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for 48 h, snap-fractured in liquid nitrogen, and sputter-coated with gold before imaging. To assess

swelling behavior, PMs were blended into the GelMA bioink and crosslinked. After demolding,

samples were rinsed with PBS (pH 7.4) and blotted to remove excess liquid. The initial dry weight

was recorded. Samples were immersed in 20 mL PBS at 37°C under shaking (50 rpm). At specified

intervals (1-24 h), samples were removed, blotted, and weighed. Swelling equilibrium was defined

as a weight change ≤5% between two consecutive points. The swelling ratio (SR) and moisture

ratio (MR) were calculated accordingly. Rheological properties were characterized using a dynamic

shear rheometer Discovery HR-1 (TA, Newcastle, Delaware, USA) with a 50 mm parallel-plate

geometry (1 mm gap). Both uncrosslinked (PMs/GelMA mixture with photoinitiator, degassed) and

crosslinked (1 mm thick discs, photocured) samples were tested. Shear viscosity was measured at

-1
room temperature from 0 to 1000 s . Temperature-dependent viscosity and moduli (G' and G'')

were recorded during cooling from 40°C to 0°C at 5°C/min.

2.5. Construction of Biomimetic Osteochondral Tissue Model

The mixture of C-MT or EO-MT and GelMA hydrogel was layer-printed by an extruded 3D

bioprinter to construct a biomimetic osteochondral tissue model. First, EO-MT composite GelMA

hydrogel (50 microtissue/mL) was printed in 6-well plates and cured by blue light irradiation for

10 s. The C-MT composite hydrogel (50 microtissue/mL) was then printed on the EO-MT layer

and cured by blue light irradiation. Then 1 mL of complete medium was added and placed in an

incubator. Meanwhile, MTs/GelMA bioink was directly added into sterilized silicone molds,

photocrosslinked with blue light, demolded, and transferred to 6-well plates for culture as the

casting group. On days 1, 4, and 7, cell viability of both the casting group and the scaffold group

was assessed using the CCK-8 assay. On day 14, the scaffolds were retrieved, washed with PBS to

remove residual medium, and their structural integrity was observed. Additionally, on day 14, the

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