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improvement in compressive modulus (Es). This indicates that the incorporation of PMs can

effectively enhance the mechanical strength of the hydrogel, which may be attributed to PMs acting

as rigid fillers to bear stress transfer within the gel network. Matrix stiffness is known to effectively

regulate cell behavior: higher stiffness promotes osteogenic differentiation, while moderate or

lower stiffness favors chondrogenesis 54,55 . This suggests that matrix stiffness could be regulated by

adjusting the incorporation number of PMs in potential future studies.

Rheological analysis further confirmed that PMs improved the printability of GelMA bioinks.

Both GelMA and PMs/GelMA displayed thermo-responsive gelation, with G' surpassing G'' near

15 °C (Figure 7G), indicating sol–gel transition unaffected by PM addition. Temperature-viscosity

curves further demonstrate the thermal responsiveness of GelMA and PMs/GelMA; however, the

initial viscosity of PM-containing inks was significantly higher than that of pure GelMA (Figure

7H), which may be due to the increased internal friction of particle-polymer interactions, as well

as the complexity of the microstructure. This property is advantageous for 3D bioprinting, as higher

static viscosity enhances shape fidelity. Importantly, shear-thinning behavior was preserved

(Figure 7I), satisfying the extrusion printing requirement of high viscosity at rest and low viscosity

under shear. In conclusion, the incorporation of PMs not only achieves effective regulation of the

swelling behavior and mechanical strength of GelMA hydrogels but also endows them with good

printability by optimizing rheological properties, laying the experimental foundation for the

application of this composite bioink in the field of bone/cartilage tissue engineering.

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