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Figure 2. (A) The states of collagen protein hydrogel at different temperatures. Adapted with permission
from ref. [29] Copyright © 2025 ACS. (B) Schematic process for the developed, bioinspired composite
DZ-MS@scaffold. Adapted from [35] .

2.2. Chemical cross-linking method

Due to the unique mechanism of action and significant advantages, chemical
cross-linking method had become a research hotspot in the field of biomaterials. The

chemical cross-linking method could achieve precise control of the degradation rate of
hydrogels by precisely regulating the type and concentration of cross-linking agents, so

as to meet the diverse varied and specific requirements of different treatment scenarios.

The key factor in preparing hydrogels via the chemical cross-linking method lay in

selecting the appropriate cross-linking agents, as this choice significantly influenced

the hydrogel's properties, degradation rate, and overall performance in targeted

applications. By directional modification of key functional groups such as -CHO and -

NH2 within the molecule structure, specific chemical reactions were triggered to

facilitate the formation of cross-linking between molecular chains. This tailored

approach enabled the fabrication of hydrogel structures that were precisely engineered

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to meet distinct functional requirements for targeted applications. Meanwhile, the 3D
printed hydrogel obtained through chemical cross-linking method provided an ideal
solution for solving personalized medical demands, especially in the treatment of

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