Design and experimental characterization of antennas and wireless systems for innovative wearable and implantable ultra low–power applications

The present PhD thesis exploits the design skills I have been improving since my master thesis’ research. A brief description of the chapters’ content follows. Chapter 1: the simulation of a complete front–end is a very complex problem and, in particular, is the basis upon which the prediction of the overall performance of the system is possible. By means of a commercial EM simulation tool and a rigorous nonlinear/EM circuit co–simulation based on the Reciprocity Theorem, the above–mentioned prediction can be achieved and exploited for wireless links characterization. This will represent the theoretical basics of the entire present thesis and will be supported by two RF applications. Chapter 2: an extensive dissertation about Magneto–Dielectric (MD) materials will be presented, together with their peculiar characteristics as substrates for antenna miniaturization purposes. A designed and tested device for RF on–body applications will be described in detail. Finally, future research will be discussed. Chapter 3: this chapter will deal with the issue regarding the exploitation of renewable energy sources for low–energy consumption devices. Hence the problem related to the so–called energy harvesting will be tackled and a first attempt to deploy THz solar energy in an innovative way will be presented and discussed. Future research will be proposed as well. Chapter 4: graphene is a very promising material for devices to be exploited in the RF and THz frequency range for a wide range of engineering applications, including those ones marked as the main research goal of the present thesis. This chapter will present the results obtained during my research period at the National Institute for Research and Development in Microtechnologies (IMT) in Bucharest, Romania. It will concern the design and manufacturing of antennas and diodes made in graphene–based technology for detection/rectification purposes.

Differenziamento macrofagico: gli effetti dei polimeri sintetici

Research for new biocompatible and easily implantable materials continuously proposes new molecules and new substances with biological, chemical and physical characteristics, that are more and more adapted to aesthetic and reconstructive surgery and to the development of biomedical devices such as cardiovascular prostheses. Two classes of polymeric biomaterials seem to meet better these requirements: “hydrogels” , which includes polyalkylimide (PAI) and polyvinylalcohol (PVA) and “elastomers”, which includes polyurethanes (PUs). The first ones in the last decade have had a great application for soft tissue augmentation, due to their similarity to this tissue for their high water content, elasticity and oxygen permeability (Dini et al., 2005). The second ones, on the contrary, are widely used in cardiovascular applications (catheters, vascular grafts, ventricular assist devices, total artificial hearts) due to their good mechanical properties and hemocompatibility (Zdrahala R.J. and Zdrahala I.J., 1999). In the biocompatibility evaluation of these synthetic polymers, that is important for its potential use in clinical applications, a fundamental aspect is the knowledge of the polymers cytotoxicity and the effect of their interaction with cells, in particular with the cell populations involved in the inflammatory responses, i.e. monocyte/macrophages. In consideration of what above said, the aim of this study is the comprehension of the in vitro effect of PAI, PVA and PU on three cell lines that represent three different stages of macrophagic differentiation: U937 pro-monocytes, THP-1 monocytes and RAW 264.7 macrophages. Cytotoxicity was evaluated by measuring the rate of viability with MTT, Neutral Red and morphological analysis at light microscope in time-course dependent experiments. The influence of these polymers on monocyte/macrophage activation in terms of cells adhesion, monocyte differentiation in macrophages, antigens distribution, aspecific phagocytosis, fluid-phase endocitosis, pro-inflammatory cytokine (TNF-α, IL-1β, IL-6) and nitric oxide (NO) release was evaluated. In conclusion, our studies have indicated that the three different polymeric biomaterials are highly biocompatible, since they scarcely affected viability of U937, THP-1 and RAW 264.7 cells. Moreover, we have found that even though hydrogels and polyurethane influences monocyte/macrophage differentiation (depending on the particular type of cell and polymer), they are immunocompatible since they not induced significantly high cytokine release. For these reasons their clinical applications are strongly encouraged.

Study of the thermal effects induced by magnetic resonance on endocardial leads: numerical models and experimental validation

Magnetic resonance imaging (MRI) is today precluded to patients bearing active implantable medical devices AIMDs). The great advantages related to this diagnostic modality, together with the increasing number of people benefiting from implantable devices, in particular pacemakers(PM)and carioverter/defibrillators (ICD), is prompting the scientific community the study the possibility to extend MRI also to implanted patients. The MRI induced specific absorption rate (SAR) and the consequent heating of biological tissues is one of the major concerns that makes patients bearing metallic structures contraindicated for MRI scans. To date, both in-vivo and in-vitro studies have demonstrated the potentially dangerous temperature increase caused by the radiofrequency (RF) field generated during MRI procedures in the tissues surrounding thin metallic implants. On the other side, the technical evolution of MRI scanners and of AIMDs together with published data on the lack of adverse events have reopened the interest in this field and suggest that, under given conditions, MRI can be safely performed also in implanted patients. With a better understanding of the hazards of performing MRI scans on implanted patients as well as the development of MRI safe devices, we may soon enter an era where the ability of this imaging modality may be more widely used to assist in the appropriate diagnosis of patients with devices. In this study both experimental measures and numerical analysis were performed. Aim of the study is to systematically investigate the effects of the MRI RF filed on implantable devices and to identify the elements that play a major role in the induced heating. Furthermore, we aimed at developing a realistic numerical model able to simulate the interactions between an RF coil for MRI and biological tissues implanted with a PM, and to predict the induced SAR as a function of the particular path of the PM lead. The methods developed and validated during the PhD program led to the design of an experimental framework for the accurate measure of PM lead heating induced by MRI systems. In addition, numerical models based on Finite-Differences Time-Domain (FDTD) simulations were validated to obtain a general tool for investigating the large number of parameters and factors involved in this complex phenomenon. The results obtained demonstrated that the MRI induced heating on metallic implants is a real risk that represents a contraindication in extending MRI scans also to patient bearing a PM, an ICD, or other thin metallic objects. On the other side, both experimental data and numerical results show that, under particular conditions, MRI procedures might be consider reasonably safe also for an implanted patient. The complexity and the large number of variables involved, make difficult to define a unique set of such conditions: when the benefits of a MRI investigation cannot be obtained using other imaging techniques, the possibility to perform the scan should not be immediately excluded, but some considerations are always needed.