Page 509 - IJB-10-4

International Journal of Bioprinting 3D-printed variable stiffness scaffolds

MPa at porosities of 77% and 48%, respectively, has been grouped zone within the native meniscus tissue. The two
reported for porous PCL. Other deposition techniques internal architectures selected to develop a full-sized
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have reported a compressive modulus of 59 MPa at 65% biomimetic scaffold were: circumferential 2 mm fiber
porosity and 21.4 MPa at 69.6% porosity. Likewise, the spacing and 1 offset for Group A; and circumferential 1
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selective laser sintering (SLS) technique has reported a mm fiber spacing and 1 offset for Group B. Both regions
compressive modulus of 47 MPa for bulk PCL and 6 MPa consisted of radial fibers with an angle between the adjacent
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for scaffolds at 55% porosity. fibers set to 4.5°. To design the meniscal scaffold replicating
the native architecture, the overall measurements of the
The addition of offsets to the internal structure had
the most significant effect on the mechanical properties meniscus were based on the dimensions of the medial
meniscus in a study by McDermott et al. The meniscal
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(Figure 2B). Across all fiber spacings and layer orientations length was set at 45.7 cm, and the meniscus body width
(single or double), there was a significant decrease in was set at 9.4 cm.
compressive properties when an offset was introduced and
an even further decrease in mechanical properties with the As displayed in Figure 4A–C, the meniscal scaffold was
addition of 2 offsets. For a 1 mm fiber spacing, single-layer successfully printed. Good control of the oriented fibers
compressive properties were found to be 2.63 MPa, 0.75 via the 3D printing process was achieved, demonstrating
MPa, and 0.40 MPa for 0, 1, and 2 offsets, respectively. This the capability of the 3D printing technique to build
decrease in compressive properties with the addition of a 3D scaffold with complex internal structures. Both
offsets can be explained by the reduction of support within circumferential and radial fibers were printed for the
the scaffold at the fiber intersections. When no offsets replication of the specific 3D collagen microstructure
4
are present within the scaffold, there is direct contact of the meniscus. Control over fiber spacing enabled
with neighboring fibers, whereby the fiber intersections the establishment of region-dependent mechanical
are supported from above and below. However, with properties. The overall diameter of the printed fibers was
the addition of offsets, this support is removed, and the approximately 200 µm, which is lower than previously
4,6
intersection is suspended, enabling a three-point bending printed PCL meniscus scaffolds. To fabricate a wedge-
of the fibers under the same compressive loads (Figure 2C). shaped meniscus, the number of circumferential fibers for
each layer was progressively decreased. The 3D-printed
Most studies using PCL create anatomically shaped scaffold mimicked the native meniscus, both in external
meniscus scaffolds that lack zonal differences in the PCL shape and internal microstructure, and displayed better
architecture, with the scaffolds possessing mechanical mechanical properties than previously reported, thus
properties far superior to the native tissue. 4,6,7 Many scaffold suggesting its potential for meniscus repair.
architectures match the criteria of Group A. However,
none of the scaffold architectures match Group B. A 1 3.5. Development of an ECM-infiltrated PCL scaffold
mm fiber spacing resulted in a scaffold with compressive Although the PCL scaffold provides the macrostructure
properties > 1.5 MPa, and a 2 mm fiber spacing led to architecture and mechanical properties of the native
compressive properties < 1. To determine the optimal meniscus, a natural-based biomaterial ink should be
fiber spacing, straight fiber scaffolds were modified to incorporated into the scaffold to enhance cell infiltration
include circumferential and radial fibers. When preparing and proliferation of cells into the PCL scaffold. Formulating
radial tie-fiber orientation, the angle between the adjacent a biomaterial ink is challenging, as it must also provide
Y-direction fibers was set to 4.5°. This led to a radial tie- an ideal environment for cells to attach, proliferate, and
fiber spacing of 1.6 mm in the peripheral region, which differentiate while possessing gelation, mechanical, and
tapered inward until 0.81 mm. The conversion of straight rheological properties that facilitate 3D printing. GelMA
fibers to curved fibers did not significantly increase was selected as the major component of the biomaterial
the mechanical properties of the scaffold. However, ink formulation due to its potential in biomedical
the introduction of radial fibers and circumferential applications. As HA and CS are abundant in cartilage
fibers significantly enhanced the mechanical properties ECM 28,38 and have been investigated for their effect in
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(Figure 3D). This increase can be attributed to more enhancing chondrogenesis, the addition of GAGs to a
fibers being supported by the fiber layer below, thereby GelMA matrix was investigated for a fibro-chondrogenic
increasing the stability of the construct. effect. GelMA was the main component of each hydrogel,
accounting for at least 87% of the dry content mass. A
3.4. Printing a PCL scaffold that mimics the simplified hybrid structure was developed that consisted
circumferential and radial fibers of native meniscus of a PCL framework and was imbedded in three different
Optimized scaffold architectures with circumferential hydrogel combinations: GelMA, GelMA/CS/HA, and
and radial fibers resulted in properties that matched each GelMA/CS/HAMA. Using an optical microscope, the

Volume 10 Issue 4 (2024) 501 doi: 10.36922/ijb.3784