A simple and robust event-detection algorithm for single-cell impedance cytometry

Microfluidic impedance cytometry is emerging as a powerful label-free technique for the characterization of single biological cells. In order to increase the sensitivity and the specificity of the technique, suited digital signal processing methods are required to extract meaningful information from measured impedance data. In this study, a simple and robust event-detection algorithm for impedance cytometry is presented. Since a differential measuring scheme is generally adopted, the signal recorded when a cell passes through the sensing region of the device exhibits a typical odd-symmetric pattern. This feature is exploited twice by the proposed algorithm: first, a preliminary segmentation, based on the correlation of the data stream with the simplest odd-symmetric template, is performed; then, the quality of detected events is established by evaluating their E2O index, that is, a measure of the ratio between their even and odd parts. A thorough performance analysis is reported, showing the robustness of the algorithm with respect to parameter choice and noise level. In terms of sensitivity and positive predictive value, an overall performance of 94.9% and 98.5%, respectively, was achieved on two datasets relevant to microfluidic chips with very different characteristics, considering three noise levels. The present algorithm can foster the role of impedance cytometry in single-cell analysis, which is the new frontier in "Omics.

A continuous model for the dynamical analysis of mistuned bladed rotors

Ideal bladed rotors are rotationally symmetric, as a consequence they exhibit couples of degenerate eigenmodes at coinciding frequencies. When even small imperfections are present destroying the periodicity of the structure (disorder or mistuning), each couple of degenerate eigenfrequencies splits into two distinct values (frequency split) and the corresponding modal shapes exhibit vibration amplitude peaks concentrated around few blades (localization phenomenon). In this paper a continuous model describing the in-plane vibrations of a mistuned bladed rotor is derived via the homogenization theory. Imperfections are accounted for as deviations of the mass and/or stiffness of some blades from the design value; a perturbation approach is adopted in order to investigate the frequency split and localization phenomena arising in the imperfect structure. Numerical simulations show the effectiveness of the proposed model, requiring much lower computational effort than classical finite element schemes

A homogenized model for dynamic analysis and vibration control of piezoactuated rotationally periodic structures

Rotationally periodic structures are commonly employed in many technological applications, e.g. satellite antennae, rotors and turbine bladed-disks. The periodic arrangement of identical substructures implies that, for any eigenmode, all the substructures exhibit the same vibration amplitude with different phases. This feature can be exploited in the dynamic analysis, enabling significant simplifications (Shen, 1994). An important issue concerning rotationally periodic structures is to control their vibrations. Some traditional typologies of passive damping devices have been proposed, essentially obtained by adding frictional dampers and viscoelastic damping treatments at the local substructure level. More recently, Wang et al. (1999) proposed to employ piezoelectric actuators, which turn out to be very suitable when size and weight constraints on the controlled structure prevent from the use of the traditional actuators. In this paper, a broadband vibration control for rotationally periodic structures, composed of many piezoactuated beams clamped to a ring basement, is investigated. It is obtained by connecting the piezoelectric actuators to purely passive periodic electric networks (Bisegna et al., 2005). A homogenization technique is employed to derive a simple analytical model of the electromechanical coupled structure, useful both for the dynamical analysis and for the design and simulation of the passive vibration control scheme. The simulation results show that the proposed passive control technique is effective for the multimodal vibration damping of rotationally periodic structures

Effective computational modeling of erythrocyte electro-deformation

Due to its crucial role in pathophysiology, erythrocyte deformability represents a subject of intense experimental and modeling research. Here a computational approach to electro-deformation for erythrocyte mechanical characterization is presented. Strong points of the proposed strategy are: (1) an accurate computation of the mechanical actions induced on the cell by the electric field, (2) a microstructurally-based continuum model of the erythrocyte mechanical behavior, (3) an original rotationfree shell finite element, especially suited to the application in hand. As proved by the numerical results, the developed tool is effective and sound, and can foster the role of electro-deformation in single-cell mechanical phenotyping

The compressive response of additively-manufactured hollow truss lattices: an experimental investigation

The mechanical response of additively-manufactured hollow truss lattices is experimentally investigated under quasi-static compression testing. Exploiting the recent developments in the Fusing Deposition Modelling (FDM) technique, two families of lattices have been fabricated, obtained as tessellation in space of octet-truss and diamond unit cells. Four specimens for each family of lattices have been designed with prescribed relative density, selecting different inner-to-outer radius ratios r/R of their hollow struts. Compression experiments prove that mechanical properties and failure mechanisms of hollow truss lattices are significantly dependent on the r/R ratio. In particular, a shift from quasi-brittle to ductile mechanical response at increasing r/R values has been revealed for the octet-truss lattice, leading to a stable collapse mechanism and increased energy absorption capacity. On the other hand, a more compliant behaviour has been observed in the diamond lattice response, with a monotonic improvement of mechanical properties as a function of the r/R ratio. Such results substantiate the potentialities of additively-manufactured hollow lattice structures as an attractive solution when lightweight, resistant and efficient energy absorption materials are required. Graphic Abstract: [Figure not available: see fulltext.

Single-cell microfluidic impedance cytometry: From raw signals to cell phenotypes using data analytics

The biophysical analysis of single-cells by microfluidic impedance cytometry is emerging as a label-free and high-throughput means to stratify the heterogeneity of cellular systems based on their electrophysiology. Emerging applications range from fundamental life-science and drug assessment research to point-of-care diagnostics and precision medicine. Recently, novel chip designs and data analytic strategies are laying the foundation for multiparametric cell characterization and subpopulation distinction, which are essential to understand biological function, follow disease progression and monitor cell behaviour in microsystems. In this tutorial review, we present a comparative survey of the approaches to elucidate cellular and subcellular features from impedance cytometry data, covering the related subjects of device design, data analytics (i.e., signal processing, dielectric modelling, population clustering), and phenotyping applications. We give special emphasis to the exciting recent developments of the technique (timeframe 2017-2020) and provide our perspective on future challenges and directions. Its synergistic application with microfluidic separation, sensor science and machine learning can form an essential tool-kit for label-free quantification and isolation of subpopulations to stratify heterogeneous biosystems

Lower-Bound Limit Analysis of Masonry Arches with Multiple Failure Sections

A computational method is proposed for the lower-bound limit analysis of masonry arches with multiple failure sections. Main motivation is the observation that, not only the position, but also the orientation of the failure sections in an arch might not be known in advance in practical applications. The lower-bound limit analysis problem is formulated as a straightforward linear programming problem. Numerical simulations highlight the predicting capabilities of the proposed approach, enabling an accurate and safe prediction of the loading capacity of masonry arches