Janet Grabow

Zirconia nanoparticles prepared by laser vaporization as fillers for dental adhesives.

Zirconia nanoparticles prepared by laser vaporization were incorporated into the primer or into the adhesive of a commercial adhesive system in order to evaluate its effect on bond strength to dentin. Zirconia nanoparticles (20-50nm) were prepared using a particular laser vaporization technique and incorporated into the primer (P) or into the adhesive (A) of the Adper Scotchbond Multi-Purpose (SBMP) system at 5, 10, 15 and 20wt.% by means of mechanical mixing (stirring) and ultrasonication. Control (unfilled) and experimental groups (filled) were applied, according to the manufacturers instructions, onto flat mid-coronal human dentin. Composite crowns were built up, stored in distilled water for 24h at 37°C and cut into 0.65±0.05mm² beams following a non-trimming microtensile technique. Specimens were fractured in tension using a universal testing machine (Zwick) and examined by scanning electron microscopy for fractographic analysis. Microtensile bond strength (μTBS) data were analyzed using a two-way ANOVA and modified LSD test at α=0.05. Analysis of the nanofiller distribution and ultramorphological characterization of the interface were performed by transmission electron microscopy (TEM). Zirconia nanoparticle incorporation into the primer or into the adhesive of SBMP significantly increased μTBS to dentin. Filler concentration only affected μTBS significantly in the P group. Statistically significant differences between groups P and A occurred only at 20wt.% filler content, with a significantly higher μTBS in group P. TEM micrographs revealed nanoparticle deposition on top of a hybrid layer when incorporated into the primer, whereas they remained dispersed through the adhesive layer in group A. Zirconia nanoparticles incorporation into SBMP increased bond strength to dentin by reinforcing the interface adhesive layer. Nanofiller incorporation into the primer solution showed a tendency of increasing bond strength with increasing concentration. At high concentrations (20wt.%) nanofiller incorporation was more efficient in increasing bond strength if incorporated in the primer solution. Adding nanofillers to the primer and to the adhesive solutions resulted in different particle distributions at the interface.

In situ synthesis of photocatalytically active hybrids consisting of bacterial nanocellulose and anatase nanoparticles.

Bacterial nanocellulose (BNC) is an extraordinary biopolymer with a wide range of potential technical applications. The high specific surface area and the interconnected pore system of the nanofibrillar BNC network suggest applications as a carrier of catalysts. The present paper describes an in situ modification route for the preparation of a hybrid material consisting of BNC and photocatalytically active anatase (TiO(2)) nanoparticles (NPs). The influence of different NP concentrations on the BNC biosynthesis and the resulting supramolecular structure of the hybrids was investigated. It was found that the number of colony forming units (CFUs) and the consumption of glucose during biosynthesis remained unaffected compared to unmodified BNC. During the formation of the BNC network, the NPs were incorporated in the whole volume of the accruing hybrid. Their distribution within the hybrid material is affected by the anisotropic structure of BNC. The photocatalytic activity (PCA) of the BNC-TiO(2) hybrids was determined by methanol conversion (MC) under UV irradiation. These tests demonstrated that the NPs retained their PCA after incorporation into the BNC carrier structure. The PCA of the hybrid material depends on the amount of incorporated NPs. No alteration of the photocatalysts efficiency was found during repeated PCA tests. In conclusion, the in situ integration of photocatalytically active NPs into BNC represents an attractive possibility to extend its fields of application to porous filtering media for drinking water purification and air cleaning.

New ZrO2/Al2O3 Nanocomposite Fabricated from Hybrid Nanoparticles Prepared by CO2 Laser Co-Vaporization

Alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) are currently the materials of choice to meet the need for tough, strong, and bioinert ceramics for medical devices. However, the mechanical properties of ZrO2/Al2O3 dispersion ceramics could be considerably increased by reducing the corresponding grain sizes and by improving the homogeneity of the phase dispersion. Here, we prepare nanoparticles with an intraparticular phase distribution of Zr(1−x)AlxO(2−x/2) and (γ-, δ-)Al2O3 by the simultaneous gas phase condensation of laser co-vaporized zirconia and alumina raw powders. During subsequent spark plasma sintering the zirconia defect structures and transition alumina phases transform to a homogeneously distributed dispersion of tetragonal ZrO2 (52.4 vol%) and α-Al2O3 (47.6 vol%). Ceramics sintered by spark plasma sintering are completely dense with average grain sizes in the range around 250 nm. Outstanding mechanical properties (flexural strength σf = 1500 MPa, fracture toughness KIc = 6.8 MPa m1/2) together with a high resistance against low temperature degradation make these materials promising candidates for next generation bioceramics in total hip replacements and for dental implants.

Characterization of Nanoparticles by Solvent Infrared Spectroscopy

The characterization of the surface chemistry of nanoparticles using infrared spectroscopy of adsorbed solvents is proposed. In conventional IR spectroscopy of nanomaterials the capability of characterizing the chemistry of the surface is limited. To overcome these limitations, we record IR spectra of different solvents inside a fixed bed of the nanopowder to be tested. Using water and different alcohols as solvents enables the characterization of the nanomaterials surface chemistry via the molecular interactions affecting the hydrogen-bonding network in the solvent. Different ceramic nanopowders (titania, two different iron oxides, and iron oxide nanocrystallites embedded in a closed silica matrix) are studied using water, ethanol, and n-butanol as solvents. The OH stretching region of the IR spectra reveals characteristic differences in the surface chemistry of the nanoparticles. The proposed method is fast and straightforward, and hence, it can be a versatile tool for rapid screening.

Laser Vaporization of Magnetic FexOy and FexOy-SiO2 Nanoparticles for Biomedical Applications

Magnetic iron oxide (FexOy) and iron oxide/silica (FexOy/SiO2) composite nanoparticles were synthesized by CO2 laser vaporization (LAVA) of an α-Fe2O3 raw powder and α-Fe2O3/quartz sand mixtures, respectively. Particle morphology, composition and iron oxide phase formation were investigated by transmission electron microscopy and X-ray diffraction. The resulting nanopowders mainly consisted of magnetite (Fe3O4) and maghemite (γ-Fe2O3). Increasing the oxygen partial pressure in the LAVA process gas an additional iron oxide phase, ε-Fe2O3, occurred. The saturation magnetization of the iron oxide nanoparticles was determined with vibrating sample magnetometry and was found to decrease with increasing oxygen partial pressure in the process gas. FexOy/SiO2 composite nanoparticles are of particular interest for biomedical applications because their silica surface can be functionalized very easily.

Nanoparticles for Biomedical Applications Prepared by CO2 Laser Vaporization

Functional ceramic nanopowders with emphasis on biomedical applications were engineered by gas-phase condensation using the CO2 laser vaporization (LAVA) technique. Europium doped strontium aluminate nanoparticles (NP) were prepared from a SrO/α-Al2O3/Eu2O3 powder mixture. Excited with ultraviolet radiation (UV), the as-prepared amorphous NP revealed red photoluminescence emission. After annealing in reductive atmosphere crystalline SrAl2O4:Eu2+ nanopowder was obtained showing strong green emission at UV excitation. Ferrimagnetic iron oxide (FexOy) nanopowders were prepared starting from α-Fe2O3 powder. In oxygen-free condensation atmosphere γ-Fe2O3 NP were obtained. Oxygen as condensation gas yielded γ-and ε-Fe2O3 NP. Superparamagnetic NP were prepared starting from α-Fe2O3/SiO2 mixtures. Depending on the mixing ratio γ-Fe2O3 nanocrystallites embedded in a SiO2 glass matrix or γ-Fe2O3-SiO2 Janus NP were obtained. These NP provide a reactive SiO2 interface for subsequent functionalizing. The co-vaporization of α-Al2O3 as the main proportion and t-ZrO2 yielded zirconia-toughened-alumina NP. Reinforcing effects of Al2O3-ZrO2 dispersion ceramics will be increased using NP with an intraparticle dispersion of these phases. Future applications of the LAVA prepared NP include biological fluorescence labeling, and drug targeting, magnetic resonance imaging, and hyperthermic cancer therapy, as well as sintering of load bearing ceramic implants, respectively.