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Research

We aim to advance the state of pulmonary healthcare through investigation of fundamental lung biomechanics. By utilizing Theory, Simulation, and Experiments to understand how tissue structure governs function, the bMECH lab ultimately strives to enable clinical translation through predictive modeling, surgical optimization, and medical diagnostics.

Interests:

  • Multi-scale computational and experimental approaches integrating organ-tissue-microstructure mechanics
  • Associative breathing forces and lung tissue deformation characterization
  • Comparative bronchial network stress distribution states of healthy, asthmatic, bronchitis, and cystic fibrosis lungs
  • Image-based airway geometry to construct lung motion during breathing cycle
  • Fluid-structure interaction models informed by tissue properties geared towards optimizing ventilation pressures
  • Surgical planning of lung ablation based on pre-and post pulmonary pressure-volume function analysis
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Establishing the First Organ-Level Digital Image Correlation of the Lung to Link Local to Global Biomechanics

 

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We collect the first non-contact, full-field deformation measures of ex vivo porcine and murine lungs and interface with our unique pressure-volume ventilation system to investigate lung behavior in real time. We share preliminary observations of heterogeneous and anisotropic strain distributions of the parenchymal surface, associative pressure-volume-strain loading dependencies during continuous loading, and consider the influence of inflation rate and maximum volume. This study serves as a crucial basis for future works to comprehensively characterize the regional response of the lung across various species, link local strains to global lung mechanics, examine the effect of breathing frequencies and volumes, investigate deformation gradients and evolutionary behaviors during breathing, and contrast healthy and pathological states. 

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Custom-Designed Volume-Pressure Machine for Novel Whole Lung Organ Measurements

 

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Asthma, emphysema, COVID-19 and other lung-impacting diseases cause the remodeling of tissue structural properties and can lead to changes in conducting pulmonary volume, viscoelasticity, and air flow distribution. Whole organ experimental inflation tests are commonly used to understand the impact of these modifications on lung mechanics. Here we introduce a novel, automated, custom-designed device for measuring the volume and pressure response of lungs, surpassing the capabilities of traditional machines and built to range size-scales to accommodate murine, porcine, and human lung tests. 

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Energy Efficiency and Temporal Dependencies

 

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This work is the first to characterize proximal and distal bronchial energy efficiency and contextualize tissue biochemical composition in view of experimental measures and viscoelastic trends. Anisotropic and heterogeneous effects on preconditioning and hysteresis are substantial, linking to energy dissipation expectancies. Stress relaxation is rheologically modeled using several classical configurations of discrete spring and dashpot elements; among them, Standard Linear Solid (SLS) and Maxwell-Weichart exhibit better fit performance. Enhanced fractional order derivative SLS (FSLS) model is also evaluated through use of a hybrid spring-pot of order α. FSLS outperforms the conventional models, demonstrating superior representation of the stress-relaxation curve's initial value and non-linear asymptotic decent. FSLS parameters exhibit notable orientation- and region-specific values, trending with observed tissue structural constituents, such as glycosaminoglycan and collagen. Results provide a foundation for future investigations, particularly for understanding the role of viscoelasticity in diseased states. 

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Constitutive Modeling

 

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Breathing involves fluid-solid interactions in the lung; however, the lack of experimental data inhibits combining the mechanics of air flow to airway deformation, making it difficult to understand how biomaterial constituents contribute to tissue response. This work formulates a structurally-motivated constitutive model, augmented with biochemical analysis and microstructural observations, to investigate the mechanical function of proximal and distal bronchi. Our systematic pulmonary tissue characterization provides a necessary foundation for understanding pulmonary mechanics; furthermore, these results enable clinical translation through simulations of airway obstruction in disease, fluid-structure interaction insights during breathing, and potentially, predictive capabilities for medical interventions.

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Experimental Insights

Understanding the mechanics of the lung is necessary for investigating disease progression. Trachea mechanics comprises the vast majority of ex vivo airway tissue characterization despite distal airways being the site of disease manifestation and occlusion. Furthermore, viscoelastic studies are scarce, whereas time-dependent behaviors could be potential physiological metrics of tissue remodeling. In this study, experimentally measured material properties of airways are reported, exploring bronchial tree anisotropic and heterogeneous behaviors.

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Physiological Patient-Specific Geometries

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Airflow obstruction has not been investigated in real airway geometries; the behavior of imperfect, non-cylindrical, continuously branching airways remains unknown. We model the effects of chronic lung disease using the nonlinear field theories of mechanics supplemented by the theory of finite growth. We perform finite element analysis of patient-specific Y-branch segments created from magnetic resonance images, finding inherent geometric imperfections cause obstruction sensitivity compared to previous idealized circular models

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Mechanics of Growth

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In contrast to inert systems, living biological systems have the advantage to adapt to their environment through growth and evolution. The need to characterize the growth of biological systems to better understand these phenomena has motivated the continuum theory of growth and stimulated the development of computational tools in systems biology. We demonstrate the potential for morphoelastic simulations through examples of volume, area, and length growth, inspired by tumor expansion, chronic bronchitis, brain development, intestine formation, plant shape, and myopia. Biology of living systems in light of biochemical and optical stimuli are reviewed and different types of growth to facilitate the design of growth models for various biological systems are classified within this framework.

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Material Evolution

 

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Living structures can undergo morphological changes in response to growth and alterations in microstructural properties in response to remodeling. Prior studies assume constant microstructural form during remodeling; yet, clinical studies now reveal progressive airway elastosis, the degeneration of elastic fibers associated with a gradual stiffening of the inner layer. Evolving material stiffnesses provoke post-bifurcation failure modes with multiple co-existing wavelengths, associated with the superposition of larger folds evolving on top of the initial smaller folds. This phenomenon is exclusive to material stiffening and conceptually different from the phenomenon of period doubling observed in constant-stiffness growth. The underlying concept highlighted by elastosis is broadly applicable to other types of remodeling including aneurysm formation or brain folding.

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The Role of Branching

 

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The geometry of the bronchial tree plays a crucial role in chronic airway obstruction and critical failure conditions vary significantly along a branching airway segment. Simulations find smaller airways are at a higher risk of narrowing than larger airways and that regions away from a branch narrow more drastically than regions close to a branch. These results agree with clinical observations and could help explain the underlying mechanisms of progressive airway obstruction. Growth-induced instabilities in constrained geometries has immediate biomedical applications beyond asthma and chronic bronchitis in the diagnostics and treatment of chronic gastritis, obstructive sleep apnea and breast cancer.

 

 

 

Engineering Education Highlights:

Challenge Me, Disagree with Me: Why Gendered Perceptions to Student Stories of Motivation Enhance Creative Approaches in Engineering

Best Research Paper Award: Provoked Emotion in Student Stories of Motivation Reveal Gendered Perceptions of What It Means to be Innovative in Engineering

O-CDIO: Emphasizing Design Thinking in CDIO Engineering Cycle*

Best Teaching Strategies Award: Open Process for Entrepreneuring Team Collaboration 

STEM program builds ties between Stanford and East Palo Alto middle school

Tell/Make/Engage: Design Methods Course Introduces Storytelling Based Learning

Conversational Storytelling: Classroom Teaching through Story Parallels Entrepreneurial Need for Engagement

Prof. Eskandari co-established I-Cubed: Inspectors, Inquirers, Inventors as Project Manager. I-Cubed was an educational startup in the Bay Area promoting interest in STEM (Science, Technology, Engineering, Math) through hands-on, student-centered learning. As an inclusive organization we strived to increase diversity in STEM fields by recruiting students who are traditionally underrepresented in STEM fields with regard to race, socioeconomic status, and/or gender.