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- Manufacturing and characterisation of a piezoresistive strain sensor based on the rGO@PDMS composite for skin and prosthetic support systemsPublication . Ferreira, Rodrigo Gonçalves; Pereira, João Pedro Nunes; Silva, Abílio Manuel Pereira daDue to the ever-increasing amount of the population focusing on their personal health, thanks to rising living standards, nowadays we are facing the need to improve personal healthcare devices, which mostly depend on laborious, time-consuming, and convoluted procedures, relying heavily on cumbersome equipment. Thus, patients repeatedly suffer from discomfort and pain caused by invasive methods related to sample-gathering, blood sampling and other traditional bench-top techniques. With this in mind, the solution lies in the development of new flexible sensors with temperature, humidity, strain, pressure and sweat detection and monitoring capabilities, mimicking some of the skin’s sensory capabilities. Therefore, the aim of this dissertation was manufacturing, characterizing, and testing possible applications of a piezoresistive strain sensor based on a polydimethylsiloxane (PDMS) composite nano reinforced with reduced graphene oxide (rGO), with the physical and electromechanical characteristics required for the effective detection of joint movement and breathing pattern monitoring. The samples were prepared via elements of solution casting and solvent casting, followed by characterization of the piezoresistive effect of the material, its mechanical properties (3-point bending and tensile), morphological (SEM), structural (FTIR), and thermal (TGA) properties, along with performance testing in volunteer’s body parts. Regarding results, it was possible to observe the influence of the used PDMS’ elastomercrosslinker ratio, cure temperature and time, chosen dispersant and rGO content in the final performance of the sensor, with the possibility to tune certain characteristics to be better adjusted to specific applications. Moreover, in cyclic piezoresistive tests, the obtained average gauge factors, a measure of the sensor’s sensitivity, ranged from 7.49-14.85 for 3 wt.%, 9.84- 30.8 for 4 wt.%, and 0.56-9.16 for 5 wt.% rGO, establishing these samples as effective piezoresistive sensors for bioengineering applications. Furthermore, it was also concluded that, for this kind of application, the indicated elastomer-crosslinker is 15:1, cured at 120ºC for 20 minutes, with isopropyl alcohol as the dispersant and a rGO content between 3-5 wt.%, depending on the necessities of the application. The composites with a rGO content between 3% and 5% exhibited good mechanical linearity (R2 = 0.995, 0.999, 0.996) and satisfactory piezoresistive performance, at the 1.54-2.87% strain range, stability in the 100 cycle 3-point bending tests, the tensile strength varied from 1.05 MPa to 3.084 MPa, the degradation temperature ranged from 380 ºC to 410 ºC, as well as composites reversibly losing their electrical component before the structure integrity is lost, when tensile tested, and the ability to detect and monitor joint movement and breathing patterns.