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Mechanical stimulation appears to be a critical modulator for many aspects of biology, both of living tissue and cells. The cell-stretcher, a novel device for the mechanical uniaxial stimulation of populations of cells, is described. The system is based on a variable stroke cam-lever-tappet mechanism which allows the delivery of cyclic stimuli with frequencies of up to 10 Hz and deformation between 1% and 20%. The kinematics is presented and a simulation of the dynamics of the system is shown, in order to compute the contact forces in the mechanism. The cells, following cultivation and preparation, are plated on an ad hoc polydimethylsiloxane membrane which is then loaded on the clamps of the cell-stretcher via force-adjustable magnetic couplings. In order to show the viability of the experimentation and biocompatibility of the cell-stretcher, a set of two in vitro tests were performed. Human epithelial carcinoma cell line A431 and Adult Mouse Ventricular Fibroblasts (AMVFs) from a dual reporter mouse were subject to 0.5 Hz, 24 h cyclic stretching at 15% strain, and to 48 h stimulation at 0.5 Hz and 15% strain, respectively. Visual analysis was performed on A431, showing definite morphological changes in the form of cellular extroflections in the direction of stimulation compared to an unstimulated control. A cytometric analysis was performed on the AMVF population. Results show a post-stimulation live-dead ratio deviance of less than 6% compared to control, which proves that the environment created by the cell-stretcher is suitable for in vitro experimentation. [ABSTRACT FROM AUTHOR]

A novel, completely transparent bio-MEMS (bio-Micro Electro Mechanical System) device has been devised and manufactured using finite element analysis (FEA) and micro-fabrication techniques. The device has been designed to be used for testing the mechanical properties of single living cells, it is versatile and suitable for coupling with other analysis techniques. Furthermore, being completely transparent, it can be used with either transmission or reflection microscopes. The transparent bio-MEMS is based on a silicon dioxide-silicon nitride structure and, since the main goal is to test living cells, it is meant to work in a liquid environment and allow for cell stretching. Sensors for cell deformation and for platform displacement are also present and the required sensitivity for single cell analyses is granted. The device will moreover allow the recording of the stress-strain curve for single living cells. [ABSTRACT FROM AUTHOR]

Discontinuously reinforced aluminium (DRA) composites were prepared by a novel ion exchange process in which the reinforcing phase, aluminium oxide, was introduced by exchanging the magnesium ions in magnesium aluminate spinel with aluminium [1]. The exchange reaction occurs by the diffusion of magnesium and aluminium ions across the interface in opposite directions. The process led to the formation of DRA composites with a remarkable resistance to high temperature deformation. We present an ab-initio density functional study of the coherent cube-on-cube interfaces between spinel (MgAl2O4) and Al metal and relevant X-ray diffraction studies of the DRA composite. We find that the presence of surface electric dipoles near the interface, originated by the ion exchange process, leads to a lowering of the Al/MgAl2O4 interface toughness, and an increased residual surface stress, which does not support the hypothesis that the ion exchange process is directly responsible for the increased creep resistance of the DRA composite. We propose instead that deep diffusion of the Al atoms into MgAl2O4, resulting in the formation of γ-Al2O3 nanograins, is the mechanism that impedes dislocation movement and thus increases the interface toughness. [ABSTRACT FROM AUTHOR]

Alumina matrix was added with metal molybdenum and different amounts of zirconia''s particles. R-curves were measured during stable crack propagation and a piezo-spectroscopic technique has been used to assess the bridging stresses developed along the crack wake at the critical condition for crack propagation. The theoretical R-curves calculated from the average (microscopic) bridging stress distribution obtained by in situ Raman spectroscopy were in good agreement with the experimental data. If the molybdenum content is kept constant but the ZrO2 amount is increased, the toughening due to t-m transformation increases, but at the same time the metal/ceramic interface is weakened by the presence of zirconia and the toughening due to metal particles bridging decreases. As a result of that, the presence of zirconia has only a limited beneficial influence on the overall toughness. The overall composite toughness is due to transformation and bridging toughening mechanisms, however, the two mechanisms do not have synergistic effects and crack bridging by molybdenum particles appears to be the dominant toughening mechanism. [Copyright &y& Elsevier]

Examines the preparation of polycrystalline alumina matrix using varying amounts of metal molybdenum particles of different grain sizes. Determination of R-curves during stable crack propagation; Use of piezo-spectroscopic technique to assess the bridging stresses; Application of Raman spectroscopy based on piezo-spectroscopy effect.

Di Lenarda R, Cadenaro M, Sbaizero O. Effectiveness of 1 mol L- 1 citric acid and 15% EDTA irrigation on smear layer removal. International Endodontic Journal, 33, 46–52, 2000. Aim The aim of this study was to evaluate in vitro the cleansing and smear layer removal capability of alternate canal irrigation with citric acid and NaOCl. Methodology Eighty-one teeth were divided into three groups on the basis of the type of instrumentation, namely, manual stainless steel, Ni-Ti mechanized ProFile .04 taper or MACXim. The groups were further divided on the basis of irrigation protocol: 5% NaOCl alone, NaOCl alternated with 1 mol L-1 citric acid solution or a combination of 15% EDTA and Cetrimide solution. After longitudinal sectioning, dentinal walls were microphotographed with scanning electron microscopy at ×300 and ×1000 magnifications. Qualitative and quantitative cleansing level evaluations were performed using computerized image analysis software. Data were statistically evaluated using Kruskal–Wallis analysis and t-test. Results Qualitative evaluation at ×300 and ×1000 showed no statistically significant differences in cleansing ability between citric acid, EDTA and NaOCl groups. Quantitative evaluation of smear layer removal, measured as open tubules/total dentinal surface ratio, showed that 1 mol L-1 citric acid solution was comparable to EDTA (11.97% vs. 10.36%) (NS); in samples treated with ProFile .04 taper instruments citric acid was most effective (16.17%), whilst in the group treated with manual instrumentation EDTA and Cetrimide were the most effective (11.94%). Specimens irrigated with 5% NaOCl demonstrated significantly more cleansing than those obtained in the other two groups (P <0.001). Conclusions 1 mol L-1 citric acid solution was as effective in removing smear layer as EDTA, but was superior in specimens treated with ProFile .04 taper instruments. [ABSTRACT FROM AUTHOR]