Dynamic, viscoelasticity-driven shape change of elastomer bilayers

Thin bilayers made of elastic sheets with different strain recoveries can be used for dynamic shape morphing through ambient stimuli, such as temperature, mass diffusion, and light. As a fundamentally different approach to designing temporal shape change, constituent polymer molecular features (rather than external fields) are leveraged, specifically the viscoelasticity of gelatin bilayers, to achieve dynamic three-dimensional (3D) curls and helical twists. After stretching and releasing, the acquired 3D shape recovers its original flat shape on a timescale originating from the polymer viscoelasticity. The bilayer time-dependent curvature can be accurately predicted from hyperelastic and viscoelastic functions using finite element analysis (FEA). FEA reveals the nonlinear shape dynamics in space and time in quantitative agreement with experiments. The findings present a new frontier in dynamic biomimetic shape-morphing by exploiting intrinsic material properties in contrast with state-of-the-art methods relying on external field variations, moving one step closer to acquiring autonomous shape-shifting capabilities of biological systems.Comment: For SI, see https://drive.google.com/file/d/1MH0kURA_OiOaePDQC06Eua1aG3kkEBV4/view?usp=sharin

Spanning Trees on Lattices and Integration Identities

For a lattice $\Lambda$ with $n$ vertices and dimension $d$ equal or higher than two, the number of spanning trees $N_{ST}(\Lambda)$ grows asymptotically as $\exp(n z_\Lambda)$ in the thermodynamic limit. We present exact integral expressions for the asymptotic growth constant $z_\Lambda$ for spanning trees on several lattices. By taking different unit cells in the calculation, many integration identities can be obtained. We also give $z_{\Lambda (p)}$ on the homeomorphic expansion of $k$-regular lattices with $p$ vertices inserted on each edge.Comment: 15 pages, 3 figures, 1 tabl

A multiscale theory for spreading and migration of adhesion-reinforced mesenchymal cells

<p>We present a chemomechanical whole-cell theory for the spreading and migration dynamics of mesenchymal cells that can actively reinforce their adhesion to an underlying viscoelastic substrate as a function of its stiffness. Our multiscale model couples the adhesion reinforcement effect at the subcellular scale with the nonlinear mechanics of the nucleus-cytoskeletal network complex at the cellular scale to explain the concurrent monotonic area-stiffness and non-monotonic speed-stiffness relationships observed in experiments: We consider that large cell spreading on stiff substrates flattens the nucleus, increasing the viscous drag force on it. The resulting force balance dictates a reduction in the migration speed on stiff substrates. We also reproduce the experimental influence of the substrate viscosity on the cell spreading area and migration speed by elucidating how the viscosity may either maintain adhesion reinforcement or prevent it depending on the substrate stiffness. Additionally, our model captures the experimental directed migration behavior of the adhesion-reinforced cells along a stiffness gradient, known as durotaxis, as well as up or down a viscosity gradient (viscotaxis or anti-viscotaxis), the cell moving towards an optimal viscosity in either case. Overall, our theory explains the intertwined mechanics of the cell spreading, migration speed and direction in the presence of the molecular adhesion reinforcement mechanism. </p&gt

A multiscale theory for spreading and migration of adhesion-reinforced mesenchymal cells

<p>We present a chemomechanical whole-cell theory for the spreading and migration dynamics of mesenchymal cells that can actively reinforce their adhesion to an underlying viscoelastic substrate as a function of its stiffness. Our multiscale model couples the adhesion reinforcement effect at the subcellular scale with the nonlinear mechanics of the nucleus-cytoskeletal network complex at the cellular scale to explain the concurrent monotonic area-stiffness and non-monotonic speed-stiffness relationships observed in experiments: We consider that large cell spreading on stiff substrates flattens the nucleus, increasing the viscous drag force on it. The resulting force balance dictates a reduction in the migration speed on stiff substrates. We also reproduce the experimental influence of the substrate viscosity on the cell spreading area and migration speed by elucidating how the viscosity may either maintain adhesion reinforcement or prevent it depending on the substrate stiffness. Additionally, our model captures the experimental directed migration behavior of the adhesion-reinforced cells along a stiffness gradient, known as durotaxis, as well as up or down a viscosity gradient (viscotaxis or anti-viscotaxis), the cell moving towards an optimal viscosity in either case. Overall, our theory explains the intertwined mechanics of the cell spreading, migration speed and direction in the presence of the molecular adhesion reinforcement mechanism. </p&gt

Dynamic, Viscoelasticity-Driven Shape Change of Elastomer Bilayers

Thin bilayers made of elastic sheets with different strain recoveries can be used for dynamic shape morphing through ambient stimuli such as temperature, mass diffusion, and light. As a fundamentally different approach to designing temporal shape change, constituent polymer molecular features (rather than external fields) are leveraged, specifically the viscoelasticity of gelatin bilayers, to achieve dynamic three-dimensional (3D) curls and helical twists with curvatures as high as 1.25 cm–1 when the strain difference between the layers is 0.45 cm/cm. After stretching and releasing, the acquired 3D shape recovers its original flat shape on a time scale originating from the polymer viscoelasticity. The recovery time is found to be dependent on formulation and applied strain such that the recovery times at an applied strain of 1 cm/cm are about 2 and 10 s when there is more and less water plasticizer, respectively. The bilayer-time-dependent curvature can be accurately predicted from hyperelastic and viscoelastic functions using finite element analysis (FEA). FEA reveals the nonlinear shape dynamics in space and time, in quantitative agreement with experiments. The bilayers exploit intrinsic material properties in contrast with state-of-the-art methods relying on external field variations, moving one step closer to acquiring the autonomous shape-shifting capabilities of biological systems for building engineered devices

Dynamic, Viscoelasticity-Driven Shape Change of Elastomer Bilayers

Thin bilayers made of elastic sheets with different strain recoveries can be used for dynamic shape morphing through ambient stimuli such as temperature, mass diffusion, and light. As a fundamentally different approach to designing temporal shape change, constituent polymer molecular features (rather than external fields) are leveraged, specifically the viscoelasticity of gelatin bilayers, to achieve dynamic three-dimensional (3D) curls and helical twists with curvatures as high as 1.25 cm–1 when the strain difference between the layers is 0.45 cm/cm. After stretching and releasing, the acquired 3D shape recovers its original flat shape on a time scale originating from the polymer viscoelasticity. The recovery time is found to be dependent on formulation and applied strain such that the recovery times at an applied strain of 1 cm/cm are about 2 and 10 s when there is more and less water plasticizer, respectively. The bilayer-time-dependent curvature can be accurately predicted from hyperelastic and viscoelastic functions using finite element analysis (FEA). FEA reveals the nonlinear shape dynamics in space and time, in quantitative agreement with experiments. The bilayers exploit intrinsic material properties in contrast with state-of-the-art methods relying on external field variations, moving one step closer to acquiring the autonomous shape-shifting capabilities of biological systems for building engineered devices

Dynamic, Viscoelasticity-Driven Shape Change of Elastomer Bilayers

Thin bilayers made of elastic sheets with different strain recoveries can be used for dynamic shape morphing through ambient stimuli such as temperature, mass diffusion, and light. As a fundamentally different approach to designing temporal shape change, constituent polymer molecular features (rather than external fields) are leveraged, specifically the viscoelasticity of gelatin bilayers, to achieve dynamic three-dimensional (3D) curls and helical twists with curvatures as high as 1.25 cm–1 when the strain difference between the layers is 0.45 cm/cm. After stretching and releasing, the acquired 3D shape recovers its original flat shape on a time scale originating from the polymer viscoelasticity. The recovery time is found to be dependent on formulation and applied strain such that the recovery times at an applied strain of 1 cm/cm are about 2 and 10 s when there is more and less water plasticizer, respectively. The bilayer-time-dependent curvature can be accurately predicted from hyperelastic and viscoelastic functions using finite element analysis (FEA). FEA reveals the nonlinear shape dynamics in space and time, in quantitative agreement with experiments. The bilayers exploit intrinsic material properties in contrast with state-of-the-art methods relying on external field variations, moving one step closer to acquiring the autonomous shape-shifting capabilities of biological systems for building engineered devices

Lamellation Fractures in the Paleogene Continental Shale Oil Reservoirs in the Qianjiang Depression, Jianghan Basin, China

Based on the data of cores, thin sections, well logs, and test experiments, the characteristics and main controlling factors of lamellation fractures in continental shales of the third and fourth members of the Paleogene Qianjiang Formation in the Qianjiang Depression, Jianghan Basin, are studied. Lamellation fractures mainly develop along laminas in shales. They have various morphological characteristics such as straightness, bending, discontinuity, bifurcation, pinching out, and merging. Lamellation fractures with high density show poor horizontal continuity and connectivity characteristics. The average linear density of the lamellation fractures is mainly between 20 m-1 and 110 m-1, and the aperture is usually less than 160 μm. The density of lamellation fractures is related to their apertures. The smaller the apertures of lamellation fractures are, the higher the density is. The development degree of lamellation fractures is mainly controlled by mineral composition, type, thickness, density of lamination, contents of organic matter and pyrite, lithofacies, structural position, etc. Lamellation fractures develop well, especially under the conditions of medium dolomite content, large lamination density, small lamination thickness, and high total organic carbon (TOC) and pyrite contents. The influences of lithofacies on the lamellation fractures are complex. The lamellation fractures are most developed in carbonaceous layered limestone dolomite and carbonaceous layered dolomite mudstone, followed by stromatolite dolomite filled with carbonaceous pyroxene. The fractures in the massive argillaceous dolomites and carbonaceous massive mudstones are poorly developed. No fractures can be found in the carbonaceous dolomitic, argillaceous glauberites or salt rocks with high glauberite content. Structure is also an important factor controlling lamination fractures. Tectonic uplifts are beneficial to the expansion and extension of lamellation fractures, which increases fracture density. Therefore, when other influence factors are similar, lamellation fractures develop better in the high part of the structure than in the low part

Analysis of the MSI PCR products by QIAxcel and GeneScan methods.

Analysis of the MSI PCR products by QIAxcel and GeneScan methods.</p