Page 507 - IJB-10-4

International Journal of Bioprinting 3D-printed variable stiffness scaffolds

region than in the peripheral region. However, in layer 2, it directly into the scaffold model. With an increase in
was found that there was no significant difference between fiber spacing from 1 to 2 mm, the theoretical pore size
the peripheral and inner regions. To develop a scaffold increased. As expected, as offsets are introduced to the
with regional mechanical properties, these zones within scaffold, the pore size decreases. This is attributed to a
the meniscus were subdivided into two groups depending fiber crossing the pore when the offset layer is printed. The
on their compressive properties. Zones with a compressive maximum theoretical porosity of 93% was achieved at 2
modulus between 0.5 and 1.1 MPa were categorized as mm fiber spacing, 0 offsets, and at a pore size of 4 mm ,
2
Group A, and zones with a compressive modulus > 1.1 while a minimum porosity of 74 % was achieved at 1 mm
MPa were categorized as shown in Figure 2A (ii). fiber spacing, 2 offsets, and a pore size of 0.16 mm (Figure
2
Therefore, the inner and peripheral regions of layer 1 3B and C). Porosity may also be increased by decreasing
and the inner region of layer 3 are categorized as Group the needle’s inner diameter; however, it was found that
A; the inner and peripheral regions of layer 2 and the attempts to produce thinner fibers using a 30 Ga needle
peripheral region of layer 3 are categorized as Group B. made inconsistent prints that were susceptible to defects.

3.2. 3D printing parameters of PCL 3.3 Mechanical properties of 3D-printed
Polycaprolactone (PCL) is a promising material for PCL scaffolds
meniscus tissue engineering due to its semi-crystalline For cartilage regeneration, scaffolds with porosity > 70% are
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nature and resorbable aliphatic properties, enabling it to deemed suitable for cell attachment and matrix deposition.
degrade in the body through hydrolysis of its aliphatic However, scaffold porosity affects the mechanical
ester linkage. Additionally, PCL retains its molecular properties, whereby high porosity compromises the
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weight longer than other aliphatic polyesters, which is structural integrity of the scaffold. When the compressive
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beneficial in meniscus regeneration as the scaffold can modulus is too low, it may result in deformation and
maintain its mechanical properties longer until tissue failure of the implant, subsequently leading to failure of the
ingrowth has occurred. PCL also plays an important role regenerated tissue. The compressive modulus was found to
in organizing the matrix and enhancing matrix content. significantly decrease with increasing fiber spacing from 1
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Traditionally, synthetic scaffolds for tissue regeneration to 2 mm as shown in Figure 2B.
are produced using electrospinning. However, electrospun When layers were printed in double format, i.e.,
meshes can display both mechanical and biological the same layer orientation printed sequentially, the
disadvantages. For example, the fibers may slide under compressive properties increased compared to single-
compression loads because they are not fused together. layer orientations. A maximum compressive modulus
Furthermore, scaffolds formed from electrospinning of 2.74 MPa was found for 1 mm fiber spacing, 0 offsets,
have small pore sizes and thus may be too dense for cell and double-layer orientations. Simply changing the fiber
infiltration. The key advantages of 3D printing compared spacing to 2 mm, while maintaining 0 offsets and double-
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to other manufacturing techniques include high resolution layer orientations, decreased the compressive modulus
and good control of fiber thickness, orientation, and to 1.73 MPa. Compared to the double layer, single-layer
pore size. orientations exhibited lower compressive properties: 2.63
To achieve a scaffold with regional mechanical MPa for 1 mm fiber spacing and 0 offsets; and 0.88 MPa for
properties, various 3D-printed PCL architectures with 2 mm fiber spacing and 0 offsets. The significant decrease
varying porosity were studied. Two different fiber spacings in compressive properties is due to the increase in pore
2
(1 and 2 mm), three different offsets (0, 1, and 2 offsets), size from 1 to 4 mm and porosity from 87% to 93%. In
and two different layer orientations (single and double) comparison to that of the human meniscus, the results
were investigated in this study. Each scaffold was 10 layers are comparable at 0.2, 0.23, and 0.28 MPa in the anterior,
high and printed in various architectures (Figure 1), with central, and posterior parts of the meniscus, respectively.
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controlled internal fiber deposition and pore size. The As the meniscus is an anisotropic material, the mode or
fabrication time for each scaffold was approximately 30 direction of the analysis and the depth of the sample tested
min. An example of printed offsets is displayed for 1 mm will all affect the reported properties.
fiber spacing single-layered scaffolds in Figure 3A. Compressive mechanical properties of PCL scaffolds

Key considerations for tissue engineering scaffolds manufactured with varying porosities have been previously
include pore size, porosity, and interconnectivity, all of reported in the literature. However, the reported porosities
which are determined by the architecture of the scaffold. are generally much lower than this study, corresponding to
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3D printing offers an advantage over other production higher compressive properties. Through fused deposition
techniques, as pore interconnectivity can be designed modeling (FDM), a compressive modulus of 4 and 77

Volume 10 Issue 4 (2024) 499 doi: 10.36922/ijb.3784