Highly Efficient and Reproducible Sonochemical Synthesis of ZnO Nanocrystals.

Sonochemical synthesis can be a facile, fast, efficient, versatile and economical way to prepare a large variety of conventional or novel nanostructured materials (metallic, magnetic, semiconducting, polymeric, etc.). In this work, zinc oxide nanocrystals were synthesized by irradiating and heating at 90 °C in a commercial ultrasonic bath a water solution of zinc nitrate hexahydrate and ammonia solution or hexamethylenetetramine as base catalysts. The evolution of the powder morphology and its crystalline structure were investigated at different times of ultrasonic irradiation (0-9 hours) and compared with those of samples obtained by only heating the solutions in a muffle furnace in order to enlighten the growth mechanism. It resulted that: i) the crystal morphology depends on the selected base, ii) for samples obtained by using ultrasounds, the homogeneity of the powders depends on the irradiation time, iii) by comparing all samples obtained at 7 hours of heating, the aspect ratio of the crystals is higher for those that also underwent to ultrasounds.

Growth Mechanisms of ZnO Micro-Nanomorphologies and Their Role in Enhancing Gas Sensing Properties.

Zinc oxide (ZnO) is one of the main functional materials used to realize chemiresistive gas sensors. In addition, ZnO can be grown through many different methods obtaining the widest family of unique morphologies. However, the relationship between the ZnO morphologies and their gas sensing properties needs more detailed investigations, also with the aim to improve the sensor performances. In this work, seven nanoforms (such as leaves, bisphenoids, flowers, needles, etc.) were prepared through simple wet chemical synthesis. Morphological and structural characterizations were performed to figure out their growth mechanisms. Then, the obtained powders were deposited through screen-printing technique to realize thick film gas sensors. The gas sensing behavior was tested toward some traditional target gases and some volatile organic compounds (acetone, acetaldehyde, etc.) and compared with ZnO morphologies. Results showed a direct correlation between the sensors responses and the powders features (morphology and size), which depend on the specific synthesis process. The sensors can be divided in two behavioral classes, following the two main morphology kinds: aggregates of nanocrystals (leaves and bisphenoids), exhibiting best performances versus all tested gases and monocrystal based (stars, needle, long needles, flowers, and prisms).

Hydroxyapatite-collagen composites. Part I: can the decrease of the interactions between the two components be a physicochemical component of osteoporosis in aged bone?

The interactions of Type I acid soluble collagen (Col) with both carbonate-free hydroxyapatite (HA(1100)) and carbonate-rich one (CHA) were investigated. The aim was to ascertain whether the increase of bone CO(3) (2-) with ageing could relate to the disease known as osteoporosis. HA(1100)-Col and CHA-Col composites with various ratios were prepared and examined. Scanning electron microscopy and differential scanning calorimetry showed a stronger adhesion of the Col matrix to the granules of HA(1100) than to those of CHA. FT-IR spectroscopy showed that with HA(1100) both multiple hydrogen bonds of Col peptide -NH groups with HA PO(4) (3-), and electrochemical interactions between Col peptide -C=O groups and HA Ca(2+) were present. In the presence of CO(3) (2-), the interactions between -NH and phosphate were diminished, and Ca(2+) interacted more strongly with CO(3) (2-) than with peptide -C=O, so causing a separation between the two components of the bone extra-cellular matrix. The results obtained strengthen the hypothesis that the substitution of PO(4) (3-) ions by CO(3) (2-) ions in the HA lattice might be a significant component of osteoporosis, although further investigation is needed.

Perspectives of the Si3N4-TiN ceramic composite as a biomaterial and manufacturing of complex-shaped implantable devices by electrical discharge machining (EDM).

PURPOSE: In this work we investigated the suitability of electroconductive silicon nitride/titanium nitride composite for biomedical implantable devices with particular attention on the processing route that allows the net-shaping of complex components by electrical discharge machining (EDM). METHODS: The composite, constituted mainly of a beta-Si3N4, dispersed TiN grains and a glassy grain boundary phase, exhibited a low density and high hardness, strength and toughness. Bulk, surface characteristics and properties of the Si3N4-TiN composite were analyzed. After the EDM process, the microstructure of the machined surface was examined. RESULTS AND CONCLUSIONS: The obtained results showed that the Si3N4-TiN ceramic composite together with the EDM manufacturing process might potentially play a key role in implantable load-bearing prosthesis applications.

On the possibility of silicon nitride as a ceramic for structural orthopaedic implants. Part II: chemical stability and wear resistance in body environment.

In Part I, the processing, microstructure and mechanical properties of three silicon nitride-based ceramics were examined and their non-toxicity was demonstrated. In this Part II, some features critical to biomedical applications were investigated: (i) the wetting behaviour against aqueous media, including physiological solutions; (ii) the chemical stability in water and in physiological solutions; and (iii) the wear resistance, measured under experimental procedures that simulate the conditions typical of the hip joint prosthesis. The results confirmed that silicon nitride may serve as a biomaterial for bone substitution in load bearing prosthesis.

On the possibility of silicon nitride as a ceramic for structural orthopaedic implants. Part I: processing, microstructure, mechanical properties, cytotoxicity.

Notwithstanding the good combination of mechanical and tribological properties, the suitability of silicon nitride for application as prosthesis in bone reconstruction or in articular joints replacements is still controversial. This study aims to design and produce three different silicon nitride-based ceramics and to test the materials. In this Part I the microstructure and mechanical properties evidence outstanding characteristics and the cytotoxicity studies confirm that all the materials are extremely inert and biocompatible. In Part II, the wear performance and the wettability and chemical stability against different aqueous media and physiological solutions are investigated and discussed.