Page 189 - IJB-9-4

International Journal of Bioprinting 3D-printed middle ear prostheses

nm) of the stapes footplate per pressure (in Pascal; Pa) in Prototyping and testing new products through 3D
the ear canal close to the tympanic membrane is displayed printing is well established. Currently, more and more
on the ordinate with frequency (in Hz) on the abscissa. applications have been seen where 3D printing is not only
Each decade on the ordinate corresponds to a 20 dB change the prototyping method but also the actual manufacturing
in the METF. When the incus was removed from the ME method. 3D printing as manufacturing fits well for spare
and the displacement of the stapes footplate for a given parts, small series production, personalized products, and
pressure was small, the METF was affected by vibration optimized parts [36,38] . In addition, it offers the possibility
from external sources coupling to the measurement setup. for local manufacturing, e.g., in hospitals . In otosurgery,
[38]
This resulted in an uneven and variable response of the individualized solutions in ME prostheses may be needed
incus-removed measurement at low frequencies. Removing to increase the likelihood of achieving better postoperative
the incus decreased the METF about 40 dB at maximum. audiological outcomes in ossiculoplasty.
The overall shape of the METFs was similar for the intact In this proof-of-concept study, 3D printing of second-
ME and for both PORPs: displacement per pressure was generation PORPs with affordable desktop 3D printer
relatively flat up to a resonance at around 1,000 Hz, and at and generally used 3D printing material was accurate
higher frequencies, the METFs decreased with frequency. and reproducible. All the first- and second-generation
The two-way ANOVA revealed that there was a statistically 3D-printed PORPs were made of rigid polymer. In terms
significant interaction between the effects of ME of surgical maneuverability, they were considered stiffer
transduction mode and frequency [F(15,71) = 4.146, p < and less flexible compared to titanium PORPs used in this
0.001]. This is seen in Figure 5, where the shape of the mean study. The acoustical performance of 3D-printed PORP
METF with the incus removed clearly deviates from the was similar to that of a commercial titanium PORP when
other conditions. The main effect of ME transduction mode comparing their METFs. In a mass-spring-damper system,
and frequency were both statistically significant [F(3,71) = the response at low frequencies is governed by stiffness,
204.8, p < 0.001 and F(5,71) = 17.08, p < 0.001, respectively]. while at high frequencies, it is governed by mass. At natural
Pairwise comparisons revealed that the METF of both the frequency, the response is governed by damping. When
titanium and the 3D-printed PORP differed significantly comparing the METFs of the two PORPs in Figure 5, the
from the intact ME (p = 0.001 and p < 0.001, respectively), response is similar in shape below 1,000 Hz. On average,
as well as from the METF with the incus removed (p < the displacement for a given pressure below 1,000 Hz
0.001 for both). However, there was no difference in METFs is approximately 1.6 times as large for the titanium
between the two PORP types (p = 0.605), suggesting that PORP than for the 3D-printed photopolymer PORP.
the acoustical performance of the 3D-printed PORP was Although the difference of about 4 dB was not statistically
equal to the commercial titanium prosthesis. significant in our sample, this is possibly due to the higher

Senior otosurgeons (S.T.S. and A.A.A.) evaluated the stiffness of titanium compared to the material used for
surgical properties of the second-generation 3D-printed 3D printing in this study. At high frequencies, the slope
PORPs. The prostheses were easy to maneuver under the at which the METF decreases with frequency appears
operating microscope. Static electric charge did not pose steeper for the titanium PORP. This may be explained by
a problem. The prostheses, in comparison to commercial the approximately four times higher density of titanium
titanium prostheses, were stiffer and less flexible, and thus compared to photopolymer.
a bit harder to insert between the stapes head and the When inspecting the absolute values of the METF for
tympanic membrane and the malleus manubrium, even an intact ME measured from the inner ear side without
though the position and angle of the prostheses were easy the cochlea, the results are well in line with a study by
to change. Thus, it was very critical to use a prosthesis with Stoppe et al. (see their Figure 3B in article ), being on
[18]
[18]
a proper length, because in the LDV setup, the tympanic the order of a few tens of nm/Pa. In their study, the acute
membrane was intact (in contrast to a clinical situation pure-tone average (PTA; an average of 500, 1,000, 2,000,
where the tympanic membrane is lifted before prosthesis and 4,000 Hz) magnitude gain for a rigid TORP was 4 dB
insertion). Altogether, the surgical properties of 3D-printed below the intact ME. Although the type of ME prosthesis
prostheses were acceptable, and no gross differences with was different in the present study, the corresponding PTA
the commercial titanium prostheses were noticed. reduction was 8 and 9 dB for the titanium and 3D-printed
PORPs, respectively. However, it should be noted that static
4. Discussion pressure variations worsen the audiological outcomes, as
[18]
Modern product development heavily utilizes 3D printing illustrated in a study by Stoppe et al. for TORPs.
across different industries such as medical, aerospace, It is well known that motion of the stapes is not
consumer products, military, and automotive [36-39] . piston-like, and therefore, in a study by Gottlieb et al. ,
[16]

Volume 9 Issue 4 (2023) 181 https://doi.org/10.18063/ijb.727