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Breast cancer becomes invasive when carcinoma cells invade through the basement membrane (BM)-a nanoporous layer of matrix that physically separates the primary tumour from the stroma. Single cells can invade through nanoporous three-dimensional matrices due to protease-mediated degradation or force-mediated widening of pores via invadopodial protrusions. However, how multiple cells collectively invade through the physiological BM, as they do during breast cancer progression, remains unclear. Here we developed a three-dimensional in vitro model of collective invasion of the BM during breast cancer. We show that cells utilize both proteases and forces-but not invadopodia-to breach the BM. Forces are generated from a combination of global cell volume expansion, which stretches the BM, and local contractile forces that act in the plane of the BM to breach it, allowing invasion. These results uncover a mechanism by which cells collectively interact to overcome a critical barrier to metastasis.
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Direct initiation of secondary explosives by a semiconductor laser is highly demanded, but it is challenging to exclude the use of sensitive primers. Most laser-sensitive energetic materials are usually mechanically sensitive. In order to reduce the mechanical sensitivity (MS) of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) while improving laser absorbance in the near-infrared band, spherical CL-20 composites (SCCs) embedded with nano aluminum (Al) powder and graphene-based catalyst (GO-CHZ-Co) were prepared by a spray drying method. These SCCs have been characterized comprehensively in terms of their morphologies, particle size distribution, laser absorbance, thermal decomposition behaviors, MS, and laser ignition properties. Results show that the maximum critical impact energy of SCCs was 3.8 J, which is 2.8 J higher than that of pristine ε-CL-20. The critical friction load was increased by at most 108 N compared to pristine CL-20. The absorbance has also been significantly increased up to almost 70% in the wavelength between 400 and 1400 nm, where the peak absorption is located in the region of 800-900 nm. In addition, the initial decomposition temperature (Ti) of SCCs is lower than that of pure CL-20, especially in the presence of GO-CHZ-Co. The apparent activation energy (Ea) for the decomposition of SCCs was largely dependent on the particle size of Al. Preliminary ignition tests indicate that the SCCs can be ignited successfully by a small-power laser.
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We have discovered a peculiar form of fracture that occurs in polymer network formed by covalent adaptable bonds. Due to the dynamic feature of the bonds, fracture of this network is rate dependent, and the crack propagates in a highly nonsteady manner. These phenomena cannot be explained by the existing fracture theories, most of which are based on steady-state assumption. To explain these peculiar characteristics, we first revisit the fundamental difference between the transient network and the covalent network in which we highlighted the transient feature of the cracks. We extend the current fracture criterion for crack initiation to a time-evolution scheme that allows one to track the nonsteady propagation of a crack. Through a combined experimental modeling effort, we show that fracture in transient networks is governed by two parameters: the Weissenberg number [Formula: see text] that defines the history path of crack-driving force and an extension parameter Z that tells how far a crack can grow. We further use our understanding to explain the peculiar experimental observation. To further leverage on this understanding, we show that one can "program" a specimen's crack extension dynamics by tuning the loading history.
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Bioinspired architectural design for composites with much higher fracture resistance than that of individual constituent remains a major challenge for engineers and scientists. Inspired by the survival war between the mantis shrimps and abalones, we design a discontinuous fibrous Bouligand (DFB) architecture, a combination of Bouligand and nacreous staggered structures. Systematic bending experiments for 3D-printed single-edge notched specimens with such architecture indicate that total energy dissipations are insensitive to initial crack orientations and show optimized values at critical pitch angles. Fracture mechanics analyses demonstrate that the hybrid toughening mechanisms of crack twisting and crack bridging mode arising from DFB architecture enable excellent fracture resistance with crack orientation insensitivity. The compromise in competition of energy dissipations between crack twisting and crack bridging is identified as the origin of maximum fracture energy at a critical pitch angle. We further illustrate that the optimized fracture energy can be achieved by tuning fracture energy of crack bridging, pitch angles, fiber lengths, and twist angles distribution in DFB composites.
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Nonpenetrating traumatic brain injuries (TBIs) are linked to cavitation. The structural organization of the brain makes it particularly susceptible to tears and fractures from these cavitation events, but limitations in existing characterization methods make it difficult to understand the relationship between fracture and cavitation in this tissue. More broadly, fracture energy is an important, yet often overlooked, mechanical property of all soft tissues. We combined needle-induced cavitation with hydraulic fracture models to induce and quantify fracture in intact brains at precise locations. We report here the first measurements of the fracture energy of intact brain tissue that range from 1.5 to 8.9 J/m2, depending on the location in the brain and the model applied. We observed that fracture consistently occurs along interfaces between regions of brain tissue. These fractures along interfaces allow cavitation-related damage to propagate several millimeters away from the initial injury site. Quantifying the forces necessary to fracture brain and other soft tissues is critical for understanding how impact and blast waves damage tissue in vivo and has implications for the design of protective gear and tissue engineering.
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Lesões Encefálicas Traumáticas , Encéfalo , Explosões , Humanos , Fenômenos FísicosRESUMO
We investigate the rate-dependent fracture of vitrimers by conducting a tear test. Based on the relationship between the fracture energy and the thickness of vitrimer films, we, for the first time, obtain the intrinsic fracture energy and bulk dissipation of vitrimers during crack extension. The intrinsic fracture energy strongly depends on tear speed, and such dependence can be well explained by Eyring theory. In contrast, the bulk dissipation only weakly depends on tear speed, which is drastically different from observations on traditional viscoelastic polymers. We ascribe such a weak rate-dependence to the strong force-sensitivity of the exchange reaction of the dynamic covalent bond in the vitrimer.
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The majority of 3D-printed biodegradable biomaterials are brittle, limiting their potential application to compliant tissues. Poly (glycerol sebacate) acrylate (PGSA) is a synthetic biodegradable and biocompatible elastomer, compatible with light-based 3D printing. In this work we employed digital-light-processing (DLP)-based 3D printing to create a complex PGSA network structure. Nature-inspired double network (DN) structures with two geometrically interconnected segments with different mechanical properties were printed from the same material in a single shot. Such capability has not been demonstrated by any other fabrication technique. The biocompatibility of PGSA after 3D printing was confirmed via cell-viability analysis. We used a finite element analysis (FEA) model to predict the failure of the DN structure under uniaxial tension. FEA confirmed the soft segments act as sacrificial elements while the hard segments retain structural integrity. The simulation demonstrated that the DN design absorbs 100% more energy before rupture than the network structure made by single exposure condition (SN), doubling the toughness of the overall structure. Using the FEA-informed design, a new DN structure was printed and the FEA predicted tensile test results agreed with tensile testing of the printed structure. This work demonstrated how geometrically-optimized material design can be easily and rapidly achieved by using DLP-based 3D printing, where well-defined patterns of different stiffnesses can be simultaneously formed using the same elastic biomaterial, and overall mechanical properties can be specifically optimized for different biomedical applications.
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In order to explore the salt-stress responses of two rice varieties, the physiological responses and biochemical responses were investigated using proteomics and classical biochemical methods. The results showed that the seedling growth was inhibited under salt condition in two rice varieties, the seedling growth in the tolerant variety was better than the sensitive variety. The sensitive variety(L7) appeared obvious salt-injury under 3-day salt stress, the tolerant variety (T07339) keep normal growth under 7-day salt stress except that the shoot length was decreased. Through the growth-parameters analysis, most of them in L7 were restrained by salinity and most in T07339 were unaffected. In T07339, the fresh root weight, the content of chlorophyll and the fresh shoot weight were even increased after 7 days of salt stress. A comparison of two-dimensional gel electrophoresis (2-DGE) protein profiles revealed 8 differently expressed proteins. Four proteins were expressed in different pattern between sensitive and tolerant varieties. These results provide novel insights into the investigations of the salt-response proteins that involved in improved salt tolerance.
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The fracture behaviors of disulfide vitrimers are highly rate-dependent. Our investigation revealed that the temperature-dependent fracture behaviors of disulfide vitrimers cannot be entirely explained by a simple time-temperature superposition model. This Letter explores the impact of the dynamic nature of molecular defects on the temperature- and rate-dependent fracture behaviors of disulfide vitrimers. Considering that the high cross-linking density remains constant during the associated bond exchange reaction, we identify loop defects in the network as the primary dynamic defects. By employing small amplitude oscillatory shear, we measured the loop defect fraction in EPS25 disulfide vitrimers at varied temperatures, revealing an increased presence of loop defects at elevated temperatures. Furthermore, our findings indicate that the temperature-dependent fracture behaviors are attributed to the temperature-dependent number of loop defects in disulfide vitrimers.
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Compounding functional nanoparticles with highly conductive and porous carbon scaffolds is a basic pathway for engineering many important functional devices. However, enabling uniform spatial distribution of functional particles within a massively conjugated, monolithic and mesoporous structure remains challenging, as the high processing temperature for graphitization can arouse nanoparticle ripening, agglomerations and compositional changes. Herein, we report a unique "popcorn-making-mimic" strategy for preparing a highly conjugated and uniformly compounded graphene@NiFe2O4 composite film through a laser-assisted instantaneous compounding method in ambient condition. It can successfully inhibit the unwanted structural disintegration and mass loss during the laser treatment by avoiding oxidation, bursting, and inhomogeneous heat accumulations, thus achieving a highly integrated composite structure with superior electrical conductivity and high saturated magnetization. Such a single-sided film exhibits an absolute shielding effectiveness of up to 20906 dB cm2 g-1 with 75% absorption rate, superior mechanical flexibility and excellent temperature/humidity aging reliability. These performance indexes signify a substantial advance in EMI absorption capability, fabrication universality, small form-factor and device reliability toward commercial applications. Our method provides a paradigm for fabricating sophisticated composite materials for versatile applications.
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Small brown planthopper (SBPH) and rice stripe virus (RSV) disease transmitted by SBPH cause serious damage to rice (Oryza sativa L.) in China. In the present study, we screened 312 rice accessions for resistance to SBPH. The indica variety, N22, is highly resistant to SBPH. One hundred and eighty two recombinant inbred lines (RILs) derived from a cross of N22 and the highly susceptible variety, USSR5, were used for quantitative trait locus (QTL) analysis of resistances to SBPH and RSV. In a modified seedbox screening test, three QTLs for SBPH resistance, qSBPH2, qSBPH3 and qSBPH7.1, were mapped on chromosomes 2, 3 and 7, a total explaining 35.1% of the phenotypic variance. qSBPH7.2 and qSBPH11.2, conferring antibiosis against SBPH, were detected on chromosomes 7 and 11 and accounted for 20.7% of the total phenotypic variance. In addition, qSBPH5 and qSBPH7.3, expressing antixenosis to SBPH, were detected on chromosomes 5 and 7, explaining 23.9% of the phenotypic variance. qSBPH7.1, qSBPH7.2 and qSBPH7.3, located in the same region between RM234 and RM429 on chromosome 7, using three different phenotyping methods indicate that the locus or region plays a major role in conferring resistance to SBPH in N22. Moreover, three QTLs, qSTV4, qSTV11.1 and qSTV11.2, for RSV resistance were detected on chromosomes 4 and 11. qSTV11.1 and qSTV11.2 are located in the same region between RM287 and RM209 on chromosome 11. Molecular markers spanning these QTLs should be useful in the development of varieties with resistance to SBPH and RSV.
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Hemípteros/patogenicidade , Oryza/genética , Doenças das Plantas/genética , Tenuivirus/patogenicidade , Animais , China , Mapeamento Cromossômico , Cromossomos de Plantas/genética , Genes de Plantas , Oryza/parasitologia , Oryza/virologia , Doenças das Plantas/parasitologia , Doenças das Plantas/virologia , Locos de Características QuantitativasRESUMO
Liquid crystal elastomer (LCE) is a newly emerging soft actuating material that has been extensively explored for building novel soft robots and diverse active devices, thanks to its large actuation stress and strain, high work density, and versatile actuation modes. However, there have also been several widely recognized limitations of LCE-based actuators for practical applications, including slow response and narrow range of operation temperature. Herein, we develop fluid-driven disulfide LCE actuators through facile laminate manufacturing enabled by a dynamic bond exchange reaction. Because of the merits of the active heating/cooling mechanism of the fluidic structure, this newly developed disulfide LCE actuator can generate large cyclic actuation at a frequency around 1 Hz and can operate in a wide range of temperatures. The unique combination of the fluidic structure design and the dynamic covalent bonds in the elastomer has also enabled the full recyclability and self-repairability of the actuator. Using the newly developed actuator as building block, we further constructed soft robotic systems that can realize manipulating and programmable movement. The design principle demonstrated in the current work opens a promising avenue for exploring more novel applications of LCE-based soft actuators.
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Twisted or oscillated plywood structure can be often found in biological composites such as claws of lobsters, bone of mammals, dactyl club of mantis shrimps, and exoskeleton of beetles, which exhibits a combination of high stiffness, high fracture toughness and low density. However, there lacks a quantitative understanding of the relationship between the fracture toughness of the composite and its internal geometry. In this article, we propose that a combination of crack tilting and crack bridging determines the effective fracture toughness of the fiber-reinforced composite with the plywood structure. During the fracturing process, a crack plane initially propagates in the matrix-fiber interface following the twisted fiber alignment. Such crack tilting mechanism can significantly enlarge the area of cracking surface and thus enhance the effective fracture toughness of the composite. With the propagation of the tilted crack plane, the local energy release rate becomes too small to maintain the growth of the tilted crack plane, leading the crack to grow into the matrix, crossing the fibers. Because of the high strength of the fiber, a few fibers can maintain unbroken behind the crack tip, corresponding to crack bridging mechanism. Based on our quantitative analysis, it is found that the effective fracture toughness of the composite can be maximized for a certain pitch angle of the oscillated/twisted plywood structure, which agrees well with experiments. STATEMENTS OF SIGNIFICANCE: Fiber-reinforced composites can be widely found in nature and engineering applications. Recently, it has been discovered that many fiber-reinforced composites in biology have twisted or oscillated plywood structure with high fracture toughness, high mechanical stiffness and low density. Detailed experiments have indicated that an optimal pitch angle may exist for the plywood structure to maximize the fracture toughness of the composites. However, there lacks a quantitative model of revealing such pitch angle-dependent fracture toughness. In this work, we propose a hybrid toughening mechanism and predict the optimal pitch angle in twisted/oscillated plywood structure for maximizing the fracture toughness. Our predictions agree reasonably well with experimental results. As such, the theory may help the design of better fiber-reinforced composites.
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Teste de Materiais , Estresse Mecânico , MadeiraRESUMO
Exploration of graphene-based artificial nacres with excellent mechanical properties demonstrates the potential to surpass natural nacre. Recent experimental studies report that optimal crosslink density defined as concentration of the surface functional groups is usually observed in these artificial nacres towards superb mechanical performance. A hybrid model integrating a nonlinear shear-lag model and atomistic simulations reveals the emergence of an optimal crosslink density at which the maximum strength and toughness are achieved. The origin is due to the balance among the reduction of in-plane tensile properties of the graphene sheets, the enhancement of the shear strength of the interlayer and the reduction of interface plasticity. In addition, our results also reveal that the size insensitivity of the graphene sheet appears when the shear stress of the interlayer is highly localized, the increase of the crosslink density intensifies the nonuniformity of the shear stress and the optimal mechanical properties of the artificial nacre cannot be further enhanced by tuning the size of the graphene sheets. Three kinds of interface molecular interactions with their optimal crosslink densities are also proposed to simultaneously maximize the strength and toughness of graphene-based artificial nacres.
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Various methods have been exploited to replicate nacre features into artificial structural materials with impressive structural and mechanical similarity. However, it is still very challenging to produce nacre-mimetics in three-dimensional bulk form, especially for further scale-up. Herein, we demonstrate that large-sized, three-dimensional bulk artificial nacre with comprehensive mimicry of the hierarchical structures and the toughening mechanisms of natural nacre can be facilely fabricated via a bottom-up assembly process based on laminating pre-fabricated two-dimensional nacre-mimetic films. By optimizing the hierarchical architecture from molecular level to macroscopic level, the mechanical performance of the artificial nacre is superior to that of natural nacre and many engineering materials. This bottom-up strategy has no size restriction or fundamental barrier for further scale-up, and can be easily extended to other material systems, opening an avenue for mass production of high-performance bulk nacre-mimetic structural materials in an efficient and cost-effective way for practical applications.Artificial materials that replicate the mechanical properties of nacre represent important structural materials, but are difficult to produce in bulk. Here, the authors exploit the bottom-up assembly of 2D nacre-mimetic films to fabricate 3D bulk artificial nacre with an optimized architecture and excellent mechanical properties.