b S Supporting Information ' INTRODUCTIONColloidal nanomaterials show unique properties and are widely explored for a variety of applications. 1À4 Lanthanidebased nanomaterials have versatile utility in biological applications, as they can be made either as luminescent, magnetic, or as dual probe by selective doping of lanthanide ions. 5 In particular, paramagnetic Gd 3+ -doped NPs show tremendous potential as contrast agents (CAs) for magnetic resonance imaging (MRI). 6,7 MRI is a powerful medical diagnostic tool, where the relaxation of water protons exposed to an external magnetic field is used to obtain morphological and anatomical information with unlimited tissue penetration and yet high spatial resolution. 8 CAs are used to improve the sensitivity, because they interact with the surrounding water protons and shorten their relaxation time to provide better contrast. Two types of CAs are clinically prevalent: (i) paramagnetic Gd 3+ chelates, which affect the longitudinal relaxivity (r 1 ), and are termed positive (T 1 ) CAs, because they enhance the contrast; 9 and (ii) superparamagnetic iron oxide (SPIO) NPs, which affect transverse relaxivity (r 2 ) and are referred to as negative (T 2 ) CAs, because they diminish the signal intensity at the region of interest. 7,10 T 1 contrast agents are preferred over the T 2 agents as their enhanced brightening effect can easily be used to differentiate the signal from other pathogenic or biological conditions. 7 Gd 3+ chelates that are used clinically have very low body circulation time, because of their low molecular weight and show limitations as molecular probes for long-term tracking. 6 They also provide very low local contrast, because each chelate has only one Gd 3+ ion. To increase the local contrast and relaxivity, second-generation agents have been developed by covalently anchoring Gd 3+ chelates to different nanostructure frameworks, 11 or bundling multiple Gd 3+ chelates together using polymers, dendrimers, liposomes, and viral capsids. 12 These structures have been shown to have high relaxivity and increased local contrast as multiple Gd 3+ ions are coupled to a single nanostructure. The main disadvantage of this class of agents concerns their functionalization, which is tedious, expensive, and the number of ions that can be loaded to a NP is further limited by the number of anchoring sites available. Moreover, some of these aggregates are too large to be clinically useful. 6,7 Recently,

The pathogenesis of spinal cord injury (SCI) remains poorly understood and treatment remains limited. Emerging evidence indicates that post-SCI inflammation is severe but the role of reactive astrogliosis not well understood given its implication in ongoing inflammation as damaging or neuroprotective. We have completed an extensive systematic study with MRI, histopathology, proteomics and ELISA analyses designed to further define the severe protracted and damaging inflammation after SCI in a rat model. We have identified 3 distinct phases of SCI: acute (first 2 days), inflammatory (starting day 3) and resolution (>3 months) in 16 weeks follow up. Actively phagocytizing, CD68 + /CD163macrophages infiltrate myelin-rich necrotic areas converting them into cavities of injury (COI) when deep in the spinal cord. Alternatively, superficial SCI areas are infiltrated by granulomatous tissue, or arachnoiditis where glial cells are obliterated. In the COI, CD68+/CD163macrophage numbers reach a maximum in the first 4 weeks and then decline. Myelin phagocytosis is present at 16 weeks indicating ongoing inflammatory damage. The COI and arachnoiditis are defined by a wall of progressively hypertrophied astrocytes. MR imaging indicates persistent spinal cord edema that is linked to the severity of inflammation. Microhemorrhages in the spinal cord around the lesion are eliminated, presumably by reactive astrocytes within the first week post-injury. Acutely increased levels of TNF-alpha, IL-1beta, IFN-gamma and other proinflammatory cytokines, chemokines and proteases decrease and anti-inflammatory cytokines increase in later phases. In this study we elucidated a number of fundamental mechanisms in pathogenesis of SCI and have demonstrated a close association between progressive astrogliosis and reduction in the severity of inflammation.

Size-Tunable, Ultrasmall NaGdF 4 Nanoparticles: Insights into Their T 1 MRI Contrast Enhancement. -Paramagnetic β-NaGdF4 nanoparticles are synthesized by addition of a MeOH solution containing NaOH and NH4F to a mixture of GdCl3, oleic acid, and octadecene. The size of the nanoparticles can precisely be controlled by varying reaction time and temperature. Particles of 2.5 nm sizes are obtained at 260°C for 10 min, 4.0 nm sized particles at 270°C for 40 min, 6.5 nm sized particles at 280°C for 90 min, and 8.0 nm particles at 285°C for 100 min. The prepared nanoparticles show magnetic resonance longitudinal relaxitivities per nanoparticle at 1.5 T which are 200-3000 times larger than that of the clinically used Gd-DTPA contrast agent, showing great potential as local contrast enhancement probes. β-NaGdF4 nanoparticles are good hosts for upconverting emission which is demonstrated by the preparation of luminescent ultrasmall β-NaGdF4:Yb 3+ /Tm 3+ nanoparticles as potential bimodal probes. -(JOHNSON, N. J. J.; OAKDEN, W.; STANISZ, G. J.; PROSSER, R. S.; VAN VEGGEL*, F. C. J. M.; Chem. Mater. 23 (2011) 16, 3714-3722, http://dx.

We report a single-step approach to producing small and stable bubbles functionalized with nanoparticles. The strategy includes the following events occurring in sequence: (i) a microfluidic generation of bubbles from a mixture of CO(2) and a minute amount of gases with low solubility in water, in an aqueous solution of a protein, a polysaccharide, and anionic nanoparticles; (ii) rapid dissolution of CO(2) leading to the shrinkage of bubbles and an increase in acidity of the medium in the vicinity of the bubbles; and (iii) co-deposition of the biopolymers and nanoparticles at the bubble-liquid interface. The proposed approach yielded microbubbles with a narrow size distribution, long-term stability, and multiple functions originating from the attachment of metal oxide, metal, or semiconductor nanoparticles onto the bubble surface. We show the potential applications of these bubbles in ultrasound and magnetic resonance imaging.

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Poly(acrylic acid) consisting of 25 monomer units (PAA 25 ) was used to stabilize nanoparticle aggregates (NPAs) consisting of either NaGdF 4 or 50/50 mixtures of GdF 3 and CeF 3 . The resulting polymer-stabilized nanoparticle aggregates (NPAs) were developed and tested for their application as contrast agents for magnetic resonance imaging (MRI) and computed tomography (CT). The PAA 25 -stabilized NPAs exhibit low polydispersity and are colloidally stable at concentrations of 40 mg/mL, while their sizes can be be controlled by choosing a specific ratio of Gd 3þ to Ce 3þ . Scanning transmission electron microscopy (STEM) reveals that NaGdF 4 NPAs possess an average diameter of 400 nm. High-resolution STEM and powder X-ray diffraction (XRD) both show that these NPAs consist of a stable aggregate of smaller NPs, whose diameters are 20-22 nm. PAA 25stabilized NPAs consisting of a 50/50 mixture of GdF 3 and CeF 3 possess an average diameter of 70 nm, while the fundamental unit size is estimated to be 10-12 nm in diameter. The PAA 25 -stabilized GdF 3 /CeF 3 NPAs possess mass relaxivities of 40 ( 2 and 30 ( 2 s -1 (mg/mL) -1 at 1.5 T and 3.0 T, respectively. Their effectiveness as contrast agents for CT X-ray imaging at various X-ray energies was also tested and compared to that of equivalent mass concentrations of Gd 3þ -diethylene triamine pentaacetic acid (Gd 3þ -DTPA) and iopromide. Gd-based NPAs exhibit superior CT contrast to equal-mass concentrations of either iopromide or Gd 3þ -DTPA below 30 keV and above 50 keV. Finally, PAA 25 was functionalized by folic acid to explore targeted imaging. Confocal microscopy revealed that, by functionalizing the PAA 25 -stabilized NaGdF 4 :Tb 3þ NPAs with ∼0.8 folates per polymer, binding and endocytosis occurred in SK-BR-3 human breast cancer cells. The utility of the PAA 25 -stabilized GdF 3 /CeF 3 NPAs for MRI is demonstrated in rat perfusion MRI experiments, where T 1 -weighted MRI images of equivalent concentrations of either Gd 3þ -DTPA or the above NPAs are directly compared. The high relaxivities provide an opportunity to conduct perfusion MRI experiments with significantly lower concentrations than those needed for current commercial agents.

Current therapies to limit the neural tissue destruction following the spinal cord injury are not effective. Our recent studies indicate that the injury to the white matter of the spinal cord results in a severe inflammatory response where macrophages phagocytize damaged myelin and the fluid-filled cavity of injury extends in size with concurrent and irreversible destruction of the surrounding neural tissue over several months. We previously established that a high dose of 4mg/rat of dexamethasone administered for 1 week via subdural infusion remarkably lowers the numbers of infiltrating macrophages leaving large amounts of un-phagocytized myelin debris and therefore inhibits the severity of inflammation and related tissue destruction. But this dose was potently toxic to the rats. In the present study the lower doses of dexamethasone, 0.125-2.0mg, were administered via the subdural infusion for 2 weeks after an epidural balloon crush of the mid-thoracic spinal cord. The spinal cord cross-sections were analyzed histologically. Levels of dexamethasone used in the current study had no systemic toxic effect and limited phagocytosis of myelin debris by macrophages in the lesion cavity. The subdural infusion with 0.125-2.0mg dexamethasone over 2 week period did not eliminate the inflammatory process indicating the need for a longer period of infusion to do so. However, this treatment has probably lead to inhibition of the tissue destruction by the severe, prolonged inflammatory process.

Non-invasive gene delivery across the blood-spinal cord barrier (BSCB) remains a challenge for treatment of spinal cord injury or disease. Here, we demonstrate the use of magnetic resonance imaging-guided focused ultrasound (MRIgFUS) to mediate non-surgical gene delivery to the spinal cord, using self-complementary adeno-associated virus serotype 9 (scAAV9). scAAV9 encoding green fluorescent protein (GFP) was injected intravenously in rats. MRIgFUS allows for transient, targeted permeabilization of the BSCB through the interaction of FUS with systemically-injected Definity® lipid-shelled microbubbles. scAAV9-GFP was delivered at 3 dosages: 4×108, 2×109, and 7×109 vector genomes per gram (VG/g). Viral delivery at 2×109 and 7×109 VG/g leads to robust GFP expression in the targeted length and side of the spinal cord. At a dose of 2×109 VG/g, GFP expression was found in 36% of oligodendrocytes, and in 87% of neurons in FUS-treated areas. FUS applications to the spinal cord could address a long-term goal of gene therapy: delivering vectors from the circulation to diseased areas in a noninvasive manner.