**4. Discussion**

The acoustic response using a metalized printed PVDF sample is presented in **Figure 12**. The electrical signal from the light detector was recorded after PVDF reflected the laser beam. Variations of the laser intensity correspond to fluctuations of amplitude and frequency in the

**Figure 12.** Reference signal for printed PVDF (Ch1) and the signal obtained from a commercial light detector (Ch2).

Results of photopyroelectric response of printed PVDF prosthesis at 10 and 100 Hz are shown

**Figure 13.** (a) Printed PVDF sample photopyroelectric response (100 Hz), (b) printed PVDF sample photopyroelectric

The results in **Figure 13a, b** showed an asymptotic behavior, similar to the ones described in the theory in the case of frequency modulation of laser stimulation. References amply illustrate

The prosthesis was also tested as a pressure sensor, applying pressure loads between 0 and

the use of PVDF in the photopyroelectric technique [11–13].

electrical signal.

154 Piezoelectric Materials

in **Figure 13a, b**, respectively.

response (10 Hz).

16.35 kPa.

The fabrication of an ear prosthesis at present has led to restore the functionality of the middle or inner ear with an electronic hearing aid or implant, respectively [21–26], for patient suffering a dysfunction in the mentioned parts of the ear. By the other side, the ear prosthesis developed in this work focuses on aesthetics and the recovery of acoustic functionality involving only the reconstruction of some of the outer and middle ear structures [27–29]. Both kind of prosthesis (electronic and mechanical) had been designed by separate but an active prosthesis, which covers both aesthetic functionality and the electronic hearing aid (in cases where external, middle, and even the inner ear are damaged either by accident or by a congenital malforma‐ tion) has not been developed so deeply as the first two mentioned above [30]. In this context, our 3D prosthesis is oriented to provide an aesthetic prosthesis with the ability to sense sound waves without the requirement of another kind of sensor like a microphone or membrane that needs to be placed on the patient's as cochlear implants does. PVDF has demonstrated its ability to work as a microphone [3, 31] due to its piezoelectric properties which can be exploited in the proposed 3D-printed prosthesis.

Regarding the light response of PVDF, results (**Figure 13a, b**) showed an asymptotic behavior, coinciding with the one reported in photopyroelectric techniques [11–13].

In the case of the prosthesis as a temperature sensor, it was observed that it works linearly between 5 and 90°C; after this temperature, there are no more variations. The latter consider‐ ation has no impact on the use of the prosthesis usually, as the ambient temperature does not exceed these ranges and the direct application of a higher temperature may cause deformation thereof. It has also been reported that the optimum working temperature is 80°C [14].

The experimental results show an almost linear and inversely proportional behavior between the stimuli of pressure (**Figure 7**) and temperature (**Figure 8**) with the frequency response. The repeatability of the results allows to evaluate the PVDF as a reliable material because each stimulus applied (pressure and temperature) was tested in triplicate, thus obtaining results with slight variations but the same trend. The prosthesis tested as a pressure sensor showed effectiveness in the range of 0–16.35 kPa, values that also fall within the range of applied pressure that could hold an ear without malformation [32, 33].

Biocompatibility is a subject that is also covered by a prosthesis because of their permanent contact with the skin or any other organ. That is why a PVDF prosthesis is ideal to prevent exposure to hazardous substances. This polymer has been used in many other kinds of biocompatible applications, and it has been widely studied as a safety material for biomedical applications [34, 35]. By the other hand, using a 3D printer, a functional ear prosthesis could be fabricated in a few hours with all the advantages mentioned above.
