Tissue-specific mechanical and geometrical control of cell viability and actin cytoskeleton alignment

Microarchitected Compliant Scaffolds of Pyrolytic Carbon for 3D Muscle Cell Growth

The integration of additive manufacturing technologies with the pyrolysis of polymeric precursors enables the design-controlled fabrication of architected 3D pyrolytic carbon (PyC) structures with complex architectural details. Despite great promise, their use in cellular interaction remains unexplored. This study pioneers the utilization of microarchitected 3D PyC structures as biocompatible scaffolds for the colonization of muscle cells in a 3D environment. PyC scaffolds are fabricated using micro-stereolithography, followed by pyrolysis. Furthermore, an innovative design strategy using revolute joints is employed to obtain novel, compliant structures of architected PyC. The pyrolysis process results in a pyrolysis temperature- and design-geometry-dependent shrinkage of up to 73%, enabling the geometrical features of microarchitected compatible with skeletal muscle cells. The stiffness of architected PyC varies with the pyrolysis temperature, with the highest value of 29.57 ± 0.78 GPa for 900 °C. The PyC scaffolds exhibit excellent biocompatibility and yield 3D cell colonization while culturing skeletal muscle C2C12 cells. They further induce good actin fiber alignment along the compliant PyC construction. However, no conclusive myogenic differentiation is observed here. Nevertheless, these results are highly promising for architected PyC scaffolds as multifunctional tissue implants and encourage more investigations in employing compliant architected PyC structures for high-performance tissue engineering applications.

Vibration acceleration enhances proliferation, migration, and maturation of C2C12 cells and promotes regeneration of muscle injury in male rats

Vibration acceleration (VA) using a whole-body vibration device is beneficial for skeletal muscles. However, its effect at the cellular level remains unclear. We aimed to investigate the effects of VA on muscles in vitro and in vivo using the C2C12 mouse myoblast cell line and cardiotoxin-induced injury in male rat soleus muscles. Cell proliferation was evaluated using the WST/CCK-8 assay and proportion of Ki-67 positive cells. Cell migration was assessed using wound-healing assay. Cell differentiation was examined by the maturation index in immunostained cultured myotubes and real-time polymerase chain reaction. Regeneration of soleus muscle in rats was assessed by recruitment of satellite cells, cross-sectional area of regenerated muscle fibers, number of centrally nucleated fibers, and conversion of regenerated muscle from fast- to slow-twitch. VA at 30 Hz with low amplitude for 10 min promoted C2C12 cell proliferation, migration, and myotube maturation, without promoting expression of genes related to differentiation. VA significantly increased Pax7-stained satellite cells and centrally nucleated fibers in injured soleus muscles on Day 7 and promoted conversion of fast- to slow-twitch muscle fibers with an increase in the mean cross-sectional area of regenerated muscle fibers on Day 14. VA enhanced the proliferation, migration, and maturation of C2C12 myoblasts and regeneration of injured rat muscles.

Biomechanical, biophysical and biochemical modulators of cytoskeletal remodelling and emergent stem cell lineage commitment

Across complex, multi-time and -length scale biological systems, redundancy confers robustness and resilience, enabling adaptation and increasing survival under dynamic environmental conditions; this review addresses ubiquitous effects of cytoskeletal remodelling, triggered by biomechanical, biophysical and biochemical cues, on stem cell mechanoadaptation and emergent lineage commitment. The cytoskeleton provides an adaptive structural scaffold to the cell, regulating the emergence of stem cell structure-function relationships during tissue neogenesis, both in prenatal development as well as postnatal healing. Identification and mapping of the mechanical cues conducive to cytoskeletal remodelling and cell adaptation may help to establish environmental contexts that can be used prospectively as translational design specifications to target tissue neogenesis for regenerative medicine. In this review, we summarize findings on cytoskeletal remodelling in the context of tissue neogenesis during early development and postnatal healing, and its relevance in guiding lineage commitment for targeted tissue regeneration. We highlight how cytoskeleton-targeting chemical agents modulate stem cell differentiation and govern responses to mechanical cues in stem cells' emerging form and function. We further review methods for spatiotemporal visualization and measurement of cytoskeletal remodelling, as well as its effects on the mechanical properties of cells, as a function of adaptation. Research in these areas may facilitate translation of stem cells' own healing potential and improve the design of materials, therapies, and devices for regenerative medicine.

Bioengineered 3D Living Fibers as In Vitro Human Tissue Models of Tendon Physiology and Pathology

Clinically relevant in vitro models of human tissue's health and disease are urgently needed for a better understanding of biological mechanisms essential for the development of novel therapies. Herein, physiological (healthy) and pathological (disease) tendon states are bioengineered by coupling the biological signaling of platelet lysate components with controlled 3D architectures of electrospun microfibers to drive the fate of human tendon cells in different composite living fibers (CLFs). In the CLFs-healthy model, tendon cells adopt a high cytoskeleton alignment and elongation, express tendon-related markers (scleraxis, tenomodulin, and mohawk) and deposit a dense tenogenic matrix. In contrast, cell crowding with low preferential orientation, high matrix deposition, and phenotypic drift leading to increased expression of nontendon related and fibrotic markers, are characteristics of the CLFs-diseased model. This diseased-like profile, also reflected in the increase of COL3/COL1 ratio, is further evident by the imbalance between matrix remodeling and degradation effectors, characteristic of tendinopathy. In summary, microengineered 3D in vitro models of human tendon healthy and diseased states are successfully fabricated. Most importantly, these innovative and versatile microphysiological models offer major advantages over currently used systems, holding promise for drugs screening and development of new therapies.

Micro-patterned cell populations as advanced pharmaceutical drugs with precise functional control

Human cells are both advanced pharmaceutical drugs and 'drug deliverers'. However, functional control prior to or after cell implantation remains challenging. Micro-patterning cells through geometrically defined adhesion sites allows controlling morphogenesis, polarity, cellular mechanics, proliferation, migration, differentiation, stemness, cell-cell interactions, collective cell behavior, and likely immuno-modulatory properties. Consequently, generating micro-patterned therapeutic cells is a promising idea that has not yet been realized and few if any steps have been undertaken in this direction. This review highlights potential therapeutic applications, summarizes comprehensively the many cell functions that have been successfully controlled through micro-patterning, details the established micro-pattern designs, introduces the available fabrication technologies to the non-specialized reader, and suggests a quality evaluation score. Such a broad review is not yet available but would facilitate the manufacturing of therapeutically patterned cell populations using micro-patterned cell-instructive biomaterials for improved functional control as drug delivery systems in the context of cells as pharmaceutical products.

3D Microwell Platforms for Control of Single Cell 3D Geometry and Intracellular Organization

Introduction

Cell structure and migration is impacted by the mechanical properties and geometry of the cell adhesive environment. Most studies to date investigating the effects of 3D environments on cells have not controlled geometry at the single-cell level, making it difficult to understand the influence of 3D environmental cues on single cells. Here, we developed microwell platforms to investigate the effects of 2D vs. 3D geometries on single-cell F-actin and nuclear organization.

Methods

We used microfabrication techniques to fabricate three polyacrylamide platforms: 3D microwells with a 3D adhesive environment (3D/3D), 3D microwells with 2D adhesive areas at the bottom only (3D/2D), and flat 2D gels with 2D patterned adhesive areas (2D/2D). We measured geometric swelling and Young's modulus of the platforms. We then cultured C2C12 myoblasts on each platform and evaluated the effects of the engineered microenvironments on F-actin structure and nuclear shape.

Results

We tuned the mechanical characteristics of the microfabricated platforms by manipulating the gel formulation. Crosslinker ratio strongly influenced geometric swelling whereas total polymer content primarily affected Young's modulus. When comparing cells in these platforms, we found significant effects on F-actin and nuclear structures. Our analysis showed that a 3D/3D environment was necessary to increase actin and nuclear height. A 3D/2D environment was sufficient to increase actin alignment and nuclear aspect ratio compared to a 2D/2D environment.

Conclusions

Using our novel polyacrylamide platforms, we were able to decouple the effects of 3D confinement and adhesive environment, finding that both influenced actin and nuclear structure.

Stretching of fibroblast cells on micropatterned gelatin on silicone elastomer

Micropatterned gelatin was formed on the silicone elastomer surface. The micropattern enabled cell alignment, regulation of the cell shape, and endowed the cells with resistance against mechanical stress.

A Novel Conductive and Micropatterned PEG-Based Hydrogel Enabling the Topographical and Electrical Stimulation of Myoblasts

In this study, we designed a cell-adhesive poly(ethylene glycol) (PEG)-based hydrogel that simultaneously provides topographical and electrical stimuli to C2C12 myoblasts. Specifically, PEG hydrogels with microgroove structures of 3 μm ridges and 3 μm grooves were prepared by micromolding; in situ polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) was then performed within the micropatterned PEG hydrogels to create a microgrooved conductive hydrogel (CH/P). The CH/P had clear replica patterns of the silicone mold and a conductivity of 2.49 × 10^-3 S/cm, with greater than 85% water content. In addition, the CH exhibited Young's modulus (45.84 ± 7.12 kPa) similar to that of a muscle tissue. The surface of the CH/P was further modified via covalent bonding with cell-adhesive peptides to facilitate cell adhesion without affecting conductivity. An in vitro cell assay revealed that the CH/P was cytocompatible and enhanced the cell alignment and elongation of C2C12 myoblasts. The microgrooves and conductivity of the CH/P had the greatest positive effect on the myogenesis of C2C12 myoblasts compared to the other PEG hydrogel samples without conductivity or/and microgrooves, even in the absence of electrical stimulation. Electrical stimulation studies indicated that the combination of topographical and electrical cues maximized the differentiation of C2C12 myoblasts into myotubes, confirming the synergetic effect of incorporating microgroove surface features and a conductive PEDOT component into hydrogels.

Cell alignment and accumulation using acoustic nozzle for bioprinting

Bioprinting could spatially align various cells in high accuracy to simulate complex and highly organized native tissues. However, the uniform suspension and low concentration of cells in the bioink and subsequently printed construct usually results in weak cell-cell interaction and slow proliferation. Acoustic manipulation of biological cells during the extrusion-based bioprinting by a specific structural vibration mode was proposed and evaluated. Both C2C12 cells and human umbilical vein endothelial cells (HUVECs) could be effectively and quickly accumulated at the center of the cylindrical tube and consequently the middle of the printed construct with acoustic excitation at the driving frequency of 871 kHz. The full width at half maximum (FWHM) of cell distributions fitted with a Gaussian curve showed a significant reduction by about 2.2 fold in the printed construct. The viability, morphology, and differentiation of these cells were monitored and compared. C2C12 cells that were undergone the acoustic excitation had nuclei oriented densely within ±30° and decreased circularity index by 1.91 fold or significant cell elongation in the printing direction. In addition, the formation of the capillary-like structure in the HUVECs construct was found. The number of nodes, junctions, meshes, and branches of HUVECs on day 14 was significantly greater with acoustic excitation for the enhanced neovascularization. Altogether, the proposed acoustic technology can satisfactorily accumulate/pattern biological cells in the printed construct at high biocompatibility. The enhanced cell interaction and differentiation could subsequently improve the performance and functionalities of the engineered tissue samples.

Actin stress fiber dynamics in laterally confined cells

Multiple cellular processes are affected by spatial constraints from the extracellular matrix and neighboring cells. In vitro experiments using defined micro-patterning allow for in-depth analysis and a better understanding of how these constraints impact cellular behavior and functioning. Herein we focused on the analysis of actin cytoskeleton dynamics as a major determinant of mechanotransduction mechanisms in cells. We seeded primary human umbilical vein endothelial cells onto stripe-like cell-adhesive micro-patterns with varying widths and then monitored and quantified the dynamic reorganization of actin stress fibers, including fiber velocities, orientation and density, within these live cells using the cell permeable F-actin marker SiR-actin. Although characteristic parameters describing the overall stress fiber architecture (average orientation and density) were nearly constant throughout the observation time interval of 60 min, we observed permanent transport and turnover of individual actin stress fibers. Stress fibers were more strongly oriented along stripe direction with decreasing stripe width, (5° on 20 μm patterns and 10° on 40 μm patterns), together with an overall narrowing of the distribution of fiber orientation. Fiber dynamics was characterized by a directed movement from the cell edges towards the cell center, where fiber dissolution frequently took place. By kymograph analysis, we found median fiber velocities in the range of 0.2 μm/min with a weak dependence on pattern width. Taken together, these data suggest that cell geometry determines actin fiber orientation, while it also affects actin fiber transport and turnover.

Synthesizing Living Tissues with Microfluidics

In native tissues, various cell types organize and spatiotemporally function and communicate with neighboring or remote cells in a highly regulated way. How can we replicate these amazing functional structures in vitro? From the view of a chemist, the heterogeneous cells and extracellular matrix (ECM) could be regarded as various chemical substrate materials for "synthetic" reactions during tissue engineering. But how can we accelerate these reactions? Microfluidics provides ideal solutions. Microfluidics could be metaphorically regarded as a miniature "biofactory", whereas the on-chip critical chemical cues such as biomolecule gradients and physical cues such as geometrical confinement, topological guidance, and mechanical stimulations, along with the external stimulations such as light, electricity, acoustics, and magnetics, could be regarded as "catalytic cues" which can accelerate the "synthetic reactions" by precisely and effectively manipulating a series of cell behaviors including cell adhesion, migration, growth, proliferation, differentiation, cell-cell interaction, and cell-matrix interaction to reduce activation energy of the "synthetic reactions". Thus, on the microfluidics platform, the "biofactory", various "synthetic" reactions take place to change the substrate materials (cells and ECM) into products (tissues) in a nonlinear way, which is a typical feature of a biological process. By precisely organizing the substrate materials and spatiotemporally controlling the activity of the products, as a "biofactory", the microfluidics system can not only "synthesize" living tissues but also recreate physiological or pathophysiological processes such as immune responses, angiogenesis, wound healing, and tumor metastasis in vitro to bring insights into the mechanisms underlying these processes taking place in vivo. In this Account, we borrow the concept of chemical "synthesis" to describe how to "synthesize" artificial tissues using microfluidics from a chemist's view. Accelerated by the built-in physiochemical cues on microfluidics and external stimulations, various tissues could be "synthesized" on a microfluidics platform. We summarize that there are "step-by-step synthesis" and "one-step synthesis" on microfluidics for creating desired tissues with unprecedented precision, accuracy, and speed. In recent years, researchers developed various microfluidic techniques including creating adhesive domains for mediating reverse and precise adhesion, chemical gradients for directing cell growth, geometrical confinements and topological cues for manipulating cell migration, and mechanics for stimulating cell differentiation. By employing and orchestrating these on-chip tissue "synthetic" conditions, "step-by-step synthesis" could be realized on chips to develop multilayered tissues such as blood vessels. "One-step synthesis" on chips could develop functional three-dimensional tissue structures such as neural networks or nephron-like structures. Based on these on-chip studies, many critical physiological and pathophysiological processes such as wound healing, tumor metastasis, and atherosclerosis could be deeply investigated, and the drugs or therapeutic approaches could also be evaluated or screened conveniently. The "synthetic tissues on microfluidics" system would pave an avenue for precise creation of artificial tissues for not only fundamental research but also biomedical applications such as tissue engineering.

Matrix stiffness modulates the differentiation of neural crest stem cells in vivo

Stem cells are often transplanted with scaffolds for tissue regeneration; however, how the mechanical property of a scaffold modulates stem cell fate in vivo is not well understood. Here we investigated how matrix stiffness modulates stem cell differentiation in a model of vascular graft transplantation. Multipotent neural crest stem cells (NCSCs) were differentiated from induced pluripotent stem cells, embedded in the hydrogel on the outer surface of nanofibrous polymer grafts, and implanted into rat carotid arteries by anastomosis. After 3 months, NCSCs differentiated into smooth muscle cells (SMCs) near the outer surface of the polymer grafts; in contrast, NCSCs differentiated into glial cells in the most part of the hydrogel. Atomic force microscopy demonstrated a stiffer matrix near the polymer surface but much lower stiffness away from the polymer graft. Consistently, in vitro studies confirmed that stiff surface induced SMC genes whereas soft surface induced glial genes. These results suggest that the scaffold's mechanical properties play an important role in directing stem cell differentiation in vivo, which has important implications in biomaterials design for stem cell delivery and tissue engineering.

Live cell imaging reveals focal adhesions mechanoresponses in mammary epithelial cells under sustained equibiaxial stress

Mechanical stimuli play a key role in many cell functions such as proliferation, differentiation and migration. In the mammary gland, mechanical signals such as the distension of mammary epithelial cells due to udder filling are proposed to be directly involved during lactation and involution. However, the evolution of focal adhesions -specialized multiprotein complexes that mechanically connect cells with the extracellular matrix- during the mammary gland development, as well as the influence of the mechanical stimuli involved, remains unclear. Here we present the use of an equibiaxial stretching device for exerting a sustained normal strain to mammary epithelial cells while quantitatively assessing cell responses by fluorescence imaging techniques. Using this approach, we explored changes in focal adhesion dynamics in HC11 mammary cells in response to a mechanical sustained stress, which resembles the physiological stimuli. We studied the relationship between a global stress and focal adhesion assembly/disassembly, observing an enhanced persistency of focal adhesions under strain as well as an increase in their size. At a molecular level, we evaluated the mechanoresponses of vinculin and zyxin, two focal adhesion proteins postulated as mechanosensors, observing an increment in vinculin molecular tension and a slower zyxin dynamics while increasing the applied normal strain.

The relative composition of actin isoforms regulates cell surface biophysical features and cellular behaviors

BACKGROUND

Cell surface mechanics is able to physically and biomechanically affect cell shape and motility, vesicle trafficking and actin dynamics. The biophysical properties of cell surface are strongly influenced by cytoskeletal elements. In mammals, tissue-specific expression of six actin isoforms is thought to confer differential biomechanical properties. However, the relative contribution of actin isoforms to cell surface properties is not well understood. Here, we sought to investigate whether and how the composition of endogenous actin isoforms directly affects the biomechanical features of cell surface and cellular behavior.

METHODS

We used fibroblasts isolated from wild type (WT), heterozygous (HET) and from knockout (KO) mouse embryos where both β-actin alleles are not functional. We applied a combination of genome-wide analysis and biophysical methods such as RNA-seq and atomic force microscopy.

RESULTS

We found that endogenous β-actin levels are essential in controlling cell surface stiffness and pull-off force, which was not compensated by the up-regulation of other actin isoforms. The variations of surface biophysical features and actin contents were associated with distinct cell behaviors in 2D and 3D WT, HET and KO cell cultures. Since β-actin in WT cells and smooth muscle α-actin up-regulated in KO cells showed different organization patterns, our data support the differential localization and organization as a mechanism to regulate the biophysical properties of cell surface by actin isoforms.

CONCLUSIONS

We propose that variations in actin isoforms composition impact on the biophysical features of cell surface and cause the changes in cell behavior.

Protein-Substrate Adhesion in Microcontact Printing Regulates Cell Behavior

Microcontact printing (μCP) is widely used to create patterns of biomolecules essential for studies of cell mechanics, migration, and tissue engineering. However, different types of μCPs may create micropatterns with varied protein-substrate adhesion, which may change cell behaviors and pose uncertainty in result interpretation. Here, we characterize two μCP methods for coating extracellular matrix (ECM) proteins (stamp-off and covalent bond) and demonstrate for the first time the important role of protein-substrate adhesion in determining cell behavior. We found that, as compared to cells with weaker traction force (e.g., endothelial cells), cells with strong traction force (e.g., vascular smooth muscle cells) may delaminate the ECM patterns, which reduced cell viability as a result. Importantly, such ECM delamination was observed on patterns by stamp-off but not on the patterns by covalent bonds. Further comparisons of the displacement of the ECM patterns between the normal VSMCs and the force-reduced VSMCs suggested that the cell traction force plays an essential role in this ECM delamination. Together, our results indicated that μCPs with insufficient adhesion may lead to ECM delamination and cause cell death, providing new insight for micropatterning in cell-biomaterial interaction on biointerfaces.

Adult Stem Cells in Vascular Remodeling

Understanding the contribution of vascular cells to blood vessel remodeling is critical for the development of new therapeutic approaches to cure cardiovascular diseases (CVDs) and regenerate blood vessels. Recent findings suggest that neointimal formation and atherosclerotic lesions involve not only inflammatory cells, endothelial cells, and smooth muscle cells, but also several types of stem cells or progenitors in arterial walls and the circulation. Some of these stem cells also participate in the remodeling of vascular grafts, microvessel regeneration, and formation of fibrotic tissue around biomaterial implants. Here we review the recent findings on how adult stem cells participate in CVD development and regeneration as well as the current state of clinical trials in the field, which may lead to new approaches for cardiovascular therapies and tissue engineering.

Can the Drosophila model help in paving the way for translational medicine in heart failure?

Chronic heart failure is a common consequence of various heart diseases. Mechanical force is known to play a key role in heart failure development through regulating cardiomyocyte hypertrophy. In order to understand the complex disease mechanism, this article discussed a multi-disciplinary approach that may aid the illustration of heart failure molecular process.

Preferred cell alignment along concave microgrooves

The radius of curvature affects cell body characteristics on microfabricated concave microgrooves.

Gtf2ird1-Dependent Mohawk Expression Regulates Mechanosensing Properties of the Tendon

Mechanoforces experienced by an organ are translated into biological information for cellular sensing and response. In mammals, the tendon connective tissue experiences and resists physical forces, with tendon-specific mesenchymal cells called tenocytes orchestrating extracellular matrix (ECM) turnover. We show that Mohawk (Mkx), a tendon-specific transcription factor, is essential in mechanoresponsive tenogenesis through regulation of its downstream ECM genes such as type I collagens and proteoglycans such as fibromodulin both in vivo and in vitro Wild-type (WT) mice demonstrated an increase in collagen fiber diameter and density in response to physical treadmill exercise, whereas in Mkx(-/-) mice, tendons failed to respond to the same mechanical stimulation. Furthermore, functional screening of the Mkx promoter region identified several upstream transcription factors that regulate Mkx In particular, general transcription factor II-I repeat domain-containing protein 1 (Gtf2ird1) that is expressed in the cytoplasm of unstressed tenocytes translocated into the nucleus upon mechanical stretching to activate the Mkx promoter through chromatin regulation. Here, we demonstrate that Gtf2ird1 is essential for Mkx transcription, while also linking mechanical forces to Mkx-mediated tendon homeostasis and regeneration.

Patterning of Fibroblast and Matrix Anisotropy within 3D Confinement is Driven by the Cytoskeleton

Effects of 3D confinement on cellular growth and matrix assembly are important in tissue engineering, developmental biology, and regenerative medicine. Polydimethylsiloxane wells with varying anisotropy are microfabicated using soft-lithography. Microcontact printing of bovine serum albumin is used to block cell adhesion to surfaces between wells. The orientations of fibroblast stress fibers, microtubules, and fibronectin fibrils are examined 1 day after cell seeding using laser scanning confocal microscopy, and anisotropy is quantified using a custom autocorrelation analysis. Actin, microtubules, and fibronectin exhibit higher anisotropy coefficients for cells grown in rectangular wells with aspect ratios of 1:4 and 1:8, as compared to those in wells with lower aspect ratios or in square wells. The effects of disabling individual cytoskeletal components on fibroblast responses to anisotropy are then tested by applying actin or microtubule polymerization inhibitors, Rho kinase inhibitor, or by siRNA-mediated knockdown of AXL or cofilin-1. Latrunculin A decreases cytoskeletal and matrix anisotropy, nocodazole ablates both, and Y27632 mutes cellular polarity while decreasing matrix anisotropy. AXL siRNA knockdown has little effect, as does siRNA knockdown of cofilin-1. These data identify several specific cytoskeletal strategies as targets for the manipulation of anisotropy in 3D tissue constructs.

Nuclear deformability and telomere dynamics are regulated by cell geometric constraints

Forces generated by the cytoskeleton can be transmitted to the nucleus and chromatin via physical links on the nuclear envelope and the lamin meshwork. Although the role of these active forces in modulating prestressed nuclear morphology has been well studied, the effect on nuclear and chromatin dynamics remains to be explored. To understand the regulation of nuclear deformability by these active forces, we created different cytoskeletal states in mouse fibroblasts using micropatterned substrates. We observed that constrained and isotropic cells, which lack long actin stress fibers, have more deformable nuclei than elongated and polarized cells. This nuclear deformability altered in response to actin, myosin, formin perturbations, or a transcriptional down-regulation of lamin A/C levels in the constrained and isotropic geometry. Furthermore, to probe the effect of active cytoskeletal forces on chromatin dynamics, we tracked the spatiotemporal dynamics of heterochromatin foci and telomeres. We observed increased dynamics and decreased correlation of the heterochromatin foci and telomere trajectories in constrained and isotropic cell geometry. The observed enhanced dynamics upon treatment with actin depolymerizing reagents in elongated and polarized geometry were regained once the reagent was washed off, suggesting an inherent structural memory in chromatin organization. We conclude that active forces from the cytoskeleton and rigidity from lamin A/C nucleoskeleton can together regulate nuclear and chromatin dynamics. Because chromatin remodeling is a necessary step in transcription control and its memory, genome integrity, and cellular deformability during migration, our results highlight the importance of cell geometric constraints as critical regulators in cell behavior.

Contractility of single cardiomyocytes differentiated from pluripotent stem cells depends on physiological shape and substrate stiffness

Single cardiomyocytes contain myofibrils that harbor the sarcomere-based contractile machinery of the myocardium. Cardiomyocytes differentiated from human pluripotent stem cells (hPSC-CMs) have potential as an in vitro model of heart activity. However, their fetal-like misalignment of myofibrils limits their usefulness for modeling contractile activity. We analyzed the effects of cell shape and substrate stiffness on the shortening and movement of labeled sarcomeres and the translation of sarcomere activity to mechanical output (contractility) in live engineered hPSC-CMs. Single hPSC-CMs were cultured on polyacrylamide substrates of physiological stiffness (10 kPa), and Matrigel micropatterns were used to generate physiological shapes (2,000-µm(2) rectangles with length:width aspect ratios of 5:1-7:1) and a mature alignment of myofibrils. Translation of sarcomere shortening to mechanical output was highest in 7:1 hPSC-CMs. Increased substrate stiffness and applied overstretch induced myofibril defects in 7:1 hPSC-CMs and decreased mechanical output. Inhibitors of nonmuscle myosin activity repressed the assembly of myofibrils, showing that subcellular tension drives the improved contractile activity in these engineered hPSC-CMs. Other factors associated with improved contractility were axially directed calcium flow, systematic mitochondrial distribution, more mature electrophysiology, and evidence of transverse-tubule formation. These findings support the potential of these engineered hPSC-CMs as powerful models for studying myocardial contractility at the cellular level.

High-content imaging with micropatterned multiwell plates reveals influence of cell geometry and cytoskeleton on chromatin dynamics

Understanding the mechanisms underpinning cellular responses to microenvironmental cues requires tight control not only of the complex milieu of soluble signaling factors, extracellular matrix (ECM) connections and cell-cell contacts within cell culture, but also of the biophysics of human cells. Advances in biomaterial fabrication technologies have recently facilitated detailed examination of cellular biophysics and revealed that constraints on cell geometry arising from the cellular microenvironment influence a wide variety of human cell behaviors. Here, we create an in vitro platform capable of precise and independent control of biochemical and biophysical microenvironmental cues by adapting microcontact printing technology into the format of standard six- to 96-well plates to create MicroContact Printed Well Plates (μCP Well Plates). Automated high-content imaging of human cells seeded on μCP Well Plates revealed tight, highly consistent control of single-cell geometry, cytoskeletal organization, and nuclear elongation. Detailed subcellular imaging of the actin cytoskeleton and chromatin within live human fibroblasts on μCP Well Plates was then used to describe a new relationship between cellular geometry and chromatin dynamics. In summary, the μCP Well Plate platform is an enabling high-content screening technology for human cell biology and cellular engineering efforts that seek to identify key biochemical and biophysical cues in the cellular microenvironment.

Dynamically tunable polymer microwells for directing mesenchymal stem cell differentiation into osteogenesis

Dynamically tunable geometric microwells have great capacity to regulate the cytoskeletal structure and differentiation of mesenchymal stem cells along adipogenesis and osteogenesis pathways.

Designing ordered micropatterned hydroxyapatite bioceramics to promote the growth and osteogenic differentiation of bone marrow stromal cells

HAp bioceramics with micropatterned surfaces significantly enhance cell responses.