[1] C. de las H. Alarcon, S. Pennadam, C. Alexander, Stimuli responsive polymers for biomedical applications, Chem. Soc. Rev. 34 (2005) 276–285. doi:10.1039/B406727D.[2] Mingwu Shen and Hongdong Cai and Xifu Wang and Xueyan Cao and Kangan Li and Su He Wang and Rui Guo and Linfeng Zheng and Guixiang Zhang and Xiangyang Shi, Facile one-pot preparation, surface functionalization, and toxicity assay of APTS-coated iron oxide nanoparticles, Nanotechnology. 23 (2012) 105601.[3] K. Matyjaszewski, J. Spanswick, Controlled/living radical polymerization, Mater. Today. 8 (2005) 26–33. doi:10.1016/S1369-7021(05)00745-5.[4] R. Pelton, Poly(N-isopropylacrylamide) (PNIPAM) is never hydrophobic, J. Colloid Interface Sci. 348 (2010) 673–674. doi:10.1016/j.jcis.2010.05.034.

[5] M. Jaiswal, A. Pradhan, R. Banerjee, D. Bahadur, Dual pH and temperature stiumuli-responsive magnetic nanohydrogels for thermo-chemotherapy, Journal of Nanoscience and Nanotechnology, volume 14 issue 6. 

Multifunctional Nanocomposites Comprised of Magnetic Nanoparticles Grafted with pH and Temperature Responsive Polymer

Swati Kumari*, Cayla Cook**, Evan Prehn*, Erick S. Vasquez***, Keisha B. Walters**Dave C. Swalm School of Chemical Engineering, Mississippi State University

**Department of Civil and Environmental Engineering, Mississippi State University*** Department of Chemical and Materials Engineering, University of Dayton

AcknowledgmentsThis research was supported in part by the National Science Foundation (IIA-1430364, EPS-0903787, CBET-1403872). We appreciate I2AT at Mississippi State University for TEM imaging assistance.

AbstractStimuli responsive polymers (SRPs) have been of great interest in the last few decades because of their potential in biomedical and environmental applications. When SRPs are grafted from surface-modified magnetic-core nanoparticles, they can be utilized for drug delivery and magnetic resonance imaging. In this study, a one-step 3-aminopropyltrimethoxysilane (APTS) hydrothermal approach was used to synthesize APTS-coated iron oxide (Fe3O4@APTS) nanoparticles with reactive surface amine groups. Using two successive surface initiated atom transfer radical polymerizations (SI-ATRP), a pH and temperature responsive block copolymer, poly-(itaconic acid)-b-poly(N-isopropylacrylamide) (Fe3O4@PIA-b-PNIPAM) were grown from the surface of Fe3O4@APTS. The nanocomposite consisting of a magnetic nanoparticle (MNP) core and a polymer shell were characterized over a range of temperature and pH using transmission electron microscopy (TEM), light scattering, zeta potential, and Fourier transform infrared spectroscopy (FTIR) to verify particle morphology, size distribution, charge, and chemical composition. Results showed a successful synthesis, and the resultant Fe3O4@PIA-b-PNIPAM demonstrated temperature and pH responsiveness.

IntroductionCurrently biomedical uses for magnetic nanoparticles includes drug delivery, imaging and targeting [1]. Stimuli responsive polymers, or ‘smart’ polymers, can be grafted from MNPs via SI-ATRP to add polymers with well-controlled molecular weight, chemical composition, and architecture [2, 3]. Furthermore, PIA-b-NIPAM is of particular interest since it has significant relevance for biomedical applications due to its lower critical solubility temperature (LCST) of 32 °C [4], similar to human body temperature. It’s potential has been highlighted in recent medical applications [5].

Materials & MethodsMagnetic nanoparticles were synthesized through a hydrothermal reaction, followed by a sequence of ATRP reactions to produce Fe3O4@PIA-b-NIPAM , and characterized with: Transmission electron microscopy (TEM) Dynamic light scattering (DLS) Fourier transform infrared (FITR) spectroscopy.

Results and Discussion

References

Conclusions The structure, morphology, composition, and surface properties of

the formed particles were characterized by TEM, FTIR, and dynamic light scattering measurements. A pH- and thermo-responsive block copolymer comprised of PIA and PNIPAM was successfully polymerized from the surface of nanoparticles.

FTIR, TEM, and DLS was used to characterize the polymers and showed that the modified MNPs were well dispersed and stable in water as well as some organic solvents. In particular, these thermoresponsive and pH responsive polymers can be used in smart drug delivery and other biomedical applications that is guided by external stimuli.

Experimental Scheme

Fourier Transform Infrared Spectroscopy (FTIR)

❖ Transmission Electron Microscopy (TEM)

TEM image of (a) Fe3O4@APTS, (b) Fe3O4@APTS-PIA, and (c,d) Fe3O4@APTS-PIA-b-PNIPAM. (a) The effective diameter of Fe3O4@APTS is ~300 nm. (b) The effective diameter of Fe3O4@APTS-PIA more than doubles to ~800 nm. The grafted stimuli responsive polymer is visible around the MNP. (c) Uniform nanocomposite size (narrow polydispersity) and effective diameter of the block copolymer-modified ferrofluid/MNPs are shown. No nanoparticle agglomeration was observed. (d) A magnified image of Fe3O4@APTS-PIA-b-PNIPAM shows an effective diameter of ~1000 nm (or ~1 micron).

❖ Dynamic Light Scattering (DLS)DLS analysis was conducted on a dilute solution of approximately 1 μL of Fe3O4@PIA-b-PNIPAM in a 3 mL solution with pH varying from 2 to 12. Next, these samples were analyzed from 25 °C to 45 °C. DLS allows for the measurement of the effective particle diameter and polydispersity.

At pH 12, pH 7, and pH 2—comprising the extreme and neutral pH values examined—all effective diameters began < 600 nm. Previous DLS data denoted the effective hydrodynamic diameter at ~1100 nm; therefore, the PIA-b-PNIPAM coating was in a contracted state. Results show that at pH 10 the polymer shell expands initially and then contracts at higher temperatures, matching the expected LCST behavior.

25 27 29 31 33 35 37 39 41 43 450

200

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800

1000

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1400

pH 2pH 4pH 7pH 10pH 12

Temperature (C)

Effe

ctiv

e D

iam

eter

(nm

)

FTIR spectra of Fe3O4@APTS nanoparticles (blue spectrum) and Fe3O4@APTS-PIA-b-PNIPAM (red spectrum). The white region indicates the regions for peaks assigned to hydroxyl, amine, alkane, and carbonyl functional groups which matches the expected compositions of these SRP-MNP samples.

FTIR data characterizes the chemical functional groups present in the sample using absorbance of infrared light.

TEM analysis allows for the visual interrogation of the samples on the micro- to nano-scale in order to examine particle shape, polydispersity, and other characteristics.

Sample Effective Hydrodynamic Diameter

Fe3O4@APTS 208.5 ± 2.7 nm

Fe3O4@PIA 880.9 ± 8.2 nm

Fe3O4@PIA-b-PNIPAM 1164.1 ± 63.1 nm

(a)

(d)(c)

(b)

Fe3Cl2NH4OH

M N P s

c leaned

Po lymer i za t ionin N i t rogen

PIA MNPs

Copolymer i za t ionin N i t rogen

PIA-b-PNIPAM MNPs

APTS Hydro therma l Reac t ion

NHO

( )n

COOHCOOH

( )n

Polymer and Surface Engineering Laboratory(PolySEL)

http://www.polysel.che.msstate.edu//