Page 228 - IJB-10-1

International Journal of Bioprinting 3D printing of costal cartilage models

were two-component liquid silicones. They consisted and 75 A and 80 A silicone materials. As a measure of a
of two components that were mixed in equal parts. The material’s stiffness, Young’s modulus measures an object’s
curing mechanism was a hydrosilylation addition reaction. ability to resist deformation. Indentation or abrasion can
60
Siloxane containing Si–V bonds and siloxane containing cause localized plastic deformation, which is measured as
Si–H bonds underwent hydrosilylation addition reactions hardness. Cutting and stabbing would be extremely difficult
under the action of platinum catalysts to crosslink. The if a model exceeds the hardness of the native cartilage. In
material is available in various levels of Shore A hardness contrast, an oversoft material would relax the indentation
from 20 to 80. Based on our previous knowledge of costal stress rapidly and cause viscous hysteresis during cutting.
cartilage hardness and our previous practice, 65 A, 75 A, The results indicated that the 75 A and 80 A materials are
and 80 A materials were developed for printing costal flexible enough and would not easily deform with suitable
cartilage models, and they were printable through the hardness similar to native cartilage. Ear frameworks are
method of extrusion. stitched together with wires, and suture retention ability
is essential in determining how difficult it is to suture
3.1. Mechanical test of costal cartilage and printed the ear and whether the connection is firm enough. The
silicone materials results showed that the performance of 65 A and 75 A
The mechanical properties of costal cartilage in microtia materials was comparable to native cartilage (Figure 3E–
patients were investigated. A total of 21 patients (7 females G). Although there was no significant difference in suture
and 14 males) with an age range of 7–25 years were retention ability or Young’s modulus between the 65A
included in the study. The mean elastic modulus of costal material and costal cartilage, the hardness of the 65A
cartilage was 29.25 ± 14.20 MPa, ranging from 9.67 to material was lower than that of costal cartilage. On the
67.02 MPa, and the mean hardness was 78.40 ± 3.46 A, contrary, although there was no significant difference in
ranging from 73 to 85 A, which is similar to the results of hardness between the 80 A material and costal cartilage,
some previous studies 49,54,55 (Table S4 and Figures S3 and there is an insufficiency of suture retention ability, which
S4 in Supplementary File). would lead to insecure connection. Based on the present
Costal cartilage is a type of hyaline cartilage that data, the 75 A material showed no significant difference
connects the sternum and ribs and exhibits viscoelastic from native cartilage in objective evaluation and could be
behavior. The modulus of costal cartilage varies with the best choice as a simulation material.
56
time, degree of deformation, remodeling, and the geometry
of forces applied. This variation is due to the structural 3.2. Rheological behavior and printability of
complexity and anisotropy. Then, the subjective nature of 3DP silicone
57
the modulus determination method must be acknowledged Figure 4D–F display the rheological curves of 3DP
and may result in a certain degree of error. Our study silicone. At the lowest evaluated shear rate (0.1/s), 65 A,
focused on patients undergoing surgery for microtia, with 75 A, and 80 A materials recorded viscosities of 2076.8,
a small age range of 7–25 years, and 19 of total 21 of them 2428.5, and 2935.9 Pa⋅s, respectively, and demonstrated
were minors. The smaller age difference in cartilage origin shear-thinning (pseudoplastic) behavior. At lower shear
may be the reason no association was found (Figures S3 rates, the pseudocrosslinking phenomenon caused by
and S4 in Supplementary File) compared with previous the van der Waals force between SiO particles and
2
research. While the mechanical properties of costal polydimethylsiloxane (PDMS) molecular chains made the
56
cartilage may be influenced by calcification, which tends composites exhibit higher viscosity. As the shear rates
61
55
to increase with age, patients with calcified cartilage rose from 0.1 to 100/s, the pseudocrosslinking structure
58
were excluded from the study, and previous research has was gradually destroyed, and the PDMS molecular chains
indicated that the rate of calcification in costal cartilage relaxed, which caused the viscosity of the composites to
among individuals in this age group is low. Therefore, it is decrease, and the material exhibited a drop in viscosity
59
considered that calcification does not significantly impact to 13.9, 9.2, and 20.8 Pa⋅s, respectively; moreover, the
the results of this test. relationship between them was a power function during
this period. The three formulations showed fair rheological
Figure 3B and D show the results of compression
and tension tests for three different printed silicones. properties, which indicate low viscosity before curing and
capacity for shear thinning.
The mechanical properties of different costal cartilage
models were further comprehensively evaluated and The anatomical structures of the ear and nose were well
compared to test their potential as a mimicking curving represented, and the costal cartilage with special-shaped
tool. No significant difference in Young’s modulus and structures can also be printed (Figure 4A–C). Generally,
Shore hardness was observed between the costal cartilage the influence of gravity may lead to the collapse of the

Volume 10 Issue 1 (2024) 220 https://doi.org/10.36922/ijb.1007