TRPV4 activation enhances compressive properties and glycosaminoglycan deposition of equine neocartilage sheets.

Objective: To evaluate the effect of Transient Receptor Potential Vanilloid 4 (TRPV4) cation channel modulation on mesenchymal stromal cell (MSC)-derived neocartilage.

Methods: RT-PCR was performed to evaluate mRNA levels of chondrogenic, hypertrophic and candidate mechanoresponsive genes in equine neocartilage sheets exposed to pulses of the TRPV4 agonist (GSK101) at different concentrations (N ​= ​10). Biochemical assays and mechanical tests (double indentation and unconfined compression) evaluated neocartilage properties (N ​= ​5).

Cell Cycle Synchronization of Primary and Cultured Articular Chondrocytes.

Cell cycle synchronization allows cells in a culture, originally at different stages of the cell cycle, to be brought to the same phase. It is normally performed by applying cell cycle arresting chemical agents to cells cultured in monolayer. While effective, isolated chondrocytes tend to dedifferentiate when cultured in monolayer and typically require 3D culturing methods to ensure phenotypic stability.

Lithium chloride-induced primary cilia recovery enhances biosynthetic response of chondrocytes to mechanical stimulation.

Mechanical stimulation is commonly used in cartilage tissue engineering for enhancing tissue formation and improving the mechanical properties of resulting engineered tissues. However, expanded chondrocytes tend to dedifferentiate and lose expression of their primary cilia, which is necessary for chondrocyte mechanotransduction. As treatment with lithium chloride (LiCl) can restore passaged chondrocytes in monolayer, in this study, we investigated whether this approach would be effective in 3D culture and restore chondrocyte mechanosensitivity.

Effect of nutrient metabolism on cartilaginous tissue formation.

A major shortcoming in cartilage tissue engineering is the low biosynthetic response of chondrocytes. While different strategies have been investigated, a novel approach may be to control nutrient metabolism. Although known for their anaerobic metabolism, chondrocytes are more synthetically active under conditions that elicit mixed aerobic-anaerobic metabolism.

Characterization of Mechanical and Dielectric Properties of Silicone Rubber.

Silicone rubber's silicone-oxygen backbones give unique material properties which are applicable in various biomedical devices. Due to the diversity of potential silicone rubber compositions, the material properties can vary widely. This paper characterizes the dielectric and mechanical properties of two different silicone rubbers, each with a different cure system, and in combination with silicone additives.

Optimization of culture media to enhance the growth of tissue engineered cartilage.

Tissue engineering is a promising option for cartilage repair. However, several hurdles still need to be overcome to develop functional tissue constructs suitable for implantation. One of the most common challenges is the general low capacity of chondrocytes to synthesize cartilage-specific extracellular matrix (ECM).

Cell Cycle Synchronization of Primary Articular Chondrocytes Enhances Chondrogenesis.

Objective: Although tissue engineering is a promising option for articular cartilage repair, it has been challenging to generate functional cartilaginous tissue. While the synthetic response of chondrocytes can be influenced by various means, most approaches treat chondrocytes as a homogeneous population that would respond similarly. However, isolated cells heterogeneously progress through the cell cycle, which can affect macromolecular biosynthesis.

Engineering of scaffold-free tri-layered auricular tissues for external ear reconstruction.

Objectives: Current strategies for external ear reconstruction can lead to donor site morbidity and/or surgical complications. Tissue-engineered auricular tissues may provide readily available reconstructive materials that resemble native auricular tissue, which is composed of a cartilaginous region sandwiched between two perichondrial layers. We previously developed scaffold-free bi-layered auricular tissues, consisting of a perichondrial layer and a cartilaginous layer, by cultivating chondrocytes and perichondrial cells in a continuous flow bioreactor.

Stochastic Resonance with Dynamic Compression Improves the Growth of Adult Chondrocytes in Agarose Gel Constructs.

Dynamic mechanical stimulation has been an effective method to improve the growth of tissue engineering cartilage constructs derived from immature cells. However, when more mature cell populations are used, results are often variable due to the differing responses of these cells to external stimuli. This can be especially detrimental in the case of mechanical loading.

Comparisons of Auricular Cartilage Tissues from Different Species.

Objectives: Tissue engineering of auricular cartilage has great potential in providing readily available materials for reconstructive surgeries. As the field of tissue engineering moves forward to developing human tissues, there needs to be an interspecies comparison of the native auricular cartilage in order to determine a suitable animal model to assess the performance of engineered auricular cartilage in vivo.

Methods: Here, we performed interspecies comparisons of auricular cartilage by comparing tissue microstructure, protein localization, biochemical composition, and mechanical properties of auricular cartilage tissues from rat, rabbit, pig, cow, and human.

Scaffold-free cartilage tissue engineering with a small population of human nasoseptal chondrocytes.

Objective: Cartilage tissue engineering is a promising approach to provide suitable materials for nasal reconstruction; however, it typically requires large numbers of cells. We have previously shown that a small number of chondrocytes cultivated within a continuous flow bioreactor can elicit substantial tissue growth, but translation to human chondrocytes is not trivial. Here, we aimed to demonstrate the application of the bioreactor to generate large-sized tissues from a small population of primary human nasoseptal chondrocytes.

Hydrogels with integrin-binding angiopoietin-1-derived peptide, QHREDGS, for treatment of acute myocardial infarction.

Background: Hydrogels are being actively investigated for direct delivery of cells or bioactive molecules to the heart after myocardial infarction (MI) to prevent cardiac functional loss. We postulate that immobilization of the prosurvival angiopoietin-1-derived peptide, QHREDGS, to a chitosan-collagen hydrogel could produce a clinically translatable thermoresponsive hydrogel to attenuate post-MI cardiac remodeling.

Methods And Results: In a rat MI model, QHREDGS-conjugated hydrogel (QHG213H), control gel, or PBS was injected into the peri-infarct/MI zone.

Biomaterials in myocardial tissue engineering.

Cardiovascular disease is the leading cause of death in the developed world, and as such there is a pressing need for treatment options. Cardiac tissue engineering emerged from the need to develop alternative sources and methods of replacing tissue damaged by cardiovascular diseases, as the ultimate treatment option for many who suffer from end-stage heart failure is a heart transplant. In this review we focus on biomaterial approaches to augmenting injured or impaired myocardium, with specific emphasis on: the design criteria for these biomaterials; the types of scaffolds - composed of natural or synthetic biomaterials or decellularized extracellular matrix - that have been used to develop cardiac patches and tissue models; methods to vascularize scaffolds and engineered tissue; and finally, injectable biomaterials (hydrogels) designed for endogenous repair, exogenous repair or as bulking agents to maintain ventricular geometry post-infarct.

Perfusable branching microvessel bed for vascularization of engineered tissues.

Vascularization is critical for the survival of engineered tissues in vitro and in vivo. In vivo, angiogenesis involves endothelial cell proliferation and sprouting followed by connection of extended cellular processes and subsequent lumen propagation through vacuole fusion. We mimicked this process in engineering an organized capillary network anchored by an artery and a vein.

Controlled delivery of thymosin β4 for tissue engineering and cardiac regenerative medicine.

Thymosin β4 (Tβ4) is a peptide with multiple biological functions. Here, we focus on the role of Tβ4 in vascularization, and review our studies of the controlled delivery of Tβ4 through its incorporation in biomaterials. Tβ4 promotes vascularization through VEGF induction and AcSDKP-induced migration and differentiation of endothelial cells.

Hydrogel substrate stiffness and topography interact to induce contact guidance in cardiac fibroblasts.

Previous studies demonstrated the importance of substrate stiffness and topography on the phenotype of many different cell types including fibroblasts. Yet the interaction of these two physical parameters remains insufficiently characterized, in particular for cardiac fibroblasts. Most studies focusing on contact guidance use rigid patterned substrates.

Biofabrication enables efficient interrogation and optimization of sequential culture of endothelial cells, fibroblasts and cardiomyocytes for formation of vascular cords in cardiac tissue engineering.

We previously reported that preculture of fibroblasts (FBs) and endothelial cells (ECs) prior to cardiomyocytes (CMs) improved the structural and functional properties of engineered cardiac tissue compared to culture of CMs alone or co-culture of all three cell types. However, these approaches did not result in formation of capillary-like cords, which are precursors to vascularization in vivo. Here we hypothesized that seeding the ECs first on Matrigel and then FBs 24 h later to stabilize the endothelial network (sequential preculture) would enhance cord formation in engineered cardiac organoids.

Controlled release of thymosin β4 from injected collagen-chitosan hydrogels promotes angiogenesis and prevents tissue loss after myocardial infarction.

Aims: Acute myocardial infarction (MI) leads to fibrosis and severe left ventricular wall thinning. Enhancing vascularization within the infarct reduces cell death and maintains a thick left ventricular wall, which is essential for proper cardiac function. Here, we evaluated the controlled delivery of thymosin β4 (Tβ4), which supports cardiomyocyte survival by inducing vascularization and upregulating Akt activity, in the treatment of MI.

Vascular endothelial growth factor secretion by nonmyocytes modulates Connexin-43 levels in cardiac organoids.

We previously showed that the sequential, but not simultaneous, culture of endothelial cells (ECs), fibroblasts (FBs), and cardiomyocytes (CMs) resulted in elongated, beating cardiac organoids. We hypothesized that the expression of Cx43 and contractile function are mediated by vascular endothelial growth factor (VEGF) released by nonmyocytes during the preculture period. Cardiac organoids (~200 μm diameter) were cultivated in microchannels to enable rapid screening.

Engineering of oriented myocardium on three-dimensional micropatterned collagen-chitosan hydrogel.

Introduction: Surface topography and electrical field stimulation are important guidance cues that aid the organization and contractility of cardiomyocytes in vivo. We report here on the use of these biomimetic cues in vitro to engineer an implantable contractile cardiac tissue.

Methods: Photocrosslinkable collagen-chitosan hydrogels with microgrooves of 10 µm, 20 µm and 100 µm in width were fabricated using polydimethylsiloxane (PDMS) molds.

Cardiac tissue engineering: current state and perspectives.

The goal of cardiac tissue engineering is to treat cardiovascular diseases through the implantation of engineered functional tissue replacements or the injection of cells and biomaterials, as well as to provide engineered cardiac constructs that can be used as an in vitro model of healthy or diseased heart tissues. This field is rapidly advancing with the new discoveries and improvements in stem cell technologies, materials science, and bioreactor design. In this review, some of the progress made in cardiac tissue engineering in the recent years, as well as the challenges that need to be overcome in future studies, will be discussed.

A peptide-modified chitosan-collagen hydrogel for cardiac cell culture and delivery.

Myocardial infarction (MI) results in the death of cardiomyocytes (CM) followed by scar formation and pathological remodeling of the heart. We propose that chitosan conjugated with the angiopoietin-1 derived peptide, QHREDGS, and mixed with collagen I forms a thermoresponsive hydrogel better suited for the survival and maturation of transplanted cardiomyocytes in vitro compared to collagen and chitosan-collagen hydrogels alone. Conjugation of QHREDGS peptide to chitosan does not interfere with the gelation, structure or mechanical properties of the hydrogel blends.

Controlled release of thymosin β4 using collagen-chitosan composite hydrogels promotes epicardial cell migration and angiogenesis.

Rapid vascularization at the infarcted site is crucial for cardiac repair following myocardial infarction. Thymosin β4 (Tβ4), a 43-amino acid peptide, is both angiogenic and cardioprotective. Tβ4 in soluble form was previously shown to promote cell migration from quiescent adult cardiac explants.

Endothelial cells guided by immobilized gradients of vascular endothelial growth factor on porous collagen scaffolds.

A key challenge in tissue engineering is overcoming cell death in the scaffold interior due to the limited diffusion of oxygen and nutrients therein. We here hypothesize that immobilizing a gradient of a growth/survival factor from the periphery to the center of a porous scaffold would guide endothelial cells into the interior of the scaffold, thus overcoming a necrotic core. Proteins were immobilized by one of three methods on porous collagen scaffolds for cardiovascular tissue engineering.

Engineered cardiac tissues.

Cardiac tissue engineering offers the promise of creating functional tissue replacements for use in the failing heart or for in vitro drug screening. The last decade has seen a great deal of progress in this field with new advances in interdisciplinary areas such as developmental biology, genetic engineering, biomaterials, polymer science, bioreactor engineering, and stem cell biology. We review here a selection of the most recent advances in cardiac tissue engineering, including the classical cell-scaffold approaches, advanced bioreactor designs, cell sheet engineering, whole organ decellularization, stem cell-based approaches, and topographical control of tissue organization and function.