Poly (acrylic acid-stat-methyl methacrylate-block-(2-dimethylamino) ethyl methacrylate) magnetic composite microspheres and its application in controlled release of drug

Materials Science and Engineering C 31 (2011) 938–944

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Materials Science and Engineering C j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m s e c

Preparation of pH-responsive Fe3O4/Poly (acrylic acid-stat-methyl methacrylate-block-(2-dimethylamino) ethyl methacrylate) magnetic composite microspheres and its application in controlled release of drug Feige Guo, Qiuyu Zhang ⁎, Wenwen Wang, Hepeng Zhang, Jiuli Sun Applied Chemistry Department, School of Science, Northwestern Polytechnical University, Xi'an 710072, China

a r t i c l e

i n f o

Article history: Received 30 June 2010 Received in revised form 26 November 2010 Accepted 17 February 2011 Available online 24 February 2011 Keywords: Preparation Magnetic composite microsphere pH-responsive DPE method Controlled release

a b s t r a c t Controlled radical polymerization based on 1, 1-diphenylethylene (DPE method) was used to prepare pHresponsive magnetic composite microspheres. By this method, Fe3O4/Poly (acrylic acid-stat-methyl methacrylate-block-(2-dimethylamino) ethyl methacrylate) (Fe3O4/P(AA-MMA-DMA)) microspheres were prepared via emulsifier free emulsion polymerization of acrylic acid (AA), methyl methacrylate (MMA) and (2-dimethylamino) ethyl methacrylate (DMA) using 1, 1-diphenylethylene (DPE) as radical control agent in the presence of Fe3O4 nanoparticles. The structure and properties of Fe3O4/P (AA-MMA-DMA) microspheres were characterized by IR, 1H NMR, SEC-MALLS, TEM, TGA, VSM and DLS. The application of Fe3O4/P (AA-MMADMA) microspheres in controlled release of drug was also investigated. It was found that the DPE method allowed the preparation of pH-responsive magnetic composite microspheres, and Fe3O4/P (AA-MMA-DMA) microspheres obtained were pH-responsive, perfect sphere-shaped morphologies, superparamagnetism with a saturation magnetization of 14.36 emu/g, and high magnetic content with a value of 29%. Moreover, Fe3O4/P (AA-MMA-DMA) microspheres could control the release of phenolphthalein in a buffer solution by adjusting the pH value. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Magnetic composite materials are of great interest and have been studied for a multitude of applications [1–8]. Environmentally responsive (pH- or temperature-responsive) magnetic composite microspheres especially captured considerable attention due to their wide applications in controlled release of drug, separation and purification of protein, and magnetic targeting [9–17]. In most applications, the composite microspheres are required to possess non-toxicity, high concentration of magnetite and functional groups, controlled morphology, and fast responsiveness to external environment. Therefore, it is of crucial significance to establish a method to prepare environmentally responsive magnetic composite microspheres not only satisfying the above-mentioned requirements but also having wide applicability. Several methods have been developed for preparing environmentally responsive magnetic composite microspheres, such as emulsion polymerization, in-situ polymerization, seed polymerization, and surfaceinitiated atom transfer radical polymerization. For example, Shamim [16,17] reported the preparation of Poly(N-isopropylacrylamide) (PNIPAM)-coated magnetic nanoparticles via seed polymerization. The

⁎ Corresponding author. Tel.: +86 02988431675. E-mail address: [email protected] (Q. Zhang). 0928-4931/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2011.02.014

surface of Fe3O4 nanoparticles was first modified by thiodiglycolic acid and 4-vinylaniline, respectively, and then the PNIPAM-coated magnetic nanoparticles were prepared via the seed polymerization of N-isopropylacrylamide using the surface modified Fe3O4 nanoparticles as the seeds. It was found that the PNIPAM-coated magnetic nanoparticles were thermosensitive. Lien [18] also prepared thermosensitive PNIPAMgrafted SiO2/Fe3O4 nanoparticles via reverse microemulsion and free radical polymerization. The SiO2/Fe3O4 nanoparticles were first obtained by surface modification of Fe3O4 nanoparticles with tetraethyl orthosilicate. And then the PNIPAM grafted SiO2/Fe3O4 nanoparticles were prepared via reverse microemulsion polymerization of N-isopropylacrylamide in the presence of SiO2/Fe3O4 nanoparticles. Lee [19] prepared thermosensitive poly (N-isopropylacrylamide-co-acrylic acid)/Fe3O4 magnetic composite microspheres via in-situ polymerization. The crosslinked poly(NIPAAm-AA) polymer latex particles were first synthesized by emulsifier free emulsion polymerization, then Fe2+ and Fe3+ ions were introduced to bond with the ―COOH groups of AA segments in poly (NIPAAm-AA) polymer latex particles. Finally, poly (N-isopropylacrylamide-co-acrylic acid)/Fe3O4 microspheres were obtained by the reaction of NH4OH and iron ion coated polymer latex particles where Fe3O4 nanoparticles were generated in situ. Zhou [20] prepared a pH-sensitive poly ((2-dimethylamino) ethyl methacrylate) (PDMAEMA)/Fe3O4 magnetic composite microsphere via atom transfer radical polymerization. The preparation consists of the synthesis of N-bromoisobutyric acid-

F. Guo et al. / Materials Science and Engineering C 31 (2011) 938–944

a b

3500

3000

2500

2000

1500

585 1144

1270 1240

1387 4000

1449

The polymerization was carried out in a three-necked flask equipped with a stirrer, a condenser and a thermometer. Firstly, 0.05 g of DPE, 0.15 g of AA, 3 g of MMA and 30 g of water were added into reactor and stirred. When the mixture was heated to 80 °C, 10 g of KPS solution (1% w/w in water) was introduced to initiate the polymerization. After a period of time, 25.2 g of sonicated magnetic fluid (0.2 g Fe3O4 nanoparticles in 25 g of water) was dropped into the stirred mixture and the system was allowed to polymerize for 4 h. Then polymerization was ended by cooling the mixture to room temperature. And Fe3O4 nanoparticles coated with precursor polymer P (AA-MMA) formed in the system. The residual monomers were removed by rotary evaporation. Subsequently, the pH value of the mixture was adjusted to 8.0 by adding ammonia and then the mixture was heated to 80 °C again. 3 g of DMA was added to continue polymerization on the surface of magnetic nanoparticles. After 8 h, the mixture was cooled to room temperature and the polymerization stopped. The environmentally responsive magnetic composite microspheres were collected by magnetic separation and then washed with ethanol and deionized water several times.

1733

2.2. Synthesis of pH-responsive magnetic composite microspheres Fe3O4/P (AA-MMA-DMA)

2847

Acrylic acid (AA) and methyl methacrylate (MMA) were purchased from Bodi Chemical Reagent Company, and distilled before use. 2-(dimethylamino) ethyl methacrylate (DMA) was purchased from Acros Organics, and distilled before use. Potassium persulfate (KPS), sodium hydroxide (NaOH), ferric chloride hexahydrate (FeCl3·6H2O), ferrous sulfate heptahydrate (FeSO4·7H2O), hydrofluoric acid (HF), toluene, tetrahydrofuran (THF) and cyclohexane were all purchased from Tianjin Kermel Chemical Reagent Company, and used as received. 1, 1-diphenylethylene (DPE, 98%, Alfa) was used without further purification. Fe3O4 nanoparticles were prepared via coprecipitation method according to the literature [25]. All of the reaction medium was deionized water.

Infrared spectrum (IR) was acquired on a TENSOR27 FTIR spectrometer (Bruker). The sample was prepared by mixing Fe3O4/P (AA-MMA-DMA) microspheres with KBr and pressing into a compact pellet. 1 H NMR and 13C NMR spectra were recorded by INOVA-400 spectrometer (Varian), DMSO-d6 and CDCl3 as solvents, and tetramethylsilane (TMS) as internal standard. Polymer molecular weight was determined by size-exclusion chromatography with multi-angle laser light-scattering detection (SEC-MALLS). SEC was performed using a HPLC pump (Waters 515) and a column (300 mm × 0.8 mm, MZ-Gel SDplus 500 Å 5 μm). Column effluent was monitored sequentially with a miniDawn light-scattering detector (Wyatt technology, Santa, Barbara, CA, USA) and an Optilab rEX differential refractometer (Wyatt Technology). Two 25 mm high-pressure filters with 0.22 and 0.1 μm pore (Millipore) were used for on-line filtration of the mobile phase. The mobile phase was DMF with a flow rate of 0.5 ml/min. The microscopic morphologies of Fe3O4 and Fe3O4/P (AA-MMADMA) particles were observed in a transmission electron microscope (TEM, JEOL JEM-3010). The hydrophilicity of Fe3O4/P (AA-MMA-DMA) microspheres was evaluated on a contact angle determination apparatus (JY-82, Chengde Equipment Company, Chengde, China). The sample was prepared through pressing magnetic composite microspheres into a compact pellet on the glass substrate, and then the contact angle between sample and water was measured. The magnetic content of Fe3O4/P (AA-MMA-DMA) microspheres was determined through thermogravimetric analysis (TGA) using a HCT-1 instrument (Beijing Henven Scientific Instrument Factory,

3390

2.1. Materials

2.3. Characterization of Fe3O4/P (AA-MMA-DMA) microspheres

2948

2. Experimental section

Finally, the separated product (Fe3O4/P (AA-MMA-DMA)) was dried under vacuum at 40 °C for 24 h. The polymer shell P (AA-MMA-DMA) of Fe3O4/P (AA-MMA-DMA) microspheres was cleaved from the magnetic composite microspheres according to the following procedure. 0.1 g of Fe3O4/P (AAMMA-DMA) microsphere was vigorously stirred in a flask containing 3.5 ml of toluene and 3.5 ml of 5 wt.% HF aqueous solution. After 2 h, the aqueous layer was removed, and then 3.5 ml of 5 wt.% HF aqueous solution was added and stirred for another 2 h. This process was repeated five times. Then organic layer containing cleaved polymer was washed with NaHCO3 aqueous solution and water, filtered to remove solid impurities, and dried under vacuum. Finally, the polymer shell was obtained.

3558

functionalized magnetite nanoparticles (Fe3O4-Br) and the polymerization of 2-(N, N-dimethylamino) ethyl methacrylate using poisonous CuBr as the catalyst. As can be seen from above-cited examples, traditional methods for preparing environmentally responsive magnetic composite microspheres usually involve the surface modification of Fe3O4 nanoparticle, which will make the preparation process complex. Recently, it was found that the use of 1, 1-diphenylethylene (DPE) in conventional free radical polymerization allows a high degree of polymer structural control [21–23]. This method (DPE method) has been widely used to synthesize block polymers [24]. In this work, DPE method was extended to prepare environmentally responsive magnetic composite microsphere for the first time. The strategy consists of a two-stage procedure (1) the synthesis of an amphiphilic precursor polymer in the presence of DPE, and the induced copolymerization of the amphiphilic precursor polymer and residual monomers onto the surface of Fe3O4 particles to form magnetic nanoparticle surface modified by the DPE-containing precursor polymer (2) a second polymerization of environmentally responsive monomer (such as (2-dimethylamino) ethyl methacrylate) initiated by the activated precursor polymer on the surface of magnetic nanoparticles to form environmentally responsive magnetic composite microspheres. The strategy would be promising since it is mild, organic solvent- and surfactant-free, and with wide applicability. By this method, a pH-responsive Fe3O4/P (AA-MMA-DMA) magnetic composite microsphere was prepared in this work. The application of Fe3O4/P (AA-MMA-DMA) in controlled release of drug was also investigated.

939

1000

Wave number (cm-1) Fig. 1. Infrared spectra of Fe3O4 (a) and Fe3O4/P (AA-MMA-DMA) (b).

500

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F. Guo et al. / Materials Science and Engineering C 31 (2011) 938–944

Fig. 2. The TEM images of Fe3O4 nanoparticles (a) Fe3O4/P(AA-MMA) particles (b) and Fe3O4/P (AA-MMA-DMA) microspheres (c).

China) in the temperature range from 25 °C to 800 °C with a heating rate of 10 °C/min under nitrogen atmosphere. The magnetic properties of magnetic particles were assessed using a vibrating sample magnetometer (VSM, LakeShore 7307). The particle size of Fe3O4/P (AA-MMA-DMA) microspheres was measured using the Malvern Zetasizer ZS (Malvern Instruments) in aqueous solutions with different pH values (1.0–11.0) at 37 °C. The pH value of the solution was measured by Leici PHS-3 C pH Measurer. 2.4. Drug loading and release Controlled release of drug was carried out using phenolphthalein as a model drug, and the experiment consisted of drug loading and its release. Drug was loaded by dissolving phenolphthalein (40 mg) and Fe3O4/P (AA-MMA-DMA) microspheres (100 mg) in 40 ml of alcohol– water solution (V/V, 3/7). The mixture was stirred at room temperature for 24 h, and some phenolphthalein was encapsulated into Fe3O4/P (AA-MMA-DMA) microspheres. The drug-loading microspheres could be obtained by precipitation, washing and drying. The residual phenolphthalein in the solution was measured by UV–vis analysis. The encapsulation efficiency (EE) of phenolphthalein was calculated as: EE = ðW0 −W1 Þ = W0

where W0 and W1 represent the weight of initial and residual phenolphthalein, respectively. The controlled release behavior of Fe3O4/P (AA-MMA-DMA) microspheres was investigated by the dialysis method at 37 °C. 10 mg of drug-loading microspheres was transferred into a dialysis bag (molecular weight cut-off 25,000 g/mol). The dialysis bag was immersed in 200 ml of buffer solution with different pH values at 37 °C. Periodically, 20 ml of release medium was withdrawn and 20 ml of fresh buffer solution was added to hold the volume of release medium constant after each sampling. The amount of drug released from Fe3O4/P (AA-MMA-DMA) microspheres was measured by UV–vis spectrophotometer (LabTech, China). 3. Results and discussion 3.1. Characterization of Fe3O4/P (AA-MMA-DMA) microspheres Fig. 1 shows the FTIR spectra of Fe3O4 nanoparticles and Fe3O4/P (AAMMA-DMA) microspheres. In Fig. 1a, the characteristic absorption of Fe3O4 appears at 585 cm− 1. The broad band centered around 3390 cm− 1 is assigned to the hydroxyl group, which is attributed to residual water on the surface of Fe3O4 nanoparticles. While in Fig. 1b, the characteristic absorption of Fe3O4 is much weaker than that in Fig. 1a, and many absorption bands of P (AA-MMA-DMA) appear. For example, the peak at 1733 cm− 1 corresponds to the stretching vibration of carbonyl. The peak at 1387 cm− 1 is due to the bending vibration of methyl. The peaks at

1.1 1100 1.0 1000 0.9

b

0.8

800

Mass loss

Particle size (nm)

900

700 600

a

500

0.7 0.6 0.5 0.4

400 0.3 300

0

2

4

6

8

10

12

pH Fig. 3. The pH dependence of the average particle sizes of Fe3O4/P (AA-MMA) particles (a) and Fe3O4/P (AA-MMA-DMA) microspheres (b) at 37 °C.

0.2

0

200

400

600

800

Temperature (oC) Fig. 4. TGA thermogram of Fe3O4/P (AA-MMA-DMA) microspheres.

1000

F. Guo et al. / Materials Science and Engineering C 31 (2011) 938–944

80

a M(emu/g)

60 40

b

20 0

-10000

-5000

0 -20

H(Oe)

5000

10000

-40 -60 -80 Fig. 5. The magnetization curves measured at room temperature for Fe 3 O 4 nanoparticles (a) and Fe3O4/P (AA-MMA-DMA) microspheres (b).

Table 1 The magnetic parameters of Fe3O4 nanoparticles and Fe3O4/P (AA-MMA-DMA) microspheres. Sample

Ms (emu/g)

Mr (emu/g)

Hc (Oe)

Fe3O4 nanoparticles Fe3O4/P (AA-MMA-DMA) microsphere

60.714 14.360

2.002 0.330

34.587 27.890

2948 cm− 1, 2847 cm− 1 and 1449 cm− 1 are ascribed to the stretching and bending vibrations of methylene, respectively. The peaks at 1144 cm− 1 and 1240 cm− 1 arise from the stretching vibration of methoxyl. The peak at 1270 cm− 1 belongs to C―N stretching vibration. All these results suggest that the surface of Fe3O4 nanoparticles has been successfully coated with polymer shell. Fig. 2 shows the TEM images of Fe3O4 nanoparticles, Fe3O4/P(AAMMA) particles and Fe3O4/P (AA-MMA-DMA) microspheres. As shown

in Fig. 2a, the Fe3O4 nanoparticles are aggregated due to their very small average particle size of around 10 nm. Fig. 2b clearly displays that Fe3O4 nanoparticles were dispersed and encapsulated by the polymer, and core–shell composite particles Fe3O4/P (AA-MMA) were formed. The composite particles are roughly spherical in shape. While Fig. 2c shows that the dispersed Fe3O4/P (AA-MMA-DMA) microspheres are perfect sphere-shaped morphologies, which consist of a dark core and a light shell. The dark inner corresponds to Fe3O4 nanoparticles, while the light outer attributes to the polymer shell P (AA-MMA-DMA). The responsive behaviors of Fe3O4/P(AA-MMA) particles and Fe3O4/P (AA-MMA-DMA) microspheres in aqueous solutions with different pH values were investigated by dynamic light scattering (DLS) analysis. Fig. 3(a) shows the change behavior of Fe3O4/P (AA-MMA) particle size in response to pH. As can be seen, the Fe3O4/P (AA-MMA) particles don't exhibit pH response. Between pH 1.5 and 10.0 the average diameter of Fe3O4/P (AA-MMA) particles remains at about 486 nm. The polymer shell of Fe3O4/P (AA-MMA) particles consists mostly of MMA segment which has no pH response, thus there is no noticeable change in the particle size of Fe3O4/P (AA-MMA) particles as a function of pH. In contrast to Fe3O4/P (AA-MMA) particles, Fe3O4/P (AA-MMA-DMA) microspheres show pH response. The relationship between average particle size of Fe3O4/P (AA-MMA-DMA) microspheres and pH value was shown in Fig. 3(b). As can be seen, the particle size decreases with the increase in pH value. When the pH value of the solution is low, the DMA segment of polymer shell P (AA-MMA-DMA) is entirely protonated and highly stretches along the radial direction due to the geometrical constraint and the electrostatic repulsion between polymer chains, which results a larger particle size. As pH value increases, DMA segment gradually shrinks from solution due to the deprotonation of amine groups. As a result, the particle size of Fe3O4/P (AA-MMA-DMA) microspheres decreases. Magnetic response is a vital property of magnetic materials. The magnetic response of magnetic composite microspheres usually increases with magnetic content. In order to determine the magnetic content of Fe3O4/P (AA-MMA-DMA) microspheres, a TGA was carried out, and the result is shown in Fig. 4. As can be seen, when temperature reaches about 800 °C the weight of sample is constant and the residue is 29%. This indicates that the magnetic content of Fe3O4/P (AA-MMA-DMA) microspheres is 29%.

COOCH3 Ph COOH KPS CH2=CH + CH2 C + H2C C Ph CH3 COOCH3 OH +

O O

CH2 CH CH2 C COOH CH3

COOCH3 COOCH3 Ph CH2 C CH2 C CH2 CH CH2 C CH3 Ph COOH CH3

COOCH3 Ph

CH2 C CH2 C CH3 Ph

COOCH3 Ph CH2 C CH2 C Ph CH3

COOCH3 C CH CH2 C CH3 CH2

941

COOCH3 CH2 CH CH2 C CH2 C COOH CH3

DMA 80oC

CH3 CH2 C CH2CH2CH COOCH3 COOH

Scheme 1. Illustration of formation process of Fe3O4/P (AA-MMA-DMA) microspheres.

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Scheme 2. The chemical structure of precursor polymer.

The hysteresis loops of Fe3O4 nanoparticles and Fe3O4/P (AA-MMADMA) microspheres measured at room temperature are shown in Fig. 5. The magnetic parameters of two samples are collected in Table 1. In the case of Fe3O4 nanoparticles, a value of saturation magnetization of 60.714 emu/g was determined, and the small coercivity and remanence values indicate a superparamagnetic behavior. The data of coercivity and remanence demonstrate that the Fe3O4/P (AA-MMADMA) microspheres also exhibit superparamagnetism. The saturation magnetization value of Fe3O4/P (AA-MMA-DMA) microspheres was found to be 14.36 emu/g, which is lower than that of the Fe3O4 nanoparticles. This can be explained by containing the nonmagnetic polymer shell on Fe3O4/P (AA-MMA-DMA) microspheres. 3.2. Preparation of Fe3O4/P (AA-MMA-DMA) microspheres As illustrated in Scheme 1, the preparation of Fe3O4/P (AA-MMADMA) microspheres consists of two steps. One is the synthesis of

a

5

3 4 6

10

8

1

2

6

4

2

0

(ppm)

8

b

6.0

5.8

5.6

5.4

7

5.2

5.0

4.8

(ppm) Fig. 6. The 1H NMR spectrum (a) and its locally magnified spectrum (b) of precursor polymer (DMSO-d6 as solvent).

amphiphilic precursor polymer by a surfactant-free polymerization of MMA, AA, and DPE, and the immobilization of precursor polymer on the surface of Fe3O4 nanoparticles through chemisorptions, namely, the interaction between the carboxyl of precursor polymer and the hydroxyl group from the Fe3O4 nanoparticle's surface. The other is the polymerization of DMA initiated by the DPE-containing precursor polymer absorbed on the Fe3O4 nanoparticle's surface to form pH-responsive magnetic composite microspheres. In the first step, because many carboxylic groups in the polymer chain, P (AA-MMA) can be grafted on the surface of Fe3O4 nanoparticles through carboxylates linkage between the Fe3O4 and the polymer chain (Scheme 1). This process led to the surface modification of magnetic nanoparticle. As a result, the hydrophobicity of magnetic nanoparticle increased, and the contact angle changed from 17° (pure Fe3O4 nanoparticle) to 50° (encapsulation for 4 h). The hydrophobic modification contributes to the dispersion of magnetic nanoparticle in the second polymerization system. Furthermore, this interaction also immobilized a lot of semi-quinoid structures (Scheme 2) on the surface of Fe3O4 nanoparticles, which was verified by the 1H NMR analysis of P (AA-MMA) cleaved from the magnetic nanoparticles as shown in Fig. 6, besides the peaks between 1 and 4 ppm due to P (AA-MMA), the spectra show that the characteristic signals of aromatic protons of the DPE units and the semi-quinoid ring are at 6.8–7.5 and 5.0–6.0 ppm, respectively [26]. In the second step, according to the structural control mechanism of DPE in radical polymerization as discussed in reference [27], the semiquinoid is able to form macromolecular radicals by attack of foreign radicals. And then the macromolecular radicals initiated DMA polymerization on the surface of magnetic nanoparticles to form pH-responsive magnetic composite microspheres. In order to verify the existence of copolymerization on the magnetic nanoparticles, we compared the characterization results of polymer shell P (AA-MMA-DMA) with those of DPE-containing precursor P (AA-MMA). Fig. 7 shows the 1H NMR spectrum of polymer shell P (AA-MMADMA). In this spectrum, the peaks from 0.8 to 1.2 are attributed to the alfa-methyl protons (dH and gH) from MMA and DMA units with different tacticities. The peaks at 0.84, 1.02 and 1.21 ppm arise from syndiotactic (rr), atactic (mr), and isotactic (mm) methyls, respectively [28–30]. The peaks at 3.6–3.8 ppm are ascribed to the protons (eH and hH) of methyl ester from MMA unit [31] and methylene from DMA unit [32]. The peaks from 1.4 to 2.1 ppm are due to the methylene protons (aH, cH, and fH) from AA, MMA and the methyl, methylene protons (f H, jH, and iH) from DMA unit [33], respectively, and the absorption of methine proton (bH) from AA unit is also overlapped in this region [34–37]. Fig. 8 shows the 13C NMR spectrum of polymer shell of Fe3O4/P (AA-MMA-DMA) microspheres. As can be seen, the peaks at 177(4C), 174(5C), 60(10C), 56(11C) 54 (8C), 51(2C), 45(7C), 44(1C, 3C), 30(9C) and 19(6C) are due to the carbons of AA, MMA and DMA units [38–40]. Comparing the NMR spectra of polymer shell P (AA-MMA-DMA) with that of DPE-containing precursor P (AA-MMA), it was found that the characteristic peaks of semi-quinoid structure of DPE disappeared in Figs. 7 and 8. In addition, the molecular weight of P (AA-MMA-DMA) increases (see Table 2) compared with DPE-containing precursor P (AAMMA). All results showed that copolymerization of DMA and precursor polymer P (AA-MMA) occurred on the surface of magnetic nanoparticles.

F. Guo et al. / Materials Science and Engineering C 31 (2011) 938–944

a b CH2 CH

m C O OH

c CH2

d CH3 f C CH2 p C O O e CH3

g CH3 C

e, h

n C O

j OCH2CH2N CH3 h i CH3 k

CDCl

10

943

8

d,g a, b, c,f, j, i

3

6

ppm

4

2

0

Fig. 7. 1H NMR spectrum of polymer shell of Fe3O4/P (AA-MMA-DMA) (CDCl3 as solvent).

3.3. Drug loading and in vitro release In order to investigate the controlled release behavior of Fe3O4/P (AA-MMA-DMA) microspheres, phenolphthalein was used as a model drug molecule. Phenolphthalein is a drug as relief laxative effect in the colon, and it is also itself a weak acid, which can react with tertiary amine of DMA segment on the surface of Fe3O4/P (AA-MMA-DMA) microspheres. Therefore, ionic complexation and hydrophobic interaction are considered as the major loading mechanisms between the drug (phenolphthalein) and the carrier (Fe3O4/P (AA-MMA-DMA) microspheres) in the neutral medium. It was found that 6.4 mg of phenolphthalein could be loaded in 25 mg of Fe3O4/P (AA-MMADMA) microspheres. And the encapsulation efficiency (EE) of phenolphthalein was 64%. Fig. 9 shows the curve of cumulative release of phenolphthalein. As can be seen, the cumulative amounts of phenolphthalein released from the Fe3O4/P (AA-MMA-DMA) microspheres were 39% at pH 10, 27% at pH 7.4 and 16% at pH 2, respectively, for the initial 10 h. Over 72 h, the cumulative amounts were 56% at pH 10, 47% at pH 7.4 and 25% at pH 2, respectively. This means that the Fe3O4/P (AA-MMA-DMA) microspheres can indeed

control the release of phenolphthalein. Furthermore, in the same release time, the amount of phenolphthalein released increases with the increase in pH value of the release medium. There are two reasons for this. Firstly, with the increase of pH value, the DMA segment on the surface of magnetic composite microspheres loses protons and changes from the quaternary ammonium to the tertiary amine. And the charge interaction between the drug molecules and the magnetic composite microspheres weakens. As a result, the release rate of phenolphthalein from the magnetic composite microspheres will increase. Secondly, the DMA segment is soluble at lower pH value and the segment is in a stretched and swollen state, inhibiting the transport of drug molecules through the matrix. At higher pH value, the DMA segment shrinks and collapses, squeezing out drug molecules, resulting in rapid drug release. 4. Conclusions In this paper, controlled radical polymerization based on DPE was used to prepare pH-responsive magnetic composite microspheres Fe3O4/P (AA-MMA-DMA). The Fe3O4/P (AA-MMA-DMA) microspheres

6 6 CH CH 3 1 2 2 3 3 11 CH2 CH CH2 C CH2 C 9 p n m 4C O 5C O 4C O 7 O OCH2CH2N CH3 OH 10 11 CH3 CH3 8 7

2 1,3

6 CDCl 3

11 10

4

8 7

5

9

200

180

160

140

120

100

80

60

40

20

ppm Fig. 8. 13C NMR spectrum of polymer shell of Fe3O4/P (AA-MMA-DMA) (CDCl3 as solvent).

0

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Table 2 The molecular weights of polymer shell at different stages of polymerization. Sample

Mn/(g/mol)

Mw/Mn

P(AA-MMA) P(AA-MMA-DMA)

7910 18,030

1.351 1.803

65 60

Cumulative release (%)

55 c

50 45

b

40 35 30 25

a

20 15 10 5 0 0

10

20

30

40

50

60

70

80

Release time (h) Fig. 9. The pH-dependence of drug release from the microspheres at 37 °C. (a) pH = 2.0 (b) pH = 7.4 and (c) pH = 10.0.

obtained showed perfect sphere-shaped morphologies, high magnetic content, superparamagnetism and pH response. The particle size of Fe3O4/P (AA-MMA-DMA) microspheres could be modulated by pH value. The Fe3O4/P (AA-MMA-DMA) microspheres could control the release of phenolphthalein. And the release rate could be adjusted by the pH value of the release medium. Therefore, the dual-responsive composite microspheres show great potential application in smart drug delivery system. References [1] J.H. Kim, F.F. Fang, H.J. Choi, Y. Seo, Materials Letters 26 (2008) 2897. [2] F.F. Fang, J.H. Kim, H.J. Choi, Polymer 50 (2009) 2290. [3] F.F. Fang, H.J. Choi, Y. Seo, Applied Materials and Interfaces 2 (2010) 54.

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