An efficient 3D cell-based discrete fracture-matrix flow model for digitally captured fracture networks.

Complex hydraulic fracture networks are critical for enhancing permeability in unconventional reservoirs and mining industries. However, accurately simulating the fluid flow in realistic fracture networks (compared to the statistical fracture networks) is still challenging due to the fracture complexity and computational burden. This work proposes a simple yet efficient numerical framework for the flow simulation in fractured porous media obtained by 3D high-resolution images, aiming at both computational accuracy and efficiency. The fractured rock with complex fracture geometries is numerically constructed with a cell-based discrete fracture-matrix model (DFM) having implicit fracture apertures. The flow in the complex fractured porous media (including matrix flow, fracture flow, as well as exchange flow) is simulated with a pipe-based cell-centered finite volume method. The performance of this model is validated against analytical/numerical solutions. Then a lab-scale true triaxial hydraulically fractured shale sample is reconstructed, and the fluid flow in this realistic fracture network is simulated. Results suggest that the proposed method achieves a good balance between computational efficiency and accuracy. The complex fracture networks control the fluid flow process, and the opened natural fractures behave as primary fluid pathways. Heterogeneous and anisotropic features of fluid flow are well captured with the present model.

The residues 4 to 6 at the N-terminus in particular modulate fibril propagation of ß-microglobulin.

The ΔN6 truncation is the main posttranslational modification of ß-microglobulin (ßM) found in dialysis-related amyloid. Investigation of the interaction of wild-type (WT) ßM with N-terminally truncated variants is therefore of medical relevance. However, it is unclear which residues among the six residues at the N-terminus are crucial to the interactions and the modulation of amyloid fibril propagation of ßM. We herein analyzed homo- and heterotypic seeding of amyloid fibrils of WT human ßM and its N-terminally-truncated variants ΔN1 to ΔN6, lacking up to six residues at the N-terminus. At acidic pH 2.5, we produced amyloid fibrils from recombinant, WT ßM and its six truncated variants, and found that ΔN6 ßM fibrils exhibit a significantly lower conformational stability than WT ßM fibrils. Importantly, under more physiological conditions (pH 6.2), we assembled amyloid fibrils only from recombinant, ΔN4, ΔN5, and ΔN6 ßM but not from WT ßM and its three truncated variants ΔN1 to ΔN3. Notably, the removal of the six, five or four residues at the N-terminus leads to enhanced fibril formation, and homo- and heterotypic seeding of ΔN6 fibrils strongly promotes amyloid fibril formation of WT ßM and its six truncated variants, including at more physiological pH 6.2. Collectively, these results demonstrated that the residues 4 to 6 at the N-terminus particularly modulate amyloid fibril propagation of ßM and the interactions of WT ßM with N-terminally truncated variants, potentially indicating the direct relevance to the involvement of the protein's aggregation in dialysis-related amyloidosis.

Hybrid Magnetic Micropillar Arrays for Programmable Actuation.

Stimuli-responsive micro/nanostructures that can dynamically and reversibly adapt their configurations according to external stimuli have stimulated a wide scope of engineering applications, ranging from material surface engineering to micromanipulations. However, it remains a challenge to achieve a precise local control of the actuation to realize applications that require heterogeneous and on-demand responses. Here, a new experimental technique is developed for large arrays of hybrid magnetic micropillars and achieve precise local control of actuation using a simple magnetic field. By manipulating the spatial distribution of magnetic nanoparticles within individual elastomer micropillars, a wide range of the magnetomechanical responses from less than 5% to ≈50% for the ratio of the bending deflection to the original length of the pillars is realized. It is demonstrated that the micropillars with different degrees of bending deformation can be configured in any spatial pattern using a photomask-assisted template-casting technique to achieve heterogeneous, site-specific, and programmed bending actuations. This unprecedented local control of the micropillars offers exciting novel applications, as demonstrated here in encryptable surface printing and stamping, direction- and track-programmable microparticle/droplet transport, and smart magnetic micro-tweezers. The hybrid magnetic micropillars reported here provide a versatile prototype for heterogeneous and on-demand actuation using programmable stimuli-responsive micro/nanostructures.

Bioinspired Wear-Resistant and Ultradurable Functional Gradient Coatings.

For mechanically protective coatings, the coating material usually requires sufficient stiffness and strength to resist external forces and meanwhile matched mechanical properties with the underneath substrate to maintain the structural integrity. These requirements generate a conflict that limits the coatings from achieving simultaneous surface properties (e.g., high wear-resistance) and coating/substrate interfacial durability. Herein this conflict is circumvented by developing a new manufacturing technique for functional gradient coatings (FGCs) with the material composition and mechanical properties gradually varying crossing the coating thickness. The FGC is realized by controlling the spatial distribution of magnetic-responsive nanoreinforcements inside a polymer matrix through a magnetic actuation process. By concentrating the reinforcements with hybrid sizes at the surface region and continuously diminishing toward the coating/substrate interface, the FGC is demonstrated to exhibit simultaneously high surface hardness, stiffness, and wear-resistance, as well as superb interfacial durability that outperforms the homogeneous counterparts over an order of magnitude. The concept of FGC represents a mechanically optimized strategy in achieving maximal performances with minimal use and site-specific distribution of the reinforcements, in accordance with the design principles of many load-bearing biological materials. The presented manufacturing technique for gradient nanocomposites can be extended to develop various bioinspired heterogeneous materials with desired mechanical performances.