Despite the vigorous development of bionic materials, it is still difficult to match the characteristics of natural soft tissues. For example, natural soft tissues can exhibit unique mechanical properties through the interaction of structure and local component changes. In contrast, the current synthetic soft materials have not yet achieved controllability at this level, which severely limits the further development and application of synthetic soft materials.
In response to this problem, the Esther Amstad team at the Federal Institute of Technology in Lausanne, Switzerland, developed a method that can produce strong double-network particle hydrogels (DNGHs).3D printingStrategy. Researchers add polyelectrolyte-based microgels (which can be swelled in the monomer solution) to the monomer solution to form ink materials; when the ink is additively manufactured, these monomers can be UV-cured to form a percolation network, and combine with Together, the microgel network forms DNGHs. Due to the improved contact performance between particles in the microgel network and the existence of the dual network structure, the hardness of DNGHs is significantly improved, and can repeatedly support tensile loads up to 1.3MPa; its toughness is also an order of magnitude higher than that of the single-material polymer network . Research believes that the emergence of this new type of DNGHs provides new ideas for the design of high-strength hydrogels that can be used in advanced fields such as soft machine manufacturing. Related work was published in Advanced Functional Materials with the title “3D Printing of Strong and Tough Double Network Granular Hydrogels”.
Design and preparation of microgel ink
In the DNGHs system studied in this article, polyelectrolyte-based microgels are introduced to give the synthetic hydrogel the natural soft tissue material properties of “local changes in components”. However, the small contact surface of the microgel often results in low strength of the superstructure formed. Therefore, in order to improve the mechanical properties of hydrogels, propanesulfonic acid (AMPS) microgels with high swelling ability have been studied and synthesized. After the microgel is formed, the researchers place it in an aqueous solution of acrylamide (AM) monomer; in this solution, the microgel can swell and enlarge the contact surface to ensure good adhesion between particles.exist3D printingLater, the AM monomer can be transformed into a percolating PAM network after UV curing, and together with the optimized microgel, it can form DNGHs with excellent mechanical properties.
Characterization of mechanical properties of DNGHs
The study firstly found that the hardness and toughness of DNGHs are better than AMPS-based hydrogels and AM-based hydrogels. The test showed that the Young’s modulus of DNGHs was 5 times and 3 times higher than that of AMPS-based hydrogel and AM-based hydrogel, respectively. Studies believe that this performance improvement is mainly due to the AM polymer (PAM) chain and microgel network that can limit chain entanglement, thereby restricting the substitution behavior. In addition, the breaking strength of DNGHs is more than ten times higher than AMPS-based hydrogels and AM-based hydrogels, indicating that DNGHs have excellent toughness.
Potential applications of DNGHs
The study also explored the potential applications of DNGHs. By changing the types of components contained in the microgels, the researchers synthesized a variety of microgels; mixing these microgels and placing them in the same monomer solution can form a variety of inks.In this way, the ink has a variety of microgels containing different components;3D printingA complex structure containing multiple components and characteristics can then be formed. In order to verify the feasibility, the researchers used diversified ink systems with microgels with a variety of crosslinking densities (that is, different swelling capabilities) to successfully print a double-layer gradual flower structure. Since the double-layer structure of the flower is composed of two microgel layers with different crosslinking densities, the flower can be repeatedly folded after being dried or immersed in water.
in conclusion
This work introduces a strategy for additive manufacturing of high-strength composite hydrogels.This strategy combines the rheological properties of microgels with the mechanical properties of dual-network hydrogels, and successfully3D printingA high-strength hydrogel material was developed.Therefore, this work expands the3D printingThe high-strength complex material system. Not only that, the ink developed by this work has the characteristics of flexible design and controllable printing structure, which provides new possibilities for the design and manufacture of new soft machines and implants that can be locally adjusted in response to external stimuli.
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