**6. Applications of IPT to flexible PE**

The increase of the printing resolution leads to an increased number of applications. Lee et al. [84] developed a flexible capacitive pressure sensor for plantar pressure measurement, using a flexible printed circuit film as a sensor substrate and PDMS as dielectric layer. Cheng et al. [5] developed a tactile sensor with PDMS using a highly reliable capacitive mechanism. However, the required manufacturing process involved multiple factoring steps and the use of several material layers, which consequently leads to time consumption, large material waste and high manufacturing costs, preventing the process automation to an industrial level. When the goal is large area sensing platforms, manufacture premium prices constitute a problem. In recent years, the interest for IPT to sensor fabrication has attracted attention [39, 85]. First IPT prototypes start to appear and has already been selected to step in the production of several devices, such as, integrated circuits [30, 33], transistors [32, 86], conducting polymer devices [30], structural polymers and ceramics [85], biomaterials, and printed scaffolds for growth of living tissues [30, 31]. In the field of flexible sensors, IPT it is just taking the first steps. IPT of an intrinsically conducting polymer [87] onto a flexible substrate for humidity and gas sensing applications [88] are two of many of the rapidly emerging IPT examples. Only a few examples of IPT sensors combining IPT polymer conductive ink (PEDOT:PSS and P3HT) [79, 89] or silver ink [90], printed on polymer substrate have been reported so far. Someya et al. [91] has developed flexible pressure sensors with a complex designed structure using OFET active matrices manufactured by IPT and screen printing technology. Basiricó et al. [92] have proposed a totally IPT flexible OFET assembled on plastic films as sensors for mechanical variables using a PEDOT:PSS as electrodes and a P3HT as a semiconductor. The results obtained were promising despite the lower charge carrier mobility measured. Cruz et al. [89] have developed a inkjet printed pressure sensing platform capable of measuring the central plantar pressure (CPP). The use of PEDOT:PSS for definition of the electrodes over a TPU substrate resulted in pressure sensors with higher sensitivities and better linearity. Good performance results (comparable with existing solutions) were achieved, with the particularity of offering a low-cost alternative. The printed substrate presented high flexibility, was able to follow and deform along with the substrate, without breaking or losing adhesion and its conductivity properties. The ink piezo-resistive effect and high gauge factors (>300) were demonstrated (higher than the typical value of flexible metallic strain gauges) showing the potential of the material to be used in several sensing applications [79].
