Biological materials exhibit excellent fracture toughness due to their ability to dissipate energy during crack propagating through the combination of various constituents with different stiffnesses. Replicating this mechanism in engineering materials is important in mechanical systems and emerging applications such as flexible electronics and soft robotics. Here a novel liquid metal (LM)‐filled polymer microlattice metamaterial, fabricated by projection micro‐stereolithography (PμSL) 3D printing and vacuum filling of gallium (Ga), exhibiting high fracture toughness of 0.8 MJ m−3, is reported. Moreover, the LM metamaterials demonstrate shape memory effect and even essentially recover its original shape upon severe fractures. These unique features arise from the tunable properties of gallium at a relatively low temperature range. The result offers new insights into design and manufacturing mechanical metamaterials with tunable properties and high recoverability for soft robots, flexible electronics, and biomedical applications.

With the development of microfluidics, electro-osmotic (EO) driven flow has gained intense research interest as a result of its unique flow profile and the corresponding benefits in its application in the transportation of sensitive samples. Sensitive samples, such as DNA, are incapable of enduring strong flow shear induced by conventional hydrodynamic driven methods. EO driven flow is thus a niche area. However, even though there are a few research studies focusing on bio-fluidic samples related to EO driven flow, the majority of them are merely theoretical modeling without solid evidence from experiments due to the inherent complex rheological behavior of the bio-fluids. Challenges occur when the EO driven mechanism meets with complex rheology; vital questions such as can the zeta potential still be assumed to be constant when dealing with fluids with complex rheology? and "Does the shear thinning effect enhance electro-osmotic driven flow?" need to be answered. We conducted experiments using current monitoring and microscopy fluorescence methods, and developed a theoretical model by coupling a generalized Smoluchowski approach with the power-law constitutive model. We calculated the zeta potential and compared the experimental results with modeling to answer the questions. The results show a reduction of zeta potential in the presence of PEO aqueous solutions. A constant zeta potential is also indicated by varying the PEO concentration and the electric field strength.The shear thinning effect is also addressed via experimental data and theoretical calculations. The results show a promising enhancement of the EO driven velocity due to the shear thinning effect.

Biological materials such as conch shells with crossed-lamellar textures hold impressive mechanical properties due to their capability to realize effective crack control and energy dissipation through the structural synergy of interfacial modulus mismatch and lamellar orientation disparity. Integrating this mechanism with mechanical metamaterial design can not only avoid the catastrophic post-yield stress drop found in traditional architectural materials with uniform lattice structures but also effectively maintain the stress level and improve the energy absorption ability. Herein, a novel bioinspired design strategy that combines regional particularity and overall cyclicity is proposed to innovate the connotation of long-range periodicity inside the metamaterial, in which the node constraint gradient and crossed-lamellar struts corresponding to the core features of conch shells are able to guide the deformation sequence with a self-strengthening response during compression. Detailed in situ experiments and finite element analysis confirm that the rotated broad layer stacking can shorten and impede the shear bands, further transforming the deformation of bioinspired metamaterial into a progressive, hierarchical way, highlighted by the cross-layer hysteresis. Even based on a brittle polymeric resin, excellent specific energy absorption capacity [4544 kJ/kg] has been achieved in this architecture, which far exceeds the reported metal-based syntactic foams for two orders of magnitude. These results offer new opportunities for the bioinspired metamaterials to substitute the widespread syntactic foams in specific applications required for both lightweight and energy absorption.

Lightweight hollow ceramic microfibers/microparticles hold promising prospects in numerous applications. To date, it remains a challenge to develop a fabrication strategy that well balances product quality and efficiency. In this article, an all-aqueous microfluidic method was proposed to prepare tubular polymeric fiber as the preceramic template. The relevant dimensional parameters could be promptly regulated via simple flow rate control. This approach could serve as a general technical route to preparing different kinds of ceramics by switching the types of nanoparticles. Here, silica nanoparticles were introduced and the ceramic microfiber could be got via calcination. Afterward, the tubular silica microfiber was employed to synthesize geopolymer composite by mold casting. The chemically formed interfacial bonding between the silica microfiber and geopolymer matrix was confirmed by elemental analysis. The addition of 10% volume fraction silica microfiber could not only increase the flexural modulus of geopolymer composite by 3.5 times but also effectively inhibited crack propagation under thermal circumstances.

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