Probe-free optical chromatin deformation and measurement of differential mechanical properties in the nucleus.

The nucleus is highly organized to facilitate coordinated gene transcription. Measuring the rheological properties of the nucleus and its sub-compartments will be crucial to understand the principles underlying nuclear organization. Here, we show that strongly localized temperature gradients (approaching 1°C/µm) can lead to substantial intra-nuclear chromatin displacements (>1 µm), while nuclear area and lamina shape remain unaffected.

Mechanical memory stored through epigenetic remodeling reduces cell therapeutic potential.

Understanding how cells remember previous mechanical environments to influence their fate, or mechanical memory, informs the design of biomaterials and therapies in medicine. Current regeneration therapies, such as cartilage regeneration procedures, require 2D cell expansion processes to achieve large cell populations critical for the repair of damaged tissues. However, the limit of mechanical priming for cartilage regeneration procedures before inducing long-term mechanical memory following expansion processes is unknown, and mechanisms defining how physical environments influence the therapeutic potential of cells remain poorly understood.

Dynamic biophysical responses of neuronal cell nuclei and cytoskeletal structure following high impulse loading.

Cells are continuously exposed to dynamic environmental cues that influence their behavior. Mechanical cues can influence cellular and genomic architecture, gene expression, and intranuclear mechanics, providing evidence of mechanosensing by the nucleus, and a mechanoreciprocity between the nucleus and environment. Force disruption at the tissue level through aging, disease, or trauma, propagates to the nucleus and can have lasting consequences on proper functioning of the cell and nucleus.

Nuclear deformation guides chromatin reorganization in cardiac development and disease.

In cardiovascular tissues, changes in the mechanical properties of the extracellular matrix are associated with cellular de-differentiation and with subsequent functional declines. However, the underlying mechanoreceptive mechanisms are largely unclear. Here, by generating high-resolution, full-field strain maps of cardiomyocyte nuclei during contraction in vitro, complemented with evidence from tissues from patients with cardiomyopathy and from mice with reduced cardiac performance, we show that cardiomyocytes establish a distinct nuclear organization during maturation, characterized by the reorganization of H3K9me3-marked chromatin towards the nuclear border.

Dedifferentiation alters chondrocyte nuclear mechanics during in vitro culture and expansion.

The biophysical features of a cell can provide global insights into diverse molecular changes, especially in processes like the dedifferentiation of chondrocytes. Key biophysical markers of chondrocyte dedifferentiation include flattened cellular morphology and increased stress-fiber formation. During cartilage regeneration procedures, dedifferentiation of chondrocytes during in vitro expansion presents a critical limitation to the successful repair of cartilage tissue.

Feedback-based positioning and diffusion suppression of particles via optical control of thermoviscous flows.

The ability to control the position of micron-size particles with high precision using tools such as optical tweezers has led to major advances in fields such as biology, physics and material science. In this paper, we present a novel optical strategy to confine particles in solution with high spatial control using feedback-controlled thermoviscous flows. We show that this technique allows micron-size particles to be positioned and confined with subdiffraction precision (24 nm), effectively suppressing their diffusion.

Image-Based Elastography of Heterochromatin and Euchromatin Domains in the Deforming Cell Nucleus.

Chromatin of the eukaryotic cell nucleus comprises microscopically dense heterochromatin and loose euchromatin domains, each with distinct transcriptional ability and roles in cellular mechanotransduction. While recent methods are developed to characterize the mechanics of nucleus, measurement of intranuclear mechanics remains largely unknown. Here, the development of "nuclear elastography," which combines microscopic imaging and computational modeling to quantify the relative elasticity of the heterochromatin and euchromatin domains, is described.

Optical plasticity of mammalian cells.

Transparency is widespread in nature, ranging from transparent insect wings to ocular tissues that enable you to read this text, and transparent marine vertebrates. And yet, cells and tissue models in biology are usually strongly light scattering and optically opaque, precluding deep optical microscopy. Here we describe the directed evolution of cultured mammalian cells toward increased transparency.

TENSCell: Imaging of Stretch-Activated Cells Reveals Divergent Nuclear Behavior and Tension.

Mechanisms of cellular and nuclear mechanosensation are unclear, partially because of a lack of methods that can reveal dynamic processes. Here, we present a new concept for a low-cost, three-dimensionally printed device that enables high-magnification imaging of cells during stretch. We observed that nuclei of mouse embryonic skin fibroblasts underwent rapid (within minutes) and divergent responses, characterized by nuclear area expansion during 5% strain but nuclear area shrinkage during 20% strain.

Deformation Microscopy for Dynamic Intracellular and Intranuclear Mapping of Mechanics with High Spatiotemporal Resolution.

Structural heterogeneity is a hallmark of living cells that drives local mechanical properties and dynamic cellular responses. However, the robust quantification of intracellular mechanics is lacking from conventional methods. Here, we describe the development of deformation microscopy, which leverages conventional imaging and an automated hyperelastic warping algorithm to investigate strain history, deformation dynamics, and changes in structural heterogeneity within the interior of cells and cell nuclei.

Densification of Type I Collagen Matrices as a Model for Cardiac Fibrosis.

Cardiac fibrosis is a disease state characterized by excessive collagenous matrix accumulation within the myocardium that can lead to ventricular dilation and systolic failure. Current treatment options are severely lacking due in part to the poor understanding of the complexity of molecular pathways involved in cardiac fibrosis. To close this gap, in vitro model systems that recapitulate the defining features of the fibrotic cellular environment are in need.

Dissociated and Reconstituted Cartilage Microparticles in Densified Collagen Induce Local hMSC Differentiation.

Hybrid usage of native tissue signals and the engineering control of collagen matrices show the ability to induce local infiltration and differentiation of hMSCs. Additionally, the solid cartilage microparticles inhibit bulk cell-mediated contraction of the composite.

Mechanisms and Microenvironment Investigation of Cellularized High Density Gradient Collagen Matrices via Densification.

Biological tissues and biomaterials are often defined by unique spatial gradients in physical properties that impart specialized function over hierarchical scales. The structure and organization of these materials forms continuous transitional gradients and discrete local microenvironments between adjacent (or within) tissues, and across matrix-cell boundaries, which can be difficult to replicate with common scaffold systems. Here, we studied the matrix densification of collagen leading to gradients in density, mechanical properties, and fibril morphology.