Toughening elastomers via microstructured thermoplastic fibers with sacrificial bonds and hidden lengths

Soft materials capable of large inelastic deformation play an essential role in high-performance nacre-inspired architectured materials with a combination of stiffness, strength and toughness. The rigid "building blocks" made from glass or ceramic in these architectured materials lack inelastic deformation capabilities and thus rely on the soft interface material that bonds together these building blocks to achieve large deformation and high toughness. Here, we demonstrate the concept of achieving large inelastic deformation and high energy dissipation in soft materials by embedding microstructured thermoplastic fibers with sacrificial bonds and hidden lengths in a widely used elastomer. The microstructured fibers are fabricated by harnessing the fluid-mechanical instability of a molten polycarbonate (PC) thread on a commercial 3D printer. Polydimethylsiloxane (PDMS) resin is infiltrated around the fibers, creating a soft composite after curing. The failure mechanism and damage tolerance of the composite are analyzed through fracture tests. The high energy dissipation is found to be related to the multiple fracture events of both the sacrificial bonds and elastomer matrix. Combining the microstructured fibers and straight fibers in the elastomer composite results in a ~ 17 times increase in stiffness and a ~ 7 times increase in total energy to failure compared to the neat elastomer. Our findings in applying the sacrificial bonds and hidden lengths toughening mechanism in soft materials at the microscopic scale will facilitate the development of novel bioinspired laminated composite materials with high mechanical performance

Bibliometric and visual analysis on research of freeze-thaw of rock slopes based on CNKI Data

In order to explore the research status of rock slope freeze-thaw problems, 228 domestic and foreign rock slope freeze_x005fthaw papers were retrieved as the samples based on the CNKI database. CiteSpace was used to conduct bibliometric and knowledge map analysis on the number of paper publications, authors, and keywords. The results show that the annual publication volume in this fi eld are generally increasing, indicating a large development space in future. There are many research teams and institutions in this fi eld, but there is less collaboration between diff erent teams. According to the timeline map, revealing that earlier literature focused mainly on understanding and prevention of rock slope freeze-thaw problems. New technologies from other fi elds have been gradually applied for innovation in recent years. The future research trend will involve micro-damage, multi-fi eld coupling, dynamic responses, monitoring and warning of rock slope freeze-thaw problems

Experimental and numerical investigation of interface damage in composite L-angle sections under four-point bending

© The Author(s) 2020. Curved laminates in aero-structures, such as the L-angle sections where webs and flanges meet, are prone to delamination due to high interlaminar stresses in these regions. Some efforts to investigate delamination in these structures can be found in the literature but commonly structures are limited to unidirectional layups or modelling approaches are constrained to the cohesive element based methods. In this work, multi-directional L-angle laminates were manufactured using unidirectional prepregs and tested under four-point bending load conditions to examine the interface damage. Acoustic emission technique was used to assist the capture of damage initiation and propagation. Three interface modelling strategies for predicting delamination, namely cohesive element, cohesive surface and perfectly bonded interface were used in the numerical study. The interface damage behaviour was successfully predicted by the simulation methods and differences among the strategies were compared

Failure mechanisms of coiling fibers with sacrificial bonds made by instability-assisted fused deposition modeling

Instability-assisted 3D printing is a method for producing microstructured fibers with sacrificial bonds and hidden lengths which mimic nature’s toughening mechanisms found in spider silk. This hierarchical structure increases the effective toughness of poly(lactic acid) (PLA) fibers by 240% − 340% in some specimens. Nevertheless, many specimens show worse toughness as low as 25% of that of the benchmark straight fiber due to the incomplete release of hidden lengths caused by premature failures. Here, we report mechanical tests and simulations of microstructured fibers with coiling loops that identify the material plastic deformation as being crucial to fully release the hidden lengths. Without sufficient material yielding, high local tensile stress results from the bending-torsion-tension coupled deformation of the coiling loop and induces crack initiation at the fiber backbone during the loop unfolding process. On the other hand, the influence of bond-breaking defect is found to be negligible here. Moreover, for a number of broken bonds beyond a critical value, the accumulated elastic energy along the released loops induces a high strain rate (~ 1500 mm/mm/s) in quasi-static tensile test, which fractures the fiber backbone within 0.1 ms after the breaking of a new bond. We also show a size effect in fused deposition modeling (FDM) extruded PLA fibers, which results in higher effective toughness (~ 5 times the performance of the straight fiber benchmark) in small coiling fibers (dia. = 0.37 mm), due to the better ductility in bending and torsion than large fibers (dia. = 1.20 mm). The failure mechanisms of single microstructured fiber presented here lay the groundwork for further optimizations of fiber arrays in the next generation of high energy-absorption composites for impact protection and safety-critical applications

Spiderweb-inspired, transparent, impact-absorbing composite

Transparent materials with high impact absorption are required for many safety-critical engineering systems. Existing transparent tough composites have increased impact resistance but often fail catastrophically because of poor impact absorption. We propose a transparent impact-absorbing composite that reproduces the toughening mechanism involving sacrificial bonds and hidden lengths in spider silk. Our material consists of an elastomer matrix and an instability-assisted, 3D-printed, bidirectional fabric of microstructured fibers with sacrificial bonds and alternating loops. Under impact, the hidden loops unfold after bond breaking and matrix cracking, resisting impactor penetration with graceful failure. The large-scale plastic deformation of the unfolding loops significantly increases energy dissipation and leads to hysteresis of 95.6% (dissipated energy/total absorbed energy × 100%), minimizing the released elastic energy and reducing the rebounding damage. Our approach opens a new avenue for designing and manufacturing transparent high-energy-absorbing composites for impact protection applications

The Role of Protein Arginine Methyltransferase 1 in Gastrointestinal Cancers

Mammals can produce nine kinds of arginine methylation enzymes that can be divided into three types (I, II, and III) according to their catalytic activity. Arginine methyltransferase 1 (PRMT1), as the first discovered arginine methyltransferase type I, has been reported to be involved in cell signal transduction, DNA damage repair, RNA transcription and other processes. Its imbalance or abnormal expression is also involved in cancer metastasis. PRMT1 is highly expressed in gastrointestinal tumors and promotes tumor biomarkers expression, chemotherapy resistance and tumorigenicity to promote cancer progression, while downregulation of PRMT1 expression can inhibit the migration and invasion of related tumor cells or promote tumor cells apoptosis and inhibit the progression of cancer. Therefore, PRMT1 may be a cancer therapeutic target. In this paper, arginine methylase 1 expression in various types of gastrointestinal tumors, the tumorigenic mechanism and the role of PRMT1 in tumorigenesis and development were reviewed

p300/CBP Methylation is Involved in the Potential Carcinogenic Mechanism of Lung Cancer

p300/CBP is involved in the expression of a wide range of genes, both as a histone acetyltransferase (HAT) and as a coactivator of transcription factors. p300/CBP is the specific substrate of CARM1, and its KIX domain and GBD domain are the main sites methylated by arginine methyltransferase 4 (PRMT4/CARM1). p300/CBP plays an important role in lung cancer, which is a cell cycle disease. More importantly, the methylation of p300/CBP by CARM1 affects the progression of lung cancer through the cAMP-PKA pathway, p53 pathway and ER pathway. The structure, function, methylation modification sites, methylation-related enzymes, genes associated with lung cancer and the possible mechanisms of p300/CBP action are reviewed

An efficient multiscale surrogate modelling framework for composite materials considering progressive damage based on artificial neural networks

© 2020 Elsevier Ltd Modelling of the progressive damage behaviour of large-scale composite structures presents a significant challenge in terms of computational cost. This is due to the detailed description in finite element (FE) models for the materials, i.e., with each unidirectional layer defined as required by the applicability of laminate failure criteria, and numerous iterations required to capture the highly nonlinear behaviour after damage initiation. In this work, we propose a method to accelerate the nonlinear FE analysis by using a pre-computed surrogate model which acts as a general material database representing the nonlinear effective stress-strain relationship and the possible failure information. Developed using artificial neural network algorithms, the framework is separated into an offline training phase and an online application phase. The surrogate model is first trained with a vast number of sampling data obtained from mesoscale unit cell models offline, and then used for online predictions on a macroscale FE model. The prediction accuracy of the surrogate model was examined by comparing the results with conventional FE modelling and good agreement was observed. The presented method enables progressive damage analysis of composite structures with significant savings of the online computational cost. Lastly, the surrogate model is only based on material designs and is reusable for other structures with the same material

A Retrofit Sensing Strategy for Soft Fluidic Robots

Soft robots are intrinsically capable of adapting to different environments by changing their shape in response to interaction forces with the environment. However, sensing and feedback are still required for higher level decisions and autonomy. Most sensing technologies developed for soft robots involve the integration of separate sensing elements in soft actuators, which presents a considerable challenge for both the fabrication and robustness of soft robots due to the interface between hard and soft components and the complexity of the assembly. To circumvent this, here we present a versatile sensing strategy that can be retrofitted to existing soft fluidic devices without the need for design changes. We achieve this by measuring the fluidic input that is required to activate a soft actuator and relating this input to its deformed state during interaction with the environment. We demonstrate the versatility of our sensing strategy by tactile sensing of the size, shape, surface roughness and stiffness of objects. Moreover, we demonstrate our approach by retrofitting it to a range of existing pneumatic soft actuators and grippers powered by positive and negative pressure. Finally, we show the robustness of our fluidic sensing strategy in closed-loop control of a soft gripper for practical applications such as sorting and fruit picking. Based on these results, we conclude that as long as the interaction of the actuator with the environment results in a shape change of the interval volume, soft fluidic actuators require no embedded sensors and design modifications to implement sensing. We believe that the relative simplicity, versatility, broad applicability and robustness of our sensing strategy will catalyze new functionalities in soft interactive devices and systems, thereby accelerating the use of soft robotics in real world applications

HIV-1 variants with a single-point mutation in the gp41 pocket region exhibiting different susceptibility to HIV fusion inhibitors with pocket- or membrane-binding domain

AbstractEnfuvirtide (T20), the first FDA-approved peptide HIV fusion/entry inhibitor derived from the HIV-1 gp41 C-terminal heptad-repeat (CHR) domain, is believed to share a target with C34, another well-characterized CHR-peptide, by interacting with the gp41 N-terminal heptad-repeat (NHR) to form six-helix bundle core. However, our previous studies showed that T20 mainly interacts with the N-terminal region of the NHR (N-NHR) and lipid membranes, while C34 mainly binds to the NHR C-terminal pocket region. But so far, no one has shown that C34 can induce drug-resistance mutation in the gp41 pocket region. In this study, we constructed pseudoviruses in which the Ala at the position of 67 in the gp41 pocket region was substituted with Asp, Gly or Ser, respectively, and found that these mutations rendered the viruses highly resistant to C34, but sensitive to T20. The NHR-peptide N36 with mutations of A67 exhibited reduced anti-HIV-1 activity and decreased α-helicity. The stability of six-helix bundle formed by C34 and N36 with A67 mutations was significantly lower than that formed by C34 and N36 with wild-type sequence. The combination of C34 and T20 resulted in potent synergistic anti-HIV-1 effect against the viruses with mutations in either N- or C-terminal region in NHR. These results suggest that C34 with a pocket-binding domain and T20 containing the N-NHR- and membrane-binding domains inhibit HIV-1 fusion by interacting with different target sites and the combinatorial use of C34 and T20 is expected to be effective against HIV-1 variants resistant to HIV fusion inhibitors