RGDS-functionalized polyethylene glycol hydrogel-coated magnetic iron oxide nanoparticles enhance specific intracellular uptake by HeLa cells

Abstract

The objective of this study was to develop thin, biocompatible, and biofunctional hydrogel-coated small-sized nanoparticles that exhibit favorable stability, viability, and specific cellular uptake. This article reports the coating of magnetic iron oxide nanoparticles (MIONPs) with covalently cross-linked biofunctional polyethylene glycol (PEG) hydrogel. Silanized MIONPs were derivatized with eosin Y, and the covalently cross-linked biofunctional PEG hydrogel coating was achieved via surface-initiated photopolymerization of PEG diacrylate in aqueous solution. The thickness of the PEG hydrogel coating, between 23 and 126 nm, was tuned with laser exposure time. PEG hydrogel-coated MIONPs were further functionalized with the fibronectin-derived arginine-glycine-aspartic acid-serine (RGDS) sequence, in order to achieve a biofunctional PEG hydrogel layer around the nanoparticles. RGDS-bound PEG hydrogel-coated MIONPs showed a 17-fold higher uptake by the human cervical cancer HeLa cell line than that of amine-coated MIONPs. This novel method allows for the coating of MIONPs with nano-thin biofunctional hydrogel layers that may prevent undesirable cell and protein adhesion and may allow for cellular uptake in target tissues in a specific manner. These findings indicate that the further biofunctional PEG hydrogel coating of MIONPs is a promising platform for enhanced specific cell targeting in biomedical imaging and cancer therapy.

Keywords: PEG hydrogel; agglomeration; nanoparticle encapsulation; surface-initiated photopolymerization.

Figure 1

(A) Schematic representation of the coating of an iron oxide nanoparticle with biofunctional polyethylene glycol (PEG) hydrogel via surface-initiated photopolymerization; (B) schematic representation of acrylate (Acr)-PEG-arginine-glycine-aspartic acid-serine (RGDS) synthesis. Abbreviation: MIONP, magnetic iron oxide nanoparticle.

Figure 2

(A) Schematic representation of eosin binding onto the surface of amine-functionalized magnetic iron oxide nanoparticles (MIONPs); (B) encapsulation of eosin-bound MIONPs within arginine-glycine-aspartic acid-serine (RGDS)-functionalized polyethylene glycol (PEG) hydrogel. Abbreviations: Acryl, acrylate; APTMS, 3-aminopropylsilane; WRK, Woodward’s reagent K.

Figure 3

(A) X-ray diffraction patterns of 3-aminopropylsilane (APTMS)-coated magnetic iron oxide nanoparticles (MIONPs); (B) ferrofluid under an external magnetic field.

Figure 4

Fourier transform infrared spectra of (1) polyethylene glycol (PEG) diacrylate, (2) PEG hydrogel-coated magnetic iron oxide nanoparticles, (3) PEG hydrogel-coated magnetic iron oxide nanoparticles functionalized with arginine-glycine-aspartic acid-serine, and (4) arginine-glycine-aspartic acid-serine.

Figure 5

(A) Size distribution of various magnetic iron oxide nanoparticles (MIONPs) obtained via dynamic light scattering. (B) Change of hydrodynamic diameter before and after polyethylene glycol (PEG) hydrogel coating: (1) 3-aminopropylsilane (APTMS)-coated MIONPs, (2) eosin-bound MIONPs, (3) eosin-bound MIONPs in prepolymer solution (PPS), (4) PEG hydrogel-coated MIONP-20, (5) arginine-glycine-aspartic acid-serine (RGDS)-functionalized PEG hydrogel-coated MIONP-20, (6) PEG hydrogel-coated MIONP-30, (7) RGDS-functionalized PEG hydrogel-coated MIONP-30, (8) PEG hydrogel-coated MIONP-60, (9) RGDS-functionalized PEG hydrogel-coated MIONP-60. Note: Numbers in abbreviations MIONP-20, MIONP-30, MIONP-60 indicate corresponding illumination times in seconds.

Figure 6

Zeta potential measurement before and after polyethylene glycol (PEG) hydrogel coating: (1) 3-aminopropylsilane-coated magnetic iron oxide nanoparticles (MIONPs), (2) eosin, (3) eosin-bound MIONPs, (4) PEG diacrylate, (5) eosin-bound MIONPs in prepolymer solution, (6) PEG hydrogel-coated MIONP-20, (7) PEG hydrogel-coated MIONP-30, (8) PEG hydrogel-coated MIONP-60, (9) arginine-glycine-aspartic acid-serine (RGDS)-functionalized PEG hydrogel-coated MIONP-20, (10) RGDS-functionalized PEG hydrogel-coated MIONP-30, (11) RGDS functionalized PEG hydrogel-coated MIONP-60. Note: Numbers in abbreviations MIONP-20, MIONP-30, MIONP-60 indicate corresponding illumination times in seconds.

Figure 7

Microscopic characterization of polyethylene glycol hydrogel-coated magnetic iron oxide nanoparticles with an illumination period of 20 seconds: scanning electron microscopy image (scale bar: 200 nm) (20 kV; magnification: 75 KX).

Figure 8

Cytotoxicity profiles of varied magnetic iron oxide nanoparticles (MIONPs) after 24 and 48 hours of incubation with HeLa cells. Note: Numbers in abbreviations MIONP-20, MIONP-30, MIONP-60 indicate corresponding illumination times in seconds. Abbreviations: APTMS, 3-aminopropylsilane; PEG, polyethylene glycol; RGDS, arginine-glycine-aspartic acid-serine.

Figure 9

Uptake of magnetic iron oxide nanoparticles (MIONPs) by HeLa cells after 24 hours of incubation, as measured by inductively coupled plasma optical emission spectrometry: (1) control, (2) 3-aminopropylsilane-coated MIONPs, (3) polyethylene glycol (PEG) hydrogel-coated MIONP-30, (4) PEG hydrogel-coated MIONP-30 functionalized with arginine-glycine-aspartic acid-serine, (5) PEG hydrogel-coated MIONP-60, and (6) PEG hydrogel-coated MIONP-60 functionalized with arginine-glycine-aspartic acid-serine. Note: Numbers in abbreviations MIONP-20, MIONP-30, and MIONP-60 indicate corresponding illumination times in seconds.