Page 338 - IJB-10-3

International Journal of Bioprinting Acoustic analysis of 3D-printed ossicles

line represents the result of finite element numerical PCL, and the incus is 316L; in Figure 7i, both the malleus
simulation, while the dotted line represents the result of the and incus are HA/PCL and exhibit similar trends in the
experiment. The error band between them is also shown in experimental and simulation results when the stapes is
the figure. The transmission characteristics of the healthy replaced.
human middle ear can be simplified by considering two Based on the overall curve trend, the positions
areas: the lower-frequency platform area and the higher- obtained through simulation are smoother compared
frequency roll-off area. with the experiment, where the data fluctuated in some

From Figure 7, it can be observed that the stapes floor positions. In the preferred material combinations, most
vibration displacement measured via the laser vibration intervals between 250 Hz to 750 Hz show an upward trend.
measurement system in the experiment is generally lower At around 1000 Hz, there is a relatively stable stage. After
than the results of finite element analysis. The displacement 4000 Hz, there is a significant roll-off area. The human ear
values are 10% to 38% lower than the finite element values. cannot perceive sounds below 20 Hz and above 20,000
While the overall curve trend is roughly consistent, some Hz. The clinical hearing test frequency range is generally
local curves of the ossicular material combination exhibit 125 Hz to 8000 Hz, and human speech frequencies fall
resonance, which is not clearly reflected in the actual between 500 Hz and 2000 Hz. The clinical calculation of
measurement process. The main factors contributing to the decibels of hearing loss involves averaging the hearing
discrepancies between the two are as follows: thresholds of 500 Hz, 1000 Hz, and 2000 Hz. Comparing
the above combinations of ossicular chain materials with
(i) In the experiment, the 3D-printed ossicular chain the model itself, specific analysis selects the combination of
omits the ligaments (malleus ligament, incus materials resembling the normal human ear. The frequency
ligament, and stapes ligament). These ligaments displacement parameters of this combination are shown
play a crucial role in supporting and positioning the in Table 4. Although there is a discrepancy between the
ossicles, allowing for sound amplification during the
transmission process. simulation and experimental values, the general trend is
essentially consistent. In theory, the simulation results are
(ii) The 3D-printed ossicles are bonded with glue, and also reliable.
the contact position angle between the ossicles can
also impact the measured values. 4. Discussion
(iii) The experiment uses normal saline to replace the 4.1. Corrosion resistance analysis
impedance brought by the inner ear lymph, and The 10 mm × 10 mm × 10 mm sample block’s corroded
the tympanic membrane is replaced with a silicone contact surface was ground and polished until no scratches
rubber turnover mold. were present. Wires were drawn from other surfaces and
Despite these experimental factors, the overall trend insulated with glue to conduct the open circuit potential
aligns well with the existing literature on the subject. and moving point polarization curves. During the open
The simulation and experimental results resonate in the circuit potential test, the metal sample block was immersed
frequency range of 750 Hz to 1000 Hz, with the frequency in a NaCl solution without any external current applied.
of 1000 Hz marking the transition from the plateau This allows the sample to reach a stable potential value in a
area to the roll-off area. The response displacement corrosive state. The results obtained indicate the material’s
of the 3D-printed model can be measured in this stability in the corrosive solution. A more positive open
frequency range. circuit potential value in the material test reflects better
stability, less corrosion tendency, and stronger corrosion
When the malleus was fixed to TC4, and the incus resistance. Conversely, a poorer electrochemical stability
material was the same, the stapes material being HA/PCL was indicated by a less positive value.
resulted in the highest stapes displacement value, followed
by TC4, and finally 316L. The same trend was observed Figure 8 illustrates the potentiodynamic polarization
when the stapes material was kept constant, and the incus curve, which is obtained by adjusting the potential to
was replaced accordingly. In Figure 7d, the malleus is observe changes in current density. This curve reflects
made of 316L and the incus is TC4; in Figure 7e, both the the polarization and passivation process characteristics
malleus and incus are 316L; in Figure 7f, the malleus is of the sample block, allowing the extraction of relevant
316L, and the incus is HA/PCL; the trend of experimental parameters for analysis.
results roughly aligns with that of simulation results. In It can be observed that although the corrosion
Figure 7g, the malleus of the auditory ossicle is HA/PCL, potential and current of TC4 and 316L are different,
and the incus is TC4; in Figure 7h, the malleus is HA/ the overall trend of the potentiodynamic polarization

Volume 10 Issue 3 (2024) 330 doi: 10.36922/ijb.2040