A. Hannecart1, D. Stanicki1, L. Vander Elst , L. Mespouille ,...
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Clustering of iron oxide nanoparticles into poly(ethylene oxide)-block-poly(ε-caprolactone) nanoassemblies as ultrasensitive MRI probes A. Hannecart 1 , D. Stanicki 1 , L. Vander Elst 1, 2 , L. Mespouille 3 , R. N. Muller 1,2 , S. Laurent 1,2 1 NMR and Molecular Imaging Laboratory, General, Organic and Biomedical Chemistry Department, University of Mons, B-7000 Mons, Belgium 2 Center for Microscopy and Molecular Imaging, B-6041 Charleroi, Belgium 3 Laboratory of Polymeric and Composite Materials, University of Mons, B-7000 Mons, Belgium Introduction Polymer vesicles, called polymersomes, are hollow spheres formed by the self-assembly of amphiphilic polymers with long hydrophobic blocks (Fig 1.). Thanks to their high robustness, polymersomes have emerged as promising nanocarriers. The objective of this project is to study the self-assembly of PEO 2000 -b-PCL 12650 copolymers with ultrasmall iron oxide nanoparticles (USPIO). A composition close to PEO 2000 -b-PCL 12000 was chosen owing to the tendency of these copolymers to form a vesicular morphology. Several studies have reported the formation of poly(ethylene oxide)-block-poly(ε- caprolactone) (PEO-b-PCL) based vesicles due to their high potential for biomedical applications. However, to the best of our knowledge, no work has be done on the incorporation of USPIO into nanoassemblies produced from PEO-b-PCL copolymers with long PCL blocks. Material and methods Amphiphilic block copolymer Hydrophobic block Hydrophilic block Figure 1. Schematic representation of a polymersome PEO-b-PCL USPIO in tetrahydrofuran (THF) 1) Self-assembly in THF/H 2 O (0.5:9) 2) Dialysis to remove THF THF Distilled water Dialysis membrane (MWCO:12-14000) + centrifugation + extrusions Figure 2. Self-assembly of PEO 2000 -b-PCL 12650 with USPIO by the nanoprecipitation method USPIO (magnetic core size of 4.2 nm and 7.5 nm) were produced by thermal decomposition of iron(III) acetylacetonate in the presence of surfactants in an organic solvent at high temperature (>200°C). Nanoprecipitation of PEO 2000 -b-PCL 12650 with iron oxide nanoparticles was performed by varying the initial nanoparticle concentration (Fig. 2). The best results were obtained by mixing 10 mg of copolymer with 500 μl of THF containing USPIO ([Fe] 0 = 40 mM for d USPIO = 7.5 nm, [Fe] 0 = 80 mM for d USPIO = 4.2 nm). Results and discussions Size and morphology Dynamic light scattering (DLS), transmission electron microscopy (TEM) and cryo-TEM analyses (Fig. 3) showed that nano-objets produced by the self-assembly of PEO 2000 -b-PCL 12650 with USPIO are spherical, possess a high USPIO content and a diameter close to 100 nm r 1 and r 2 relaxivities Table 1. Relaxivities (r 1 and r 2 ) at 37°C and 60 MHz r 1 (s -1 mM -1 ) r 2 (s -1 mM -1 ) r 2 /r 1 r 1 (s -1 mM -1 ) r 2 (s -1 mM -1 ) r 2 /r 1 USPIO (THF) USPIO loaded in PEO 2000 -b-PCL 12650 (water) d USPIO = 7.5 nm d USPIO = 4.2 nm 12.9 7.8 37.8 17.9 3.0 2.3 1.22 0.28 198 110 162 389 The efficiency of a MRI (magnetic resonance imaging) contrast agent is quantified by its longitudinal and transverse relaxivities (r 1 and r 2 ). T 2 -weighted contrast agents decrease MRI signal intensity where they accumulate. The most effective T 2 -weighted contrast agents are those characterized by the higher r 2 /r 1 ratio. Incorporation of USPIO into PEO-b-PCL nanoparticles leads to a significant increase of r 2 /r 1 ratios (r 1 decreases due to a reduced accessibility of water protons to USPIO and r 2 increases due to USPIO clustering) (table 1). Figure 3. Cryo-TEM images* of PEO 2000 -b-PCL 12650 nanoassemblies loaded with USPIO (d USPIO = 7.5 nm) USPIO possessing two different diameters (d = 4.2 nm and d = 7.5 nm) were produced by the thermal decomposition method and incorporated into PEO 2000 -b-PCL 12650 nanoassemblies by a nanoprecipitation method. Extrusions were performed to produce 100 nm diameter polymeric nanoparticles with a narrow size distribution which is ideal for in vivo applications. These polymeric nanoparticles were loaded with a high USPIO content by optimizing the initial USPIO concentration and are characterized by very high r 2 /r 1 ratios which demonstrates that they are promising candidates as T 2 - contrast agents. Further research will focus on the incorporation of an anti-cancer drug into these nanocarriers and the attachment of an active targeting group such as an RGD-containing peptide to their surfaces. Conclusions and perspectives *The authors thank O . Ersen and D . Ihiawakrim from Institut de Physique et Chimie des Matériaux of Strasbourg for cryo - TEM analyses .
Transcript of A. Hannecart1, D. Stanicki1, L. Vander Elst , L. Mespouille ,...
Clustering of iron oxide nanoparticles into poly(ethylene oxide)-block-poly(ε-caprolactone) nanoassemblies as ultrasensitive MRI probes
A. Hannecart1, D. Stanicki1, L. Vander Elst1, 2, L. Mespouille3, R. N. Muller1,2, S. Laurent1,2
1NMR and Molecular Imaging Laboratory, General, Organic and Biomedical Chemistry Department, University of Mons, B-7000 Mons, Belgium2Center for Microscopy and Molecular Imaging, B-6041 Charleroi, Belgium
3Laboratory of Polymeric and Composite Materials, University of Mons, B-7000 Mons, Belgium
Introduction
Polymer vesicles, called polymersomes, are hollow spheres formed by the self-assembly of amphiphilic polymers with long hydrophobic blocks (Fig 1.).Thanks to their high robustness, polymersomes have emerged as promising nanocarriers. The objective of this project is to study the self-assembly ofPEO2000-b-PCL12650 copolymers with ultrasmall iron oxide nanoparticles (USPIO). A composition close to PEO2000-b-PCL12000 was chosen owing to thetendency of these copolymers to form a vesicular morphology. Several studies have reported the formation of poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) based vesicles due to their high potential for biomedical applications. However, to the best of our knowledge, no work has bedone on the incorporation of USPIO into nanoassemblies produced from PEO-b-PCL copolymers with long PCL blocks.
Material and methods
Amphiphilic block copolymerHydrophobic block
Hydrophilic block
Figure 1. Schematic representation of a polymersome
PEO-b-PCL USPIO in tetrahydrofuran(THF)
1) Self-assembly in THF/H2O (0.5:9)
2) Dialysis to remove THF
THF
Distilled water
Dialysis membrane (MWCO:12-14000)
+ centrifugation + extrusions
Figure 2. Self-assembly of PEO2000-b-PCL12650 with USPIO by the nanoprecipitation method
USPIO (magnetic core size of 4.2 nm and 7.5 nm) wereproduced by thermal decomposition of iron(III)acetylacetonate in the presence of surfactants in an organicsolvent at high temperature (>200°C).
Nanoprecipitation of PEO2000-b-PCL12650 with ironoxide nanoparticles was performed by varying the initialnanoparticle concentration (Fig. 2). The best results wereobtained by mixing 10 mg of copolymer with 500 µl of THFcontaining USPIO ([Fe]0 = 40 mM for dUSPIO = 7.5 nm, [Fe]0 =80 mM for dUSPIO= 4.2 nm).
Results and discussions
Size and morphology
Dynamic light scattering (DLS), transmission electronmicroscopy (TEM) and cryo-TEM analyses (Fig. 3) showed thatnano-objets produced by the self-assembly of PEO2000-b-PCL12650
with USPIO are spherical, possess a high USPIO content and adiameter close to 100 nm
r1 and r2 relaxivities
Table 1. Relaxivities (r1 and r2) at 37°C and 60 MHz
r1 (s-1mM-1) r2 (s-1mM-1) r2/r1 r1 (s-1mM-1) r2 (s-1mM-1) r2/r1
USPIO (THF) USPIO loaded in PEO2000-b-PCL12650 (water)
dUSPIO = 7.5 nm
dUSPIO = 4.2 nm
12.9
7.8
37.8
17.9
3.0
2.3
1.22
0.28
198
110
162
389
The efficiency of a MRI (magnetic resonance imaging) contrast agent isquantified by its longitudinal and transverse relaxivities (r1 and r2). T2-weightedcontrast agents decrease MRI signal intensity where they accumulate. The mosteffective T2-weighted contrast agents are those characterized by the higher r2/r1
ratio. Incorporation of USPIO into PEO-b-PCL nanoparticles leads to a significantincrease of r2/r1 ratios (r1 decreases due to a reduced accessibility of water protonsto USPIO and r2 increases due to USPIO clustering) (table 1).
Figure 3. Cryo-TEM images* of PEO2000-b-PCL12650 nanoassembliesloaded with USPIO (dUSPIO = 7.5 nm)
USPIO possessing two different diameters (d = 4.2 nm and d = 7.5 nm) were produced by the thermal decomposition method and incorporated intoPEO2000-b-PCL12650 nanoassemblies by a nanoprecipitation method. Extrusions were performed to produce 100 nm diameter polymeric nanoparticleswith a narrow size distribution which is ideal for in vivo applications. These polymeric nanoparticles were loaded with a high USPIO content byoptimizing the initial USPIO concentration and are characterized by very high r2/r1 ratios which demonstrates that they are promising candidates as T2-contrast agents. Further research will focus on the incorporation of an anti-cancer drug into these nanocarriers and the attachment of an active targetinggroup such as an RGD-containing peptide to their surfaces.
Conclusions and perspectives
*The authors thank O. Ersen and D. Ihiawakrim from Institut de Physique et Chimie des Matériaux of Strasbourg for cryo-TEM analyses.
