Significance: The current cleanroom-based soft lithography microfabrication process is complicated and expensive. There is a need for low-cost, ready-to-use, modular components that can be easily assembled into microfluidic devices by users lacking proficiency or access to microfabrication facilities. We present a facile, low-cost, and efficient method of fabricating soft, elastic microtubes with different cross-sectional shapes and dimensions. These microtubes can be used as basic building blocks for the rapid construction of various 2D and 3D microfluidic devices with complex geometries, topologies, and functions. This approach avoids the conventional cumbersome photolithography process and thus, provides a feasible way for scaling up the production of microfluidic devices.

The distribution and location of mast cells are closely related to their physiological and pathological functions, such as allergic responses, immunity, and fibrosis, and are used in acupuncture. In this study, the distribution of mast cells in vivo was observed, and mechanical clues for understanding their distribution based on mechanical niches were explored. By toluidine blue staining and immunohistochemical staining, we examined the distribution and location of mast cells in rat skin and found that mast cells are distributed in a spatially nonuniform manner, preferring to locate at regions in the tissue and extracellular matrix with stiffness changes. In vitro experiments for studying the distribution of rat basophilic leukemia (RBL-2H3) mast cell line on poly-di-methyl-siloxane (PDMS) substrates with stiffness variations were performed. It was found that RBL-2H3 cells migrate and tend to remain in the areas with stiffness variations. The present research suggests that changing the stiffness of local tissues may stimulate mast cell recruitment, which may be the method by which some traditional Chinese medicine treatments, such as acupuncture. On the basis of the origin of mast cells and our experimental results, we predict that mast cells exist in tissues that contain permeable capillaries and prefer regions with stiffness changes. We discussed this prediction using examples of specific tissues from some cases.

The deformation of multiple red blood cells in a capillary flow was studied numerically. The immersed boundary method was used for the fluid red blood cells interaction. The membrane of the red blood cell was modeled as a hyperelastic thin shell. The numerical results show that the apparent viscosity in the capillary flow is more sensitive to the change of shear coefficient of the membrane than the bending coefficient and surface dilation coefficient, and the increase in the shear coefficient results in an increase in the pressure drop in the blood flow in capillary vessels in order to sustain the same flux rate of red blood cells.