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1. Mechanochemical induction of wrinkling morphogenesis on elastic shells

   https://doi.org/10.1039/D1SM00003A  

   Zakharov, Andrei; Dasbiswas, Kinjal (May 2021, Soft Matter)

   Morphogenetic dynamics of tissue sheets require coordinated cell shape changes regulated by global patterning of mechanical forces. Inspired by such biological phenomena, we propose a minimal mechanochemical model based on the notion that cell shape changes are induced by diffusible biomolecules that influence tissue contractility in a concentration-dependent manner – and whose concentration is in turn affected by the macroscopic tissue shape. We perform computational simulations of thin shell elastic dynamics to reveal propagating chemical and three-dimensional deformation patterns arising due to a sequence of buckling instabilities. Depending on the concentration threshold that actuates cell shape change, we find qualitatively different patterns. The mechanochemically coupled patterning dynamics are distinct from those driven by purely mechanical or purely chemical factors, and emerge even without diffusion. Using numerical simulations and theoretical arguments, we analyze the elastic instabilities that result from our model and provide simple scaling laws to identify wrinkling morphologies. 

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2. Electron-positronium scattering and Ps ^- photodetachment

   https://doi.org/10.1088/1361-6455/adbfe9  

   Mitchell, William; Ward_Quintanilla, Sandra (March 2025, Journal of Physics B: Atomic, Molecular and Optical Physics)

   Abstract We investigate the fundamental three-body Coulomb process of elastic electron-positronium (e^--Ps) scattering below the Ps(n = 2) threshold. Using the complex Kohn variational method and trial wave functions that contain highly correlated Hylleraas-type terms, we accurately compute^1,3S-,^1,3P-, and^1,3D-wave phase shifts, which may be considered as benchmark results. We explicitly investigate the effect of the mixed symmetry term in the short-range part of the^1,3D-wave trial wave function on the phase shifts and resonances. Using the complex Kohn phase shifts we compute, for e⁻-Ps scattering, the elastic differential, elastic integrated, momentum-transfer, and ortho-para conversion cross sections and determine the importance of the complex Kohn D-wave phase shifts on these cross sections. In addition, using the short-range part of the¹S-wave trial wave function for the bound state of the purely leptonic ion of Ps⁻, and the complex Kohn¹P trial wave function for the continuum state, we determine the Ps⁻photodetachment cross section in the length, velocity, and acceleration forms. 

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3. Phonon stability boundary and deep elastic strain engineering of lattice thermal conductivity

   https://doi.org/10.1073/pnas.2313840121  

   Shi, Zhe; Tsymbalov, Evgenii; Shi, Wencong; Barr, Ariel; Li, Qingjie; Li, Jiangxu; Chen, Xing-Qiu; Dao, Ming; Suresh, Subra; Li, Ju (February 2024, Proceedings of the National Academy of Sciences)

   Recent studies have reported the experimental discovery that nanoscale specimens of even a natural material, such as diamond, can be deformed elastically to as much as 10% tensile elastic strain at room temperature without the onset of permanent damage or fracture. Computational work combining ab initio calculations and machine learning (ML) algorithms has further demonstrated that the bandgap of diamond can be altered significantly purely by reversible elastic straining. These findings open up unprecedented possibilities for designing materials and devices with extreme physical properties and performance characteristics for a variety of technological applications. However, a general scientific framework to guide the design of engineering materials through such elastic strain engineering (ESE) has not yet been developed. By combining first-principles calculations with ML, we present here a general approach to map out the entire phonon stability boundary in six-dimensional strain space, which can guide the ESE of a material without phase transitions. We focus on ESE of vibrational properties, including harmonic phonon dispersions, nonlinear phonon scattering, and thermal conductivity. While the framework presented here can be applied to any material, we show as an example demonstration that the room-temperature lattice thermal conductivity of diamond can be increased by more than 100% or reduced by more than 95% purely by ESE, without triggering phonon instabilities. Such a framework opens the door for tailoring of thermal-barrier, thermoelectric, and electro-optical properties of materials and devices through the purposeful design of homogeneous or inhomogeneous strains. 

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4. Extracellular matrix viscoelasticity regulates TGFβ1‐induced epithelial‐mesenchymal transition and apoptosis via integrin linked kinase

   https://doi.org/10.1002/jcp.31165  

   Sacco, Jessica L.; Vaneman, Zachary T.; Gomez, Esther W. (December 2023, Journal of Cellular Physiology)

   Abstract Transforming growth factor (TGF)‐β1 is a multifunctional cytokine that plays important roles in health and disease. Previous studies have revealed that TGFβ1 activation, signaling, and downstream cell responses including epithelial‐mesenchymal transition (EMT) and apoptosis are regulated by the elasticity or stiffness of the extracellular matrix. However, tissues within the body are not purely elastic, rather they are viscoelastic. How matrix viscoelasticity impacts cell fate decisions downstream of TGFβ1 remains unknown. Here, we synthesized polyacrylamide hydrogels that mimic the viscoelastic properties of breast tumor tissue. We found that increasing matrix viscous dissipation reduces TGFβ1‐induced cell spreading, F‐actin stress fiber formation, and EMT‐associated gene expression changes, and promotes TGFβ1‐induced apoptosis in mammary epithelial cells. Furthermore, TGFβ1‐induced expression of integrin linked kinase (ILK) and colocalization of ILK with vinculin at cell adhesions is attenuated in mammary epithelial cells cultured on viscoelastic substrata in comparison to cells cultured on nearly elastic substrata. Overexpression of ILK promotes TGFβ1‐induced EMT and reduces apoptosis in cells cultured on viscoelastic substrata, suggesting that ILK plays an important role in regulating cell fate downstream of TGFβ1 in response to matrix viscoelasticity. 

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5. Wetting and wrapping of a floating droplet by a thin elastic filament

   https://doi.org/10.1039/D0SM01863E  

   Prasath, S Ganga; Marthelot, Joel; Menon, Narayanan; Govindarajan, Rama (February 2021, Soft Matter)

   null (Ed.)

   We study the wetting of a thin elastic filament floating on a fluid surface by a droplet of another, immiscible fluid. This quasi-2D experimental system is the lower-dimensional counterpart of the wetting and wrapping of a droplet by an elastic sheet. The simplicity of this system allows us to study the phenomenology of partial wetting and wrapping of the droplet by measuring angles of contact as a function of the elasticity of the filament, the applied tension and the curvature of the droplet. We find that a purely geometric theory gives a good description of the mechanical equilibria in the system. The estimates of applied tension and tension in the filament obey an elastic version of the Young–Laplace–Dupré relation. However, curvatures close to the contact line are not captured by the geometric theory, possibly because of 3D effects at the contact line. We also find that when a highly-bendable filament completely wraps the droplet, there is continuity of curvature at the droplet-filament interface, leading to seamless wrapping as observed in a 3D droplet. 

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