Zyxin and actin structure confer anisotropic YAP mechanotransduction.

Tissues and the embedded cells experience anisotropic deformations due to their functions and anatomical locations. The resident cells, such as tenocytes and muscle cells, are often restricted by their extracellular matrix and organize parallel to their major loading direction, yet most studies on cellular responses to strains use isotropic substrates without predetermined organizations. To understand how confined cells sense and respond to anisotropic loading, we combine cell patterning and uniaxial stretch to have precise geometric control.

Deformation of the nucleus by TGFβ1 via the remodeling of nuclear envelope and histone isoforms.

The cause of nuclear shape abnormalities which are often seen in pre-neoplastic and malignant tissues is not clear. In this study we report that deformation of the nucleus can be induced by TGFβ1 stimulation in several cell lines including Huh7. In our results, the upregulated histone H3.

3D-Printed Collagen-Based Waveform Microfibrous Scaffold for Periodontal Ligament Reconstruction.

Reconstruction of the periodontal ligament (PDL) to fulfill functional requirement remains a challenge. This study sought to develop a biomimetic microfibrous system capable of withstanding the functional load to assist PDL regeneration. Collagen-based straight and waveform microfibers to guide PDL cell growth were prepared using an extrusion-based bioprinter, and a laminar flow-based bioreactor was used to generate fluidic shear stress.

Aberrant mechanosensing in injured intervertebral discs as a result of boundary-constraint disruption and residual-strain loss.

In fibrous tissues, prestressed boundary constraints at bone interfaces instil residual strain throughout the tissue, even when unloaded. For example, internal swelling pressures in the central nucleus pulposus of the intervertebral disc generate prestrain in the outer annulus fibrosus. With injury and depressurization, these residual strains are lost.

Chemical Optimization for Functional Ligament Tissue Engineering.

Electrospun materials are widely used for functional tissue engineering for its robust production and biomimetic properties. Several issues persist, however, including heterogeneous cell distribution, insufficient matrix elaboration/accumulation, and limited construct size. We took three synergistic approaches to address these issues by modifying the chemical microenvironment for the seeded cells.

Defined cell adhesion for silicon-based implant materials by using vapor-deposited functional coatings.

The field of implantable electronics relies on using silicon materials due to the merits of a well-established fabrication process and favorable properties; of particular interest is the surface modification of such materials. In the present study, we introduce a surface modification technique based on coatings of functionalized Parylene on silicon substrates, where the modified layers provide a defined cell adhesion capability for the resultant silicon materials/devices. Functionalization of Parylene was achieved during a one-step chemical vapor deposition (CVD) polymerization process, forming NHS ester-functionalized Parylene, and subsequent RGD attachment was enabled via a conjugation reaction between the NHS ester and amine groups.

Crimped Electrospun Fibers for Tissue Engineering.

Collagen fibers exist in many parts of the body as parallel bundles with a wavy morphology, known as crimp. This crimp structure contributes to the nonlinear mechanical properties of the tissue, such as ligament, blood vessels, and intestine, which provide elasticity and prevent injury. To recapitulate the native collagen crimp structure, we report a robust method using electrospinning and post-processing to generate parallel polymeric fibers with crimp that simulate the structure-function relationship of native tissue mechanics.

Crimped Nanofibrous Biomaterials Mimic Microstructure and Mechanics of Native Tissue and Alter Strain Transfer to Cells.

To fully recapitulate tissue microstructure and mechanics, fiber crimping must exist within biomaterials used for tendon/ligament engineering. Existing crimped nanofibrous scaffolds produced via electrospinning are dense materials that prevent cellular infiltration into the scaffold interior. In this study, we used a sacrificial fiber population to increase the scaffold porosity and evaluated the effect on fiber crimping.

Lipid rafts sense and direct electric field-induced migration.

Endogenous electric fields (EFs) are involved in developmental regulation and wound healing. Although the phenomenon is known for more than a century, it is not clear how cells perceive the external EF. Membrane proteins, responding to electrophoretic and electroosmotic forces, have long been proposed as the sensing molecules.

Stem cell delivery in tissue-specific hydrogel enabled meniscal repair in an orthotopic rat model.

Interest in non-invasive injectable therapies has rapidly risen due to their excellent safety profile and ease of use in clinical settings. Injectable hydrogels can be derived from the extracellular matrix (ECM) of specific tissues to provide a biomimetic environment for cell delivery and enable seamless regeneration of tissue defects. We investigated the in situ delivery of human mesenchymal stem cells (hMSCs) in decellularized meniscus ECM hydrogel to a meniscal defect in a nude rat model.

Silk microfiber-reinforced silk hydrogel composites for functional cartilage tissue repair.

Cartilage tissue lacks an intrinsic capacity for self-regeneration due to slow matrix turnover, a limited supply of mature chondrocytes and insufficient vasculature. Although cartilage tissue engineering has achieved some success using agarose as a scaffolding material, major challenges of agarose-based cartilage repair, including non-degradability, poor tissue-scaffold integration and limited processing capability, have prompted the search for an alternative biomaterial. In this study, silk fiber-hydrogel composites (SF-silk hydrogels) made from silk microfibers and silk hydrogels were investigated for their potential use as a support material for engineered cartilage.

Micro-composite substrates for the study of cell-matrix mechanical interactions.

The chemical and physical gradients in the native cell microenvironment induce intracellular polarization and control cell behaviors such as morphology, migration and phenotypic changes. Directed cell migration in response to substrate stiffness gradients, known as durotaxis or mechanotaxis, has drawn attention due to its significance in development, metastasis, and wound healing. We developed a microcomposite substrate (μCS) platform with a microfabricated base and collagen hydrogel top to generate physiological linear stiffness gradients without any variation in chemical or transport properties.

Electrical stimulation enhances cell migration and integrative repair in the meniscus.

Electrical signals have been applied towards the repair of articular tissues in the laboratory and clinical settings for over seventy years. We focus on healing of the meniscus, a tissue essential to knee function with limited innate repair potential, which has been largely unexplored in the context of electrical stimulation. Here we demonstrate for the first time that electrical stimulation enhances meniscus cell migration and integrative tissue repair.

Transient hypoxia improves matrix properties in tissue engineered cartilage.

Adult articular cartilage is a hypoxic tissue, with oxygen tension ranging from <10% at the cartilage surface to <1% in the deepest layers. In addition to spatial gradients, cartilage development is also associated with temporal changes in oxygen tension. However, a vast majority of cartilage tissue engineering protocols involves cultivation of chondrocytes or their progenitors under ambient oxygen concentration (21% O(2)), that is, significantly above physiological levels in either developing or adult cartilage.

The influence and interactions of substrate thickness, organization and dimensionality on cell morphology and migration.

Cells reside in a complex microenvironment in situ, with a number of chemical and physical parameters interacting to modulate cell phenotype and activities. To understand cell behavior in three dimensions recent studies have utilized natural or synthetic hydrogel or fibrous materials. Taking cues from the nucleation and growth characteristics of collagen fibrils in shear flow, we generate cell-laden three-dimensional collagen hydrogels with aligned collagen fibrils using a simple microfluidic device driven by hydrostatic flow.

Chondrocyte nuclear response to osmotic loading.

Cartilage compression results in changes in the shape, volume as well as hydrostatic and osmotic pressure of chondrocytes in situ. For example, changes in the cellular osmotic environment have been shown to modulate chondrocyte biosynthesis and gene expression, however, the mechanosensing mechanisms mediating these responses are relatively unknown. Nuclear shape and size changes resulting from cell deformation have been suggested to alter cell functions, and as such we recently performed a study that reported that chondrocytes and their nuclei respond to osmotic loading with alterations in their size.

Electric field-induced polarization of charged cell surface proteins does not determine the direction of galvanotaxis.

Galvanotaxis, that is, migration induced by DC electric fields, is thought to play a significant role in development and wound healing, however, the mechanisms by which extrinsic electric fields orchestrate intrinsic motility responses are unknown. Using mammalian cell lines (3T3, HeLa, and CHO cells), we tested one prevailing hypothesis, namely, that electric fields polarize charged cell surface molecules, and that these polarized molecules drive directional motility. Negatively charged sialic acids, which contribute the bulk of cell surface charge, redistribute preferentially to the surface facing the direction of motility, as measured by labeling with fluorescent wheat germ agglutinin.