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A strong bio-ink for Meniscus Regeneration
A B C

D E F

G H I

Figure 1. The result of the SEM images and the rheometer. (A) The SEM images of the natural meniscus, (B) the 40-20 PVA/dECM
hydrogel group, and (C) the control group (scale bar: 50 μm). Results of rheometer: (D) Relationship between frequency and pressure under
fixed stress and (E) relationship between stress and pressure under fixed frequency. The shear-thinning experiments of the control (F), 20-20
(G), 40-20 (H), and 120-20 (I) PVA/dECM hydrogel groups.
was observed in the 20-20 PVA/dECM hydrogel group, S13). The relaxation time was affected by the cycles of
and the energy dissipation became smaller with the freezing/thawing or the alkaline treatment time (Figure
extension of sodium hydroxide soaking time. The S14). The reason for this phenomenon may be the
control group showed a similar energy dissipation with diversity of crystallization or water content caused by
the 40-20 in the uniaxial compression-relaxation curves. the abovementioned physical operation.
The reason of energy dissipation may be related to the Taken together, these results demonstrated that the
change of the PVA crystalline domains and breaking the PVA/dECM hydrogel exhibited excellent and reliable
ionic bonds. mechanical properties. Moreover, the fast recovery
The fast recovery capability of the hydrogel was and stress bearing capabilities of the designed PVA/
tested by applying continuous compression-relaxation dECM hydrogel can mimic other mechanical properties
cycles under 50% strain to the same hydrogels for of natural meniscus. Thus, the PVA/dECM hydrogel
20 cycles without any time interval between two can be regarded as a substantial candidate for meniscus
cycles (Figure 2C-F and Figure S10), and the trend of regeneration.
maximum stress and energy dissipation in each cycle
is summarized in Figure 2G-H and Figure S11-S12. 3.3. 3D printing test
According to the results, the relative maximum stress
of each cycle slightly decreased and remained at N80% According to the measurement of the 3D reconstruction
after continuous compression-relaxation for 20 cycles. model, the longitudinal axis of meniscus was
Similarly, the energy dissipation was attenuated under 9.20 mm and the horizontal axis was 25.12 mm. The
compression-relaxation cycles and remained at N20% dimension of the 3D printed scaffold can precisely
after 20 cycles. The control group showed a greater reproduce this size. A microscope could clearly
reduction of maximum stress and energy dissipation. show that the pore size (≈1000 μm) and filament
There results suggested that the PVA/dECM hydrogel diameter (≈400 μm) were uniform (Figure 3A). The
kept an excellent elasticity and a fast recovery ability. semi-quantitative analysis revealed that there was
The introduction of PVA increased the elasticity and no significant difference between the dimension
the long-term mechanical properties of hydrogels. The of the original model and the 3D printed scaffold
addition of PVA can obviously improve the stress- (Figure 3B). In addition, the scaffold exhibited an
relaxation behavior of the bio-ink (Figure 2I and Figure outstanding deformation capability. It could quickly

36 International Journal of Bioprinting (2022)–Volume 8, Issue 4