Nowadays, wearable devices for physiological-biomechanical systems monitoring allow individuals to manage their own health, and professionals to receive quickly information about their patients' conditions. Sensors are essential components in wearable electronics, enabling the key functions that make devices be worn. In particular, advances with pressure sensors heavily affect wearable technology.
The project is aimed at developing novel extremely soft, lightweight proof-of-concept piezoresistive pressure sensors characterized by a high sensitivity in a wide pressure range (10 Pa - 100 kPa). It is focused on the experimental characterization and electro-mechanical modelling of open cell, sponge-like, low density materials with pressure dependent conducting properties and fabricated through a cost effective approach. A flexible porous 3D silicon rubber skeleton will be obtained by infiltrating with EcoFlex a template formed by polymeric micro beads that will be dissolved in acetone. The elastomeric foam, after porogens leaching will be dipped in a colloidal suspension of multilayer-graphene nanoplatelets (MLG) and ethanol. The assisted evaporation of the solvent leaves a thin layer of MLG over the pores' surface: the final material is a piezoresistive, extremely soft and free-standing foam of a novel type, characterized by a high compression sensing capability attributable to the rearrangement of the conducting nanofiller network during compression loading. The electromechanical performances of the novel sensors will be experimentally assessed. New theoretical models able to predict the resistance of the materials as a function of the MLG characteristics and weight fractions, porosity and applied compression will be developed and experimentally validated. A proof-of-concept pressure sensor for blood pressure and heart rate real-time monitoring will be finally fabricated at laboratory level, calibrated and tested.
The proposed novel piezoresistive graphene/elastomeric foams represent a promising class of materials for the fabrication of ultra-soft and highly sensitive pressure sensors that can be applied for the real-time monitoring of body signals (e.g., blood pressure and heart rate) and, more generally, can meet in the near future the pressing requirements of mechanical compliance and electrical performance in health monitoring and medical diagnosis applications. The main advantages compared to state-of-the-art materials and devices will be the high sensitivity in a very broad pressure range while maintaining excellent strength and flexibility, and the easy synthesis procedures that do not need any complex chemical functionalization to produce electrical conducting polymeric foam with piezoresistive characteristics. For all these reasons, the developed materials can be also considered as possible candidates in other emerging applications in the field of robotics, artificial intelligence, and human-machine interfaces. For example, a possible further application may be the electronic skins, which in general need to sense a large range of pressures, from a gentle touch ( In particular the project aims to pursue scientific and technological achievements that represent a significant advance over the state of the art.
As it concerns the scientific goals the project is aimed at:
a) Understanding through microscopic investigations and electrical/mechanical experimental tests the correlation between the morphological/structural characteristics of the produced foams (pore dimensions, porosity, density, MLG sizes, MLG coverage) and their macroscopic physical and functional properties (conductivity, stress-strain response, piezoresistivity).
b) Developing new effective equivalent models capable of describing the relationship between the structural complexity of the conducting foams with their physical properties.
c) Developing new multi-physics semi-empirical models able to predict the piezoresistive behaviour of foams in the presence of quasi-static and dynamic mechanical compression stresses of different forms and levels.
Regarding technological achievements, the project is aimed at:
a) Developing methods for the fabrication of novel conducting, soft and free-standing foams which are characterized by a high compression sensing capability due to their unique piezoresistive properties.
b) Fabrication of reliable proof-of-concept pressure sensors characterized by an optimal trade-off between piezoresistive sensitivity, pressure range and mechanical properties to be exploited for real-time monitoring of body signals.
Given the novelty of the present research, it is possible to foresee considerable margins for the submission of several articles in international high-impact Journals and/or the proposal of different patents. The project has the potential to strongly impact the market of wearable devices for health-care and fitness in the near future, introducing new cost-effective technologies that will enhance lightweight, softness, multifunctionality, and wearability of consumer electronics.