Z. Del Prete

A novel pressure array sensor based on contact resistance variation: Metrological properties

The working principle and the metrological performances of a novel array sensor devoted to pressure map measurements are experimentally analyzed here. The physical principle on which the sensor elements are sensitive to the pressure is the variation of the contact resistance. Pressure maps from 1 up to 500 kPa can be measured. The prototype here utilized for the metrological characterization has been an 8×8 matrix sensor with a 5 mm spatial resolution over both x and y direction and a total thickness of 150 μm. The materials that have been chosen to assemble the prototype yielded to a very flexible and robust sensor which can easily be fitted over round surfaces without being damaged or leading to an alteration of its measuring properties. The static and the dynamic metrological performances of the sensor that have been studied and discussed are the response function and the calibration curve, the repeatability, the sensitivity, the time drift, the hysteresis, and the dynamic response. In spite of its fun...

Blue second harmonic generation from aluminum nitride films deposited onto silicon by sputtering technique

We studied the second order optical nonlinearity of aluminum nitride films grown by sputtering onto silicon substrates. The crystalline properties of the films were investigated by x-ray diffraction measurements. Preliminary linear optical characterization of the films was carried out by spectrophotometric optical reflectance measurements at different incidence angles; thus the dispersion laws for both ordinary and extraordinary refractive indices were retrieved. Finally, second harmonic generation measurements in reflection mode were performed at a fixed angle from a fundamental beam provided by a picosecond Ti:sapphire laser system at λ=800nm. In the experiments a high blue light conversion efficiency was found for samples 1.5 and 2μm thick, and the second order nonlinear coefficient d33=11±1pm∕V was found.

Experimental analysis of a new strain-gage signal conditioner based on a constant-current method

Abstract A strain-gage signal-conditioning scheme, which appears to be innovative, has been proposed. It is based on a potentiometric circuit with twin constant-current supplies. From the experimental tests carried out on our prototype, the following have been highlighted; a satisfying sensitivity (⋟1 μm m −1 ), a calibration curve that might be considered linear (non-linearity error less than 1 μm m −1 ), low values of zero-shift ( −1 ) throughout 60 hour test, and, finally, a global temperature coefficient that can be considered negligible (0.1 μm m −1 °C −1 ).

Measuring tendon properties in mdx mice: Cell viability and viscoelastic characteristics

Muscular dystrophy is a genetic disorder of skeletal muscle characterized by progressive muscle weakness. Here we assessed whether muscle wasting affects cell viability and mechanical properties of extensor digitorum longus (EDL) and of tibialis anterior (TA) tendons from mdx dystrophic mice compared to wild type (WT) mice. mdx mice represent the classical animal model for human Duchenne muscular dystrophy, and show several signs of the pathology, including a decrease in specific force and an increase of fibrotic index. Cell viability of tendons was evaluated by histological analysis, and viscoelastic properties have been assessed by a rapid measurement protocol that allowed us to compute, at the same time, tissue complex compliance for all the frequencies of interest. Confocal microscopy and mechanical properties measurements revealed that mdx tendons, compared to WT ones, have an increase in the number of dead cells and a significant reduction in tissue elasticity for all the frequencies that were tested. These findings indicate a reduced quality of the tissue. Moreover, mdx tendons have an increase in the viscous response, indicating that during dynamic loading, they dissipate more energy compared to WT. Our results demonstrate that muscular dystrophy involves not only muscle wasting, but also alteration in the viscoelastic properties of tendons, suggesting a paracrine effect of altered skeletal muscle on tendinous tissue.

Zero-shift Evaluation of Automatic Strain-gage Systems Based on Direct and Reverse Current Method

Solid-state digital-multimeters are being used in multichannel automatic data-acquisition systems to determine strain values from strain-gage resistance evaluation rather than using conventional Wheatstone bridge. Both the direct-resistance method and the reverse current one are examined in two tests. Each one lasted for two weeks. Irrelevant differences were observed between the two methods in spite of the adopted general-purpose low-cost switch-control unit.

An experimental analysis of accuracy and precision of a high-speed strain-gage system based on the direct-resistance method

An experimental study about the relative merits of using a high-speed digital-acquisition system to measure directly the strain-gage resistance rather than using a conventional Wheatstone bridge, is carried out.Both strain gages, with a nominal resistance of 120 Ω and 1 kΩ, are simulated with precision resistors and the output signals were acquired over a time of 48 and 144 hours; furthermore, the effects in metrological performances caused by a statistical filtering are evaluated.The results show that the implementation of the statistical filtering gains a considerable improvement in gathering straingage-resistance readings. On the other hand such a procedure causes, obviously, a loss of performance with regard to the acquisition rate, therefore to the dynamic data-collecting capabilities. In any case the intrinsic resolution of the 12-bit a/d converter, utilized in the present experimental analysis, causes a limitation for measurement accuracy in the range of hundreds μ m/m.

Effects of vibration-induced fatigue on the H-reflex

Vibration exercise (VE) has been suggested as an effective training for improving muscle strength and coordination. However, the underlying physiological adaptation processes are not yet fully understood, limiting the development of safe and effective exercise protocols. To better understand the neuromuscular responses elicited by VE, we aimed at investigating the acute effects of superimposed vibration on the Hoffmann reflex (H-reflex), measured after fatiguing exercise. Twenty-five volunteers performed four isometric contractions of the right Flexor Carpi Radialis (FCR) with baseline load at 80% of their maximal voluntary contraction (MVC), both with no vibration and with superimposed vibration at 15, 30, and 45 Hz. Fatigue was estimated by MVC test and estimation of electromyographic spectral compression. H-reflex suppression was estimated as the relative decrease after exercise. Our results show that fatiguing exercise determined a decrease in H-reflex amplitude compared to rest condition while vibration determined a lower H-reflex suppression as compared to no vibration. The superimposition of 30-Hz vibration determined the largest acute reduction in force generating capacity (36 N, p < 0.05) and the lowest H-reflex suppression (20%, p < 0.05). These results suggest VE to be particularly suitable in rehabilitation programs for rapid restoration of muscle form and function after immobilization periods.

Dystrophic tendon functionality is recovered by muscle-specific expression of insulin-like growth factor in mdx mice

Duchenne muscular dystrophy (DMD) is a severe genetic disorder of skeletal muscle, characterized by a steady muscle weakness. By using the animal model for DMD, the mdx mice, we have previously demonstrated that biomechanical properties of tendinous tissue are also significantly affected in this muscle pathology. Muscle specific over-expression of insulin like growth factor-1 (mIgf-1) is known to induce a partial recovery in muscle functionality, in particular increasing the muscle absolute force, but not the specific force. To test whether Igf-1 muscle specific over-expression helps the recovery also in tendinous tissue, mechanical and cellular evaluation of mdx and mdx:MLC/mIgf-1 mice tendons has been performed. Mechanical properties were investigated by measuring the viscoelastic response of the tissue, while cell viability was evaluated by molecular assays. An absolute recovery in the mechanical properties of EDL and TA tendons was observed through the measurement of tissue viscoelasticity for several different frequencies of interest. Moreover, when compared with tendons from dystrophic mdx animals, mdx:MLC/mIgf-1 specimens showed an almost complete recovery in the number of viable cells for both extensor digitorum longus (EDL) and tibialis anterior (TA) tendons. Of note, the partial recovery in muscle functionality and the full recovery in tendons response, suggests that mIgf-1 muscle specific over-expression exerts its effect on tendons either indirectly, improving the tendon viability and its functional properties as a consequence of the reduction of the hostile muscle dystrophic environment, or acting directly on the tendon tissue, as a paracrine trophic factor.

New ac microammeter for leakage current measurement of biomedical equipment

A new inexpensive current probe for on‐line leakage current measurement of biomedical devices in hospital environment is described. The prototype is designed to detect and measure leakage currents on the ground wire of the device’s power cord so that its integrity can be monitored in real time. Realized with a sensing coil specially matched to a low‐noise op amp, this probe adds only negligible impedance on the monitored ground lines. From this preliminary study about the device’s metrological performances, a sensitivity of 10 nArms for a current range 1–500 μArms has emerged, together with a mean linearity error of 0.03% and a frequency response flat within 1% of gain from 50 to 2000 Hz.

Morpho-Functional Interaction Between Muscle and Tendon in Hypertrophic MLC/mIGF-1 Mice

Tendons and ligaments are uniaxial viscoelastic connective tissues and, during normal activity, tendons transmit forces from muscles to bones, while ligaments stabilize the joints. Many experiments have been carried out to study ligaments and tendons mechanical properties [1], and the effects of training protocols [2] or specific pathologies. Recently, different transgenic mice models have been proposed as a new way to study in depth tendons’ function and development [3]. Within this context, we made use of pathological and transgenic animal models to investigate the morpho-functional interaction between muscles with an altered functionality and their tendons. In a previous work, by using the animal model of human Duchenne dystrophy, mdx, we found out that tendons connected to muscles with functional defects present reduced mechanical properties and an altered balance between alive and dead cells [4]. Here, we evaluated whether hypertrophic muscles would also involve alterations in tendon biomechanical properties. To do this, we used the transgenic animal model MLC/mIgf-1, were the local form of Igf-1 is over-expressed under a muscle specific promoter [5] inducing an increase in skeletal muscle mass and a proportional increment of force. To determine tendons’ elastic and viscous response separately, complex compliance has been computed with a new experimental method [6] which uses a pseudorandom Gaussian noise (PGN) to stimulate all the frequencies of interest within its bandwidth. Elasticity determines the tissue response to loading while viscous dissipation affects the likelihood of injuries to tendons. Indeed, knowing tendinous tissue viscoelasticity is central to better understand the mechanism between energy dissipation and tissue injuries. Finally, the hypothesis that changes in tendons’ mechanical properties could be correlated with alterations in the balance between alive and dead cells has been tested with an in situ cellular analysis.Copyright