Polymer nanocomposites (PNCs) are defined as polymers bonded with nanoparticles to create materiais with improved properties. The development of this type of material is rapidly emerging as a multidisciplinary research activity, since their final properties can benefit many different fields of application, namely in the development of electrical devices as studied herein. A fabrication technique to produce conductive PNCs was developed in this work and used to fabricate flexible capacitive pressure sensors. The process is based on vertically aligned-carbon nanotubes (A-CNTs) embedded in a flexible and biocompatible matrix of polydimethylsiloxane (PDMS). Thin A-CNTs/PDMS nanocomposite films ( ~ 400 Jlm) were produced using wetting of as-grown A-CNTs with uncured PDMS and the resulting nanocomposites were used to fabricate flexible pressure sensors. The sensing capability of this A-CNTs/PDMS nanocomposite is attributed to the distinctive combination of mechanical flexibility and electrical properties. The fabricated nanocomposites were characterized and mechanical and electrical properties evaluated. The PDMS is significantly modified by the reinforcing A-CNT fibers, demonstrating non-isotropic (as opposed to the isotropic neat PDMS) elastic properties ali different than the PDMS (Young's modulus of 0.8 MPa), including an anisotropy ratio of 4.8 and increases in the modulus of A-CNTs/PDMS nanocomposites over PDMS by more than 900 % and I 00 %, in the CNTs longitudinal and transverse directions, respectively. Regarding the electrical measurements, A-CNTs/PDMS nanocomposites presented an electrical conductivity of 0.35 Sim. The rather low conductivity does not compromise the developed capacitive sensor, but since passive telemetry is required to measure and power the sensor, solutions to overcome this problem were also studied. The configuration of the developed flexible sensor is similar to typical silicon-based capacitive pressure sensors. It is composed of three thin films, where two of them are A-CNTs/PDMS nanocomposites (defining the diaphragm type electrodes) separated by a film made of neat PDMS (defining the dielectric) and its operating principie is based on the change of the deflection of the nanocomposite layers due to the change of an externa! pressure. The developed flexible pressure sensors tested for pressures between O kPa and I 00 kPa (operation required to measure the blood pressure in the aneurysm sac) showed good linearity, mainly in the region near to the atmospheric pressure (pressure inside of dielectric ). ln the sarne range, the dynamic response of the pressure sensors presented two distinct comportments, which are related with the viscoelastic behaviour of the PDMS-based nanocomposites used to build the pressure sensor. ln addition, from the experimental measurements of the prototype pressure sensors used, the sensitivities are in the range of2.5- 20 fF/kPa. To demonstrate feasibility for practical applications, the flexible sensor technology was used in a biomedical application, more specifically in the context of abdominal aortic aneurysms. The proposed implantable flexible pressure sensing system (capacitive sensor plus inductor) consists of a mixed technology that uses A-CNTs/nanocomposites to build the capacitar electrodes and flexible printed circuit board (PCB) technology to build an inductor. The complete system was assessed by applying pressures varying from O kPa to 1 00 kPa. The results showed that the flexible sensors responded to pressure variations with a well-defined characteristic curve and oscillation frequencies centered around 5.3 MHz (the sensor receives energy and reflects back its oscillation frequency by means of inductive coupling). ln addition to these experiments, the performance of both pressure sensors and reader system was assessed using a hydraulic model that mimics the abdominal aorta. The proof-of-concept experiments validated the proposed telemetry system functionality and showed feasibility in integrating the flexible, biocompatible and passive sensor into a stent-graft, in arder to the detect blood pressure in the aneurysm sac. Finally, the developed technology to fabricate flexible pressure sensors based on A-CNTs/PDMS nanocomposites proved successful in sensing applications and due to its biocompatibility and versatility, can be used in other fields of application such as portable medical devices and e-textiles (to monitor the vital signs of an individual, such as heart rate and temperature, by using textile substrates with integrated electronics).