Page 183 - IJB-9-4

International Journal of Bioprinting 3D-printed middle ear prostheses

1. Introduction (sound transmission efficacy and stability) of titanium
prostheses have not been found significantly better when
In ossiculoplasty, the ossicular chain of the middle ear compared to other materials [13,21,22,24-27] .
(ME) is reconstructed in an attempt to improve hearing.
In the reconstruction, a so-called lever arm system of the Three-dimensional (3D) printing has become more
[1]
ossicular chain is replaced with a prosthesis . The most common in various medical applications. It reduces the time
common types of ME prostheses are partial ossicular and cost of manual work [17,28] . It is used, e.g., for training and
replacement prostheses (PORPs) and total ossicular planning surgical procedures or manufacturing medical
replacement prostheses (TORPs). Although ossicular aids, tools, or implants [29,30] . Other additive manufacturing
chain reconstruction (OCR) in many cases results in methods can be combined with 3D printing to create
better hearing soon after the operation, failures and complex bioartificial constructs . 3D-printed objects
[31]
complications may arise in the long term. Studies showed can be produced with different 3D printing processes and
that with TORPs, for instance, after an average of 2.5 years materials to achieve optimal result according to the purpose
(range 1–7 years), a good audiological outcome (air-bone of use . In bone tissue engineering, scaffolds used in
[32]
gap ≤ 20 dB) was achieved only on average in 49% (range bone cell growth and differentiation can be 3D-printed .
[33]
25%–75%) of the cases [2-15] . Because about half of the In otorhinolaryngology, microsurgical practice using 3D
ossiculoplasties fail in the long term, there is clear need for models is becoming more common and hearing aid molds
novel prosthetic solutions. and orbital implants have been 3D-printed for many
Nowadays, there are many different designs of years [29,30] .
prostheses with various lengths, but they are not In the development of new types of the prostheses, their
designed individually to patients’ MEs. Some commercial adaptation to individual anatomical variations needs to
adjustable-length prostheses have been launched and be addressed. Customizing the prostheses to the patient’s
their acoustical performance has been studied with laser ME could improve the stability of the prosthesis and
Doppler vibrometry (LDV) . Failures in OCR are mainly improve hearing outcomes by increasing the probability of
[16]
due to inadequate length or shape of the prosthesis, or a proper fit after implantation . Novel OCR prostheses’
[19]
defects in the surgical procedure . Too long a prosthesis designs, materials, fabrication processes, and acoustical
[17]
can cause compression, high tension, or additional damage performance have been studied before. Hirsch et al.
[17]
to the tympanic membrane or the chain structure [17,18] . On and Kamrava et al. utilized CT imaging and created
[34]
the other hand, too short a prosthesis may tilt and move 3D-printed PORPs in suitable shape for the imaged ME.
or dislocate because of changes in ventilation or static The studies succeeded in their objective, but no information
pressure in the ME [12,19] . The intact ossicular chain has two of 3D-printed prostheses’ functional properties was
synovial joints, and the movement of the chain is flexible provided. Acoustical performance of novel non–3D-
and gentle. Current ME prostheses are mainly rigid and do printed prostheses with different designs and materials
not fully correspond to an intact ossicular chain in terms of has been studied earlier with different LDV setups [16,18,19]
their biomechanics. Peak amplitudes of impulsive sounds but also with other applications [20,35] . Therefore, to the best
can be inhibited by a flexible ossicular chain and, therefore, of our knowledge, no information considering acoustical
replacing that with a rigid prosthesis can negatively affect performance of 3D-printed ME prostheses has not been
the inner ear sensory structures . Rigid prostheses do not provided before.
[16]
fully take into account possible changes in ME anatomy
due to disease progression. The future prostheses should The small size of the ME and its ossicles present
focus on better long-term stability and, therefore, challenges to imaging, 3D modeling, and printing . It
[18]
[17]
the material should also be as well-fitting as possible. In is currently unknown how reliable and reproducible 3D
many cases, autologous bone from the ossicles is a good printing is in terms of tiny ME prostheses, and what the
option for prosthesis, but in some cases, the ossicles are functional properties of such prostheses are. The aim of
absent due to the disease process, and thus, other types this study was to explore the potential of 3D modeling and
of ossicular chain substitutes are needed. In a preclinical printing in ossiculoplasty. In this proof-of-concept study,
study by Milazzo et al. , cortical bone allografts were we describe designing and 3D printing of a plastic PORP
[20]
studied as OCR material. Various synthetic materials have with generally used 3D printing material as well as its
been used in OCR, such as metal, ceramic, or plastic [1,21,22] . refinement to a second-generation prototype, and finally
Most modern prostheses are made of titanium, which is test its acoustical performance in middle ear transfer
biocompatible [4,21,23] and has well-recognized surgical function (METF) in comparison to a commercial titanium
and audiological properties, but the functional outcomes prosthesis.

Volume 9 Issue 4 (2023) 175 https://doi.org/10.18063/ijb.727