Design and Control of Nanoconfinement to Achieve Magnetic Resonance Contrast Agents with High Relaxivity.

The enhanced relaxation of hydrogen atoms of surrounding water from suitable contrast agent promotes magnetic resonance imaging as one of the most important medical diagnosis technique. The key challenge for the preparation of performant contrast agents for magnetic resonance imaging with high relaxivity is to ensure a high local concentration of contrast agent while allowing a contact between water and the contrast agent. Both requirements are answered by tailoring a semipermeable confinement for a gadolinium complex used as contrast agent. A locally high concentration is achieved by successfully encapsulating the complex in polymer nanocontainers that serves to protect and retain the complex inside a limited space. The access of water to the complex is achieved by carefully controlling the chemistry of the shell and the core of the nanocontainers. The confinement of the nanocontainers enables an increased relaxivity compared to an aqueous solution of the contrast agent. The nanocontainers are successfully applied in vivo to yield enhanced contrast in magnetic resonance imaging.

Certain types of iron oxide nanoparticles are not suited to passively target inflammatory cells that infiltrate the brain in response to stroke.

Intravenous administration of iron oxide nanoparticles during the acute stage of experimental stroke can produce signal intensity changes in the ischemic region. This has been attributed, albeit controversially, to the infiltration of iron-laden blood-borne macrophages. The properties of nanoparticles that render them most suitable for phagocytosis is a matter of debate, as is the most relevant timepoint for administration. Both of these questions are examined in the present study. Imaging experiments were performed in mice with 30 minutes of middle cerebral artery occlusion (MCAO). Iron oxide nanoparticles with different charges and sizes were used, and mice received 300 µmol Fe/kg intravenously: either superparamagnetic iron oxide nanoparticles (SPIOs), ultrasmall SPIOs, or very small SPIOs. The particles were administered 7 days before MCAO, at the time of reperfusion, or 72 hours after MCAO. Interestingly, there was no observable signal change in the ischemic brains that could be attributed to iron. Furthermore, no Prussian blue-positive cells were found in the brains or blood leukocytes, despite intense staining in the livers and spleens. This implies that the nanoparticles selected for this study are not phagocytosed by blood-borne leukocytes and do not enter the ischemic mouse brain.

Studying the effect of particle size and coating type on the blood kinetics of superparamagnetic iron oxide nanoparticles.

PURPOSE: Magnetic resonance imaging (MRI), one of the most powerful imaging techniques available, usually requires the use of an on-demand designed contrast agent to fully exploit its potential. The blood kinetics of the contrast agent represent an important factor that needs to be considered depending on the objective of the medical examination. For particulate contrast agents, such as superparamagnetic iron oxide nanoparticles (SPIOs), the key parameters are particle size and characteristics of the coating material. In this study we analyzed the effect of these two properties independently and systematically on the magnetic behavior and blood half-life of SPIOs. METHODS: Eleven different SPIOs were synthesized for this study. In the first set (a), seven carboxydextran (CDX)-coated SPIOs of different sizes (19-86 nm) were obtained by fractionating a broadly size-distributed CDX-SPIO. The second set (b) contained three SPIOs of identical size (50 nm) that were stabilized with different coating materials, polyacrylic acid (PAA), poly-ethylene glycol, and starch. Furthermore, small PAA-SPIOs (20 nm) were synthesized to gain a global insight into the effects of particle size vs coating characteristics. Saturation magnetization and proton relaxivity were determined to represent the magnetic and imaging properties. The blood half-life was analyzed in rats using MRI, time-domain nuclear magnetic resonance, and inductively coupled plasma optical emission spectrometry. RESULTS: By changing the particle size without modifying any other parameters, the relaxivity r(2) increased with increasing mean particle diameter. However, the blood half-life was shorter for larger particles. The effect of the coating material on magnetic properties was less pronounced, but it had a strong influence on blood kinetics depending on the ionic character of the coating material. CONCLUSION: In this report we systematically demonstrated that both particle size and coating material influence blood kinetics and magnetic properties of SPIO independently. These data provide key information for the selection of a contrast agent for a defined application and are additionally valuable for other nano areas, such as hyperthermia, drug delivery, and nanotoxicology.

Current limitations of molecular magnetic resonance imaging for tumors as evaluated with high-relaxivity CD105-specific iron oxide nanoparticles.

OBJECTIVE: Tumor imaging via molecular magnetic resonance imaging (MRI) that uses specific superparamagnetic iron oxide particles (SPIOs) has been addressed in the literature several times in the last 20 years. To our knowledge, none of the reported approaches is currently used for routine clinical diagnostic evaluation, nor are any in clinical development. This raises questions as to whether SPIO-enhanced molecular MRI is sensitive and specific enough for use in clinical practice. The aim of our preclinical study was to investigate the minimum requirements for obtaining sensitive molecular MRI for use in tumor evaluations under optimal conditions. The well-vascularized F9 teratocarcinoma tumor model, which exhibits high levels of the highly accessible target CD105 (endoglin), was used to compare the accumulation and visualization of target-specific SPIOs by MRI. MATERIAL AND METHODS: Superparamagnetic iron oxide particles were optimized in the following ways: (a) proton relaxivity was increased for higher imaging sensitivity, (b) a coating material was used for optimal loading density of the αCD105 antibody, and (c) binding activity to the target CD105 was increased. Binding activity and specificity were confirmed in vitro using enzyme-linked immunosorbent assay and in vivo using pharmacokinetic and biodistribution studies of 11 F9 teratoma-bearing mice together with micro-autoradiography. CD105 target expression was determined using immunohistochemistry and quantitative enzyme-linked immunosorbent assay. The transverse relaxation rate R2* was quantified by 3.0-T MRI in the tumors, kidneys, and muscles before and up to 60 minutes after injection in 11 mice. The use of [Fe]-labeled SPIOs for all in vivo experiments allowed for the direct correlation of the imaging results with SPIO accumulation. RESULTS: High-relaxivity αCD105-polyacrylic acid-SPIOs (r2 up to 440 L mmol Fe s) with strong binding activity accumulated specifically in tumors (1.4% injected dose/g) and kidneys (4.1% injected dose/g) in a manner dependent on the target concentration. The accumulation occurred within the first 3 minutes after injection. Visualization of specific SPIOs was accomplished with MRI. In contrast to the successful use of MRI in all examined kidneys (mean ± SEM ΔR2*, 61 ± 11 s), only 6 of 11 tumors (mean ± SEM ΔR2*, 15 ± 7 s) showed a clear signal when compared with the control even though optimal conditions were used. CONCLUSION: The accumulation of CD105-specific SPIOs in F9 mouse teratomas was robust. However, visualization of the specifically accumulated SPIOs by MRI was not reliable because of its limited signal detection sensitivity. We postulate that it will be challenging to improve the imaging properties of targeted SPIOs further. Therefore, molecular MRI by targeted SPIOs is currently not suitable for clinical tumor imaging using routinely applicable sequences and field strength.

Monitoring bisphosphonate surface functionalization and acid stability of hierarchically porous titanium zirconium oxides.

To take advantage of the full potential of functionalized transition metal oxides, a well-understood nonsilane based grafting technique is required. The functionalization of mixed titanium zirconium oxides was studied in detail using a bisphosphonic acid, featuring two phosphonic acid groups with high surface affinity. The bisphosphonic acid employed was coupled to a UV active benzamide moiety in order to track the progress of the surface functionalization in situ. Using different material compositions, altering the pH environment, and looking at various annealing conditions, key features of the functionalization process were identified that consequently will allow for intelligent material design. Loading with bisphosphonic acid was highest on supports calcined at 650 °C compared to lower calcination temperatures: A maximum capacity of 0.13 mmol g(-1) was obtained and the adsorption process could be modeled with a pseudo-second-order rate relationship. Heating at 650 °C resulted in a phase transition of the mixed binary oxide to a ternary oxide, titanium zirconium oxide in the srilankite phase. This phase transition was crucial in order to achieve high loading of the bisphosphonic acid and enhanced chemical stability in highly acidic solutions. Due to the inert nature of phosphorus-oxygen-metal bonds, materials functionalized by bisphosphonic acids showed increased chemical stability compared to their nonfunctionalized counterparts in harshly acidic solutions. Leaching studies showed that the acid stability of the functionalized material was improved with a partially crystalline srilankite phase. The materials were characterized using nitrogen sorption, X-ray powder diffraction, and UV-vis spectroscopy; X-ray photoelectron spectroscopy was used to study surface coverage with the bisphosphonic acid molecules.

One-pot preparation and uranyl adsorption properties of hierarchically porous zirconium titanium oxide beads using phase separation processes to vary macropore morphology.

A simple and engineering friendly one-step process has been used to prepare zirconium titanium mixed oxide beads with porosity on multiple length scales. In this facile synthesis, the bead diameter and the macroporosity can be conveniently controlled through minor alterations in the synthesis conditions. The precursor solution consisted of poly(acrylonitrile) dissolved in dimethyl sulfoxide to which was added block copolymer Pluronic F127 and metal alkoxides. The millimeter-sized spheres were fabricated with differing macropore dimensions and morphology through dropwise addition of the precursor solution into a gelation bath consisting of water (H(2)O beads) or liquid nitrogen (LN(2) beads). The inorganic beads obtained after calcination (550 °C in air) had surface areas of 140 and 128 m(2) g(-1), respectively, and had varied pore architectures. The H(2)O-derived beads had much larger macropores (5.7 µm) and smaller mesopores (6.3 nm) compared with the LN(2)-derived beads (0.8 µm and 24 nm, respectively). Pluronic F127 was an important addition to the precursor solution, as it resulted in increased surface area, pore volume, and compressive yield point. From nonambient XRD analysis, it was concluded that the zirconium and titanium were homogeneously mixed within the oxide. The beads were analyzed for surface accessibility and adsorption rate by monitoring the uptake of uranyl species from solution. The macropore diameter and morphology greatly impacted surface accessibility. Beads with larger macropores reached adsorption equilibrium much faster than the beads with a more tortuous macropore network.

Tunable porosity in bridged organosilicas using self-organizing precursors.

Functionalized, mesoporous organosilicas with tunable porosity were prepared by a direct and simple approach from rationally designed precursors, combining the function of a network builder and a porogen in one molecule. The precursors are synthesized using a dual hydroboration reaction, fulfilling the criteria of "click-chemistry", first on an ethylene-bridged organosilica and then on a long-chain alkene. Thus, in the final molecule the boron atom connects the sol-gel precursor (the bridged organosilica) with the porogen (the long-chain alkene). The so-prepared precursors do self-organize when hydrolysis of their inorganic moiety takes place via an aggregation of their organic side chains into hydrophobic domains. The length of the attached chain influences the size of the hydrophobic domain and thus, after a condensation-aminolysis sequence, the finally observed porosity of the organosilicas. Depending on chain length micro- to mesoporous materials with average pore sizes from 1.5 to 4.1 nm (for attached pentene to hexadecene chains) are observed. Furthermore, the boron entity enables the subsequent introduction of various functional groups into the pore walls of the organosilica networks. Amine or hydroxyl functionalities can be easily introduced, dependent on the experimental conditions used during the borane cleavage and extraction step. The accessibility of these functionalities can be proven by a significant metal adsorption onto the functional organosilica walls.

Enantioselective equilibration-access to chiral aldol adducts of mandelic acid esters.

[Structure: see text] Syn-configured aldol products of mandelic acid esters and aldehydes were synthesized by the catalytic use of amines in the presence of titanium(IV) tert-butoxide. Used along with chiral N-methylephedrine, anti-configured alpha,beta-dihydroxyesters were isolated with a high degree of enantioselectivity for the first time.