Micromotors are extensively applied in various fields, including cell separation, drug delivery and environmental protection. Micromotors with high speed and good biocompatibility are highly desirable. Bubble-driven micromotors, propelled by the recoil effect of bubbles ejection, show good performance of motility. The toxicity of concentrated hydrogen peroxide hampers their practical applications in many fields, especially biomedical ones. In this paper, the latest progress was reviewed in terms of constructing fast, bubble-driven micromotors which use biocompatible fuels, including low-concentration fuels, bioactive fluids, and enzymes. The geometry of spherical and tubular micromotors could be optimized to acquire good motility using a low-concentration fuel. Moreover, magnesium- and aluminum-incorporated micromotors move rapidly in water if the passivation layer is cleared in the reaction process. Metal micromotors demonstrate perfect motility in native acid without any external chemical fuel. Several kinds of enzymes, including catalase, glucose oxidase, and ureases were investigated to serve as an alternative to conventional catalysts. They can propel micromotors in dilute peroxide or in the absence of peroxide.

Micromotors, which can be moved at a micron scale, have special functions and can perform microscopic tasks. They have a wide range of applications in various fields with the advantages of small size and high efficiency. Both high speed and efficiency for micromotors are required in various conditions. However, the dynamical mechanism of bubble-driven micromotors movement is not clear, owing to various factors affecting the movement of micromotors. This paper reviews various factors acting on micromotor movement, and summarizes appropriate methods to improve the velocity and efficiency of bubble-driven micromotors, from a mechanical view. The dynamical factors that have significant influence on the hydrodynamic performance of micromotors could be divided into two categories: environment and geometry. Improving environment temperature and decreasing viscosity of fluid accelerate the velocity of motors. Under certain conditions, raising the concentration of hydrogen peroxide is applied. However, a high concentration of hydrogen peroxide is not applicable. In the environment of low concentration, changing the geometry of micromotors is an effective mean to improve the velocity of micromotors. Increasing semi-cone angle and reducing the ratio of length to radius for tubular and rod micromotors are propitious to increase the speed of micromotors. For Janus micromotors, reducing the mass by changing the shape into capsule and shell, and increasing the surface roughness, is applied. This review could provide references for improving the velocity and efficiency of micromotors.

Acoustic metamaterials achieve the function of absorbing sound through equivalent negative parameters and bandgaps. Sound absorption is closely related to structural design. How to effectively control acoustic metamaterials’ acoustic performance through structural design is of vital importance. This paper summarizes the structural design of typical acoustic metamaterials of the membrane, plates, Helmholtz cavities, and coupling structures from the structural design perspective. Acoustic metamaterials of different structures have their suitable application scenarios. Here, we review the latest progress of acoustic metamaterials in which various structures were applied to broaden the bandgap. Furthermore, this review may provide guidance for the potential application of acoustic metamaterials in engineering practice.

There is currently no effective solution to the problem of poor prognosis and recurrence of HCC. The technology of immunotherapy and prognosis of genetic material has made continuous progress in recent years. In the study, a 5-gene signature was established for the prognosis of HCC through biological information, and the immune infiltration of HCC patients was studied. After studied HCC patients’ immune infiltration, the paper screened the differential target genes of miR-126-3p in HCC downloaded from TCGA database, and uses WGCNA method to select the modular genes highly relevant to M2 macrophage. Then we use LASSO and COX regression analysis technology to establish the 5-gene signature. The nomogram is established by combining the prognostic score and clinical phenotype. Cibersort was empolyed to observe the immune infiltration in HCC patients. We revealed the biological pathways of HCC-related genes through GSEA and Metascape. The bioinformatics analysis of 2495 differential target genes finally constructed a 5-gene signature with a reliable prognostic ability (CDCA8, SLC41A3, PPM1G, TCOF1, GRPEL2). The combination of prognostic score and AJCC_Stage resulted in a more reliable prognosis ability. At the same time, 10 immune cells that are differentially expressed in HCC patients were also found. 8 GSEA pathways related to the prognosis were found. In the study, a reliable 5-gene signature was established based on the differential target gene of miR-126-3p to study the immune infiltration in HCC patients. It provides help for HCC-related prognosis research and immunotherapy.