werewashed twice with PBS and replenished with fresh medium. Then,absorbance was measured at 570 nm using a Bio-Tek EL-311microplate reader.

Histochemistry analysis was also performed. Prussian bluestaining was used to reveal the presence of iron cations. Then, cellswere fixed with 3% formaldehyde and washed with PBS, followed byincubation with 2% potassium ferrocyanide in 6% hydrochloric acidfor 25 min. After washing, theywere counterstainedwith neutral redsolution. The samples were then examined under a light microscope.

Fig. 2. IR spectrums (A), X-ray powder diffraction patterns (B), TGA curves(C) and hysteresis loops (D) of MNPs(a), MNPs–PEG(b) and MNPs–PELA(c).

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3. Results and discussion

Fig. 2A displays the FT-IR spectrum of the functionalized Fe3O4

nanoparticles. The peak at about 580 cm−1 is related to the vibrationof Fe–O functional group which matches well with the characteristicpeak of Fe3O4. The peak at 3451 cm−1 is probably attributable to thestretching vibration of O–H bond attached on the surface. The peaks at1630 cm−1 and 1574 cm−1 are related to the asymmetric andsymmetric COO− vibration of the chelating bidentate interactionbetween oleic acid and Fe atoms on the surface of the particles. It canbe seen that the absorption peaks at 2930 cm−1 and 2850 cm−1

represent the stretching vibration of C–H bond. Exchanges of OAmolecules with PELA-silane chains are confirmed by the appearanceof bands at 1049 cm−1 characteristic of –COC vibrations in PEG. Bandsat 924 cm−1 correspond to the condensation of siloxanemolecules onthe surface of the particles. The introduction of APS to the surface ofMNPs was confirmed by the bands at 1130 cm−1 assigned to the Si–Ogroups. Also, bands at 3300 and 1560 cm−1 appeared, characteristicof the –C( O)–NH vibration in PELA, confirmed the amide bondformed between amine groups on the surface of the particle andcarboxyl groups in PEG-silane. The peaks around 1049 cm−1 and1645 cm−1 are due to the stretching vibrations of C–O and C O,respectively, and peak around 1742 cm−1 could be ascribed to theester bond in PELA. The presence of the anchored propyl group wasconfirmed by C–H stretching vibration that appeared at 2930 and2860 cm−1. Therefore, the spectrum indicated that PEG and PLA weregrafted onto the surface of MNPs successfully.

Fig. 2B shows the XRD patterns of the MNPs, which exhibit a groupof spinel-type diffraction peaks, similar to the standard data (JCPDS#72-2303), which indicates that each sample was Fe3O4 crystals withcubic spinel structure. The crystallite size of the samples was 12 nmcalculated using Debye–Scherrer equation (D=Kλ/βcosθ), where D isthe average particle size (nm) of the samples, λ is the X-raywavelength(nm), K is the constant, θ and β are the Bragg angle (radians) and theexcess line broadening (radians), respectively. The correspondingselected area electron diffraction (SAED) image displays ring char-acteristics of a structure composed of small domains with theircrystallograghic axes randomly oriented with respect to one anotheras shown in Fig. 3D. This coincided with the results of XRD analysis. Theelectron diffraction pattern consisting of rings indicates the good crystalstructure of the nanoparticles. However, it can also be seen that a littledecrease in the intension of the crystal peaks of MNPs appeared due tothe introduction of PEG and PELA polymers, which suggests that thecrystallization of MNPs was disturbed by the polymer chains. In thiswork, the average particle size of the samples is calculated by using themost intense peak (311). It is consistent with the result obtained fromthe transmission electron microscopy analysis and volume statistics ofparticle sizes of the same sample.

TGA studies were carried out for the MNPs modified with OA, PEG,and PELA as shown in Fig. 2C. TGA curve of OA coatedMNPs (Fig. 2C a)shows a weight loss of about 10.49%. The weight loss from 200 °C to350 °C is attributed to the degradation of oleic acid. After the PEGgrafted onto the surface of MNPs, the TGA curves show three weightloss stages. As shown in Fig. 2C b there is a weight loss of about 0.4%

Fig. 3. TEM images of MNPs (A), MNPs–PEG (B), MNPs–PELA (C), selected area electron diffraction (D) and size distribution of MNPs (1), MNPs–PEG (2) and MNPs–PELA (3).

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during the first stage below 100 °C due to the evaporation of theresidual water. In the second stage between 300 °C and 500 °C, thetotal weight loss is about 12.01% due to the degradation of PEG.Similarly, the TGA curves of the MNPs modified by PELA (Fig. 2C c)shows that there are two predominant weight loss steps (completedat 350 °C and 570 °C respectively). Theweight loss of the PELA-graftedMNPs increases to 12.93%. From the weight loss, we can conclude thatthe grafting was efficient.

Fig. 2D displays the hysteresis loops of the functionalized MNPs.There is no remanence from the hysteresis loops at lowmagnetic field.The remanence of the particles is equal to zero and the coercivity isalmost negligible in the absence of an external magnetic field. Theresults indicate that the magnetic nanoparticles possess super-paramagnetic properties at room temperature. The reason for thesuper-paramagnetism ofMNPs is mainly that their size is so small thateach particle is a singlemagnetic domain and the energy barrier for itsspin reversal is easily overcome by thermal vibrations. Since theaverage diameter of the as-prepared samples is less than the criticalsize of super-paramagnetism for Fe3O4 at room temperature, it isconsidered that the Fe3O4 nanoparticles are brought forth super-paramagnetism. The saturation magnetization decreased after mod-ification, which was attributed to the existence of polymer located onthe surface of the Fe3O4 nanoparticles.

Fig. 3 exhibits TEM images and volume statistics of particle sizes ofthese MNPs before and after PEG and PELA grafting. The oleic acid-stabilized Fe3O4 nanoparticles (Fig. 3A) possess an excellent disper-sion. In the TEM image (Fig. 3(B, C)), only the core of Fe3O4 can beobserved, and the polymer shell is not discernible due to the lack ofcontrast. Meanwhile, it is clear that there is a little change of theparticle size and morphology after the modification with PEG andPELA. The TEM image in Fig.3B shows that nanoparticles modifiedwith PEG are well dispersed. Nevertheless, comparing with oleic acid-stabilized MNPs, dispersion of the MNPs modified by PEG is reduceddue to the interaction of the polymer chains. In particular, themorphology and size of MNPs modified by PELA (Fig. 3C) were verydifferent comparing with the unmodified MNPs (Fig. 3A). Fig. 3Cindicates that the nanoparticles aggregate and form clusters, whichwas attributed to the interaction of the polymer chains and the changeof surface tension due to the introduction of hydrophobic segments(PLA).

To complement the TEM images which only provide informationon the size of the Fe3O4 core, DLS measurements were also carriedout. Fig. 3D displays the volume statistics of particle sizes of MNPs.The size distribution shows that the MNPs, MNPs–PEG and MNPs–PELA have narrow particle size distributions and average diametervalues of 12, 38, and 78 nm, respectively. The above values were

Fig. 4. UV–vis spectra of MNPs with increasing the time of centrifugation (from up tobottom: 0 min, 5 min, 10 min, 15 min, and 20 min) and corresponding photos(inset),(A) PEG modified MNPs depersed in water, (B) PELA modified MNPs depersed inchloroform.

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larger comparing to the TEM images, which was caused by thefollowing factors: (1) The average size increases with the introduc-ing of polymer, and furthermore, the interaction of the polymer chainsled to the aggregation and clusters; (2) Hydrophobic interation.The MNPs' aggregation was induced by the introduction of PLAhydrophobic segments, which resulted in the reduction of the surfacetension.

From the above statement, we can draw a conclusion that PEG andPELA were grafted onto the surface of MNPs successfully. As it is wellknown, magnetic nanoparticles have a strong tendency to aggregatedue to their nano size and high surface energy. In this work, our aimwas to improve the dispersion and biocompatibility of MNPs. Fig. 4shows the UV–vis spectra and corresponding photos inset of MNPs–PEG dispersed in water and MNPs–PELA dispersed in chloroform withincreasing the time of centrifugation from 0 to 20 min. After themodification, the nanoparticles can be dissolved in water or organicsolvent to form a brownish transparent dispersion without anyaggregation (Fig. 4 inset photo). This fine stability may be attributedto the existence of polymer coating on MNPs. To examine the stabilityof the polymer-modifiedMNPs, somemethodswere employed in thiswork. Firstly, polymer-modified MNPs were ultrasonically dispersedin water or chloroform for 30 min. Secondly, the solution wascentrifuged at 5000 rpm for a while (0 min, 5 min, 10 min, 15 min,20 min), and the absorbance of the solution was recorded periodical-

ly. The similar methods had been done by Takahara's group forresearching the colloidal stabilities [25]. In the case of MNPs–PEGdispersed in water, as shown in Fig. 4A, no significant change in thesolution was observed, indicating that MNPs–PEG were reasonablystable under the conditions. Simultaneously, the correspondingphotos of the samples were seemed to be almost transparent andno difference appeared with the centrifuged time increasing. On theother hand, the absorbance of MNPs–PELA dispersed in chloroformdecreased slightly. These results indicated that stable dispersionoccurred due to the steric repulsion among polymer chains. It wasseemed that the dispersion and stability were strongly influenced bythe polymers grafted on the nanoparticles surface.

Fig. 5A shows the cell viability after incubation with MNPs–PEGand MNPs–PELA, respectively. Over 80 and 90% (as comparing to thenon-toxic control) cell viability was still obtained after 2 daysincubation with MNPs–PEG and MNPs–PELA, respectively. The resultsshowed that Fe3O4 nanoparticles modified by PEG and PELA had lowtoxicity and the cyto-compatibility,, and the toxicity of Fe3O4

nanoparticles modified by PELA was lower than Fe3O4 nanoparticlesmodified by PEG. Whereas microspheres of poly(l-lactic acid),polystyrene and dextran-coated magnetic nanoparticles containing30–40 wt.% magnetite were reported to have in vitro toxicity tohuman prostate. Both the particle size and material compositionmight play an important role in the toxicity of the microspheres andnanoparticles [6].

Fig. 5B shows the prussian blue staining of osteoblasts for 3 daysincubation. Fig. 5B (b) and (c) shows that prussian blue staining ofosteoblast contained Fe3O4 nanoparticles modified by PEG and PELA,respectively, for 3 days incubation. From the three pictures, we canfind that there were no obviously changes in the quantity and shape ofosteoblasts, which showed that the cell viability was well. It alsosuggested that Fe3O4 nanoparticles modified by PEG and PELA can beconsidered to be biocompatible.

In summary, magnetic nanoparticles with excellent biocompati-bility and monodispersity were obtained by the modification of PEGand PELA. The size of the particles was enhanced with the introducingof PEG and PELA into the surface of Fe3O4. The results show thesaturation magnetization (Ms) of the magnetite nanoparticles de-creased with the incorporation of PEG and PELA. The dispersion andstability in water or organic system were improved by the polymermodification. Furthermore, MTT assay exhibited that the Fe3O4

nanoparticles modified by PEG and PELA have excellent biocompat-ibility. It may be of great potential to widen their applications in thebiomedical field, especially in magnetic targeting of drug deliverysystem.

4. Conclusions

Biocompatibility of monodisperse magnetic nanoparticles wereobtained by the controlled chemical coprecipitation method from thesolution of ferrous/ferric mixed salt-solution in aqueous ammoniumhydroxide (NH3·H2O) solution. Then, super-paramagnetic iron oxidenanoparticles were functionalized by silanization with biopolymerssuch as PEG and PELA. The results show the saturation magnetization(Ms) of the magnetite nanoparticles decreased with the modificationof PEG and PELA, and the modified magnetic nanoparticles haveexcellent dispersion in aqueous and organic solvent system, and theyalso possess good biocompatibility. Therefore, they can be promisingas a potentially good magnetic support to be employed in magneticcarrier technology.

Acknowledgements

This work was partially supported by the National Natural ScienceFoundation of China (30970723), Programs for New Century Excellent

Fig. 5. (A) Cytotoxicity of Fe3O4 nanoparticles modified by PEG and PELA at different time; (B) Prussian blue staining of Osteoblast for 3 days incubation: control (a), with MNPs–PEG(b), MNPs–PELA (c).

589L. Sun et al. / Materials Science and Engineering C 30 (2010) 583–589

Talents in University, Ministry of Education of China (NCET-07-0719)and Sichuan Prominent Young Talent Program (08ZQ026-040).

References

[1] B. Chertok, B.A. Moffat, A.E. David, F. Yu, C. Bergemann, B.D. Ross, Biomaterials 29(2008) 487.

[2] V.P. Torchilin, European Journal of Pharmaceutical Sciences 11 (2000) S81.[3] C. Sun, J.S.H. Lee, M. Zhang, Advanced Drug Delivery Reviews 60 (2008) 1252.[4] A. Ito, M. Shinkai, H. Honda, T. Kobayash, Journal of Bioscience and Bioengineering

100 (2005) 1.[5] T. Kikumori, T. Kobayashi, M. Sawaki, T. Imai, Breast Cancer Research and

Treatment 113 (2009) 435.[6] Y. Zhang, Biomaterials 23 (2002) 1553.[7] J. Ren, M. Jia, T. Ren, W. Yuan, Q. Tan, Materials Letters 62 (2008) 4425.[8] N. Rapoport, Progress in Polymer Science 32 (2007) 962.[9] S. Zhou, J. Sun, L. Sun, Y. Dai, L. Liu, X. Li, Journal of Biomedical Materials Research

Part B: Applied Biomaterials 87 (2008) 189.[10] H. Zhao, J. Gagnon, U.O. Hafeli, Biomagnetic Research and Technology 5 (2007) 2.[11] T.Y. Liu, S.H. Hu, D.M. Liu, S.Y. Chen, I.W. Chen, Nano Today 4 (2009) 52.[12] M. Lattuada, T.A. Hatton, Langmuir 23 (2007) 2158.[13] M. Diwan, T.G. Park, Journal of Controlled Release 73 (2001) 233.

[14] K. Yasugi, Y. Nagasaki, M. Kato, K. Kataoka, Journal of Controlled Release 62 (1999)89.

[15] S. Zhou, X. Liao, X. Li, X. Deng, H. Li, Journal of Controlled Release 86 (2003) 195.[16] M. Gou, Z. Qian, H. Wang, Y. Tang, M. Huang, Journal of Materials Science:

Materials in Medicine 9 (2008) 1033.[17] K.E. Uhrich, S.M. Cannizzaro, R.S. Langer, K.M. Shakesheff, Chemical Reviews 99

(1999) 3181.[18] S.A. Hagan, A.G. Coombes, M.C. Garnett, S.E. Dunn, M.C. Davies, L. Illum, Langmuir

12 (1996) 2153.[19] R. Nagarajan, Macromolecules 22 (1989) 4312.[20] J. Sun, S. Zhou, P. Hou, Y. Yang, J. Weng, X. Li, Journal of Biomedical Materials

Research Part A 80 (2007) 333.[21] J. Fu, J. Fiegel, J. Hanes, Macromolecules 37 (2004) 7174.[22] G. Pasut, F. Caboi, R. Schrepfer, G. Tonon, O. Schiavon, F.M. Veronese, Reactive and

Functional Polymers 67 (2007) 529.[23] Y. Sun, X. Ding, Z. Zheng, X. Cheng, X. Hu, Y. Peng, European Polymer Journal 43

(2007) 762.[24] C. Barrera, A.P. Herrera, C. Rinaldi, Journal of Colloid and Interface Science 329

(2009) 107.[25] M. Kobayashi, R. Matsuno, H. Otsuka, A. Takahara, Science and Technology of

Advanced Materials 7 (2006) 617.