Page 284 - IJB-9-6

International Journal of Bioprinting Progress in bioprinted ear reconstruction

technology is able to produce biocompatible scaffolds, which search terms ((3D *print*) OR (additive manufacturing))
can then be seeded with cells, or molds in which cartilage AND ((auricle OR pinna OR ear) reconstruction) was
can be cultivated into the desired shape. Several time- conducted. The date of the last search was 22 October
consuming, multi-staged surgical steps (particularly rib 2022, but the search was not otherwise time-limited. The
harvesting and shaping) could be bypassed [3,4] . identified papers were then imported into Covidence
Before engineering a substitute, the structure of the software by Cochrane to conduct the review and follow
auricle should be considered. At the most basic level, the PRISMA standard. This process identified 202 original
the structure is skin-covered cartilage with associated studies. After duplicates were removed, the titles and
vasculature. The complex structure has distinct 3D parts abstracts of 141 studies were screened. Seventy-three
such as the helix, antihelix, concha, tragus, and lobule. It studies were identified and underwent full-text review.
is primarily composed of elastic cartilage covered by skin, Of these, 27 studies were finally included (see Figure 2 for
with a thin layer of connective tissue, the perichondrium, workflow and inclusion and exclusion criteria).
in between. Auricular cartilage comprises proteoglycans, 3D printing technologies (see Figure 3) can aid and
type II collagen, and an elastin network. Elastic fibers enhance all of the existing reconstructive options. However,
allow the ear to undergo extensive deformation, while in this review, focus was placed on methods that could
glycosaminoglycans (GAG) confer compressibility . Both directly enhance surgical reconstruction by creating new
[9]
properties, along with the complex shape, are important implantable tissue-engineered personalized auricles for
for the auricle’s functionality and, unfortunately, from a patients. Thus, additional studies on, for example, surgeons
reconstructive perspective, are quite distinct from most using costal cartilage models to practice autografting , to
[17]
other cartilages found in the human body . create templates and guides along which to cut , or to
[18]
[10]
plan the placement of bone-anchored prosthetic devices
[19]
Cartilage is an avascular and aneural tissue, and thus
has a poor intrinsic self-repair capacity . However, were excluded.
[14]
from a tissue engineering perspective, this avascularity is
advantageous because if new elastic cartilage can be grown 3. Results
or printed in vitro, a functioning vasculature does not have In terms of design, all of the studies included (see Table 2)
to be generated with it. Vessels around the engineered were non-randomized experimental studies, except for the
ear should be able to provide essential substances to single landmark pilot clinical trial in human subjects by
chondrocytes through diffusion . Zhou et al. . While the majority (n = 15) of the studies
[15]
[20]
3D printing, as an additive manufacturing technique, involved both in vitro and in vivo experiments (including
fabricates physical constructs from digital models, layer by the human study), some were purely in vitro (n = 6) and
layer. This technology potentially facilitates the creation of some purely in vivo (n = 6) animal studies.
patient-specific, anatomically complex scaffolds. However, Several animal models were used, with the majority
limitations include time intensity for complex structures, being in rodents (n = 16) but also in rabbits (n = 2), sheep
potential discrepancies between the mechanical properties (n = 1), pigs (n = 1), and goats (n = 1). It should be noted
of printed materials and native tissues, and resolution that the species into which the scaffold was implanted
constraints that may impact the replication of intricate did not always match the donor tissue for the scaffold.
auricular structures. Despite these challenges, 3D printing For example, miniature pigs’ cartilage was inserted into
presents a unique advantage in customization compared to scaffolds that were eventually implanted into mice .
[11]
traditional fabrication methods [3,4,16] . Several rodent model studies noted that since rodents’
At least theoretically, 3D-printed auricles promise skin is different to human skin (lacking sweat glands,
relative ease of implantation, anatomic accuracy and proportionally thinner, containing an additional muscle
compatibility, and thus, excellent aesthetic results. layer, and healing by withering), they may not be the ideal
animal model . On the other hand, sheep have similar
[3]
2. Methodology fascial characteristics to humans . However, even then,
[21]
the physiology differs; thus, all studies noted that the goal
This comprehensive literature review sought to investigate was to establish human trials.
the potential role of 3D printing in creating implantable
constructs for reconstructive auricular surgery and how far 3.1. Direct versus indirect printing
it is from being routinely implemented in clinical practice.
Five of the 27 included studies utilized indirect 3D
In order to answer this, a broad systematic search in the printing, in which a negative mold of the desired
PubMed, Cochrane, and Web of Science databases using the auricular shape is printed, meaning that the accurate and

Volume 9 Issue 6 (2023) 276 https://doi.org/10.36922/ijb.0898