Chiara Schmid

Characterization of zinc-releasing three-dimensional bioactive glass scaffolds and their effect on human adipose stem cell proliferation and osteogenic differentiation

While the addition of zinc ions to bioactive ceramics has been shown to enhance the proliferation and osteogenic differentiation of osteoblast-like cells, contradictory results have been found. Therefore, the effect of zinc-releasing ceramics on cell proliferation and differentiation into osteogenic lineages requires further clarification. The aim of this study was to evaluate the effects of zinc addition on the degradation profile of three-dimensional bioactive glass scaffold, and on the proliferation and osteogenesis of human adipose stem cells (hASCs) in these scaffolds. Bioactive glass scaffolds containing Na(2)O, K(2)O, MgO, CaO, B(2)O(3), TiO(2), P(2)O(5) and SiO(2) were prepared. The degradation was evaluated by weight loss measurement, scanning electron microscopy and elemental analysis. The degradation profile of bioactive glass was shown to slow down with the addition of zinc. Qualitative live/dead staining showed that zinc addition to bioactive glass inhibits cell spreading and proliferation of hASCs. However, zinc addition had no significant effect on DNA content, alkaline phosphatase activity and osteopontin concentration of hASCs when measured quantitatively. Our results suggest that the possible stimulatory effect of addition of zinc on hASC proliferation and osteogenesis was not detected because addition of zinc slowed down the degradation rate of the studied bioactive glass scaffolds.

Redistribution of Ce and La during processing of Ce(La)-TZP/Al2O3 composites

Abstract The dispersion of second-phase particles, platelets or fibres in a ceramic body offers possibilities of considerable improvements in mechanical properties. In such second-phase reinforced composites the materials properties are to a large extent controlled by the structure of the internal interfaces, i.e. the phase and grain boundaries. The microstructure/microchemistry of aluminadispersed ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP/20A) were characterized by means of analytical TEM/STEM techniques. Local variation in the concentration of Ce stabilizer as well as of La additives and Si impurities during processing of the composite ceramics were studied by EDS X-ray analysis with high spatial resolution. Emphasis was put on the segregation of Ce and La in interface regions. Evidence was found for the presence of a vitreous intergranular phase situated in small pockets at triple grain junctions. The addition of small fractions of La 2 O 3 in TZP resulted in interreaction between matrix constituents and Al 2 O 3 particles. In this reaction a stable crystalline Al-Ce-La-Zr mixed oxide phase is formed, effectively reducing the fraction of residual vitreous intergranular phase, resulting in improved fracture toughness in this material.

Raman spectroscopic study of bioactive silica-based glasses: The role of the alkali/alkali earth ratio on the Non-Bridging Oxygen/Bridging Oxygen (NBO/BO) ratio

Raman spectra of bioactive glasses of the Na2O–K2O–MgO–CaO–B2O3–P2O5–SiO2 to be used in bone reconstruction systems have been collected from samples with three different concentrations of alkali and alkali earth elements. Compositions were chosen with a constant total amount of modifiers and formers, with only minor changes among the formers. The ratio of Non-Bridging Oxygens to Bridging Oxygens (NBO/BO) has been obtained from the Raman spectra and reported as a function of the alkali/alkali earth ratio, showing a linear increase. Dissolution tests indicate also a linear dependence of the amount of Na

Analysis of the electrical behaviour of conductor/insulator composites using effective medium theories

Al2O3/8YSZ composites with a wide range of alumina compositions, from 0 to 50 wt.%, have been prepared and characterised. The electrical properties and the microstructure were studied by complex impedance spectroscopy and scanning electron microscopy techniques, respectively. Simple models derived from effective medium theories were used to predict the qualitative trend of electrical conductivity versus Al2O3 volume fraction and a comparison with the experimental data is reported. # 2002 Elsevier Science Ltd. All rights reserved.

The Synthesis of Calcium or Strontium Hexaluminate added ZTA Composite Ceramics

Abstract This paper proposes new preparation methods for alumina–tetragonal zirconia–Ca or Sr hexaluminate composites. Two powder preparation routes were explored. In the first, aluminium and calcium or strontium nitrate hydrates were added to alumina zirconia powders and in the second only calcium or strontium nitrate hydrates were used. Powders produced by the second route are to be preferred since reinforcements do not inhibit the composite sintering process.

Bioactive porous scaffolds for tissue engineering applications: investigation on the degradation process by Raman spectroscopy and scanning electron microscopy

Bioactive glasses in the Na2 O-K2 O-MgO-CaO-B2 O3 -P2 O5 -SiO2 system characterized by an unusually large working range were used for the production of fiber porous scaffolds. In vitro tests were carried out by immersing the scaffolds in simulated body fluid (SBF) solution; soaking time and glass composition effects on the degradation of the material are the principal subject of this investigation. Raman spectroscopy and scanning electron microscopy (SEM) were used as the main investigative methods. The study demonstrates the importance of the network modifiers and, in particular, of the amount of alkaline and al-kaline earths in the different stages of the material degradation and in the development of the hydroxyl-carbonate-apatite (HCA) layer.

Thermal and acoustic performance expectations on timber buildings

In recent years, building technologies have been developed in order to improve comfort and energy saving. European institutions and single countries firmly invite individuals to choose high energy-saving strategies in order to decrease carbon emissions and energy consumption. Examples could be found in thermal insulators added to façades and improvement of glazing performance. At present, two technologies are the most used in construction realization: traditional (concrete, masonry or in general heavyweight structure) or wood (timber, crosslam or in general timber lightweight structure). Designers, scientists and builders have their own opinions on these two topics, but good insulation performance are achievable with both of them. Nevertheless, for lay people as well as for designers, wooden structures seem more comfortable, reliable and insulated. Therefore, an international survey was realized in order to investigate what individuals expect from these two different construction technologies in terms of insulation performance. Results indicate that timber buildings stereotypes are confirmed for acoustic and thermal insulation and show how scientific communication may help to deal with new or untraditional constructions.

Low frequency noise and disturbance assessment methods: A brief literature overview and a new proposal

Several studies have presented the effects of environmental noise on communities, focusing attention on sleep time events. The noise introduced into a dwelling is mostly evaluated using the A-weighted sound pressure level (LAeq) as the only parameter to determine the perceived disturbance. Nevertheless, if noise is produced by activities or sources characterised by a low frequency contribution, the measurement of LAeq underestimates the real disturbance, in particular during sleep time. The aim of this contribution is to analyse the low frequency disturbance phenomenon into technical and scientific literature and to investigate if any possible objective method is available in order to assess noise disturbance inside dwellings.

Biological evaluation of the effects of the surface roughness and composition of titanium discs on an immortalized human osteoblastic cell line

In the search for methods to improve the biocompatibility of prosthetic materials, attention has recently been di- rected towards the usefulness of different surface topography and chemical modification and how they influence cellular be- havior. This in vitro study investigates the effect of surface roughness and composition of commercial grade 3 titanium (Ti) discs on a well-characterized human bone-derived cell line (Hobit). Cells were cultured on machined Ti discs (TOR), polished with ceramic particles (BUR), alumina-sand-blasted (S-Al), glass-blasted (S-V), hydroxyapatite-blasted (S-HA), hydrofluoric acid etched (HF), titanium plasma-sprayed (Ti-PS) and hydroxyapatite plasma-sprayed (HA-PS). Cell attachment, prolifera- tion, morphology and expression of alkaline phosphatase (AP), osteocalcin (OC) and type I collagen were studied. Cells at- tach to all surfaces, but proliferation differs among the variously treated materials: it is higher in TOR, BUR and HF than in S-Al, S-V, S-HA and Ti-PS, but much lower in HA-PS. Cells present the typical polygonal-morphology of the osteogenic cells and maintain the osteoblastic phenotype expressing AP activity and OC. (Journal of Applied Biomaterials & Biomechanics 2003; 1: 117-24)

Porous titanium obtained by a new powder metallurgy technique: Preliminary results of human osteoblast adhesion on surface polished substrates

This study concerns a novel powder metallurgy method for producing porous titanium (pTi) exhibiting high mechanical properties. The preparation procedure consisted of the following stages: first, the preparation of Ti and titanium hydride (TiH2) powder mixtures and their consolidation with a cold isostatic press, followed by a sintering of the green bodies performed with hot isostatic press (HIP) equipment. Thermal decomposition in controlled environment of the TiH2 phase results in the foam structure. The resulting porosity percolates with a volume fraction of approximately 20%. The final material exhibits interesting mechanical properties, comparable to those of full density titanium (between grade 2 and grade 3), with the advantage of a minor density. The samples produced were tested to verify their biological response by studying the effectiveness of osteoblast adhesion and growth. In this preliminary study, osteoblastic cell morphology was investigated and compared to that observed on fully dense commercially pure titanium (Ti-cp) (ASTM, grade 3). The preliminary results were promising regarding cellular adhesion and spreading. (Journal of Applied Biomaterials & Biomechanics 2003; 1: 172-7).