Francesca Sapuppo

Experimental Characterization of Ionic Polymer Metal Composite as a Novel Fractional Order Element

Ionic polymer metal composites (IPMCs) are electroactive materials made of ionic polymer thin membranes with platinum metallization on their surfaces. They are interesting materials due to not only their electromechanical applications as transducers but also to their electrochemical features and the relationship between the ionic/solvent current and the potential field. Their electrochemical properties thus suggest the possibility for exploiting them as compact fractional-order elements (FOEs) with a view of defining fabrication processes and production strategies that assure the desired performances. In this paper, the experimental electrical characterization of a brand new IPMC setup in a fixed sandwich configuration is proposed. Two IPMC devices with different platinum absorption times (5 h and 20 h) are characterized through experimental data: first, a preliminary linearity study is performed for a fixed input voltage amplitude in order to determine the frequency region where IPMC can be approximated as linear; then, a frequency analysis is carried out in order to identify a coherent fractional-order dynamics in the bode diagrams. Such analyses take the first steps towards a simplified model of IPMC as a compact electronic FOE for which the fractional exponent value depends on fabrication parameters as the absorption time.

An Improved Instrument for Real-Time Measurement of Blood Flow Velocity in Microvessels

A new approach for the measurement of red blood cell velocity at the level of microcirculation has been developed and characterized. The new real-time and automated measurement system is based on the dual-slit methodology, and blood flow information is extracted from images and transduced into two analog photometric signals and then processed using a hybrid analog-digital system that performs the cross correlation of the signals in real time. The characterization of the system consists of a calibration with a known velocity target, yielding to the hyperbolic calibration curve velocity versus delay and the determination of the velocity detectable range from 0.3 to 120 mm/s. A theoretical study of the measurement uncertainty and parametric studies were carried out to test the system robustness to changes of parameters and to determine the optimal configuration that is applicable to various experimental conditions. The system was further tested in in vivo experiments in the rat cremaster preparation in different types of vessels and flow velocities to verify the consistency of the results, as compared with those from conventional measuring systems. In addition, the dynamic behavior of the system and its response to changes in the measured velocity were studied through a continuous velocity record that was obtained during an experimental procedure.

A cellular nonlinear network: real-time technology for the analysis of microfluidic phenomena in blood vessels

A new approach to the observation and analysis of dynamic structural and functional parameters in the microcirculation is described. The new non-invasive optical system is based on cellular nonlinear networks (CNNs), highly integrated analogue processor arrays whose processing elements, the cells, interact directly within a finite local neighbourhood. CNNs, thanks to their parallel processing feature and spatially distributed structure, are widely used to solve high-speed image processing and recognition problems and in the description and modelling of biological dynamics through the solution of time continuous partial differential equations (PDEs). They are therefore considered extremely suitable for spatial-temporal dynamic characterization of fluidic phenomena at micrometric to nanometric scales, such as blood flow in microvessels and its interaction with the cells of the vessel wall. A CNN universal machine (CNN-UM) structure was used to implement, via simulation and hardware (ACE16k), the algorithms to determine the functional capillarity density (FCD) and red blood cell velocity (RBCV) in capillaries obtained by intravital microscopy during in vivo experiments on hamsters. The system exploits the moving particles to distinguish the functional capillaries from the stationary background. This information is used to reconstruct a map and to calculate the velocity of the moving objects.

Bio-Microfluidics Real-Time Monitoring Using CNN Technology

A new non-invasive real-time system for the monitoring and control of microfluidodynamic phenomena involving transport of particles and two phase fluids is proposed. The general purpose design of such system is suitable for in vitro and in vivo experimental setup and, therefore, for microfluidic applications in the biomedical field, such as lab-on-chip and for research studies in the field of microcirculation. The system consists of an ad hoc optical setup for image magnification providing images suitable for acquisition and processing. The main feature of the optical system is the accessibility of the information at any point of the optical path. It was designed and developed using discrete opto-mechanic components mounted on a breadboard. The optical sensing, acquisition, and processing were all performed using an integrated vision system based on cellular nonlinear networks (CNNs) analogic (analog plus logic) technology called focal plane processor (FPP, Eye-RIS, Anafocus) that was inserted in the optical path. Ad hoc algorithms were implemented for the real-time analysis and extraction of fluidodynamic parameters in micro-channels. They were firstly tested on sequences of images recorded during in vivo microcirculation experiments on hamsters and then applied on images acquired and processed in real-time during in vitro experiments on two-phase fluid flow in a continuous microfluidic device (serpentine mixer, ThinXXS).

An Enhanced Fractional Order Model of Ionic Polymer-Metal Composites Actuator

Ionic polymer-metal composites (IPMCs) are electroactive polymers which transform the mechanical forces into electric signals and vice versa. The paper proposes an enhanced fractional order transfer function (FOTF) model for IPMC membrane working as actuator. In particular the IPMC model has been characterized through experimentation, and a more detailed structure of its FOTF has been determined via optimization routines. The minimization error was attained comparing the simple genetic algorithms with the simplex method and considering the error between the experimental and model derived frequency responses as cost functions.

Microfluidic circuits and systems

The possibilities envisioned by the characterization of microfluidic systems cover a wide range of both scientific demands and industrial requirements, from life sciences to fine chemistry, from food quality to other microbiology applications. In these fields, the development of analytical methods and technological solutions oriented to the creation of a firm and structured link between models and experimentation on microfluidic systems, opens up the way for the study and characterization of microfluidic devices and phenomena from a point of view related to system and control theory.

A polymeric micro-optical interface for flow monitoring in biomicrofluidics

We describe design and miniaturization of a polymeric optical interface for flow monitoring in biomicrofluidics applications based on polydimethylsiloxane technology, providing optical transparency and compatibility with biological tissues. Design and ray tracing simulation are presented as well as device realization and optical analysis of flow dynamics in microscopic blood vessels. Optics characterization of this polymeric microinterface in dynamic experimental conditions provides a proof of concept for the application of the device to two-phase flow monitoring in both in vitro experiments and in vivo microcirculation investigations. This technology supports the study of in vitro and in vivo microfluidic systems. It yields simultaneous optical measurements, allowing for continuous monitoring of flow. This development, integrating a well-known and widely used optical flow monitoring systems, provides a disposable interface between live mammalian tissues and microfluidic devices making them accessible to detectionprocessing technology, in support or replacing standard intravital microscopy.

A multi-physics model of an IPMC actuator in the electrical, chemical, mechanical and thermal domains

IPMCs are electroactive polymers which can be used both as sensors and as actuators. A multiphysics model of IPMC devices working as actuators is here presented. The model integrates electrical, mechanical, chemical and thermal effects in a unique solution and attention is focused on the coupling factors among the physics domains. The model was validated through experimentation.

Fractional-Order Identification and Control of Heating Processes with Non-Continuous Materials

The paper presents a fractional order model of a heating process and a comparison of fractional and standard PI controllers in its closed loop system. Preliminarily, an enhanced fractional order model for the heating process on non-continuous materials has been identified through a fitting algorithm on experimental data. Experimentation has been carried out on a finite length beam filled with three non-continuous materials (air, styrofoam, metal buckshots) in order to identify a model in the frequency domain and to obtain a relationship between the fractional order of the heating process and the different materials’ properties. A comparison between the experimental model and the theoretical one has been performed, proving a significant enhancement of the fitting performances. Moreover the obtained modelling results confirm the fractional nature of the heating processes when diffusion occurs in non-continuous composite materials, and they show how the model’s fractional order can be used as a characteristic parameter for non-continuous materials with different composition and structure. Finally, three different kinds of controllers have been applied and compared in order to keep constant the beam temperature constant at a fixed length.

A Multiphysics Frequency-Dependent Model of an

Ionic polymer-polymer composites (IP2Cs) are electroactive polymers which can be used both as sensors and as actuators. In this paper, a new multiphysics model of IP2Cs working as an actuator is presented and implemented using a finite element methods solver (COMSOL Multiphysics). The model involves electrical, mechanical, chemical, and thermal effects and yields a unique solution. Knowledge acquired by measuring campaigns has been included in the model. More specifically the frequency dependence of Youngs modulus was experimentally determined and introduced in such a model. A frequency-domain investigation is performed and a model optimization procedure that integrates the Nelder-Mead simplex method with the COMSOL Multiphysics models is exploited to identify IP2C model parameter by fitting experimental data. A fractional order dynamics has been identified in the model, confirming previous studies on IPMC gray box modeling and on electroactive polymeric devices.