Tensegrity I. Cell structure and hierarchical systems biology

When Stiffness Matters: Mechanosensing in Heart Development and Disease

During embryonic morphogenesis, the heart undergoes a complex series of cellular phenotypic maturations (e.g., transition of myocytes from proliferative to quiescent or maturation of the contractile apparatus), and this involves stiffening of the extracellular matrix (ECM) acting in concert with morphogenetic signals. The maladaptive remodeling of the myocardium, one of the processes involved in determination of heart failure, also involves mechanical cues, with a progressive stiffening of the tissue that produces cellular mechanical damage, inflammation, and ultimately myocardial fibrosis. The assessment of the biomechanical dependence of the molecular machinery (in myocardial and non-myocardial cells) is therefore essential to contextualize the maturation of the cardiac tissue at early stages and understand its pathologic evolution in aging. Because systems to perform multiscale modeling of cellular and tissue mechanics have been developed, it appears particularly novel to design integrated mechano-molecular models of heart development and disease to be tested in ex vivo reconstituted cells/tissue-mimicking conditions. In the present contribution, we will discuss the latest implication of mechanosensing in heart development and pathology, describe the most recent models of cell/tissue mechanics, and delineate novel strategies to target the consequences of heart failure with personalized approaches based on tissue engineering and induced pluripotent stem cell (iPSC) technologies.

Mechanotransduction in Wound Healing and Fibrosis

Skin injury is a common occurrence and mechanical forces are known to significantly impact the biological processes of skin regeneration and wound healing. Immediately following the disruption of the skin, the process of wound healing begins, bringing together numerous cell types to collaborate in several sequential phases. These cells produce a multitude of molecules and initiate multiple signaling pathways that are associated with skin disorders and abnormal wound healing, including hypertrophic scars, keloids, and chronic wounds. Studies have shown that mechanical forces can alter the microenvironment of a healing wound, causing changes in cellular function, motility, and signaling. A better understanding of the mechanobiology of cells in the skin is essential in the development of efficacious therapeutics to reduce skin disorders, normalize abnormal wound healing, and minimize scar formation.

Identifying microbial life in rocks: Insights from population morphometry

The identification of cellular life in the rock record is problematic, since microbial life forms, and particularly bacteria, lack sufficient morphologic complexity to be effectively distinguished from certain abiogenic features in rocks. Examples include organic pore-fillings, hydrocarbon-containing fluid inclusions, organic coatings on exfoliated crystals and biomimetic mineral aggregates (biomorphs). This has led to the interpretation and re-interpretation of individual microstructures in the rock record. The morphologic description of entire populations of microstructures, however, may provide support for distinguishing between preserved micro-organisms and abiogenic objects. Here, we present a statistical approach based on quantitative morphological description of populations of microstructures. Images of modern microbial populations were compared to images of two relevant types of abiogenic microstructures: interstitial spaces and silica-carbonate biomorphs. For the populations of these three systems, the size, circularity, and solidity of individual particles were calculated. Subsequently, the mean/SD, skewness, and kurtosis of the statistical distributions of these parameters were established. This allowed the qualitative and quantitative comparison of distributions in these three systems. In addition, the fractal dimension and lacunarity of the populations were determined. In total, 11 parameters, independent of absolute size or shape, were used to characterize each population of microstructures. Using discriminant analysis with parameter subsets, it was found that size and shape distributions are typically sufficient to discriminate populations of biologic and abiogenic microstructures. Analysis of ancient, yet unambiguously biologic, samples (1.0 Ga Angmaat Formation, Baffin Island, Canada) suggests that taphonomic effects can alter morphometric characteristics and complicate image analysis; therefore, a wider range of microfossil assemblages should be studied in the future before automated analyses can be developed. In general, however, it is clear from our results that there is great potential for morphometric descriptions of populations in the context of life recognition in rocks, either on Earth or on extraterrestrial bodies.

Structural Elements of the Biomechanical System of Soft Tissue

In living organisms, forces are constantly generated and transmitted throughout tissue. Such forces are generated through interaction with the environment and as a result of the body’s endogenous movement. If these internally or externally originating forces exceed the ability of tissues to cope with the applied forces, (i.e. “tissue thresholds”), they will cause force-related tissue harm. However, biotensegrity systems act to prevent these forces from causing structural damage to cells and tissues. The mechanism and structure of soft tissues that enable them to maintain their integrity and prevent damage under constantly changing forces is still not fully understood. The current anatomical and physical knowledge is insufficient to assess and predict how, why, where, and when to expect force-related tissue harm.

When including the concept of tensegrity and the related principles of the hierarchical organisation of the elements of the subcellular tensional homeostatic structure into current biomechanical concepts, it increases our understanding of the events in force handling in relation to the onset of force-related tissue harm: Reducing incident forces in tissue to a level that is not harmful to the involved structures is achieved by dissipation, transduction and transferring the force in multiple dimensions. To enable this, the biomechanical systems must function in a continuous and consistent way from the cellular level to the entire body to prevent local peak forces from causing harm. In this article, we explore the biomechanical system with a focus on biotensegrity concepts across several organisational levels, describing in detail how it may function and reflecting on how this might be applied to patient management.

The Mechanical Role of Microtubules in Tissue Remodeling

During morphogenesis, tissues undergo extensive remodeling to get their final shape. Such precise sculpting requires the application of forces generated within cells by the cytoskeleton and transmission of these forces through adhesion molecules within and between neighboring cells. Within individual cells, microtubules together with actomyosin filaments and intermediate filaments form the composite cytoskeleton that controls cell mechanics during tissue rearrangements. While studies have established the importance of actin-based mechanical forces that are coupled via intercellular junctions, relatively little is known about the contribution of other cytoskeletal components such as microtubules to cell mechanics during morphogenesis. In this review the focus is on recent findings, highlighting the direct mechanical role of microtubules beyond its well-established role in trafficking and signaling during tissue formation.

The Plot Thickens: The Emerging Role of Matrix Viscosity in Cell Mechanotransduction

Cell mechanotransduction is an area of intense research focus. Until now, very limited tools have existed to study how cells respond to changes in the extracellular matrix beyond, for example, mechanical deformation studies and twisting cytometry. However, emerging are a range of elastic, viscoelastic and even purely viscous materials that deform and dissipate on cellular length and timescales. This article reviews developments in these materials, typically translating from 2D model surfaces to 3D microenvironments and explores how cells interact with them. Specifically, it focuses on emerging concepts such as the molecular clutch model, how different extracellular matrix proteins engage the clutch under viscoelastic-stress relaxation conditions, and how mechanotransduction can drive transcriptional control through regulators such as YAP/TAZ.

Hypergravity Activates a Pro-Angiogenic Homeostatic Response by Human Capillary Endothelial Cells

Capillary endothelial cells are responsible for homeostatic responses to organismic and environmental stimulations. When malfunctioning, they may cause disease. Exposure to microgravity is known to have negative effects on astronauts’ physiology, the endothelium being a particularly sensitive organ. Microgravity-related dysfunctions are striking similar to the consequences of sedentary life, bed rest, and ageing on Earth. Among different countermeasures implemented to minimize the effects of microgravity, a promising one is artificial gravity. We examined the effects of hypergravity on human microvascular endothelial cells of dermal capillary origin (HMEC-1) treated at 4 g for 15 min, and at 20 g for 15 min, 3 and 6 h. We evaluated cell morphology, gene expression and 2D motility and function. We found a profound rearrangement of the cytoskeleton network, dose-dependent increase of Focal Adhesion kinase (FAK) phosphorylation and Yes-associated protein 1 (YAP1) expression, suggesting cell stiffening and increased proneness to motility. Transcriptome analysis showed expression changes of genes associated with cardiovascular homeostasis, nitric oxide production, angiogenesis, and inflammation. Hypergravity-treated cells also showed significantly improved motility and function (2D migration and tube formation). These results, expanding our knowledge about the homeostatic response of capillary endothelial cells, show that adaptation to hypergravity has opposite effect compared to microgravity on the same cell type.

Sensing and Modelling Mechanical Response in Large Deformation Indentation of Adherent Cell Using Atomic Force Microscopy

The mechanical behaviour of adherent cells when subjected to the local indentation can be modelled via various approaches. Specifically, the tensegrity structure has been widely used in describing the organization of discrete intracellular cytoskeletal components, including microtubules (MTs) and microfilaments. The establishment of a tensegrity model for adherent cells has generally been done empirically, without a mathematically demonstrated methodology. In this study, a rotationally symmetric prism-shaped tensegrity structure is introduced, and it forms the basis of the proposed multi-level tensegrity model. The modelling approach utilizes the force density method to mathematically assure self-equilibrium. The proposed multi-level tensegrity model was developed by densely distributing the fundamental tensegrity structure in the intracellular space. In order to characterize the mechanical behaviour of the adherent cell during the atomic force microscopy (AFM) indentation with large deformation, an integrated model coupling the multi-level tensegrity model with a hyperelastic model was also established and applied. The coefficient of determination between the computational force-distance (F-D) curve and the experimental F-D curve was found to be at 0.977 in the integrated model on average. In the simulation range, along with the increase in the overall deformation, the local stiffness contributed by the cytoskeletal components decreased from 75% to 45%, while the contribution from the hyperelastic components increased correspondingly.

The hydromechanics in arteriogenesis

Coronary heart diseases are tightly associated with aging. Although current revascularization therapies, such as percutaneous coronary interventions (PCI) and coronary artery bypass graft (CABG), improve the clinical outcomes of patients with coronary diseases, their application and therapeutic effects are limited in elderly patients. Thus, developing novel therapeutic strategies, like prompting collateral development or the process of arteriogenesis, is necessary for the treatment of the elderly with coronary diseases. Arteriogenesis (ie, the vascular remodeling from pre‐existent arterioles to collateral conductance networks) functions as an essential compensation for tissue hypoperfusion caused by artery occlusion or stenosis, and its mechanisms remain to be elucidated. In this review, we will summarize the roles of the major hydromechanical components in laminar conditions in arteriogenesis, and discuss the potential effects of disturbed flow components in non‐laminar conditions.

Closed-Form Solutions for the Form-Finding of Regular Tensegrity Structures by Group Elements

An analytical form-finding method for regular tensegrity structures based on the concept of force density is presented. The self-equilibrated state can be deduced linearly in terms of force densities, and then we apply eigenvalue decomposition to the force density matrix to calculate its eigenvalues. The eigenvalues are enforced to satisfy the non-degeneracy condition to fulfill the self-equilibrium condition. So the relationship between force densities can also be obtained, which is followed by the super-stability examination. The method has been developed to deal with planar tensegrity structure, prismatic tensegrity structure (triangular prism, quadrangular prism, and pentagonal prism) and star-shaped tensegrity structure by group elements to get closed-form solutions in terms of force densities, which satisfies the super stable conditions.

Intracellular Restructured Reduced Glutathione-Responsive Peptide Nanofibers for Synergetic Tumor Chemotherapy

Self-assembled peptide nanofibers have been widely studied in cancer nanotherapeutics with their excellent biocompatibility and low toxicity of degradation products, showing the significant potential in inhibiting tumor progression. However, poor solubility prevents direct intravenous administration of nanofibers. Although water-soluble peptide precursors have been formed via the method of phosphorylation for intravenous administration, their opportunities for broad in vivo application are limited by the weak capacity of encapsulating drugs. Herein, we designed a novel restructured reduced glutathione (GSH)-responsive drug delivery system encapsulating doxorubicin for systemic administration, which achieved the intracellular restructuration from three-dimensional micelles into one-dimensional nanofibers. After a long blood circulation, micelles endocytosed by tumor cells could degrade in response to high GSH levels, achieving more release and accumulation of doxorubicin at desired sites. Further, the synergistic chemotherapy effects of self-assembled nanofibers were confirmed in both in vitro and in vivo experiments.

On-chip surface acoustic wave and micropipette aspiration techniques to assess cell elastic properties

The cytoskeletal mechanics and cell mechanical properties play an important role in cellular behaviors. In this study, in order to provide comprehensive insights into the relationship between different cytoskeletal components and cellular elastic moduli, we built a phase-modulated surface acoustic wave microfluidic device to measure cellular compressibility and a microfluidic micropipette-aspiration device to measure cellular Young's modulus. The microfluidic devices were validated based on experimental data and computational simulations. The contributions of structural cytoskeletal actin filament and microtubule to cellular compressibility and Young's modulus were examined in MCF-7 cells. The compressibility of MCF-7 cells was increased after microtubule disruption, whereas actin disruption had no effect. In contrast, Young's modulus of MCF-7 cells was reduced after actin disruption but unaffected by microtubule disruption. The actin filaments and microtubules were stained to confirm the structural alteration in cytoskeleton. Our findings suggest the dissimilarity in the structural roles of actin filaments and microtubules in terms of cellular compressibility and Young's modulus. Based on the differences in location and structure, actin filaments mainly contribute to tensile Young's modulus and microtubules mainly contribute to compressibility. In addition, different responses to cytoskeletal alterations between acoustophoresis and micropipette aspiration demonstrated that micropipette aspiration was better at detecting the change from actin cortex, while the response to acoustophoresis was governed by microtubule networks.

Discovery and design of soft polymeric bio-inspired materials with multiscale simulations and artificial intelligence

Establishing the “Materials 4.0” paradigm requires intimate knowledge of the virtual space in materials design.

Bodywide fluctuations support manual exploration: Fractal fluctuations in posture predict perception of heaviness and length via effortful touch by the hand

The human haptic perceptual system respects a bodywide organization that responds to local stimulation through full-bodied coordination of nested tensions and compressions across multiple nonoverlapping scales. Under such an organization, the suprapostural task of manually hefting objects to perceive their heaviness and length should depend on roots extending into the postural control for maintaining upright balance on the ground surface. Postural sway of the whole body should thus carry signatures predicting what the hand can extract by hefting an object. We found that fractal fluctuations in Euclidean displacement in the participants' center of pressure (CoP) contributed to perceptual judgments by moderating how the participants' hand picked up the informational variable of the moment of inertia. The role of fractality in CoP displacement in supporting heaviness and length judgments increased across trials, indicating that the participants progressively implicate their fractal scaling in their perception of heaviness and length. Traditionally, we had to measure fractality in hand movements to predict perceptual judgments by manual hefting. However, our findings suggest that we can observe what is happening at hand in the relatively distant-from-hand measure of CoP. Our findings reveal the complex relationship through which posture supports manual exploration, entailing perception of the intended properties of hefted objects (heaviness or length) putatively through the redistribution of forces throughout the body.

Insight into Mechanobiology: How Stem Cells Feel Mechanical Forces and Orchestrate Biological Functions

The cross-talk between stem cells and their microenvironment has been shown to have a direct impact on stem cells' decisions about proliferation, growth, migration, and differentiation. It is well known that stem cells, tissues, organs, and whole organisms change their internal architecture and composition in response to external physical stimuli, thanks to cells' ability to sense mechanical signals and elicit selected biological functions. Likewise, stem cells play an active role in governing the composition and the architecture of their microenvironment. Is now being documented that, thanks to this dynamic relationship, stemness identity and stem cell functions are maintained. In this work, we review the current knowledge in mechanobiology on stem cells. We start with the description of theoretical basis of mechanobiology, continue with the effects of mechanical cues on stem cells, development, pathology, and regenerative medicine, and emphasize the contribution in the field of the development of ex-vivo mechanobiology modelling and computational tools, which allow for evaluating the role of forces on stem cell biology.

Nucleoplasmin is a limiting component in the scaling of nuclear size with cytoplasmic volume

How is nuclear size regulated relative to cell size? Using microfluidic encapsulation of Xenopuslaevis embryo extracts, biochemical fractionation, and in vivo experiments, Chen et al. demonstrate that reductions in cytoplasmic volume and limiting components, including the histone chaperone nucleoplasmin, contribute to developmental nuclear size scaling.

How nuclear size is regulated relative to cell size is a fundamental cell biological question. Reductions in both cell and nuclear sizes during Xenopus laevis embryogenesis provide a robust scaling system to study mechanisms of nuclear size regulation. To test if the volume of embryonic cytoplasm is limiting for nuclear growth, we encapsulated gastrula-stage embryonic cytoplasm and nuclei in droplets of defined volume using microfluidics. Nuclei grew and reached new steady-state sizes as a function of cytoplasmic volume, supporting a limiting component mechanism of nuclear size control. Through biochemical fractionation, we identified the histone chaperone nucleoplasmin (Npm2) as a putative nuclear size effector. Cellular amounts of Npm2 decrease over development, and nuclear size was sensitive to Npm2 levels both in vitro and in vivo, affecting nuclear histone levels and chromatin organization. We propose that reductions in cell volume and the amounts of limiting components, such as Npm2, contribute to developmental nuclear size scaling.

The Effect of Matrix Stiffness of Biomimetic Gelatin Nanofibrous Scaffolds on Human Cardiac Pericyte Behavior

Congenital heart disease (CHD) is the most common and deadly congenital anomaly, accounting for up to 7.5% of all infant deaths. Survival in children born with CHD has improved dramatically over the past several decades (this positive trend being counterbalanced by the fact that more patients develop heart failure). Seminal data indicate an alteration of the extracellular matrix occurs with time in these hearts due to diffuse and abundant interstitial fibrosis. This results in an escalation in the stiffness of the local myocardial microenvironment. However, the influence of matrix stiffness in regulating the function of resident human stromal cells has not been reported. The objective of this study was to determine the impact of scaffold stiffness on the antigenic and functional profile of cardiac pericytes (CPs) isolated from patients with CHD. To this end, we have first manufactured gelatin nanofibrous scaffolds with varying degrees of stiffness using an in situ cross-linking electrospinning technique in a pure water solvent system. We assessed Young's modulus and performed a comprehensive physicochemical characterization of the scaffolds employing scanning electron microscopy and Fourier transform infrared spectroscopy. We next evaluated the changes induced by a different scaffold stiffness on CP morphology, antigenic profile, viability, proliferation, angiocrine activity, and induced differentiation. Results indicate that soft matrixes with a fiber diameter of ∼400 nm increase CP proliferation, secretion of angiopoietin 2, and F-actin stress fiber formation, without affecting the antigenic profile, viability, or differentiation. These data indicate for the first time that human CPs can be functionally influenced by slight changes in matrix stiffness. The study elucidates the importance of mechanical/morphological cues in modulating the behavior of stromal cells isolated from patients with CHD.

Designing stem cell niches for differentiation and self-renewal

Mesenchymal stem cells, characterized by their ability to differentiate into skeletal tissues and self-renew, hold great promise for both regenerative medicine and novel therapeutic discovery. However, their regenerative capacity is retained only when in contact with their specialized microenvironment, termed the stem cell niche Niches provide structural and functional cues that are both biochemical and biophysical, stem cells integrate this complex array of signals with intrinsic regulatory networks to meet physiological demands. Although, some of these regulatory mechanisms remain poorly understood or difficult to harness with traditional culture systems. Biomaterial strategies are being developed that aim to recapitulate stem cell niches, by engineering microenvironments with physiological-like niche properties that aim to elucidate stem cell-regulatory mechanisms, and to harness their regenerative capacity in vitro In the future, engineered niches will prove important tools for both regenerative medicine and therapeutic discoveries.

Viscoelasticity in natural tissues and engineered scaffolds for tissue reconstruction

Viscoelasticity of living tissues plays a critical role in tissue homeostasis and regeneration, and its implication in disease development and progression is being recognized recently. In this review, we first explored the state of knowledge regarding the potential application of tissue viscoelasticity in disease diagnosis. In order to better characterize viscoelasticity with local resolution and non-invasiveness, emerging characterization methods have been developed with the potential to be supplemented to existing facilities. To understand cellular responses to matrix viscoelastic behaviors in vitro, hydrogels made of natural polymers have been developed and the relationships between their molecular structure and viscoelastic behaviors, are elucidated. Moreover, how cells perceive the viscoelastic microenvironment and cellular responses including cell attachment, spreading, proliferation, differentiation and matrix production, have been discussed. Finally, some future perspective on an integrated mechanobiological comprehension of the viscoelastic behaviors involved in tissue homeostasis, cellular responses and biomaterial design are highlighted. STATEMENT OF SIGNIFICANCE: Tissue- or organ-scale viscoelastic behavior is critical for homeostasis, and the molecular basis and cellular responses of viscoelastic materials at micro- or nano-scale are being recognized recently. We summarized the potential applications of viscoelasticity in disease diagnosis enabled by emerging non-invasive characterization technologies, and discussed the underlying mechanism of viscoelasticity of hydrogels and current understandings of cell regulatory functions of them. With a growing understanding of the molecular basis of hydrogel viscoelasticity and recognition of its regulatory functions on cell behaviors, it is important to bring the clinical insights on how these characterization technologies and engineered materials may contribute to disease diagnosis and treatment. This review explains the basics in characterizing viscoelasticity with our hope to bridge the gap between basic research and clinical applications.

Cellular nanoscale stiffness patterns governed by intracellular forces

Cell stiffness measurements have led to insights into various physiological and pathological processes^1,2. Although many cellular behaviours are influenced by intracellular mechanical forces^3-6 that also alter the material properties of the cell, the precise mechanistic relationship between intracellular forces and cell stiffness remains unclear. Here we develop a cell mechanical imaging platform with high spatial resolution that reveals the existence of nanoscale stiffness patterns governed by intracellular forces. On the basis of these findings, we develop and validate a cellular mechanical model that quantitatively relates cell stiffness to intracellular forces. This allows us to determine the magnitude of tension within actin bundles, cell cortex and plasma membrane from the cell stiffness patterns across individual cells. These results expand our knowledge on the mechanical interaction between cells and their environments, and offer an alternative approach to determine physiologically relevant intracellular forces from high-resolution cell stiffness images.

Electrophysiological-mechanical coupling in the neuronal membrane and its role in ultrasound neuromodulation and general anaesthesia

The current understanding of the role of the cell membrane is in a state of flux. Recent experiments show that conventional models, considering only electrophysiological properties of a passive membrane, are incomplete. The neuronal membrane is an active structure with mechanical properties that modulate electrophysiology. Protein transport, lipid bilayer phase, membrane pressure and stiffness can all influence membrane capacitance and action potential propagation. A mounting body of evidence indicates that neuronal mechanics and electrophysiology are coupled, and together shape the membrane potential in tight coordination with other physical properties. In this review, we summarise recent updates concerning electrophysiological-mechanical coupling in neuronal function. In particular, we aim at making the link with two relevant yet often disconnected fields with strong clinical potential: the use of mechanical vibrations-ultrasound-to alter the electrophysiogical state of neurons, e.g., in neuromodulation, and the theories attempting to explain the action of general anaesthetics. STATEMENT OF SIGNIFICANCE: General anaesthetics revolutionised medical practice; now an apparently unrelated technique, ultrasound neuromodulation-aimed at controlling neuronal activity by means of ultrasound-is poised to achieve a similar level of impact. While both technologies are known to alter the electrophysiology of neurons, the way they achieve it is still largely unknown. In this review, we argue that in order to explain their mechanisms/effects, the neuronal membrane must be considered as a coupled mechano-electrophysiological system that consists of multiple physical processes occurring concurrently and collaboratively, as opposed to sequentially and independently. In this framework the behaviour of the cell membrane is not the result of stereotypical mechanisms in isolation but instead emerges from the integrative behaviour of a complexly coupled multiphysics system.

Flow-induced mechanotransduction in skeletal cells

Human body is subject to many and variegated mechanical stimuli, actuated in different ranges of force, frequency, and duration. The process through which cells "feel" forces and convert them into biochemical cascades is called mechanotransduction. In this review, the effects of fluid shear stress on bone cells will be presented. After an introduction to present the major players in bone system, we describe the mechanoreceptors in bone tissue that can feel and process fluid flow. In the second part of the review, we present an overview of the biological processes and biochemical cascades initiated by fluid shear stress in bone cells.

In Situ Subcellular Detachment of Cells Using a Cell-Friendly Photoresist and Spatially Modulated Light

Dynamic adhesion and detachment of subcellular regions occur during cell migration, thus a technique allowing precise control of subcellular detachment of cells will be useful for cell migration study. Previous methods for cell detachment were developed either for harvesting cells or cell sheets attached on surfaces with low resolution patterning capability, or for detaching subcellular regions located on predefined electrodes. In this paper, a method that allows in situ subcellular detachment of cells with ≈1.5 µm critical feature size while observing cells under a fluorescence microscope is introduced using a cell-friendly photoresist and spatially modulated light. Using this method, a single cell, regions in cell sheets, and a single focal adhesion complex within a cell are successfully detached. Furthermore, different subcellular regions of migrating cells are detached and changes in cell polarity and migration direction are quantitatively analyzed. This method will be useful for many applications in cell detachment, in particular when subcellular resolution is required.

Characterization of 3D Printed Stretching Devices for Imaging Force Transmission in Live-Cells

Introduction

Cell stretch is a method which can rapidly apply mechanical force through cell-matrix and cell-cell adhesions and can be utilized to better understand underlying biophysical questions related to intracellular force transmission and mechanotransduction.

Methods

3D printable stretching devices suitable for live-cell fluorescent imaging were designed using finite element modeling and validated experimentally. These devices were then used along with FRET based nesprin-2G force sensitive biosensors as well as live cell fluorescent staining to understand how the nucleus responds to externally applied mechanical force in cells with both intact LINC (linker of nucleoskeleton and cytoskeleton) complex and cells with the LINC complex disrupted using expression of dominant negative KASH protein.

Results

The devices were shown to provide a larger strain ranges (300% uniaxial and 60% biaxial) than currently available commercial or academic designs we are aware of. Under uniaxial deformation, the deformation of the nucleus of NIH 3T3 cells per unit of imposed cell strain was shown to be approximately 50% higher in control cells compared to cells with a disrupted LINC complex. Under biaxial deformation, MDCK II cells showed permanent changes in the nuclear morphology as well as actin organization upon unloading, indicating that failure, plastic deformation, or remodeling of the cytoskeleton is occurring in response to the applied stretch.

Conclusion

Development and open distribution of low-cost, 3D-printable uniaxial and biaxial cell stretching devices compatible with live-cell fluorescent imaging allows a wider range of researchers to investigate mechanical influences on biological questions with only a minimal investment of resources.

Dissecting fat-tailed fluctuations in the cytoskeleton with active micropost arrays

The ability of animal cells to crawl, change their shape, and respond to applied force is due to their cytoskeleton: A dynamic, cross-linked network of actin protein filaments and myosin motors. How these building blocks assemble to give rise to cells' mechanics and behavior remains poorly understood. Using active micropost array detectors containing magnetic actuators, we have characterized the mechanics and fluctuations of cells' actomyosin cortex and stress fiber network in detail. Here, we find that both structures display remarkably consistent power law viscoelastic behavior along with highly intermittent fluctuations with fat-tailed distributions of amplitudes. Notably, this motion in the cortex is dominated by occasional large, step-like displacement events, with a spatial extent of several micrometers. Overall, our findings for the cortex appear contrary to the predictions of a recent active gel model, while suggesting that different actomyosin contractile units act in a highly collective and cooperative manner. We hypothesize that cells' actomyosin components robustly self-organize into marginally stable, plastic networks that give cells' their unique biomechanical properties.

Myofascial chains of the upper limb: A systematic review of anatomical studies

The presence of structural in-series continuity between skeletal muscles has been confirmed in the trunk and lower extremity. However, it is not yet clear whether the same architecture can be found in the upper limb. Therefore, the aim of the present study was to review the available literature considering the existence of myofascial chains in the shoulder-arm region. Two independent investigators performed a systematic literature search using MEDLINE (PubMed) and Google Scholar (each 1900-2019). Peer-reviewed anatomical dissection studies reporting myofascial in-series continuity in the upper extremity were included. The methodological quality of the included studies was assessed by the QUACS scale. Thirteen studies were included in the review. Analysis of these papers led to the identification of three myofascial chains: the ventral arm chain (pectoralis major, brachial fascia/biceps brachii, flexor carpi ulnaris/brachioradialis/supinator, based on five studies); the lateral arm chain (trapezius, deltoideus, lateral intermuscular septum/brachialis, brachioradialis, four studies); and the dorsal arm chain (latissiumus dorsi/teres minor/infraspinatus, triceps brachii, anconeus, extensor carpi ulnaris, six studies). There is good evidence for direct serial tissue continuity extending from the neck and shoulder region to the forearm. Despite this intriguing finding, which could have implications for health professionals and the treatment of musculoskeletal disorders, further research is needed to establish the mechanical relevance of the identified myofascial chains. Clin. Anat. 32:934-940, 2019. © 2019 Wiley Periodicals, Inc.

A one-dimensional individual-based mechanical model of cell movement in heterogeneous tissues and its coarse-grained approximation

Mechanical heterogeneity in biological tissues, in particular stiffness, can be used to distinguish between healthy and diseased states. However, it is often difficult to explore relationships between cellular-level properties and tissue-level outcomes when biological experiments are performed at a single scale only. To overcome this difficulty, we develop a multi-scale mathematical model which provides a clear framework to explore these connections across biological scales. Starting with an individual-based mechanical model of cell movement, we subsequently derive a novel coarse-grained system of partial differential equations governing the evolution of the cell density due to heterogeneous cellular properties. We demonstrate that solutions of the individual-based model converge to numerical solutions of the coarse-grained model, for both slowly-varying-in-space and rapidly-varying-in-space cellular properties. We discuss applications of the model, such as determining relative cellular-level properties and an interpretation of data from a breast cancer detection experiment.

Fluorescent Tau-derived Peptide for Monitoring Microtubules in Living Cells

Microtubules (MTs) are key cytoskeletal components that modulate various cellular activities with their dynamic structural changes, including polymerization and depolymerization. To monitor the dynamics of MTs in living cells, many drug-based fluorescent probes have been developed; however, these also potentially disturb the polymerization/depolymerization of MTs. Here, we report nondrug, peptide-based fluorescent probes to monitor MTs in living cells. We employed a Tau-derived peptide (TP) that has been shown to bind MTs without inhibiting polymerization/depolymerization in vitro. We show that a tetramethylrhodamine (TMR)-labeled TP (TP-TMR) is internalized into HepG2 cells and binds to intracellular MTs, enabling visualization of MTs as clear, fibrous structures. The binding of TP-TMR shows no apparent effects on polymerization/depolymerization of MTs induced by MT-targeted drugs and temperature change. The main uptake mechanism of TP-TMR was elucidated as endocytosis, and partial endosomal escape resulted in the binding of TP-TMR to MTs. TP-TMR exhibited no cytotoxicity compared with MT-targeted drug scaffolds. These results indicate that TP scaffolds can be exploited as useful MT-targeted tools in living cells, such as in long-term imaging of MTs.

Nuclear Migration: An Indicator of Plant Salinity Tolerance in vitro

In order to understand the mechanisms underlying acquisition of tolerance to salinity, we recently produced callus tissues of tobacco and Medicago truncatula resistant to NaCl-induced salt stress following application of a step-up recurrent selection method. The effects of salinity on cell size are known, but those on cell morphometry including cell and nuclear surface area and position of nuclei within salt stress resistant cells were never studied before. This work fills that gap, using suspension cultured cells of M. truncatula A17 initiated from callus, and Nicotiana tabacum BY-2 cell line resistant to increasing NaCl concentrations up to 150 mM NaCl. The surface area of salinity resistant cells of M. truncatula A17 and N. tabacum BY2 and their nuclei, produced by step-up recurrent selection, were reduced, and cells elongated as NaCl increased, but these parameters proved to be unreliable in explaining cell survival and growth at high NaCl. Conversely, nuclei of resistant cells migrated from the center to the periphery of the cytoplasm close to the walls. Nuclear marginalization was for the first time observed as a result of salt stress in plant cells, and could be a novel helpful morphological marker of acquisition of salinity tolerance.

Integrated lung tissue mechanics one piece at a time: Computational modeling across the scales of biology

The lung is a delicately balanced and highly integrated mechanical system. Lung tissue is continuously exposed to the environment via the air we breathe, making it susceptible to damage. As a consequence, respiratory diseases present a huge burden on society and their prevalence continues to rise. Emergent function is produced not only by the sum of the function of its individual components but also by the complex feedback and interactions occurring across the biological scales - from genes to proteins, cells, tissue and whole organ - and back again. Computational modeling provides the necessary framework for pulling apart and putting back together the pieces of the body and organ systems so that we can fully understand how they function in both health and disease. In this review, we discuss models of lung tissue mechanics spanning from the protein level (the extracellular matrix) through to the level of cells, tissue and whole organ, many of which have been developed in isolation. This is a vital step in the process but to understand the emergent behavior of the lung, we must work towards integrating these component parts and accounting for feedback across the scales, such as mechanotransduction. These interactions will be key to unlocking the mechanisms occurring in disease and in seeking new pharmacological targets and improving personalized healthcare.

Regulation of ezrin tension by S-nitrosylation mediates non-small cell lung cancer invasion and metastasis

Cancer invasion and metastasis depend on accurate and rapid modulation of both chemical and mechanical activities. The S-nitrosylation (SNO) of membrane cytoskeletal cross-linker protein ezrin may regulate the malignant process in a tension-dependent manner. Methods: The level of nitrosylated ezrin in non-small cell lung cancer (NSCLC) tissues and A549 cell line were evaluated by biotin-switch assay. A few cysteine mutated plasmids of ezrin were used to identify active site for SNO. Newly designed ezrin or mutated-ezrin tension probes based on Förster resonance energy transfer (FRET) theory were applied to visually observe real-time tension changes. Cytoskeleton depolymerizing and motor molecular inhibiting experiments were performed to reveal the alternation of the mechanical property of ezrin after SNO. Transwell assays and xenograft mouse model were used to assess aggressiveness of A549 cells in different groups. Fluorescent staining was also applied to examine cellular location and structures. Results: High inducible nitric oxide synthase (iNOS) levels were observed to induce ezrin-SNO, and then promote malignant behaviors of NSCLC cells both in vitro and in vivo. Cys¹¹⁷ was identified as the only active site for ezrin-SNO. Meanwhile, an increased level of ezrin tension was observed after iNOS-induced SNO. Enhanced ezrin tension was positively correlated with aggressiveness of NSCLC. Moreover, Microfilament (MF) forces instead of microtubule (MT) forces played dominant roles in modulating ezrin tension, especially after ezrin nitrosylation. Conclusion: This study revealed a SNO-associated mechanism underlying the mechanical tension of ezrin. Ezrin-SNO promotes NSCLC cells invasion and metastasis through facilitating mechanical transduction from the cytoskeleton to the membrane. These studies implicate the therapeutic potential by targeting ezrin in the inhibition NSCLC invasion and metastasis.

In silico approach to quantify nucleus self-deformation on micropillared substrates

Considering the major role of confined cell migration in biological processes and diseases, such as embryogenesis or metastatic cancer, it has become increasingly important to design relevant experimental set-ups for in vitro studies. Microfluidic devices have recently presented great opportunities in their respect since they offer the possibility to study all the steps from a suspended to a spread, and eventually crawling cell or a cell with highly deformed nucleus. Here, we focus on the nucleus self-deformation over a micropillared substrate. Actin networks have been observed at two locations in this set-up: above the nucleus, forming the perinuclear actin cap (PAC), and below the nucleus, surrounding the pillars. We can then wonder which of these contractile networks is responsible for nuclear deformation. The cytoplasm and the nucleus are represented through the superposition of a viscous and a hyperelastic material and follow a series of processes. First, the suspended cell settles on the pillars due to gravity. Second, an adhesive spreading force comes into play, and then, active deformations contract one or both actin domains and consequently the nucleus. Our model is first tested on a flat substrate to validate its global behaviour before being confronted to a micropillared substrate. Overall, the nucleus appears to be mostly pulled towards the pillars, while the mechanical action of the PAC is weak. Eventually, we test the influence of gravity and prove that the gravitational force does not play a role in the final deformation of the nucleus.

Response of Single Cells to Shock Waves and Numerically Optimized Waveforms for Cancer Therapy

Shock waves are used clinically for breaking kidney stones and treating musculoskeletal indications. The mechanisms by which shock waves interact with tissue are still not well understood. Here, ultra-high-speed imaging was used to visualize the deformation of individual cells embedded in a tissue-mimicking phantom when subject to shock-wave exposure from a clinical source. Three kidney epithelial cell lines were considered to represent normal healthy (human renal epithelial), cancer (CAKI-2), and virus-transformed (HK-2) cells. The experimental results showed that during the compressive phase of the shock waves, there was a small (<2%) decrease in the projected cell area, but during the tensile phase, there was a relatively large (∼10%) increase in the projected cell area. The experimental observations were captured by a numerical model with a constitutive material framework consisting of an equation of state for the volumetric response and hyper-viscoelasticity for the deviatoric response. To model the volumetric cell response, it was necessary to change from a higher bulk modulus during the compression to a lower bulk modulus during the tensile shock loading. It was discovered that cancer cells showed a smaller deformation but faster response to the shock-wave tensile phase compared to their noncancerous counterparts. Cell viability experiments, however, showed that cancer cells suffered more damage than other cell types. These data suggest that the cell response to shock waves is specific to the type of cell and waveforms that could be tailored to an application. For example, the model predicts that a shock wave with a tensile stress of 4.59 MPa would increase cell membrane permeability for cancer cells with minimal impact on normal cells.

Mechanosensing and Mechanoregulation of Endothelial Cell Functions

Vascular endothelial cells (ECs) form a semiselective barrier for macromolecules and cell elements regulated by dynamic interactions between cytoskeletal elements and cell adhesion complexes. ECs also participate in many other vital processes including innate immune reactions, vascular repair, secretion, and metabolism of bioactive molecules. Moreover, vascular ECs represent a unique cell type exposed to continuous, time-dependent mechanical forces: different patterns of shear stress imposed by blood flow in macrovasculature and by rolling blood cells in the microvasculature; circumferential cyclic stretch experienced by the arterial vascular bed caused by heart propulsions; mechanical stretch of lung microvascular endothelium at different magnitudes due to spontaneous respiration or mechanical ventilation in critically ill patients. Accumulating evidence suggests that vascular ECs contain mechanosensory complexes, which rapidly react to changes in mechanical loading, process the signal, and develop context-specific adaptive responses to rebalance the cell homeostatic state. The significance of the interactions between specific mechanical forces in the EC microenvironment together with circulating bioactive molecules in the progression and resolution of vascular pathologies including vascular injury, atherosclerosis, pulmonary edema, and acute respiratory distress syndrome has been only recently recognized. This review will summarize the current understanding of EC mechanosensory mechanisms, modulation of EC responses to humoral factors by surrounding mechanical forces (particularly the cyclic stretch), and discuss recent findings of magnitude-specific regulation of EC functions by transcriptional, posttranscriptional and epigenetic mechanisms using -omics approaches. We also discuss ongoing challenges and future opportunities in developing new therapies targeting dysregulated mechanosensing mechanisms to treat vascular diseases. © 2019 American Physiological Society. Compr Physiol 9:873-904, 2019.

Deciphering Nuclear Mechanobiology in Laminopathy

Extracellular mechanical stimuli are translated into biochemical signals inside the cell via mechanotransduction. The nucleus plays a critical role in mechanoregulation, which encompasses mechanosensing and mechanotransduction. The nuclear lamina underlying the inner nuclear membrane not only maintains the structural integrity, but also connects the cytoskeleton to the nuclear envelope. Lamin mutations, therefore, dysregulate the nuclear response, resulting in abnormal mechanoregulations, and ultimately, disease progression. Impaired mechanoregulations even induce malfunction in nuclear positioning, cell migration, mechanosensation, as well as differentiation. To know how to overcome laminopathies, we need to understand the mechanisms of laminopathies in a mechanobiological way. Recently, emerging studies have demonstrated the varying defects from lamin mutation in cellular homeostasis within mechanical surroundings. Therefore, this review summarizes recent findings highlighting the role of lamins, the architecture of nuclear lamina, and their disease relevance in the context of nuclear mechanobiology. We will also provide an overview of the differentiation of cellular mechanics in laminopathy.

Suggested mechanisms underlying pollen wall development in Ambrosia trifida (Asteraceae: Heliantheae)

By a detailed ontogenetic study of Ambrosia trifida pollen, tracing each stage of development with TEM, we aim to understand the establishment of the pollen wall and to unravel the mechanisms underlying sporoderm development. The main steps of exine ontogeny in Ambrosia trifida, observed in the microspore periplasmic space, are as follows: spherical units, gradually transforming into columns, then to rod-like units; the appearance of the initial reticulate tectum; growth of columellae under the tectum and initial sporopollenin accumulation on them; the appearance of the endexine lamellae, first in fragments, then in long laminae; the cessation of the glycocalyx growth and its detachment from the plasma membrane, resulting in the appearance of gaps; massive accumulation of sporopollenin on the tectum, columellae, and endexine, and the appearance of the foot layer at the young post-tetrad stage, accompanied by establishment of caveae in sites of the former gaps; and final massive sporopollenin accumulation. This sequence of developmental events in all probability corresponds to the sequence of self-assembling micellar mesophases. This gives (together with earlier findings and experimental modeling of exine) strong evidence that the genome and self-assembly share control of exine formation. In this sense, self-assembly itself can be seen as an inherent mechanism of evolution.

On-chip cell mechanophenotyping using phase modulated surface acoustic wave

A surface acoustic wave (SAW) microfluidic chip was designed to measure the compressibility of cells and to differentiate cell mechanophenotypes. Polystyrene microbeads and poly(methylmethacrylate) (PMMA) microbeads were first tested in order to calibrate and validate the acoustic field. We observed the prefocused microbeads being pushed into the new pressure node upon phase shift. The captured trajectory matched well with the equation describing acoustic radiation force. The compressibility of polystyrene microbeads and that of PMMA microbeads was calculated, respectively, by fitting the trajectory from the experiment and that simulated by the equation across a range of compressibility values. Following, A549 human alveolar basal epithelial cells (A549 cells), human airway smooth muscle (HASM) cells, and MCF-7 breast cancer cells were tested using the same procedure. The compressibility of each cell from the three cell types was measured also by fitting trajectories between the experiment and that from the equation; the size was measured by image analysis. A549 cells were more compressible than HASM and MCF-7 cells; HASM cells could be further distinguished from MCF-7 cells by cell size. In addition, MCF-7 cells were treated by colchicine and 2-methoxyestradiol to disrupt the cell microtubules and were found to be more compressible. Computer simulation was also carried out to investigate the effect of cell compressibility and cell size due to acoustic radiation force to examine the sensitivity of the measurement. The SAW microfluidic method is capable of differentiating cell types or cells under different conditions based on the cell compressibility and the cell size.

Emerging trends in multiscale modeling of vascular pathophysiology: Organ-on-a-chip and 3D printing

Most biomedical and pharmaceutical research of the human vascular system aims to unravel the complex mechanisms that drive disease progression from molecular to organ levels. The knowledge gained can then be used to innovate diagnostic and treatment strategies which can ultimately be determined precisely for patients. Despite major advancements, current modeling strategies are often limited at identifying, quantifying, and dissecting specific cellular and molecular targets that regulate human vascular diseases. Therefore, development of multiscale modeling approaches are needed that can advance our knowledge and facilitate the design of next-generation therapeutic approaches in vascular diseases. This article critically reviews animal models, static in vitro systems, and dynamic in vitro culture systems currently used to model vascular diseases. A leading emphasis on the potential of emerging approaches, specifically organ-on-a-chip and three-dimensional (3D) printing, to recapitulate the innate human vascular physiology and anatomy is described. The applications of these approaches and future outlook in designing and screening novel therapeutics are also presented.

When Humans Met Superbugs: Strategies to Tackle Bacterial Resistances to Antibiotics

Bacterial resistance to antibiotics poses enormous health and economic burdens to our society, and it is of the essence to explore old and new ways to deal with these problems. Here we review the current status of multi-resistance genes and how they spread among bacteria. We discuss strategies to deal with resistant bacteria, namely the search for new targets and the use of inhibitors of protein-protein interactions, fragment-based methods, or modified antisense RNAs. Finally, we discuss integrated approaches that consider bacterial populations and their niches, as well as the role of global regulators that activate and/or repress the expression of multiple genes in fluctuating environments and, therefore, enable resistant bacteria to colonize new niches. Understanding how the global regulatory circuits work is, probably, the best way to tackle bacterial resistance.

Nuclear abnormalities in vascular myocytes in cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)

Cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a stroke and dementia syndrome with degeneration and loss of vascular smooth muscle cells (VSMCs). The disease is due to mutations in NOTCH3 playing an important role in VSMC differentiation, proliferation and apoptosis. Searching for a possible cause of VSMC dysfunction in CADASIL, we investigated morphology and proliferative activity the affected myocytes. In material from autopsy brains and skin-muscle biopsies of patients with CADASIL diagnosis, assessment of VSMCs in arterial vessels at the level of light and electron microscopy was performed. Proliferative activity of VSMCs was evaluated in immune reactions to proliferative markers: proliferating cell nuclear antigen, and cyclins B1 and D. In CADASIL, abnormal morphology of VSMC nuclei was observed in 18.1%, 11.5%, and 6.9% of the cerebral, skin, and skeletal muscle vessels, respectively. The affected myocytes showed variability in nuclear size, irregularity in nuclear shape, and abnormal chromatin appearance. Frequently, double nuclei of equal size or micronuclei were observed. Sometimes, even multinuclear myocytes were found. In some of the nuclei immune reactions to the examined proliferative markers were positive. Aberrant structure and number of VSCM nuclei, and their immunoreactivity to proliferative markers suggest mitotic instability of vascular myocytes in CADASIL. We speculate that mutant NOTCH3 which is unable to control properly VSMC proliferation, and may be responsible for their premature or inappropriate entry into mitosis, irreversible arrest of the cell cycle, senescence or degeneration and loss.

The micromechanics of lung alveoli: structure and function of surfactant and tissue components

The mammalian lung´s structural design is optimized to serve its main function: gas exchange. It takes place in the alveolar region (parenchyma) where air and blood are brought in close proximity over a large surface. Air reaches the alveolar lumen via a conducting airway tree. Blood flows in a capillary network embedded in inter-alveolar septa. The barrier between air and blood consists of a continuous alveolar epithelium (a mosaic of type I and type II alveolar epithelial cells), a continuous capillary endothelium and the connective tissue layer in-between. By virtue of its respiratory movements, the lung has to withstand mechanical challenges throughout life. Alveoli must be protected from over-distension as well as from collapse by inherent stabilizing factors. The mechanical stability of the parenchyma is ensured by two components: a connective tissue fiber network and the surfactant system. The connective tissue fibers form a continuous tensegrity (tension + integrity) backbone consisting of axial, peripheral and septal fibers. Surfactant (surface active agent) is the secretory product of type II alveolar epithelial cells and covers the alveolar epithelium as a biophysically active thin and continuous film. Here, we briefly review the structural components relevant for gas exchange. Then we describe our current understanding of how these components function under normal conditions and how lung injury results in dysfunction of alveolar micromechanics finally leading to lung fibrosis.

On the monolithic and staggered solution of cell contractility and focal adhesion growth

The mechanical response of cells to stimuli tightly couples biochemical and biomechanical processes, which describe fundamental properties such as cell growth and reorientation. Cells interact continuously with their external surroundings, the extracellular matrix (ECM), by establishing a bond between cell and ECM through the formation of focal adhesions. Focal adhesions are made up of integrins, which are mechanosensitive proteins and responsible for the communication between the cell and the ECM. The governing biochemomechanical processes can be modeled by means of a continuum approach considering mechanical and thermodynamic equilibrium to describe cell contractility and focal adhesion growth. The immanent multiphysical character of cell mechanics involves important aspects such as the coupling of fields of different scales and corresponding interface conditions that are sensitive to the solution of the governing numerical problem. These aspects become even more relevant when considering a feedback loop among the multiphysical solutions fields. In this contribution, we consider solution properties and sensitivity aspects of a nonlinear mechanical continuum model for the prognosis of stress fiber growth and reorientation incorporating a mechanosensitive feedback loop. We provide the governing equations of a Hill model-based stress fiber growth, which is coupled to a thermodynamical approach modeling the focal adhesions. Furthermore, a variational formulation including the algebraic equations is derived for staggered and monolithic solution approaches and the reaction-diffusion equation that models the feedback mechanism. We test both schemes with regard to reliability, accuracy, and numerical efficiency for different model parameters and loading scenarios. We present algorithmic aspects of the considered solution schemes and reveal their robustness with regard to model refinement in space and time and finally provide an assessment of their overall solution performance for multiphysics problems in the context of cell mechanics.

Graviperception in maize plants: is amyloplast sedimentation a red herring?

Land plants perceive gravity and respond to it in an organ-specific way; shoots typically direct growth upwards, roots typically downwards. Historically, at least with respect to maize plants, this phenomenon is attributed to three sequential processes, namely graviperception, the transduction of the perceived signal, and the graviresponse, resulting in a typical (re)positioning of the organ or entire plant body relative to the gravivector. For decades, sedimentation of starch-containing plastids within the cells of special tissues has been regarded as the primary and initiating process fundamental for gravitropic growth (starch-statolith hypothesis). Based on Popper's falsification principle, uncompromising experiments were executed. The results indicate that the model of graviperception based on amyloplast sedimentation does not apply to maize seedlings.

Modeling Host-Pathogen Interactions in the Context of the Microenvironment: Three-Dimensional Cell Culture Comes of Age

Tissues and organs provide the structural and biochemical landscapes upon which microbial pathogens and commensals function to regulate health and disease. While flat two-dimensional (2-D) monolayers composed of a single cell type have provided important insight into understanding host-pathogen interactions and infectious disease mechanisms, these reductionist models lack many essential features present in the native host microenvironment that are known to regulate infection, including three-dimensional (3-D) architecture, multicellular complexity, commensal microbiota, gas exchange and nutrient gradients, and physiologically relevant biomechanical forces (e.g., fluid shear, stretch, compression). A major challenge in tissue engineering for infectious disease research is recreating this dynamic 3-D microenvironment (biological, chemical, and physical/mechanical) to more accurately model the initiation and progression of host-pathogen interactions in the laboratory. Here we review selected 3-D models of human intestinal mucosa, which represent a major portal of entry for infectious pathogens and an important niche for commensal microbiota. We highlight seminal studies that have used these models to interrogate host-pathogen interactions and infectious disease mechanisms, and we present this literature in the appropriate historical context. Models discussed include 3-D organotypic cultures engineered in the rotating wall vessel (RWV) bioreactor, extracellular matrix (ECM)-embedded/organoid models, and organ-on-a-chip (OAC) models. Collectively, these technologies provide a more physiologically relevant and predictive framework for investigating infectious disease mechanisms and antimicrobial therapies at the intersection of the host, microbe, and their local microenvironments.