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Fe3O4 thermo-responsive and magnetic composite micelles
Materials Letters 62 (2008) 4425–4427
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Preparation and characterization of PNIPAAm-b-PLA/Fe3O4 thermo-responsive and magnetic composite micelles Jie Ren ⁎, Menghong Jia, Tianbin Ren, Weizhong Yuan, Qinggang Tan Institute of Nano and Bio-Polymeric Materials, School of Material Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, People's Republic of China
a r t i c l e
i n f o
Article history: Received 5 April 2008 Accepted 18 July 2008 Available online 5 August 2008 Keywords: Micelles Thermo-responsive Microstructure Magnetic materials
a b s t r a c t Novel magnetic micelles with the flowerlike morphology were prepared with Fe3O4 nanoparticles and poly (N-isopropylacrylamide)-block-polylactide (PNIPAAm-b-PLA) copolymers by a dialysis method. The diameter of flowerlike micelles was about 1 μm. The core and shell of the micelles were hydrophilic, while the other area of the micelles was hydrophobic. The lower critical solution temperature (LCST) of PNIPAAm-b-PLA was about 38 °C. The magnetic intensity of Fe3O4 nanoparticles decreased after they were encapsulated into PNIPAAm-b-PLA micelles. Thermo-responsive and magnetic properties of the micelles would provide useful applications in the target drug delivery and release system. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental part
Thermo-responsive polymeric micelles as a new drug release system have been studied widely [1–3]. When the temperature is lower than the lower critical solution temperature (LCST) of the thermo-responsive block, micelles are formed with the hydrated outer shell and the hydrophobic inner core. When the temperature exceeds the LCST, the outer shell becomes hydrophobic and shrinks. The micelles aggregate and shrink, which may enhance the drug release. Magnetic nanoparticles are playing increasingly important roles in biotechnology and biomedicine [4]. For example, they have been used as carriers for magnetic drug targeting and thermo-magnetic therapy [5,6]. Magnetite nanoparticles covered with a layer of biodegradable polymer shell or evenly distributed in the matrix of polymer nanoparticles have been reported as potential drug targeting vehicles [7–9]. The magnetite/polymer composite nanoparticles have demonstrated lower in vivo toxicity than magnetite [10,11]. However, magnetic micelles have seldom been studied before. In this study, PNIPAAm was conjugated to the PLA to improve its biocompatibility. The PNIPAAm-b-PLA copolymer was dialyzed with Fe3O4 nanoparticles to form micelles as a drug carrier; the loading of Fe3O4 nanoparticles and preparation of micelles were simultaneously carried out by a dialysis method.
2.1. Materials N-isopropylacrylamide (purchased from Shanghai Guoyao, China) was purified by recrystallization from n-hexane. DL-Lactide (Shanghai Tong-Jie-Liang Biomaterials Co., Ltd, China) was purified by recrystallization from ethyl acetate. tin(II)2-ethyl hexanoate (Shanghai Guoyao, China) was used as received. Fe3O4 with particle size of 20– 30 nm (Huaming group, Shanghai, China) was modified by silane coupling agent KH570 (γ-Methacryloxypropyl trimethoxy silane, CH2=C(CH3)C(O)OCH2CH2CH2Si–(OCH3)3, purchased from Shanghai Guoyao, China). Benzoyl peroxide (BPO), N,N-dimethylacetamide (DMAc) are all analytic grade and used as received. 2.2. Preparation of PNIPAAm-b-PLA copolymer Hydroxyl-terminated poly(N-isopropylacrylamide) precursor polymer was prepared by radical polymerization using benzoyl peroxide (BPO) as initiator and 2-hydroxyethanethiol as a chain transfer agent. Then, the diblock copolymers of PNIPAAm-b-PLA were synthesized by the ring-opening polymerization (ROP) of lactide with the hydroxyl-terminated PNIPAAm in toluene using tin(II) 2-ethyl hexanoate as the catalyst [12]. 2.3. Preparation of magnetic micelles
⁎ Corresponding author. Tel./fax: +86 21 65989238. E-mail address: [email protected] (J. Ren). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.07.051
PNIPAAm-b-PLA copolymers (50 mg) were dissolved in DMAc (10 mL), and then Fe3O4 magnetic nanoparticles (5 mg) were added into the solution. The solution was sonicated in a ultrasonicator, followed by dialysis against distilled water using a dialysis membrane
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J. Ren et al. / Materials Letters 62 (2008) 4425–4427
with 12 000–14 000 molecular weight cut-off (Spectra/Por2, Shanghai Guoyao, China) at 20 °C. 2.4. Measurements TEM (FEI, Japan) with elements spectrum analysis was used to investigate the morphology of composite micelles and the location of Fe3O4. The solution of micelles was dyed by 4% phosphotungstic acid before the examination. The optical transmittance of micelle at various temperatures was measured at 500 nm with the UV–VIS spectrometer. The LCST of the micelle was determined as a temperature showing onset of turbidity. Magnetic measurements were made with a LH-3 VSM magnetometer (Nanjing University, China). 3. Results and discussion 3.1. Formation and analysis of micelles Fig. 2. Transmittance change of composite micelles as a function of temperature. As shown in Fig. 1, the morphology of the micelles is a not perfect spheroid, but presents an unusual shape that looks like flowers. In the picture, the core of flowerlike micelles is black, and the shell is encircled with black balls. The diameter of the flowerlike micelles is about 1 μm, and the distribution is relatively narrow. The diameter of its core is about 300 nm. The diameter of the balls around the “flower” is about 100 nm. The solution of magnetic micelles was mixed with some phosphotungstic acid to dye micelles before the observation by TEM. Therefore, the black area in the micelle (Fig. 1b) is made of hydrophilic polymer blocks (PNIPAAm), because PNIPAAm could be dyed by phosphotungstic acid more effectively, while the other area in the micelle is composed of hydrophobic PLA blocks which could not be dyed by phosphotungstic acid easily. From the elements spectrum analysis in the micelle, it can be confirmed that the Fe3O4 particles distribute randomly in the micelle but not conglomerately in some area.
The micelles were prepared by dialysis processing. Firstly, PNIPAAm which had not been conjoined with PLA assembled to form PNIPAAm micelles as the core of flowerlike micelles. Secondly, the PNIPAAm segment of PNIPAAm-b-PLA block copolymer was adsorbed on the surface of the PNIPAAm micelle. Thirdly, another layer of PNIPAAm-bPLA was adsorbed on the surface of the anterior micelle, the PNIPAAm segment of PNIPAAm-b-PLA assembled on the surface of micelles as “black balls”. It can be demonstrated that Fe3O4 particles played an important role in the assembly because their magnetization could induce the adsorption between molecules. The core and out-shell of the “flower” are hydrophilic, so they can load a hydrophilic drug easily. Hence, these self-assembled micelles can be used as an effective carrier of a water-soluble drug. However, in a typical micelle carrier system, the drug is always incorporated into the hydrophobic inner core, so the water-soluble drugs cannot be encapsulated in the micelle easily. The LCST of PNIPAAm-b-PLA copolymers can be determined by measuring the optical transmittance ratio in the 500 nm in Fig. 2. The optical transmittance ratio decreases when the temperature is raised. The temperature at which the transmittance ratio descends to 50% is defined as the LCST [13]. In the experiment, when the temperature was raised to 38.3 °C, the transmittance ratio decreased by 50%, so it can be confirmed that the LCST of the copolymer is 38.3 °C. 3.2. Magnetic properties of composite micelles The B–H curves of magnetic composite micelles and Fe3O4 nanoparticles are shown in Fig. 3. The B–H curves show the relation between magnetic induction B and magnetizing force H for a magnetic material. The saturated magnetization of Fe3O4 nanoparticles is 10.0 emu g− 1 while the saturated magnetization of composite micelles is 1.2 emu g− 1. Namely, the magnetization of the Fe3O4 decreased obviously when it was absorbed or loaded into PNIPAAm-b-PLA copolymers. This should be ascribed to the enwrapping of Fe3O4 nanoparticles by copolymer, which will weaken the magnetization of Fe3O4 nanoparticles.
Fig. 1. Morphology of composite micelles.
Fig. 3. The B–H curves of magnetic composite micelles and Fe3O4 nanoparticles.
J. Ren et al. / Materials Letters 62 (2008) 4425–4427
4. Conclusion The biodegradable and thermo-responsive copolymer PNIPAAm-bPLA was dialyzed with magnetic nanoparticles to form composite micelles as a new drug carrier. The micelles with a diameter of 800 to 1200 nm present a unique flowerlike morphology. The core and shell of the “flowerlike micelle” are hydrophilic (PNIPAAm block), while the other area is composed of hydrophobic polymer blocks(PLA block). So, the self-assembled micelle can be used as an effective carrier of a hydrophilic drug. The LCST of micelles is about 38 °C which is a little higher than the normal human body temperature. The prepared thermo-responsive micelles with magnetic properties and biodegradable properties would provide useful applications in the drug targeting and controlled drug release system. Acknowledgments This work was supported by the Program for New Century Excellent Talents in University (No. NCET-05-0389) and the Program of Shanghai Subject Chief Scientist (No. 07XD14029).
4427
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Chung JE, Yokoyama M, Okano T. J Control Release 2000;65:93–103. Kohori F, Yokoyama M, Sakai K, Okano T. J Control Release 2002;78:155–63. Kim I, Jeong Y, Cho C, Kim S. Int J Pharm 2000;205:165–72. Pankhurst QA, Connolly J, Jones SK, Dobson JJ. Phys D: Appl Phys 2003;36:167–81. Hiergeist R, Andra W, Buske N, Hergt R, Hilger I, Richter U, Kaiser WJ. J Magn Magn Mater 1999;201:420–2. Jordan A, Scholz R, Wust P, Fahling H, Felix RJ. J Magn Magn Mater 1999;201:413–9. Gomez-Lopera SA, Arias JL, Gallardo V, Delgado AV. Langmuir 2006;22:2816–21. Asmatulu R, Zalich MA, Claus RO, Riffle JS. J Magn Magn Mater 2005;292:108–19. Hu FX, Neoh KG, Kang ET. Biomaterials 2006;27:5725–33. Iannone A, Magin RL, Walczak T, Federico M, Swartz HM, Tomasi A. Magn Reson Med 1991;22:435–42. Muller RH, Maaen S, Weyhers H, Specht F, Lucks JS. Int J Pharm 1996;138:85–94. Kohori F, Sakai K, Aoyagi T. J Control Release 1998;55:87–98. Nakayama M, Okano T, Miyazaki T, Kohori F, Sakai K, Yokoyama M. J Control Release 2006;115:46–56.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Preparation and characterization of PNIPAAm-b-PLA/Fe3O4 thermo-responsive and magnetic composite micelles Jie Ren ⁎, Menghong Jia, Tianbin Ren, Weizhong Yuan, Qinggang Tan Institute of Nano and Bio-Polymeric Materials, School of Material Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, People's Republic of China
a r t i c l e
i n f o
Article history: Received 5 April 2008 Accepted 18 July 2008 Available online 5 August 2008 Keywords: Micelles Thermo-responsive Microstructure Magnetic materials
a b s t r a c t Novel magnetic micelles with the flowerlike morphology were prepared with Fe3O4 nanoparticles and poly (N-isopropylacrylamide)-block-polylactide (PNIPAAm-b-PLA) copolymers by a dialysis method. The diameter of flowerlike micelles was about 1 μm. The core and shell of the micelles were hydrophilic, while the other area of the micelles was hydrophobic. The lower critical solution temperature (LCST) of PNIPAAm-b-PLA was about 38 °C. The magnetic intensity of Fe3O4 nanoparticles decreased after they were encapsulated into PNIPAAm-b-PLA micelles. Thermo-responsive and magnetic properties of the micelles would provide useful applications in the target drug delivery and release system. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental part
Thermo-responsive polymeric micelles as a new drug release system have been studied widely [1–3]. When the temperature is lower than the lower critical solution temperature (LCST) of the thermo-responsive block, micelles are formed with the hydrated outer shell and the hydrophobic inner core. When the temperature exceeds the LCST, the outer shell becomes hydrophobic and shrinks. The micelles aggregate and shrink, which may enhance the drug release. Magnetic nanoparticles are playing increasingly important roles in biotechnology and biomedicine [4]. For example, they have been used as carriers for magnetic drug targeting and thermo-magnetic therapy [5,6]. Magnetite nanoparticles covered with a layer of biodegradable polymer shell or evenly distributed in the matrix of polymer nanoparticles have been reported as potential drug targeting vehicles [7–9]. The magnetite/polymer composite nanoparticles have demonstrated lower in vivo toxicity than magnetite [10,11]. However, magnetic micelles have seldom been studied before. In this study, PNIPAAm was conjugated to the PLA to improve its biocompatibility. The PNIPAAm-b-PLA copolymer was dialyzed with Fe3O4 nanoparticles to form micelles as a drug carrier; the loading of Fe3O4 nanoparticles and preparation of micelles were simultaneously carried out by a dialysis method.
2.1. Materials N-isopropylacrylamide (purchased from Shanghai Guoyao, China) was purified by recrystallization from n-hexane. DL-Lactide (Shanghai Tong-Jie-Liang Biomaterials Co., Ltd, China) was purified by recrystallization from ethyl acetate. tin(II)2-ethyl hexanoate (Shanghai Guoyao, China) was used as received. Fe3O4 with particle size of 20– 30 nm (Huaming group, Shanghai, China) was modified by silane coupling agent KH570 (γ-Methacryloxypropyl trimethoxy silane, CH2=C(CH3)C(O)OCH2CH2CH2Si–(OCH3)3, purchased from Shanghai Guoyao, China). Benzoyl peroxide (BPO), N,N-dimethylacetamide (DMAc) are all analytic grade and used as received. 2.2. Preparation of PNIPAAm-b-PLA copolymer Hydroxyl-terminated poly(N-isopropylacrylamide) precursor polymer was prepared by radical polymerization using benzoyl peroxide (BPO) as initiator and 2-hydroxyethanethiol as a chain transfer agent. Then, the diblock copolymers of PNIPAAm-b-PLA were synthesized by the ring-opening polymerization (ROP) of lactide with the hydroxyl-terminated PNIPAAm in toluene using tin(II) 2-ethyl hexanoate as the catalyst [12]. 2.3. Preparation of magnetic micelles
⁎ Corresponding author. Tel./fax: +86 21 65989238. E-mail address: [email protected] (J. Ren). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.07.051
PNIPAAm-b-PLA copolymers (50 mg) were dissolved in DMAc (10 mL), and then Fe3O4 magnetic nanoparticles (5 mg) were added into the solution. The solution was sonicated in a ultrasonicator, followed by dialysis against distilled water using a dialysis membrane
4426
J. Ren et al. / Materials Letters 62 (2008) 4425–4427
with 12 000–14 000 molecular weight cut-off (Spectra/Por2, Shanghai Guoyao, China) at 20 °C. 2.4. Measurements TEM (FEI, Japan) with elements spectrum analysis was used to investigate the morphology of composite micelles and the location of Fe3O4. The solution of micelles was dyed by 4% phosphotungstic acid before the examination. The optical transmittance of micelle at various temperatures was measured at 500 nm with the UV–VIS spectrometer. The LCST of the micelle was determined as a temperature showing onset of turbidity. Magnetic measurements were made with a LH-3 VSM magnetometer (Nanjing University, China). 3. Results and discussion 3.1. Formation and analysis of micelles Fig. 2. Transmittance change of composite micelles as a function of temperature. As shown in Fig. 1, the morphology of the micelles is a not perfect spheroid, but presents an unusual shape that looks like flowers. In the picture, the core of flowerlike micelles is black, and the shell is encircled with black balls. The diameter of the flowerlike micelles is about 1 μm, and the distribution is relatively narrow. The diameter of its core is about 300 nm. The diameter of the balls around the “flower” is about 100 nm. The solution of magnetic micelles was mixed with some phosphotungstic acid to dye micelles before the observation by TEM. Therefore, the black area in the micelle (Fig. 1b) is made of hydrophilic polymer blocks (PNIPAAm), because PNIPAAm could be dyed by phosphotungstic acid more effectively, while the other area in the micelle is composed of hydrophobic PLA blocks which could not be dyed by phosphotungstic acid easily. From the elements spectrum analysis in the micelle, it can be confirmed that the Fe3O4 particles distribute randomly in the micelle but not conglomerately in some area.
The micelles were prepared by dialysis processing. Firstly, PNIPAAm which had not been conjoined with PLA assembled to form PNIPAAm micelles as the core of flowerlike micelles. Secondly, the PNIPAAm segment of PNIPAAm-b-PLA block copolymer was adsorbed on the surface of the PNIPAAm micelle. Thirdly, another layer of PNIPAAm-bPLA was adsorbed on the surface of the anterior micelle, the PNIPAAm segment of PNIPAAm-b-PLA assembled on the surface of micelles as “black balls”. It can be demonstrated that Fe3O4 particles played an important role in the assembly because their magnetization could induce the adsorption between molecules. The core and out-shell of the “flower” are hydrophilic, so they can load a hydrophilic drug easily. Hence, these self-assembled micelles can be used as an effective carrier of a water-soluble drug. However, in a typical micelle carrier system, the drug is always incorporated into the hydrophobic inner core, so the water-soluble drugs cannot be encapsulated in the micelle easily. The LCST of PNIPAAm-b-PLA copolymers can be determined by measuring the optical transmittance ratio in the 500 nm in Fig. 2. The optical transmittance ratio decreases when the temperature is raised. The temperature at which the transmittance ratio descends to 50% is defined as the LCST [13]. In the experiment, when the temperature was raised to 38.3 °C, the transmittance ratio decreased by 50%, so it can be confirmed that the LCST of the copolymer is 38.3 °C. 3.2. Magnetic properties of composite micelles The B–H curves of magnetic composite micelles and Fe3O4 nanoparticles are shown in Fig. 3. The B–H curves show the relation between magnetic induction B and magnetizing force H for a magnetic material. The saturated magnetization of Fe3O4 nanoparticles is 10.0 emu g− 1 while the saturated magnetization of composite micelles is 1.2 emu g− 1. Namely, the magnetization of the Fe3O4 decreased obviously when it was absorbed or loaded into PNIPAAm-b-PLA copolymers. This should be ascribed to the enwrapping of Fe3O4 nanoparticles by copolymer, which will weaken the magnetization of Fe3O4 nanoparticles.
Fig. 1. Morphology of composite micelles.
Fig. 3. The B–H curves of magnetic composite micelles and Fe3O4 nanoparticles.
J. Ren et al. / Materials Letters 62 (2008) 4425–4427
4. Conclusion The biodegradable and thermo-responsive copolymer PNIPAAm-bPLA was dialyzed with magnetic nanoparticles to form composite micelles as a new drug carrier. The micelles with a diameter of 800 to 1200 nm present a unique flowerlike morphology. The core and shell of the “flowerlike micelle” are hydrophilic (PNIPAAm block), while the other area is composed of hydrophobic polymer blocks(PLA block). So, the self-assembled micelle can be used as an effective carrier of a hydrophilic drug. The LCST of micelles is about 38 °C which is a little higher than the normal human body temperature. The prepared thermo-responsive micelles with magnetic properties and biodegradable properties would provide useful applications in the drug targeting and controlled drug release system. Acknowledgments This work was supported by the Program for New Century Excellent Talents in University (No. NCET-05-0389) and the Program of Shanghai Subject Chief Scientist (No. 07XD14029).
4427
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Chung JE, Yokoyama M, Okano T. J Control Release 2000;65:93–103. Kohori F, Yokoyama M, Sakai K, Okano T. J Control Release 2002;78:155–63. Kim I, Jeong Y, Cho C, Kim S. Int J Pharm 2000;205:165–72. Pankhurst QA, Connolly J, Jones SK, Dobson JJ. Phys D: Appl Phys 2003;36:167–81. Hiergeist R, Andra W, Buske N, Hergt R, Hilger I, Richter U, Kaiser WJ. J Magn Magn Mater 1999;201:420–2. Jordan A, Scholz R, Wust P, Fahling H, Felix RJ. J Magn Magn Mater 1999;201:413–9. Gomez-Lopera SA, Arias JL, Gallardo V, Delgado AV. Langmuir 2006;22:2816–21. Asmatulu R, Zalich MA, Claus RO, Riffle JS. J Magn Magn Mater 2005;292:108–19. Hu FX, Neoh KG, Kang ET. Biomaterials 2006;27:5725–33. Iannone A, Magin RL, Walczak T, Federico M, Swartz HM, Tomasi A. Magn Reson Med 1991;22:435–42. Muller RH, Maaen S, Weyhers H, Specht F, Lucks JS. Int J Pharm 1996;138:85–94. Kohori F, Sakai K, Aoyagi T. J Control Release 1998;55:87–98. Nakayama M, Okano T, Miyazaki T, Kohori F, Sakai K, Yokoyama M. J Control Release 2006;115:46–56.