## 4 Conclusions  
The main goal of this work was to develop a piezoresistive material to use as a flexible pressure sensor based on the incorporation of GNPs onto PCL electrospun membranes. The proposed material seems to be very promising for the realization of pressure sensors in a broad range of applications, especially applications where the sensor's flexibility and light weight is of great importance, such as in military equipment. FESEM and Raman Spectroscopy validated the presence of GNPs onto the microfibers' structures, confirming their correct adhesion to the membranes. Moreover, their successful incorporation by the post-impregnation method was also visible not only by the FESEM images, but also by the measurement of the L* (lightness) parameter, proving that a homogeneous distribution of the GNPs all over the microfibers' surfaces was obtained. TGA analysis gave information about the thermal behavior of the developed samples, as well as the influence of the GNPs on the degradation temperatures. For the sample with 2% of GNPs, an increase of 8 \({}^{\circ}\)C for the maximum degradation temperature of PCL was observed when compared to the  
Figure 11: Electrical conductivity and GF in relation to the GNPs concentration. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **GF** & **Error** \\ \hline
0.1\%GNPs-PCL & 0.74 & 0.01 \\
0.2\%GNPs-PCL & 1.17 & 0.02 \\
0.5\%GNPs-PCL & 3.20 & 0.03 \\
1\%GNPs-PCL & 1.29 & 0.02 \\
2\%GNPs-PCL & 1.21 & 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average Gauge Factor (GF) values obtained for each sample. neat PCL sample, demonstrating that the maximum GNPs concentration used improved this property. Raman spectroscopy allowed the study of the GNPs structure, proving that the GNPs used in this work presented few structural defects and were composed by graphene multilayers. Further, electrical properties such as conductivity and piezoresistive performance were studied. With the increase of GNPs present on the surface of the fibers, the distance between the nanoparticles decreased, forming larger electron clouds. Consequently, the electrical resistance decreased. A maximum electrical conductivity value of 0.08 S/m was obtained for the 2%GNPs-PCL sample after five successive water/drying cycles. The samples with 0.1%, 0.2%, 0.5%, 1%, and 2% of GNPs were able to change their electrical resistance under external pressures and presented excellent durability and reversibility to repetitive compression, demonstrating their piezoresistive behavior over the cycles. The best values of GF (3.20) were obtained for the membranes with 0.5% of GNPs. The high sensitivity makes it interesting for wearable health care systems. In combination with the light weight and flexibility of the developed systems, an effective, comfortable, and adaptable sensor can be obtained. In summary, a simple and cost-effective method for the development of a very flexible piezoresistive sensor based on conductive biodegradable electrospun microfibers was proposed. This work may not only provide an electrospinning and GNPs-based approach for the building of flexible piezoresistive sensors, but also an alternative that can be used for the development of a wearable sensor, with great potential in monitoring of human motions and vital signs for soldiers' equipment applications. The developed sensors bring a novel alternative for this type of application, since they are flexible and adaptable, with a constant behavior during consecutive compression cycles. The sensors also present a high sensitivity, being highly effective without compromising the comfort and weight of the user. This work also presents a strategy for the obtention of homogenous electrospun fibers functionalized with GNPs, which are known for their agglomeration problems. [PERSON] and [PERSON] conceived and designed the experiments; [PERSON], [PERSON] and [PERSON] performed the experiments; all of the authors analyzed the data and wrote the paper. All authors have read and agreed to the published version of the manuscript.