Chemo-mechanical Model Research Articles

PD-L1 Acts Independently of PD-1 as a Marker of Pathologic Fibroblasts in Laryngotracheal Stenosis.

Laryngotracheal stenosis (LTS) describes fibrotic airway obstruction that is life-threatening without treatment. Targeted therapies are needed as an adjunct to surgical management. We have previously observed the upregulation of immune checkpoint programmed cell death (PD)-1 and its ligand, PD-L1, in patients with LTS. This study aims to determine whether PD-1 and PD-L1 play a role in the pathophysiology of LTS. Basic science. Laboratory. Fibroblasts derived from the subglottic scar of 5 iSGS patients were cultured ex vivo with transforming growth factor β (TGFβ), PD-L1 agonist (PD-1), and PD-L1 blockade (anti-PD-L1). PD-L1, TGFβ receptor II (TGFβRII), and Collagen-1 expression were quantified by flow cytometry. A validated chemomechanical injury model of subglottic stenosis was applied in PD-1 knockout and wild-type (WT) mice, and subglottic thickening was assessed by histologic analysis. TGFβ significantly increased the expression of PD-L1 and Collagen-1 in human airway scar fibroblasts (P < .05). PD-1 knockout mice demonstrated no significant difference in subglottic airway fibrosis compared to WT mice. Ex vivo PD-L1 modulation had no impact on fibroblast Collagen-1 expression. PD-L1 high-intensity fibroblasts expressed greater Collagen-1 and TGFβRII compared to PD-L1 low-intensity fibroblasts. PD-1 knockout does not protect mice from the development of laryngotracheal fibrosis. However, its ligand, PD-L1 is highly expressed on pathologic fibroblasts unique to scar, characterized by high Collagen-1 and TGFβRII expression. PD-L1 is also upregulated in conjunction with Collagen-1 by TGFβ stimulation. PD-L1 may act independently of PD-1 to sensitize fibroblasts to TGFβ, suggesting direct targeting of PD-L1 may have therapeutic potential in LTS.

A chemo-mechanical model for growth and mechanosensing of focal adhesion

Focal adhesion (FA), the complex molecular assembly across the lipid membrane, serves as a hub for physical and chemical information exchange between cells and their microenvironment. Interestingly, studies have shown that FAs can grow along the direction of contractile forces generated by actomyosin stress fibers and achieve larger sizes on stiffer substrates. In addition, the cellular traction transmitted to the substrate was observed to reach the maximum near the FA center. However, the biomechanical mechanisms behind these intriguing findings remain unclear. To answer this important question, here we first developed a one-dimensional (1D) chemo-mechanical model of FA where key features like adhesion plaque deformation, active contraction by stress fibers, force-dependent association/dissociation of integrin bonds connecting two surfaces, and substrate compliance have all been considered. Within this formulation, we showed that the rigidity-sensing capability of FAs originates from the deformability of stress fibers while the force-dependent breakage of integrin bonds leads to the appearance of the traction peak at the FA center. Furthermore, by extending the model into three-dimensional as well as incorporating assembly/dis-assembly kinetics of adhesion proteins, we also demonstrated how anisotropic stress/strain field within the adhesion plaque will be induced by the presence of contractile forces which leads to the directional growth of the FA.

Role of grain-level chemo-mechanics in composite cathode degradation of solid-state lithium batteries

Solid-state Li-ion batteries, based on Ni-rich oxide cathodes and Li-metal anodes, can theoretically reach a high specific energy of 393 Wh kg−1 and hold promise for electrochemical storage. However, Li intercalation-induced dimensional changes can lead to crystal defect formation in these cathodes, and contact mechanics problems between cathode and solid electrolyte. Understanding the interplay between cathode microstructure, operating conditions, micromechanics of battery materials, and capacity decay remains a challenge. Here, we present a microstructure-sensitive chemo-mechanical model to study the impact of grain-level chemo-mechanics on the degradation of composite cathodes. We reveal that crystalline anisotropy, state-of-charge-dependent Li diffusion rates, and lattice dimension changes drive dislocation formation in cathodes and contact loss at the cathode/electrolyte interface. These dislocations induce large lattice strain and trigger oxygen loss and structural degradation preferentially near the surface area of cathode particles. Moreover, contact loss is caused by the micromechanics resulting from the crystalline anisotropy of cathodes and the mechanical properties of solid electrolytes, not just operating conditions. These findings highlight the significance of grain-level cathode microstructures in causing cracking, formation of crystal defects, and chemo-mechanical degradation of solid-state batteries.

The importance of a full chemo-poro-mechanical coupling for the modeling of subcutaneous injections

Modeling of subcutaneous injections in soft adipose tissue – a common way to administer pharmaceutical medication – is a challenging multiphysics problem which has recently attracted the attention of the engineering community, as it could help optimize medical devices and treatments. The underlying continuum mechanics of this process is complex and involves finite strain poro-mechanics – where a viscous fluid, containing different charged species, is injected into a porous viscoelastic matrix and absorbed by blood and lymph vessels – as well as electrochemistry, that generates osmotic pressure due to electrical charges attached to the tissue. In this paper, we present a chemo-mechanical model of subcutaneous injections that accounts for the diffusion of electrically charged chemical species – contained in the interstitial fluid – into the tissue, blood and lymph vessels. This work provides the methodology to derive a general theory accounting for the electro-chemo-poro-mechanical couplings in a thermodynamically consistent framework, avoiding phenomenological biases or inconsistencies likely to arise in the derivation of nonlinear theories with many couplings. To motivate its use for the modeling of subcutaneous injections, it is complemented by a simplified, linearized boundary value problem that illustrates the importance of considering these couplings for the prediction of subcutaneous injections key performance indicators.

Salt Crystallization in Limestone: Materials Decay and Chemomechanical Approach.

Salt crystallization is a particularly relevant issue in the conservation of limestones used in Cultural Heritage sites. In this study, various facies of limestones were characterized through porosimetric and mechanical tests. The samples were subjected to experiments to determine their resistance to salt crystallization by verifying the number of cycles at which 50% of them began to lose weight. This number of experimental cycles was compared with the result calculated by the analytical procedure of a chemomechanical model found in the literature. The comparison showed a significant capability of the model to predict the experimental data.

(Invited) Using a Chemo-Mechanical Model to Investigate Electrolyte Infiltration and Surface Reconstruction within Cracked Cathode Material

One of the main goals in modeling lithium-ion batteries is to improve/predict longevity and resilience of new chemistries. To that end, this talk investigates the formation of stress-induced fracture within polycrystalline cathode particles and the impact on capacity loss. The model captures anisotropic Li diffusion within a single polycrystalline particle comprised of hundreds to thousands of randomly oriented grains. Fracture is primarily due to non-ideal grain interactions with slight dependence on high-rate charge demands. Essentially, when neighboring grains are misaligned, they expand a different rates relative to one another leading to high stresses and ultimately the formation of intraparticle cracks. A previous study showed that small particle with large or single grain geometry tend to crack less and retain the most capacity.Cracks within the cathode particle that have access to the surface can potentially fill with electrolyte. When this happens, the cracks can be considered new active surface area where the lithium intercalation reaction can occur. Under sufficient conditions, this could lead to better performance because the grains of the cracked particle start to operate more like a network of single-grain particles. However, the newly open surface area is also subject to side reactions and surface reconstruction resulting in diminished transport properties and potentially trapped lithium. The goal of this talk is to investigate this balance between improved lithium transport pathways caused by lithium infiltration and the reduced diffusion due to surface reconstruction.

Transient Chemo-Mechanical Model of Lithium Plating Impacted by External Pressure

To meet the ever-growing need for high capacity, fast-charge batteries, lithium anodes have been considered a direct upgrade to previous commercial anode materials thanks to their high gravimetric density and low coulombic efficiency. However, their implementation into crucial applications such as electric vehicles has been hindered by safety issues during and at the end of their operational lifetime. Over hundreds of cycles, nonhomogeneous plating and stripping of lithium on the anode surface encourages the growth of dendrites, which eventually lead to capacity loss, cell failure, and fire. The application of stack pressure has been found to mitigate dendrite growth to an extent; however, the impacts of long-term pressure application on lithium deposition, and subsequent lithium plastic deformation and creep, are not well understood. In this work, we present a novel method for accurately modeling the interplay between mechanical deformation and electrochemical deposition. We develop a 3D, finite-element, transient model of lithium plating and stripping at the mesoscale. A stack pressure is applied to a lithium anode in contact with a polymer separator, and the electrochemical response to an applied current density is evaluated. The lithium protrusion is then reshaped to model incremental plating or stripping, thus simulating the cumulative interfacial movement over a full charge-discharge cycle. Mechanical complexities of the materials, such as lithium plastic deformation and separator porosity, are accounted for. The interfacial response is studied with respect to applied stack pressure and assumed lithium yield strength. Through this work, the impacts of stack pressure on dendrite growth at the microscale are explored. The lithium yield strength assumption is found to be crucial for accurately predicting deposition behavior.Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Designing Stable Nanoparticles for Deforming Silicon Anodes in Lithium Ion Batteries

Silicon anodes in lithium-ion batteries are a promising next-generation battery technology offering ten times higher theoretical capacity than commercial graphite anodes. However, substantial volume changes (around 300%) associated with silicon anodes pose a significant challenge to the cycle life of these batteries. To understand the effect of the interaction between lithiation (diffusion) and mechanics (volume expansion, stress generation) on cycle life, a theoretical chemo-mechanical model of an isolated deforming silicon anode nanospherical particle is proposed in this study. Existing models, designed for low-capacity electrode materials, ignore the effect of deforming volume in the model formulation. Deforming volume, critical for high-capacity electrodes like silicon, is accounted for in the proposed model. Galvanostatic and potentiostatic operating conditions are considered. Simulations of the model help explain the importance of smaller particle sizes in observed longer cycle lives of silicon anodes. These enable mathematically accurate calibration of the partial molar volume of the material and determination of the developed mechanical stresses. Simulations of the proposed model help us optimize design parameters like particle size, particle thickness, and the charge rate/ applied voltage for elastic operation to ensure longer cycle lives of these batteries. Figure 1

A variational model for finger-driven cell diffusion in the extracellular matrix

We present a simple chemo-mechanical variational model for a fibrous material that describes (i) the emergence of the anisotropy due to microscopic buckling instabilities (ii) a diffusion in the substrate of the cell phase driven by the new created macroscopic bands characterized by intense compressive deformation. The model is applicable for simulating the spreading of cells within tissues and their interaction with tissue remodeling during mesenchymal migration.

A chemo-mechanical constitutive model for muscle activation in bat wing skins.

Birds, bats and insects have evolved unique wing structures to achieve a wide range of flight capabilities. Insects have relatively stiff and passive wings, birds have a complex and hierarchical feathered structure and bats have an articulated skeletal system integrated with a highly stretchable skin. The compliant skin of the wing distinguishes bats from all other flying animals and contributes to bats' remarkable, highly manoeuvrable flight performance and high energetic efficiency. The structural and functional complexity of the bat wing skin is one of the least understood although important elements of the bat flight anatomy. The wing skin has two unusual features: a discrete array of very soft elastin fibres and a discrete array of skeletal muscle fibres. The latter is intriguing because skeletal muscle is typically attached to bone, so the arrangement of intramembranous muscle in soft skin raises questions about its role in flight. In this paper, we develop a multi-scale chemo-mechanical constitutive model for bat wing skin. The chemo-mechanical model links cross-bridge cycling to a structure-based continuum model that describes the active viscoelastic behaviour of the soft anisotropic skin tissue. Continuum models at the tissue length-scale are valuable as they are easily implemented in commercial finite element codes to solve problems involving complex geometries, loading and boundary conditions. The constitutive model presented in this paper will be used in detailed finite element simulations to improve our understanding of the mechanics of bat flight in the context of wing kinematics and aerodynamic performance.

An Efficient FEniCS implementation for coupling lithium-ion battery charge/discharge processes with fatigue phase-field fracture

Accurately predicting the fatigue failure of lithium-ion battery electrode particles during charge–discharge cycles is essential for enhancing their structural reliability and lifespan. The fatigue failure of lithium-ion battery electrode particles during charge–discharge cycles poses a significant challenge in maintaining structural reliability and lifespan. To address this critical issue, this study presents a mathematical formulation for fatigue failure in lithium-ion batteries, utilizing the phase-field approach to fracture modeling. This approach, widely employed for fracture failure analysis, offers a comprehensive framework for capturing the complex interplay between mechanical deformation, chemical lithium concentration, and crack formation. Specifically, an additive decomposition of the strain tensor is employed to account for the swelling and shrinkage effects induced by lithium diffusion. Moreover, open-source code (https://github.com/noiiG) is provided, constituting a convenient platform for future developments, e.g., multi-field coupled problems. The developed chemo-mechanical model undergoes fatigue failure package is written in FEniCS as a popular free open-source computing platform for solving partial differential equations in which simplifies the implementation of parallel FEM simulations. Several numerical simulations with two different case studies corresponding to monotonic charge process and fatigue charge/discharge process are performed to demonstrate the correctness of our algorithmic developments.

Coupled modeling of thermal-fluid-solid and chemo-mechanical behaviors in thermal barrier coatings under flowing gas environment

This study proposes a modeling approach to simulate the thermo-chemo-mechanical responses of thermal barrier coatings (TBCs) exposed to flowing high-temperature gas. A thermal-fluid-solid analysis was performed to simulate temperature fields of the coatings under flowing gas environment, while finite element analysis was carried out to study the oxidation and stress evolutions of the coatings using a developed chemo-mechanical constitutive model. Thermal loads from thermal-fluid-solid analysis were imposed on the finite element model, by which the factors associated with flowing gas were incorporated into the thermo-chemo-mechanical modeling. The study systematically investigated the effects of flowing gas and coolant on the chemo-mechanical responses of the coatings. The results revealed that the enhanced gas factors (temperature, velocity, angle of attack, and pressure) and coolant temperatures accelerate oxidation and induce higher residual stresses, while higher coolant velocity mitigates both oxidation and stresses. The volume fraction of oxygen in the gas was found to have a negligible influence. Dimensional analysis and multiple regression were performed to derive mathematical expressions for assessing out-of-plane stress and oxidation dynamics. Design maps were proposed to guide the durable design of the coatings.

Simulation of fuel cell membrane durability under vehicle operation

In this work, a statistical fuel cell chemo-mechanical membrane degradation model is developed based on the ionomer fibrillar morphology as a framework for use-level membrane durability prediction for fuel cell electric vehicles. The mechanical and chemical degradation modes are separately calibrated with pressure differential-accelerated mechanical stress tests and accelerated membrane durability tests, respectively. Finite element simulations are used to estimate the initial stress distribution across the membrane, while the genetic algorithm with the least squares method is employed to calibrate the model parameters with experimental results, thus reaching a good agreement. Next, the validated model is utilized for a case study of fuel cell electric transit bus operation in the city of Victoria, B.C., Canada. The initial cell voltage profile is obtained using a dynamic fuel cell power system model applied to the transit bus drive cycle recorded during real-world operation. According to the model predictions, reducing the stack nominal power from 396 to 132 kW results in a 148% membrane lifetime enhancement, whereas decreasing the cell temperature from 90 to 70°C results in an 11-fold increase in the membrane lifetime under simulated transit bus operation, thereby exceeding the 25,000-h lifetime target for this application.

Modeling and FE simulation of coupled water diffusion and viscoelasticity in relaxation tests of polyamide 6

Polyamides can absorb or desorb water from or to their surrounding environment. The impact of this process is significant as water molecules lead locally to a swelling and a coupling of diffusion and deformation behavior. To model these phenomena, a strongly coupled chemo-mechanical (or diffuso-mechanical) model is required, considering both local water concentration and the viscoelastic material behavior of polyamide. In the present work, we derive and apply such a model to polyamide 6. A diffusion equation describing changes in water concentration is coupled to the balance of linear momentum in polyamide 6. The interaction between deformation and concentration is derived from thermodynamic considerations by introducing a free energy consisting of a mechanical and a chemical part. The mechanical part describes a linear viscoelastic model and includes chemical strains due to the presence of water molecules. The chemical part builds upon the theory of Flory and Huggins, that takes into account changes in enthalpy and entropy of mixing due to the interaction of polymer and water molecules. The coupling of deformation to water concentration arises due to a dependency of the water flux on the hydrostatic stress inside the polyamide. We successfully apply the derived model in Finite-Element simulations to predict the drying of polyamide 6 specimens without any coupling to mechanical loads. In addition, we reproduce experimentally obtained data from relaxation measurements, where the drying of polyamide specimens leads to an increase in relaxation modulus.

The interplay between membrane viscosity and ligand-binding receptor kinetics in lipid bilayers

Plasma membranes appear as deformable systems wherein molecules are free to move and diffuse giving rise to condensed microdomains (composed of ordered lipids, transmembrane proteins and cholesterol) surrounded by disordered lipid molecules. Such denser and thicker regions, namely lipid rafts, are important communication hubs for cells. Indeed, recent experiments revealed how the most of active signaling proteins co-localize on such domains, thereby intensifying the biochemical trafficking of substances. From a material standpoint, it is reasonable to assume the bilayer as a visco-elastic body accounting for both in-plane fluidity and elasticity. Consequently, lipid rafts contribute to membrane heterogeneity by typically exhibiting higher stiffness and viscosity and by locally altering the bilayer dynamics and proteins activity. A chemo-mechanical model of lipid bilayer coupled with interspecific dynamics among the resident species (typically transmembrane receptors and trasporters) has been recently formulated to explain and predict how proteins regulate the dynamic heterogeneity of membrane. However, the explicit inclusion of the membrane viscosity in the model was not considered. To this aim, the present work enriches the constitutive description of the bilayer by modeling its visco-elastic behavior. This is done through a strain-level dependent viscosity able to theoretically trace back the alteration of membrane fluidity experimentally observed in lipid phase transitions. This provides new insights into how the quasi-solid and fluid components of lipid membrane response interact with the evolution of resident proteins by affecting the activity of raft domains, with effects on cell mechano-signaling.

Phenomenological modelling of cycling-induced damage in the metal-ion battery electrode

This work addresses a pivotal challenge in metal-ion batteries, namely the structural degradation and damage of electrodes, which profoundly impacts the operational performance and overall longevity of metal-ion batteries. A chemo-mechanical model is introduced, including the interaction between the degradation/damage induced by chemical reaction and the damage-dependent mechanical stress/strain during electrochemical cycling. A visco-plastic constitutive relationship is developed that explicitly considers the effects of both the mechanical and chemical damages. The contributions of the mechanical and chemical damages are incorporated in the model, employing scalar damage variables to depict the damage states. We numerically analyze the dynamic evolution of stress, plastic strain, and damages throughout multiple lithiation and de-lithiation cycles and illustrate the effects of electrochemical cycling on surface damage and stress distribution. The experimental results support the developed model, with the numerical results closely matching the experimental results for the retaining of the capacity of a graphite-based lithium-ion half-cell. The numerical results reveal the importance of the damage parameters in describing the evolution of the structural damage in electrodes during electrochemical cycling. This study enriches our understanding of the structural damage in electrodes during electrochemical cycling and has great potential to improve the design of metal-ion batteries.

The role of chemo-mechanical modelling in the development of battery technology—a perspective

In the race to reduce global CO2 emissions and achieve net-zero, chemomechanics must play a critical role in the technological development of current and next-generation batteries to improve their energy storage capabilities and their lifetime. Many degradation processes arise through mechanics via the development of diffusion-induced stress and volumetric strains within the various constituent materials in a battery. From particle cracking in lithium-ion batteries to lithium dendrite-based fracture of solid electrolytes in solid-state batteries, it is clear that significant barriers exist in the development of these energy storage systems, where chemomechanics plays a central part. To accelerate technological and scientific advances in this area, multi-scale and highly coupled multiphysics modelling must be carried out that includes mechanics-based phenomena. In this perspective article, we provide an introduction to chemomechanical modelling, the various physical problems that it addresses, and the issues that need to be resolved in order to expand its use within the field of battery technology.

A chemo-mechanical model for describing sorption hysteresis in a glassy polyurethane

Hysteretic sorption and desorption of water is observed from 0 to 95% relative humidity and 298–333 K on a glassy polyurethane foam. It is postulated that sorption-induced swelling of the glassy polyurethane increases the concentration of accessible hydrogen-bonding adsorption sites for water. The accessibility of sites is kinetically controlled due to the restricted thermal motions of chains in the glassy polymer, causing a difference in accessible site concentrations during sorption and desorption. This discrepancy leads to hysteresis in the sorbed concentrations of water. A coupled chemo-mechanical model relating volumetric strain, adsorption site concentration, and sorbed water concentration is employed to describe water sorption hysteresis in the glassy polyurethane. This model not only describes the final mass uptake for each relative humidity step, but also captures the dynamics of water uptake, which exhibit diffusion and relaxation rate-controlled regimes.

Multiscale Simulation of the Coupled Chemo-Mechanical Behavior of Porous Electrode Materials by Direct FE2 Method

Application of porous electrode materials has sparked significant interest as a strategy to mitigate traditional electrode mechanical failure arising from its intercalation-induced large volume change. In this work, a thermal analogy method is employed for implementing the coupled chemo-mechanical model into the finite element (FE) package ABAQUS via user subroutines UMATHT and UMAT, which is used to model the lithium (Li) diffusion and the resulting deformation of the electrode during charge-discharge cycling. This work presents a Direct FE2 method for modeling the chemo-mechanically coupled behavior of porous electrode materials by establishing the macro-microscopic scale transitions through concentration and displacement DOFs and the representative volume element (RVE) volume scaling relationship. The two-scale numerical simulations can be implemented in a single computational scheme. Within the present computational framework, the Li diffusion and mechanical deformation in the porous silicon electrode during charging and discharging are easily simulated in the typical FE package. Benchmarked against the traditional direct full-field numerical computational method, the Direct FE2 method is validated to present significant computational efficiency improvements through two numerical examples, the constrained expansion and the pre-compression expansion of porous electrode, by 99.27% and 94.55%, respectively, while maintaining the high precision.

Stress evolution in enamel coating/Ni-based alloy systems during isothermal oxidation

This paper utilizes a coupled chemomechanical model that integrates chemical reactions, diffusion, and mechanical deformation to describe the high-temperature interfacial reactions and stress evolution within an enamel coating/Ni-based super-alloy system. Through finite element simulation, we conduct a comprehensive analysis of multiple reactions and processes at the interface. Experimental characterization of the concentration distribution of various elements is employed to verify the accuracy of the proposed chemomechanical model. Additionally, the simulation reveals that the interface region experiences compressive circumferential stress, which can potentially lead to interfacial failure due to buckling. On the other hand, the enamel coating undergoes tensile circumferential stress, resulting in the formation of vertical surface cracks. These findings hold practical implications for the development of advanced coatings with enhanced durability and performance. Future research can further optimize coating design and enhance the reliability of high-temperature applications based on these results.