Recent Advances in the Development of Magnetically Recoverable Metal Nanoparticle Catalysts

The aim of this Account is to provide an overview of our current research activities on the design and modification of superparamagnetic nanomaterials for application in the field of magnetic separation and catalysis. First, an introduction of magnetism and magnetic separation is done. Then, the synthetic strategies that have been developed for generating superparamagnetic nanoparticles spherically coated by silica and other oxides, with a focus on well characterized systems prepared by methods that generate samples of high quality and easy to scale- up, are discussed. A set of magnetically recoverable catalysts prepared in our research group by the unique combination of superparamagnetic supports and metal nanoparticles is highlighted. This Account is concluded with personal remarks and perspectives on this research field.

Rat subcutaneous tissue response to MTA Fillapex® and Portland cement

The aim of this study was to evaluate the response of rat subcutaneous tissue to MTA Fillapex® (Angelus), an experimental root canal filling material based on Portland cement and propylene glycol (PCPG), and a zinc oxide, eugenol and iodoform (ZOEI) paste. These materials were placed in polyethylene tubes and implanted into the dorsal connective tissue of Wistar rats for 7 and 15 days. The specimens were stained with hematoxylin and eosin, and evaluated regarding inflammatory reaction parameters by optical microscopy. The intensity of inflammatory response against the sealers was analyzed by two blinded and previously calibrated examiners for all experimental periods (kappa=0.96). The histological evaluation showed that all materials caused a moderate inflammatory reaction at 7 days, which subsided with time. A greater inflammatory reaction was observed at 7 days in the tubes filled with ZOEI paste. Tubes filled with MTA Fillapex presented some giant cells, macrophages and lymphocytes after 7 days. At 15 days, the presence of fibroblasts and collagen fibers was observed indicating normal tissue healing. The tubes filled with PCPG showed similar results to those observed in MTA Fillapex. At 15 days, the inflammatory reaction was almost absent at the tissue, with several collagen fibers indicating normal tissue healing. Data were analyzed by the nonparametric Kruskal-Wallis test (?=0.05). Statistically significant difference (p<0.05) was found only between PCPG at 15 days and ZOEI at 7 days groups. No significant differences were observed among the other groups/periods (p>0.05). MTA Fillapex and Portland cement added with propylene glycol had greater tissue compatibility than the PCPG paste.

In vivo evaluation of tissue response to new endodontic sealers

Introduction: The sealers can be in direct contact with the periapical tissues. Thus, these materials must have appropriate physical and biological properties, providing conditions for repair to occur. Objective: The aim of this study was to evaluate the response of rat subcutaneous tissue to endodontics sealers. Material and methods: Three materials comprised the groups: group I – Zinc Oxide, Eugenol and Iodoform paste, group II – Portland cement with propylene glycol, and group III – MTA Fillapex® (Angelus). These materials were placed in polyethylene tubes and implanted into dorsal connective tissue of Wistar rats for seven and 15 days. The specimens were stained with hematoxylin and eosin and evaluated regarding to inflammatory reaction parameters through a light microscope. The data were compared using Kruskal-Wallis test with significance level of 5%. The intensity of inflammatory response against the sealers was analyzed by two blinded and previously calibrated observers for all experimental periods. Results: The histological evaluation showed that all the materials caused a moderated inflammatory reaction at seven days which decreased with time. A greater inflammatory reaction was observed at seven days in group I. The other specimens had significantly less inflammatory cells when compared to this group. Tubes with MTA Fillapex® presented some giant cells, macrophages and lymphocytes after seven days. At 15 days, the presence of fibroblasts and collagen fibers was observed indicating normal tissue healing. The group II showed similar results to those observed in MTA Fillapex® already at seven days. At 15 days the inflammatory reaction presented was almost absent at the tissue, with many collagen fibers indicating normal tissue healing. Statistical analysis showed a significant statistical difference amongst the group I (seven days) and II (15 days) (p < 0.05). In the other groups no (Continue)

In vivo evaluation of tissue response to new endodontic sealers

Introduction: The sealers can be in direct contact with the periapical tissues. Thus, these materials must have appropriate physical and biological properties, providing conditions for repair to occur. Objective: The aim of this study was to evaluate the response of rat subcutaneous tissue to endodontics sealers. Material and methods: Three materials comprised the groups: group I – Zinc Oxide, Eugenol and Iodoform paste, group II – Portland cement with propylene glycol, and group III – MTA Fillapex® (Angelus). These materials were placed in polyethylene tubes and implanted into dorsal connective tissue of Wistar rats for seven and 15 days. The specimens were stained with hematoxylin and eosin and evaluated regarding to inflammatory reaction parameters through a light microscope. The data were compared using Kruskal-Wallis test with significance level of 5%. The intensity of inflammatory response against the sealers was analyzed by two blinded and previously calibrated observers for all experimental periods. Results: The histological evaluation showed that all the materials caused a moderated inflammatory reaction at seven days which decreased with time. A greater inflammatory reaction was observed at seven days in group I. The other specimens had significantly less inflammatory cells when compared to this group. Tubes with MTA Fillapex® presented some giant cells, macrophages and lymphocytes after seven days. At 15 days, the presence of fibroblasts and collagen fibers was observed indicating normal tissue healing. The group II showed similar results to those observed in MTA Fillapex® already at seven days. At 15 days the inflammatory reaction presented was almost absent at the tissue, with many collagen fibers indicating normal tissue healing. Statistical analysis showed a significant statistical difference amongst the group I (seven days) and II (15 days) (p < 0.05). In the other groups no significant statistical differences were observed. Conclusion: MTA Fillapex® and Portland cement with propylene glycol were more biocompatible than the other tested cements.

Healing of a tooth with an overinstrumented apex, extensive transportation and periapical lesion using a 5 mm calcium hydroxide apical plug: an 8-year follow-up report

Besides the risk of filling material extrusion throughout the apex, a satisfactory apical seal can be difficult to achieve in canals with open apices or iatrogenic enlargements of the apical constriction. These situations pose a challenge to root canal filling. This paper describes the root canal filling of a maxillary right canine with an overinstrumented apex, complete loss of the apical stop, extensive canal transportation and apical periodontitis. A 5 mm calcium hydroxide apical plug was placed before root canal filling. The plug was made by soaking paper points with saline, dipping the points in calcium hydroxide powder and then applying it to the apex several times, until a consistent apical plug was obtained. The canal was then irrigated with saline in order to remove any residual calcium hydroxide from the root canal walls, dried with paper points and obturated with an inverted #80 gutta-percha cone and zinc oxide-eugenol based sealer by the lateral condensation technique. An 8-year radiographic follow-up showed formation of mineralized tissue sealing the apical foramen, apical remodeling and no signs of apical periodontitis.

Monitoramento in vivo por imagem por ressonância magnética de células C6 de glioma marcadas com nanopartículas superparamagnéticas de óxido de ferro

OBJECTIVE: The aim of the current study was to monitor the migration of superparamagnetic iron oxide nanoparticle (SPION)-labeled C6 cells, which were used to induce glioblastoma tumor growth in an animal model, over time using magnetic resonance imaging (MRI), with the goal of aiding in tumor prognosis and therapy. METHODS: Two groups of male Wistar rats were used for the tumor induction model. In the first group (n=3), the tumors were induced via the injection of SPION-labeled C6 cells. In the second group (n=3), the tumors were induced via the injection of unlabeled C6 cells. Prussian Blue staining was performed to analyze the SPION distribution within the C6 cells in vitro. Tumor-inducing C6 cells were injected into the right frontal cortex, and subsequent tumor monitoring and SPION detection were performed using T2- and T2*-weighted MRI at a 2T field strength. In addition, cancerous tissue was histologically analyzed after performing the MRI studies. RESULTS: The in vitro qualitative evaluation demonstrated adequate distribution and satisfactory cell labeling of the SPIONs. At 14 or 21 days after C6 injection, a SPION-induced T2- and T2*-weighted MRI signal reduction was observed within the lesion located in the left frontal lobe on parasagittal topography. Moreover, histological staining of the tumor tissue with Prussian Blue revealed a broad distribution of SPIONs within the C6 cells. CONCLUSION: MRI analyses exhibit potential for monitoring the tumor growth of C6 cells efficiently labeled with SPIONs.

Rheology and Fourier-transform rheology on water-based systems

The influence of shear fields on water-based systems was investigated within this thesis. The non-linear rheological behaviour of spherical and rod-like particles was examined with Fourier-Transform rheology under LAOS conditions. As a model system for spherical particles two different kinds of polystyrene dispersions, with a solid content higher than 0.3 each, were synthesised within this work. Due to the differences in polydispersity and Debye-length, differences were also found in the rheology. In the FT-rheology both kinds of dispersions showed a similar rise in the intensities of the magnitudes of the odd higher harmonics, which were predicted by a model. The in some cases additionally appearing second harmonics were not predicted. A novel method to analyse the time domain signal was developed, that splits the time domain signal up in four characteristic functions. Those characteristic functions correspond to rheological phenomena. In some cases the intensities of the Fourier components can interfere negatively. FD-virus particles were used as a rod-like model system, which already shows a highly non-linear behaviour at concentrations below 1. % wt. Predictions for the dependence of the higher harmonics from the strain amplitude described the non-linear behaviour well at large, but no so good at small strain amplitudes. Additionally the trends of the rheological behaviour could be described by a theory for rod-like particles. An existing rheo-optical set-up was enhanced by reducing the background birefringence by a factor of 20 and by increasing the time resolution by a factor of 24. Additionally a combination of FT-rheology and rheo-optics was achieved. The influence of a constant shear field on the crystallisation process of zinc oxide in the presence of a polymer was examined. The crystallites showed a reduction in length by a factor of 2. The directed addition of polymers in combination with a defined shear field can be an easy way for a defined change of the form of crystallites.

Organokompatible Zinnoxid-Nanopartikel

In der vorliegenden Arbeit werden verschiedene Methoden der Synthese von Zinn(IV)oxid Nanopartikeln, deren Stabilisierung durch unterschiedliche Surfactants und der Einbau der Nanomaterialien in PMMA beschrieben und die erhaltenen Materialien charakterisiert. Die Darstellung der Zinnoxid Nanopartikel wurde über drei verschiedene Synthesewege durchgeführt: a) Polymeric Precursor Methode, b) Solvothermal-Synthese und c) säurekatalysierte Fällungsreaktion. Im Rahmen von a) konnte neben der thermodynamisch stabilen Phase von Zinn(IV)oxid ebenfalls die metastabile orthorhombische Phase synthetisiert werden. Durch eine Analyse der Pyrolysebedingungen konnte der Kristallisationsmechanismus des Zinnoxids ausgehend vom Precursor bis zur tetragonalen Phase des Zinn(IV)oxid diskutiert werden. Die Synthesemethoden b) und c) boten sich zur Darstellung von oberflächenmodifizierten Zinnoxid Nanopartikeln an. Als Surfactant benutzte man unter anderem Alkylphosphonsäuren, da eine hydrophobe Oberfläche die Dispersion in MMA ermöglichte. Abschließend wurde eine radikalische in situ-Polymerisation von MMA in Gegenwart von oberflächenmodifizierten Partikeln durchgeführt. Der erhaltene Verbundwerkstoff zeichnete sich durch eine erhöhte thermische Stabilität aufgrund weniger Strukturdefekte des Polymers aus. Durch eine Untersuchung des Polymerisationsmechanismus konnte die Wirkung der oberflächenmodifizierten Nanopartikel auf die Polymerisation veranschaulicht werden. Aufgrund der nicht homogenen Verteilung der Nanopartikel im Verbundwerkstoff konnte jedoch keine Charakterisierung der optischen Eigenschaften durchgeführt werden.

Mesenchymal stromal cell: new applications for regenerative medicine

In the last decades mesenchymal stromal cells (MSC), intriguing for their multilineage plasticity and their proliferation activity in vitro, have been intensively studied for innovative therapeutic applications. In the first project, a new method to expand in vitro adipose derived-MSC (ASC) while maintaining their progenitor properties have been investigated. ASC are cultured in the same flask for 28 days in order to allow cell-extracellular matrix and cell-cell interactions and to mimic in vivo niche. ASC cultured with this method (Unpass cells) were compared with ASC cultured under classic condition (Pass cells). Unpass and Pass cells were characterized in terms of clonogenicity, proliferation, stemness gene expression, differentiation in vitro and in vivo and results obtained showed that Unpass cells preserve their stemness and phenotypic properties suggesting a fundamental role of the niche in the maintenance of ASC progenitor features. Our data suggests alternative culture conditions for the expansion of ASC ex vivo which could increase the performance of ASC in regenerative applications. In vivo MSC tracking is essential in order to assess their homing and migration. Super-paramagnetic iron oxide nanoparticles (SPION) have been used to track MSC in vivo due to their biocompatibility and traceability by MRI. In the second project a new generation of magnetic nanoparticles (MNP) used to label MSC were tested. These MNP have been functionalized with hyperbranched poly(epsilon-lysine)dendrons (G3CB) in order to interact with membrane glycocalix of the cells avoiding their internalization and preventing any cytotoxic effects. In literature it is reported that labeling of MSC with SPION takes long time of incubation. In our experiments after 15min of incubation with G3CB-MNP more then 80% of MSC were labeled. The data obtained from cytotoxic, proliferation and differentiation assay showed that labeling does not affect MSC properties suggesting a potential application of G3CB nano-particles in regenerative medicine.

New biosensor applications of surface plasmon and hydrogel optical waveguide spectroscopy

Rapid and sensitive detection of chemical and biological analytes becomes increasingly important in areas such as medical diagnostics, food control and environmental monitoring. Optical biosensors based on surface plasmon resonance (SPR) and optical waveguide spectroscopy have been extensively pushed forward in these fields. In this study, we combine SPR, surface plasmon-enhanced fluorescence spectroscopy (SPFS) and optical waveguide spectroscopy with hydrogel thin film for highly sensitive detection of molecular analytes.rnrnA novel biosensor based on SPFS which was advanced through the excitation of long range surface plasmons (LRSPs) is reported in this study. LRSPs are special surface plasmon waves propagating along thin metal films with orders of magnitude higher electromagnetic field intensity and lower damping than conventional SPs. Therefore, their excitation on the sensor surface provides further increased fluorescence signal. An inhibition immunoassay based on LRSP-enhanced fluorescence spectroscopy (LRSP-FS) was developed for the detection of aflatoxin M1 (AFM1) in milk. The biosensor allowed for the detection of AFM1 in milk at concentrations as low as 0.6 pg mL-1, which is about two orders of magnitude lower than the maximum AFM1 residue level in milk stipulated by the European Commission legislation.rnrnIn addition, LRSPs probe the medium adjacent to the metallic surface with more extended evanescent field than regular SPs. Therefore, three-dimensional binding matrices with up to micrometer thickness have been proposed for the immobilization of biomolecular recognition elements with large surface density that allows to exploit the whole evanescent field of LRSP. A photocrosslinkable carboxymethyl dextran (PCDM) hydrogel thin film is used as a binding matrix, and it is applied for the detection of free prostate specific antigen (f-PSA) based on the LRSP-FS and sandwich immunoassay. We show that this approach allows for the detection of f-PSA at low femto-molar range, which is approximately four orders of magnitude lower than that for direct detection of f-PSA based on the monitoring of binding-induced refractive index changes.rnrnHowever, a three dimensional hydrogel binding matrix with micrometer thickness can also serve as an optical waveguide. Based on the measurement of binding-induced refractive index changes, a hydrogel optical waveguide spectroscopy (HOWS) is reported for a label-free biosensor. This biosensor is implemented by using a SPR optical setup in which a carboxylated poly(N-isoproprylacrylamide) (PNIPAAm) hydrogel film is attached on a metallic surface and modified by protein catcher molecules. Compared to regular SPR biosensor with thiol self-assembled monolayer (SAM), HOWS provides an order of magnitude improved resolution in the refractive index measurements and enlarged binding capacity owing to its low damping and large swelling ratio, respectively. A model immunoassay experiment revealed that HOWS allowed detection of IgG molecules with a 10 pM limit of detection (LOD) that was five-fold lower than that achieved for SPR with thiol SAM. For the high capacity hydrogel matrix, the affinity binding was mass transport limited.rnrnThe mass transport of target molecules to the sensor surface can play as critical a role as the chemical reaction itself. In order to overcome the diffusion-limited mass transfer, magnetic iron oxide nanoparticles were employed. The magnetic nanoparticles (MNPs) can serve both as labels providing enhancement of the refractive index changes, and “vehicles” for rapidly delivering the analytes from sample solution to an SPR sensor surface with a gradient magnetic field. A model sandwich assay for the detection of β human chorionic gonadotropin (βhCG) has been utilized on a gold sensor surface with metallic diffraction grating structure supporting the excitation of SPs. Various detection formats including a) direct detection, b) sandwich assay, c) MNPs immunoassay without and d) with applied magnetic field were compared. The results show that the highly-sensitive MNPs immunoassay improves the LOD on the detection of βhCG by a factor of 5 orders of magnitude with respect to the direct detection.rn

Multifunctional magnetically loaded polyorganosiloxane nanocomposites for biomedical applications

For the last few decades, the interest in functional nanomaterials is steadily increasing. Especially, in biomedicine the range of possible applications of multifunctional nanoparticles including dye-labeled makers and drug loaded carrier systems is extraordinary large. The incorporation of magnetic nanoparticles allows for an additional magnetic detection and manipulation. One promising system on the way to multifunctional nanomaterials is the polyorganosiloxane system. Via polycondensation of silan monomers in aqueous dispersion polyorganosiloxane nanoparticles with particle diameter between 10 and 150 nm can be synthesized. The versatile silane chemistry allows for the design of multifunctional network structures. In this work, hydrophilic iron oxide nanoparticles could be encapsulated into the polymeric particles in a highly efficient process whereat the superparamagnetic nature of the inorganic particles was restrained. The influence of different sized particles as well as the amount of the incorporated material was investigated. Using a core-shell architecture, controlled core and surface modifications could be achieved. An effective fluorescent labeling was performed via incorporation of dye-labeled monomers. Additionally, a hydrophilic surface modification was carried out via a grafting onto process of poly(ethylene glycol). Individual core and surface functionalization was achieved and the influence of the modification on the efficiency of the magnetic loading was tested. The applicability of the multifunctional particles in biological systems was proved via cellular uptake and toxicity testings. Furthermore, biofunctionalized particles were synthesized by EDC coupling using biotin and insulin.rnrn

Magnetische Multischalenpartikel für den Transport von siRNA

Die vorliegende Arbeit befasst sich mit der Entwicklung eines nichtviralen, effizienten Transfektionsmittels mit einer Kern-Schale-Struktur in der Größenordnung bis 100 nm. Dafür werden magnetische, negativ geladene Eisenoxid-Nanopartikel mittels Thermolyse mit einem Durchmesser von 17 nm synthetisiert und in Wasser überführt. Diese Nanopartikel bilden den Kern des Erbgut-Trägers und werden mittels Layer-by-Layer –Verfahren (LbL) mit geladenen Polymeren, den bioabbaubaren Makromolekülen Poly-L-Lysin und Heparin, beschichtet. Dafür wird zunächst eine geeignete Apparatur aufgebaut. Diese wird zur Herstellung von Kern-Schale-Strukturen mit fünf Polyelektrolytschichten verwendet und liefert Partikel mit einem hydrodynamischen Durchmesser von 58 nm, die bei Abwesenheit von niedermolekularem Salz aggregatfrei sind. Das System wird gegen Salz stabilisiert, indem die letzte Poly-L-Lysin-Schicht mit Polyethylenglycol modifiziert wird. Die so entstandenen Multischalenpartikel zeigen weder im PBS-Puffer noch in humanem Serum Aggregation. Mittels winkelabhängiger dynamischer Lichtstreuung wird die Aggregatbildung kontrolliert, während ζ-Potential-Messungen die Kontrolle der Oberflächenladung erlauben.rnDa siRNA auf Grund ihres negativ geladenen Phosphat-Rückgrats ebenfalls ein Polyelektrolyt ist, wird sie aggregatfrei auf die positiv geladenen PLL-Nanopartikel aufgetragen. Die eingesetzte siRNA ist farbstoffmarkiert, um eine Detektion in vitro zu ermöglichen. Jedoch sind die entstandenen Komplexe mittels Fluoreszenzkorrelations-spektroskopie (FCS) nicht nachweisbar. Auch die Fluoreszenzmarkierung der PEGylierten Außenschale mittels kupferfreier Click-Chemie ist in der FCS nicht sichtbar, sodass eine Fluoreszenzauslöschung der Farbstoffe in den Multischalenpartikeln vermutet wird.rn

Direct combination of nanoparticle fabrication and exposure to lung cell cultures in a closed setup as a method to simulate accidental nanoparticle exposure of humans

The tremendous application potential of nanosized materials stays in sharp contrast to a growing number of critical reports of their potential toxicity. Applications of in vitro methods to assess nanoparticles are severely limited through difficulties in exposing cells of the respiratory tract directly to airborne engineered nanoparticles. We present a completely new approach to expose lung cells to particles generated in situ by flame spray synthesis. Cerium oxide nanoparticles from a single run were produced and simultaneously exposed to the surface of cultured lung cells inside a glovebox. Separately collected samples were used to measure hydrodynamic particle size distribution, shape, and agglomerate morphology. Cell viability was not impaired by the conditions of the glovebox exposure. The tightness of the lung cell monolayer, the mean total lamellar body volume, and the generation of oxidative DNA damage revealed a dose-dependent cellular response to the airborne engineered nanoparticles. The direct combination of production and exposure allows studying particle toxicity in a simple and reproducible way under environmental conditions.

Surface charge of polymer coated SPIONs influences the serum protein adsorption, colloidal stability and subsequent cell interaction in vitro

It is known that the nanoparticle-cell interaction strongly depends on the physicochemical properties of the investigated particles. In addition, medium density and viscosity influence the colloidal behaviour of nanoparticles. Here, we show how nanoparticle-protein interactions are related to the particular physicochemical characteristics of the particles, such as their colloidal stability, and how this significantly influences the subsequent nanoparticle-cell interaction in vitro. Therefore, different surface charged superparamagnetic iron oxide nanoparticles were synthesized and characterized. Similar adsorbed protein profiles were identified following incubation in supplemented cell culture media, although cellular uptake varied significantly between the different particles. However, positively charged nanoparticles displayed a significantly lower colloidal stability than neutral and negatively charged particles while showing higher non-sedimentation driven cell-internalization in vitro without any significant cytotoxic effects. The results of this study strongly indicate therefore that an understanding of the aggregation state of NPs in biological fluids is crucial in regards to their biological interaction(s).

Adsorption of biomedical coating molecules, amino acids, and short peptides on magnetite (110)

Superparamagnetic iron oxide nanoparticles for biomedical applications are usually coated with organic molecules to form a steric barrier against agglomeration. The stability of these coatings is well established in the synthesis medium but is more difficult to assess in physiological environment. To obtain a first theoretical estimate of their stability in such an environment, we perform density functional theory calculations of the adsorption of water, polyvinyl alcohol (PVA) and polyethylene glycol (PEG) coating molecules, as well as the monomer and dimer of glycine as a prototype short peptide, on the (110) surface of magnetite (Fe3O4) in vacuo. Our results show that PVA binds significantly stronger to the surface than both PEG and glycine, while the difference between the latter two is quite small. Depending on the coverage, the wateradsorption strength is intermediate between PVA and glycine. Due to its strongly interacting OH side groups, PVA is likely to remain bound to the surface in the presence of short peptides. This stability will have to be further assessed by molecular dynamics in the solvated state for which the present work forms the basis.