The performance of porous scaffolds for tissue engineering (TE) applications is evaluated, in general, in terms of porosity, pore size and distribution, and pore tortuosity. These descriptors are often confounding when they are applied to characterize transport phenomena within porous scaffolds. On the contrary, permeability is a more effective parameter in (1) estimating mass and species transport through the scaffold and (2) describing its topological features, thus allowing a better evaluation of the overall scaffold performance. However, the evaluation of TE scaffold permeability suffers of a lack of uniformity and standards in measurement and testing procedures which makes the comparison of results obtained in different laboratories unfeasible. In this review paper we summarize the most important features influencing TE scaffold permeability, linking them to the theoretical background. An overview of methods applied for TE scaffold permeability evaluation is given, presenting experimental test benches and computational methods applied (1) to integrate experimental measurements and (2) to support the TE scaffold design process. Both experimental and computational limitations in the permeability evaluation process are also discussed.

In this work, we measured the electromagnetic field, given by the moving charges, during laboratory fracture experiments on specimens made of different heterogeneous materials. We investigated the mechanical behaviour of concrete and rocks samples loaded up to their failure by the analysis of acoustic emission (AE) and electromagnetic emission (EME). All specimens were tested in compression at a constant displacement rate and monitored by piezoelectric (PZT) transducers for AE data acquisition. Simultaneous investigation into magnetic activity was performed by a measuring device calibrated according to metrological requirements. In all the considered cases, the presence of AE signals has been always observed during the damage process, whereas it is very interesting to note that the magnetic signals were generally observed only in correspondence to sharp stress drops or the final collapse.

Bone tissue is able to self-regenerate, but, in the presence of large defects due to trauma, tumor removal or congenital diseases, surgical insertion of a bone graft is needed to promote a faster and effective tissue healing. It was estimated that more than 2 million people worldwide annually undergo bone surgery to repair critical osseous defects. 1 At present, both biological (i.e. transplant materials) and synthetic grafts are used. The latter option is usually preferred in modern bone

The present research focuses on acoustic emission (AE) and electromagnetic emission (EME) detected during laboratory compression tests on concrete and rocks specimens. We investigated their mechanical behavior up to failure by the AE and EME due to micro‐ and macrocrack growth. Among the tested specimens, a concrete sample was analyzed by applying to its surface both piezoelectric (PZT) transducers for detection of high‐frequency AE waves, and PZT accelerometric transducers for detection of low‐frequency AE (elastic emission or ELE). Besides the high‐frequency AEs, the emergence of low‐frequency ELE just before the failure describes the transition from diffused microcracking to localized macrocracks which characterizes the failure in brittle materials. For all the specimens, a simultaneous analysis of magnetic activity was performed by a measuring device calibrated according to metrological requirements. In all the considered specimens, the presence of AE events has been always observed during the damage process, whereas it is very interesting to note that the EMEs were generally observed only in correspondence with sharp stress drops or the final collapse. The experimental evidence confirms AE and EME signals as collapse precursors in materials like concrete and rocks.

The damage process in a concrete specimen subjected to uniaxial compression test is investigated by detection of the propagating elastic waves because of micro-and macrocrack growth. Besides the high-frequency acoustic emissions (AEs), the presence of low-frequency elastic emissions (ELEs), from 1 to 10 kHz, is detected just before the specimen failure. A spectral analysis of the ELEs is performed by measuring with a calibrated transducer the local acceleration of the specimen surface. Quantitative information about the macrocrack effects in terms of released energy is thus obtained. Furthermore, the evolution of damage is followed through the analysis of the amplitude distribution of AE and ELE signals, distributed according to the Gutenberg-Richter (GR) statistics.KEY WORDS: acoustic emissions, b-value analysis, elastic emissions, fracture precursors, lowfrequency Ó

Indoor working and living environments are increasingly exposed to low-frequency noise sources. The wellknown relationship between noise conditions and effects on human health requires the development of a proper procedure to evaluate the stress due to acoustical factors. For this purpose, an experiment, based on Soft Metrology principles, was designed to measure the changes of cognitive and physiological parameters (response time and heart rate) on a sample of 25 male and female volunteers, aged 19-29 years, exposed to three types of noise in a hemi-anechoic room. Participants were involved in a cognitive task (Stroop effect) for 10 min in four different conditions: silence, stochastic broadband multi-tonal noise (BBN), stochastic lowfrequency multi-tonal noise (LFN1), and low-frequency stationary noise with regular amplitude modulation (LFN2). All sounds were reproduced by two loudspeakers at equivalent sound pressure level of 93 dB. Results showed that in noise conditions, subjects reduced their response times. This is an evidence of growing stress, according to arousal theory. In particular, LFN1 and LFN2 produced cognitive stress comparable to stochastic broadband multi-tonal noise. Furthermore, subdividing the subjects in extroverts and introverts through the Eysenck Personality Questionnaire-Revised psychological test, it was shown that LFN1 and LFN2 produced higher stress effects than stochastic broadband multi-tonal noise on the cognitive performances and a physiological stress comparable to stochastic broadband multi-tonal noise in introverts, whereas no effects were observed in extroverts, as hypothesized by Eysenck. This result highlights the necessity in the future to consider the personality parameter as a key factor in the evaluation of the effects of noise on humans.

Traceability of digital sensors is a metrological challenge, as well as a present priority, as stated within the emerging metrology requirements for the future in the Strategy 2017 to 2027 document of the Consultative Committee for Acoustics, Ultrasound, and Vibration of BIPM. From this perspective, in this paper, a calibration system for 3-axis digital MEMS accelerometers is described, in order to simultaneously evaluate the main and transverse sensitivities in the frequency domain (from 5 Hz up to 3 kHz) and in static conditions, together with a proper sensitivity parameter for digital outputs, thus providing the required metrological traceability. The procedure, based on the comparison to a reference transducer, involves a single-axis excitation of inclined planes. Experimental results are expressed in terms of exploitation and sensitivities matrices. Overall expanded uncertainties of the main terms are in the order of 2%, in dynamic conditions, and 1%-2% in static conditions. The feasibility of this system can be exploited for the development of manufacturers' in-line control systems and for the investigation of large-scale calibration procedures.

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