P

Mp

CYa

b

c

a

ARRAA

KMOCID

1

iacFeiommanctpfi(ssb

0h

International Journal of Pharmaceutics 463 (2014) 155– 160

Contents lists available at ScienceDirect

International Journal of Pharmaceutics

j o ur nal ho me page: www.elsev ier .com/ locate / i jpharm

harmaceutical Nanotechnology

icrofluidic one-step synthesis of Fe3O4-chitosan compositearticles and their applications

hih-Hui Yanga, Chih-Yu Wangb,∗, Keng-Shiang Huangc, Chao-Pin Kungb,i-Ching Changa, Jei-Fu Shawa

Department of Biological Science and Technology, I-Shou University, TaiwanDepartment of Biomedical Engineering, I-Shou University, TaiwanThe School of Chinese Medicine for Post-Baccalaureate, I-Shou University, Taiwan

r t i c l e i n f o

rticle history:eceived 20 June 2013eceived in revised form 16 August 2013ccepted 18 August 2013vailable online 26 August 2013

a b s t r a c t

This paper demonstrates a simple and easy approach for the one-step synthesis of Fe3O4-chitosan com-posite particles with tadpole-like shape. The length and diameter of the particles were adjustable from638.3 �m to ca. 798 �m (length), and from 290 �m to 412 �m (diameter) by varying the flow rate of thedispersed phase. Mitoxantrone was used as the model drug in the drug release study. The encapsula-tion rate of the drug was 71% for chitosan particles, and 69% for magnetic iron oxide-chitosan particles,

eywords:icrofluidic dropletsne-step synthesishitosan

ron oxide

respectively. The iron oxide-chitosan composite particles had a faster release rate (up to 41.6% at the thirdhour) than the chitosan particles (about 24.6%). These iron oxide-chitosan composite particles are poten-tially useful for biomedical applications, such as magnetic responsive drug carriers, magnetic resonanceimaging (MRI) enhancers, in the future.

© 2013 Elsevier B.V. All rights reserved.

rug release

. Introduction

Magnetic-responsive multifunctional composites, created byntegrating polymer and Fe3O4 nanoparticles have attracted muchttention of researchers in recent years. In the literature, magneticomposite particles have been discussed extensively, includinge3O4 nanoparticles-chitosan composites (Bae et al., 2012; Lint al., 2012b; Wang et al., 2013; Yang et al., 2012b), including var-ous synthesis approaches and morphology. Encapsulation of ironxide nanoparticles in chitosan microparticles can improve theirechanical and functional properties. They can then be used inultidisciplinary fields such as magnetic responsive drug carriers

nd delivery (Arami et al., 2011; Lin et al., 2012b), magnetic reso-ance imaging (MRI) enhancers (Shao et al., 2005) and heavy metalleaners (Pirillo et al., 2009), etc. In the literature, several synthesisechnologies have been used to prepare Fe3O4-chitosan compositearticles, such as electrostatic droplets (Wang et al., 2013), emulsi-cation (Li et al., 2008), coacervation (Arias et al., 2012), sonicationMohapatra and Anand, 2010), etc. Conventional high-shear emul-

ification techniques such as precipitation, spray-drying, and phaseeparation all have some restrictions, including large size distri-ution, structure variability, and limited encapsulation efficiencies

∗ Corresponding author. Tel.: +886 937371382.E-mail address: crab@isu.edu.tw (C.-Y. Wang).

378-5173/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.ijpharm.2013.08.020

(Tran et al., 2011). The in situ microfluidic method provides aneffective, simple and easy to use synthesis process for preparinga magnetic-polymer composite.

Chitosan is a hydrolyzed derivative of chitin, contains highamount of NH2 and OH functional groups with severalapplications, such as drug carriers (Wang et al., 2013), drug deliv-ery (Bernkop-Schnurch and Dunnhaupt, 2012), wound healing(Jayakumar et al., 2011a; St. Denis et al., 2012), and adsorption oforganic acids for food control (Cruz-Romero et al., 2013). There areseveral useful features of chitosan, including non-toxicity, biocom-patibility, biodegradability, and anti-microbial property, and havebeen employed in many biomedical applications (Jayakumar et al.,2011b).

Microfluidic droplets (MFD) technology, a potentially promis-ing approach for the synthesis of microparticles produces wellcontrolled and highly uniform emulsion-based templates ormicroparticles, and allows the abovementioned limitations tobe remedied (Duncanson et al., 2012). With respect to usingspheres as drug carriers, their distribution in the body dependsstrongly upon the morphology and size of the spheres because therelease profiles of drugs differ depending on their size distribu-tion (Arias et al., 2012). In literatures, functionalized microspheres

consisting of various organic or inorganic nanoparticles withcontrollable morphology and diameters can be achieved by themicrofluidics technology (Marre and Jensen, 2010). However, theone step synthesis of Fe3O4 nanoparticles encapsulated chitosan

1 nal of

ma

rocJoaoTwwoiei2t(tmm

2

2

t((AmaS

2

b2G(Fflaalpt

2

otdsmssafpo

56 C.-H. Yang et al. / International Jour

icroparticles by the microfluidic technique has not received muchttention.

Nonspherical microparticles, which can be used in a wideange of scientific fields, are gained increasingly more attentionf researchers. Using microfluidic technology allows for the fabri-ation of various shapes of nonspherical microparticles, includinganus alginate microparticles with one magnetic hemisphere andne cell-loaded hemisphere (Zhao et al., 2009), plugs, disks, rods,nd thread shapes (Liu et al., 2006). However, sophisticated controlf the synthesis process was necessary to obtain the desired shapes.herefore, an easier way for fabricating nonspherical microparticlesith a specific shape would be very useful. In our previous work,e have shown that radial-like (nonspherical) macroporous iron-

xide loaded chitosan spheres could be created in one step usingn situ co-precipitation and gelation of ferro and ferri-gels. How-ver, the diameter was somewhat large (diameter in 1–5 mm), andt was not easy to precisely control the size distribution (Yang et al.,012b). With electrostatic droplets assisted technology, the diame-er of synthesized magnetic microparticles can be reduced to 84 �mWang et al., 2013). In this study we present a one-step processhat fabricates iron oxide-chitosan composite particles by using

icrofluidic technology. Applications of drug release and heavyetal adsorption were also presented.

. Experimental

.1. Materials

Chitosan (molecular weight: 150,000), iron (II) chlorideetrahydrate (FeCl2·4H2O, 99%), iron (III) chloride hexahydrateFeCl3·6H2O, 98%), sodium hydroxide (NaOH), and acetic acidCH3COOH) were purchased from Sigma–Aldrich, J. T. Baker, Alfaesar, Mallinckrodt, and Nihon Shiyaku Reagent, respectively. Allaterials were used as received without further processing. Mitox-

ntrone (CAS Number: 70476-82-3) was also purchased fromigma–Aldrich.

.2. Microfluidic device

The design and implementation of the microfluidic device isased on our previous studies (Lin et al., 2013, 2012a; Yang et al.,012a). In brief, we employed a CO2 laser machine (LaserPro Venus,CC, Taiwan), then we constructed a poly (methyl methacrylate)

PMMA) substrate based cross-junction channel microfluidic chip.ig. 1 shows that the PMMA microfluidic device consists of a topoor (with three reagent inlets and 20 screw orifices for binding),

middle floor (with cross-junction channels and 20 screw orifices)nd a bottom floor (with an outlet and 20 screw orifices). The threeayers were laminated together using twenty M4 screws (0.5 mmitch, 4 mm in diameter) and tightened at 1.5–2 Nm to ensure thathe device was leak proof.

.3. Synthesis of iron oxide-chitosan composite particles

Fig. 2 shows the schematic for the production of ironxide-chitosan composite particles. The chitosan solution con-ained 0.15 g chitosan, 0.05 mL CH3COOH solution (99.5 wt.%,

= 1.05 g/mL), and 4.95 mL of distilled water. The ferro and ferriolution contained FeCl2 and FeCl3 which was dissolved in 1:2olar ratios. FeCl2·4H2O (0.0224 g, dissolved in 0.5 mL of 2 N HCl

olution) and FeCl3·6H2O (0.0448 g, dissolved in 0.5 mL of 2 N HClolution) were mixed by constant stirring for 30 min to obtain

ferro and ferri solution. Then 5 mL chitosan solution and 1 mLerro and ferri solution were mixed and loaded into a single out-ut syringe as the disperse phase. The continuous phase, consistedf sun flower seed oil, was loaded into a double output syringe.

Pharmaceutics 463 (2014) 155– 160

Syringe pumps (KDS Model 220 Series, Kd Scientific, USA) wereused to simultaneously inject both the sample flow (dispersephase) and sheath flow (continuous phase) through Teflon tubesinto the microfluidic chip. A spontaneous self-assembly water-in-oil (w/o) emulsion was obtained at the cross-junction by usingtwo continuous oil streams to shear the ferro and ferri-chitosansolution. Through the other Teflon tube connected to the distinctmicrochannel, ferro-chitosan droplets were dripped into a sodiumhydroxide solution, for the solidification of chitosan droplets andthe co-precipitation of both ferrous cations and ferric cations. Aftertwo hours, black, iron oxide-chitosan composite particles wereobserved. The particles were then collected by centrifugation, andwere washed several times with 30 mL distilled deionized water toremove any alkali.

2.4. Preparation of mitoxantrone-loaded particles

A mixture of mitoxantrone solution (1 mL) and ferro and ferri-chitosan composite solution (2 mL) was used as the sample flow(disperse phase). The synthesis of mitoxantrone encapsulated,magnetic iron oxide loaded chitosan particles was similar to theprocedure described in the previous section. The fabricated parti-cles were then collected by centrifugation and washed twice with30 mL double distilled water to remove any residual mitoxantroneand alkaline.

2.5. Characterization

The average length and diameter of the particles defined inFig. 2B, and expressed as mean ± standard deviation, was measuredand calculated by photomicrographs from an optical microscopysystem (TE2000U, Nikon, USA). The size distribution of the fabri-cated particles was obtained from the random sampling of about 50individual particles to minimize any selection bias. Fourier trans-form infrared spectroscopy (FTIR) spectra were recorded with aSpectrum RXI FTIR Spectrometer, using KBr pellets in the range of400–4000 cm−1, with a resolution of 4 cm−1. X-ray diffraction (XRD,D8 Advance, PANalytical X’PERT PRO) patterns were obtained atroom temperature by using Cu K-� radiation (� = 1.5406 A) with arange of 2� = 20◦–80◦, and a scanning rate of 0.05 s−1.

3. Results and discussion

3.1. Morphology

When passing the orifice of the flow-focusing microchannel,chitosan or ferro and ferri-chitosan solution was guided into thesheath flow of oil and form droplets as a w/o emulsion. Thehomogeneously subsequent breaking-up of the dispersed-phasesolution at the cross-junction resulted in uniformly-sized chi-tosan or ferro and ferri-chitosan droplets. The competition betweenthe viscous stresses and capillary stresses of the interfacial ten-sion between the two immiscible phases resulted in various sizeddroplets. After being dropped into the NaOH solution, the chi-tosan or ferro and ferri-chitosan droplets underwent a crosslinkingreaction, thereby forming chitosan particles with or without iron-oxide nanoparticles. Figs. 3A–C show the optical images of thechitosan particles with a disperse flow rate of 0.02 mL/h, 0.2 mL/h,and 0.3 mL/h, respectively. The synthesized chitosan particles werespherical with a diameter ranging from 150 ± 19 �m, 242 ± 27 �mto 292 ± 29 �m (Fig. 3A–C). They had a light-color because of theabsence of iron oxide nanoparticles. Figs. 3D–F show the optical

images of iron oxide- chitosan composite particles under vari-ous disperse flow rates. The fabricated particles look much darkerbecause of the black color of the iron oxide nanoparticles. It shouldbe noted that they were non-spherical and tadpole shaped. The size

C.-H. Yang et al. / International Journal of Pharmaceutics 463 (2014) 155– 160 157

F iew oo ces. (C

od

3t

tbwe1ttl(

i(l2cfrsno

ig. 1. The exploded view and a photograph of the microfluidic chip. (A) Exploded vil inlets, (3) cross-junction channel, (4) observation area, (5) outlet, (6) screw orifi

f the tadpole shaped particles was determined by their length andiameter, as defined in Fig. 2B.

.2. Effects of the dispersed phase flow rate on the morphology ofhe particles

Table 1 shows the relationships between the length/diameter ofhe particles and the dispersed phase flow rate. It was observed thatoth the diameter and length of the tadpole-like particles increasedhen the flow rate of the dispersed phase increased (Table 1). How-

ver, the diameter to length ratio did not change significantly (from.9 to 2.2). The diameter of the magnetic iron oxide chitosan par-icles was larger than the diameter of the chitosan particles underhe same flow rate condition. This could have been due to the cross-inking of the iron oxide nanoparticles and the chitosan matrixWang et al., 2013).

The motion and the shape deformation of a liquid droplet fallingn an immiscible solution are well studied in fluid mechanicsSmagin et al., 2011). The formation mechanism of the tadpole-ike chitosan particle can be theoretically simulated (Potapov et al.,006) and validated by experiments (Lavrenteva et al., 2009). Thehange in shape from a sphere or ellipse to a tail shape is a dynamicorce balance between the viscous deformation and the interfacial

estoring stresses. The main dimensionless forces influencing thehape deformation behavior are the viscosity ratio and the capillaryumber (Abbassi-Sourki et al., 2012). Before falling to the bottomf the reservoir, the crosslinking process of the chitosan droplet

f the microfluidic chip. (B) Photograph of the microfluidic chip: (1) sample inlet, (2)) Design of the microfluidic chip. The scale bar is 1 cm.

with NaOH solution froze the tail shape of the chitosan droplet.This crosslinking solidification wears down the interfacial restor-ing stress. Thus, all collected chitosan droplets were tadpole-likeand spherical or elliptic chitosan droplets were not found.

3.3. Characterization

Fig. S1 shows the FTIR spectra of the chitosan particles, ironoxide nanoparticles, and the iron oxide-loaded chitosan particles,respectively. The peaks around 3453 cm−1 relate to the OH groupof adsorbed water. In the spectrum of chitosan (curve a), the char-acteristic absorption peaks appeared around 2928 cm−1 (attributedto the C H group of backbone polymer), 1582 cm−1 (attributed toN H bending vibration) and 1389 cm−1 (attributed to the C Ostretching of the primary alcoholic group in chitosan). In the spec-trum of the magnetic iron oxide@chitosan particles (curve b), inaddition to the characteristic peaks of chitosan, an additional peakappeared at 598 cm−1 (attributed to the Fe O group), indicatingthat iron oxide nanoparticles were successfully embedded in thechitosan particles.

Fig. S2 shows the XRD patterns of magnetic iron oxide@chitosanparticles. Five characteristic peaks of Fe3O4 corresponding to (2 2 0),(3 1 1), (4 0 0), (5 1 1) and (4 4 0) were observed in all samples (JCPDS

file, PDF No. 65-3107). Since the position and relative intensity ofall the diffraction peaks of the samples were consistent with thecrystalline pattern of the Fe3O4 phase (Wang et al., 2010), we pre-sumed that the synthesized nanoparticles were of the Fe3O4 phase.

158 C.-H. Yang et al. / International Journal of Pharmaceutics 463 (2014) 155– 160

F ke iroa article

Tb2au

3

tp

TT

ig. 2. (A) Schematic of microfluidic emulsification for the production of tadpole-li ferro-chitosan solution. (B) Illustration of the size measurement of tadpole-like p

he involvement of chitosan did not result in a phase change. Theroadened peaks may be caused by the chitosan polymer (Lu et al.,011). Fig. S3 shows that the fabricated particles were attractednd guided to a desired position, which indicates the possibility ofsing them as a smart drug carrier.

.4. Application in controlled drug release

The drug release efficiency of the synthesized particles is impor-ant for the exploration for their anti-pathogenic ability. In ourrevious study, the release of antibiotic drugs (such as ampicillin)

able 1he relationships between the length/diameter of the particles and the flow rate of the d

Flow rate of the continuousphase (mL/min)

Flow rate of the dispersed phase (mL/h) Lengt

0.02 638.30.5 0.2 783.3

0.3 798.1

a R.S.D.: relative standard deviation.b D/L ratio: diameter/length ratio.

n oxide-chitosan composite particles based on the co-precipitation and gelation ofs.

from magnetic chitosan particles, which were fabricated with elec-trostatic droplet assisted method, could be enhanced with externalmagnets (Wang et al., 2013). In the present study, the antitu-moral drug mitoxantrone was used as an alternative model drugto show the release efficiency for the iron oxide-chitosan com-posite particles. Following the process of Lu, B., et al. (Lu et al.,2006), the encapsulation rate of the drug was estimated to be 71%

for chitosan particles, and 69% for iron oxide-chitosan compositeparticles, respectively. In vitro release data reveal the drug releaseprofile of magnetic chitosan particles with and without iron oxidenanoparticles (synthesized under a flow rate of 0.2 mL/h) (Fig. 4).

ispersed phase. The flow rate of the continuous phase was set at 0.5 mL/min.

h (�m) R.S.D.a (%) Diameter (�m) R.S.D.a (%) D/L ratiob

15 290 9.6 2.2 9.7 370.7 8.1 2.1 12.9 411.8 8.8 1.9

C.-H. Yang et al. / International Journal of Pharmaceutics 463 (2014) 155– 160 159

Fig. 3. Micrographs of chitosan particles without iron oxide nanoparticles (A–C) and with

phase flow rates (the continuous phase flow rate was 0.5 mL/min). (A and D): The disperse(C and F): The dispersed phase flow rate is 0.3 mL/h. The scale bar is 200 �m.

0

5

10

15

20

25

30

35

40

45

180160140120100806040200

Mit

oxan

trone

rele

ase

(%)

Time (minutes)

Chitosan particles

Magnetic iron oxide@

chitosan particles

Fc

Pvi4Wmd

4

rm

ig. 4. In vitro test of mitoxantrone release from pure chitosan particles with (upperurve) and without (lower curve) iron oxide nanoparticles.

articles with and without Fe3O4 nanoparticles were put inside aessel and then immersed in a water bath at 37 ◦C. The magneticron oxide loaded chitosan particles had a faster release rate (up to1.6% at the third hour) than the chitosan particles (about 24.6%).e presume that the involvement of iron oxide made the particlesore porous, increased the drug leakage and thus enhancing the

rug release rate (Yang et al., 2012b).

. Conclusions

Iron oxide-chitosan composite particles were successfully fab-icated using the microfluidic technique in one step. This proposedethod provides an alternative way for generating non-spheroids

iron oxide nanoparticles (D–F) solidified in a NaOH solution with various dispersed-d phase flow rate is 0.02 mL/h. (B and E): The dispersed phase flow rate is 0.2 mL/h.

particles. The length and diameter of the synthesized particles wereboth controllable by tuning the flow rate of the dispersed phase. Byusing mitoxantrone as a model drug, it was found that the mag-netic iron oxide loaded chitosan particles have a faster release ratethan the chitosan particles. Compared with other approaches, themain advantages of this approach are: (i) magnetic chitosan micro-particles can be obtained in one step; (ii) uniform-sized iron-oxideloaded chitosan microparticles can be fabricated; (iii) simple andeasy control of the particle diameter by varying the flow rate of thedispersed and continuous phases. The efficiency of drug release bythe synthesized magnetic iron oxide loaded, tadpole-like chitosanparticles was investigated.

Acknowledgements

This work was financially supported by the National ScienceCouncil of Taiwan, R.O.C (NSC 102-2320-B-214-001, NSC 102-2632-B-214-001-MY3-) and I-Shou University, Taiwan.

Appendix A. Supplementary data

Supplementary data associated with this article can befound, in the online version, at http://dx.doi.org/10.1016/j.ijpharm.2013.08.020.

References

Abbassi-Sourki, F., Bousmina, M., Huneault, M., 2012. Effect of interfacial modifier onsingle drop deformation and breakup in step increasing shear flow. RheologicaActa 51, 111–126.

Arami, H., Stephen, Z., Veiseh, O., Zhang, M., 2011. Chitosan-coated iron oxidenanoparticles for molecular imaging and drug delivery. In: Jayakumar, R., Praba-haran, M., Muzzarelli, R.A.A. (Eds.), Chitosan for Biomaterials I. Springer, BerlinHeidelberg, pp. 163–184.

Arias, J.L., Reddy, L.H., Couvreur, P., 2012. Fe3O4/chitosan nanocomposite for mag-netic drug targeting to cancer. Journal of Materials Chemistry 22, 7622–7632.

Bae, K.H., Park, M., Do, M.J., Lee, N., Ryu, J.H., Kim, G.W., Kim, C., Park, T.G., Hyeon, T.,2012. Chitosan oligosaccharide-stabilized ferrimagnetic iron oxide nanocubesfor magnetically modulated cancer hyperthermia. ACS Nano 6, 5266–5273.

1 nal of

B

C

D

J

J

L

L

L

L

L

L

L

L

60 C.-H. Yang et al. / International Jour

ernkop-Schnurch, A., Dunnhaupt, S., 2012. Chitosan-based drug delivery systems.European Journal of Pharmaceutics and Biopharmaceutics: Official Journal ofArbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V 81, 463–469.

ruz-Romero, M.C., Murphy, T., Morris, M., Cummins, E., Kerry, J.P., 2013. Antimicro-bial activity of chitosan, organic acids and nano-sized solubilisates for potentialuse in smart antimicrobially-active packaging for potential food applications.Food Control 34, 393–397.

uncanson, W.J., Lin, T., Abate, A.R., Seiffert, S., Shah, R.K., Weitz, D.A., 2012. Microflu-idic synthesis of advanced microparticles for encapsulation and controlledrelease. Lab on a Chip 12, 2135–2145.

ayakumar, R., Prabaharan, M., Sudheesh Kumar, P.T., Nair, S.V., Tamura, H., 2011a.Biomaterials based on chitin and chitosan in wound dressing applications.Biotechnology Advances 29, 322–337.

ayakumar, R., Ramachandran, R., Divyarani, V.V., Chennazhi, K.P., Tamura, H.,Nair, S.V., 2011b. Fabrication of chitin-chitosan/nano TiO2-composite scaffoldsfor tissue engineering applications. International Journal of Biological Macro-molecules 48, 336–344.

avrenteva, O.M., Holenberg, Y., Nir, A., 2009. Motion of viscous drops in tubes filledwith yield stress fluid. Chemical Engineering Science 64, 4772–4786.

i, P., Zhu, A.M., Liu, Q.L., Zhang, Q.G., 2008. Fe3O4/poly(N-isopropylacrylamide)/chitosan composite microspheres with multiresponsive properties. Industrialand Engineering Chemistry Research 47, 7700–7706.

in, Y.-S., Yang, C.-H., Hsu, Y.-Y., Hsieh, C.-L., 2013. Microfluidic synthesis of tail-shaped alginate microparticles using slow sedimentation. Electrophoresis 34,425–431.

in, Y.-S., Yang, C.-H., Wang, C.-Y., Chang, F.-R., Huang, K.-S., Hsieh, W.-C., 2012a. Analuminum microfluidic chip fabrication using a convenient micromilling processfor fluorescent poly(dl-lactide-co-glycolide) microparticle generation. Sensors12, 1455–1467.

in, Y.S., Huang, K.S., Yang, C.H., Wang, C.Y., Yang, Y.S., Hsu, H.C., Liao, Y.J., Tsai, C.W.,2012b. Microfluidic synthesis of microfibers for magnetic-responsive controlleddrug release and cell culture. PLoS ONE 7, e33184.

iu, K., Ding, H.-J., Liu, J., Chen, Y., Zhao, X.-Z., 2006. Shape-controlled productionof biodegradable calcium alginate gel microparticles using a novel microfluidicdevice. Langmuir 22, 9453–9457.

u, B., Xiong, S.-B., Yang, H., Yin, X.-D., Zhao, R.-B., 2006. Mitoxantrone-loaded BSAnanospheres and chitosan nanospheres for local injection against breast cancer

and its lymph node metastases. I: Formulation and in vitro characterization.International Journal of Pharmaceutics 307, 168–174.

u, L.C., Wang, C.I., Sye, W.F., 2011. Applications of chitosan beads and porous crabshell powder for the removal of 17 organochlorine pesticides (OCPs) in watersolution. Carbohydrate Polymers 83, 1984–1989.

Pharmaceutics 463 (2014) 155– 160

Marre, S., Jensen, K.F., 2010. Synthesis of micro and nanostructures in microfluidicsystems. Chemical Society Reviews 39, 1183–1202.

Mohapatra, M., Anand, S., 2010. Synthesis and applications of nano-structured ironoxides/hydroxides-a review. International Journal of Engineering, Science andTechnology 2, 127–146.

Pirillo, S., Pedroni, V., Rueda, E., Luján Ferreira, M., 2009. Elimination of dyes fromaqueous solutions using iron oxides and chitosan as adsorbents: a comparativestudy. Química Nova 32, 1239–1244.

Potapov, A., Spivak, R., Lavrenteva, O.M., Nir, A., 2006. Motion and deformationof drops in bingham fluid. Industrial and Engineering Chemistry Research 45,6985–6995.

Shao, H., Lee, H., Huang, Y., Kwak, B., Kim, C., 2005. Synthesis of nano-size magnetitecoated with chitosan for MRI contrast agent by sonochemistry. In: MagneticsConference, 2005, INTERMAG Asia 2005, Digests of the IEEE International, pp.461–462.

Smagin, I., Pathak, M., Lavrenteva, O., Nir, A., 2011. Motion and shape of an axisym-metric viscoplastic drop slowly falling through a viscous fluid. Rheologica Acta50, 361–374.

St Denis, T.G., Dai, T., Huang, Y.-Y., Hamblin, M.R., 2012. Wound-healing propertiesof chitosan and its use in wound dressing biopharmaceuticals, chitosan-basedsystems for biopharmaceuticals. John Wiley & Sons Ltd, pp. 429–450.

Tran, V.-T., Benoît, J.-P., Venier-Julienne, M.-C., 2011. Why and how to preparebiodegradable, monodispersed, polymeric microparticles in the field of phar-macy? International Journal of Pharmaceutics 407, 1–11.

Wang, C.-Y., Yang, C.-H., Huang, K.-S., Yeh, C.-S., Wang, A.H.J., Chen, C.-H., 2013.Electrostatic droplets assisted in situ synthesis of superparamagnetic chitosanmicroparticles for magnetic-responsive controlled drug release and copper ionremoval. Journal of Materials Chemistry B 1, 2205–2212.

Wang, W.X., Wang, Y.P., Zhang, X.-G., Wang, Y., Zou, J., Han, X.F., 2010. Thicknessdependence of magnetic and transport properties in organic-CoFe discontinuousmultilayers. Journal of Applied Physics 107, 09E307.

Yang, C.-H., Huang, K.-S., Wang, C.-Y., Hsu, Y.-Y., Chang, F.-R., Lin, Y.-S.,2012a. Microfluidic-assisted synthesis of hemispherical and discoidalchitosan microparticles at an oil/water interface. Electrophoresis 33,3173–3180.

Yang, C.H., Wang, C.Y., Huang, K.S., Yeh, C.S., Wang, A.H., Wang, W.T., Lin, M.Y.,2012b. Facile synthesis of radial-like macroporous superparamagnetic chitosan

spheres with in-situ co-precipitation and gelation of ferro-gels. PLoS ONE 7,e49329.

Zhao, L.B., Pan, L., Zhang, K., Guo, S.S., Liu, W., Wang, Y., Chen, Y., Zhao, X.Z., Chan,H.L.W., 2009. Generation of Janus alginate hydrogel particles with magneticanisotropy for cell encapsulation. Lab on a Chip 9, 2981–2986.