Tropoelastin coated PLLA-PLGA scaffolds promote vascular network formation

The robust repair of large wounds and tissue defects relies on blood flow. This vascularization is the major challenge faced by tissue engineering on the path to forming viable thick, implantable tissue constructs. Without the presence of this vascular network, oxygen and nutrients cannot reach the cells located far from host blood vessels. To create viable constructs, tissue engineering takes advantage of the mechanical properties of synthetic materials, while combining them with extracellular matrix (ECM) proteins to create a natural environment for the tissue-specific cells. Tropoelastin, the precursor of the elastin, is the ECM protein responsible for elasticity in all elastic tissues in the body, including robust blood vessels. We seeded human adipose microvascular endothelial cells (HAMECs) combined with mesenchymal stem cells (MSCs) on poly(L-lactic acid)/poly(lactide-co-glycolide) (PLLA/PLGA) scaffolds treated with tropoelastin, and examined the morphology, expansion and maturity of the newly formed vessels. Our in vitro results demonstrate that the treated scaffolds show a more expanded, complex and developed vascularization, in comparison to the untreated control group. To further explore the benefits of tropoelastin-treated scaffolds, we implanted pre-vascularized constructs within the mouse abdominal wall muscle by replacing a piece of the muscle with the engineered constructs. Within 12 days after implantation, we saw enhanced perfusion by host blood vessels. These results point to the great potential of these combined materials in promoting the vascularization of implanted tissue engineered constructs

The influence of scaffold elasticity on germ layer specification of human embryonic stem cells

Mechanical forces are critical to embryogenesis, specifically, in the lineage-specification gastrulation phase, whereupon the embryo is transformed from a simple spherical ball of cells to a multi-layered organism, containing properly organized endoderm, mesoderm, and ectoderm germ layers. Several reports have proposed that such directed and coordinated movements of large cell collectives are driven by cellular responses to cell deformations and cell-generated forces. To better understand these environmental-induced cell changes, we have modeled the germ layer formation process by culturing human embryonic stem cells (hESCs) on three dimensional (3D) scaffolds with stiffness engineered to model that found in specific germ layers. We show that differentiation to each germ layer was promoted by a different stiffness threshold of the scaffolds, reminiscent of the forces exerted during the gastrulation process. The overall results suggest that three dimensional (3D) scaffolds can recapitulate the mechanical stimuli required for directing hESC differentiation and that these stimuli can play a significant role in determining hESC fate.Israel Science Foundation. F.I.R.S.T. ProgramNational Institutes of Health (U.S.) (Grant DE-016516)National Institutes of Health (U.S.) (Grant HL-060435

The Role of Biomaterials in Peripheral Nerve and Spinal Cord Injury: A Review

Peripheral nerve and spinal cord injuries are potentially devastating traumatic conditions with major consequences for patients’ lives. Severe cases of these conditions are currently incurable. In both the peripheral nerves and the spinal cord, disruption and degeneration of axons is the main cause of neurological deficits. Biomaterials offer experimental solutions to improve these conditions. They can be engineered as scaffolds that mimic the nerve tissue extracellular matrix and, upon implantation, encourage axonal regeneration. Furthermore, biomaterial scaffolds can be designed to deliver therapeutic agents to the lesion site. This article presents the principles and recent advances in the use of biomaterials for axonal regeneration and nervous system repair

Spinal Cord Repair: From Cells and Tissue Engineering to Extracellular Vesicles

Spinal cord injury (SCI) is a debilitating condition, often leading to severe motor, sensory, or autonomic nervous dysfunction. As the holy grail of regenerative medicine, promoting spinal cord tissue regeneration and functional recovery are the fundamental goals. Yet, effective regeneration of injured spinal cord tissues and promotion of functional recovery remain unmet clinical challenges, largely due to the complex pathophysiology of the condition. The transplantation of various cells, either alone or in combination with three-dimensional matrices, has been intensively investigated in preclinical SCI models and clinical trials, holding translational promise. More recently, a new paradigm shift has emerged from cell therapy towards extracellular vesicles as an exciting “cell-free” therapeutic modality. The current review recapitulates recent advances, challenges, and future perspectives of cell-based spinal cord tissue engineering and regeneration strategies

Localization of Engineered Vasculature within 3D Tissue Constructs

Today, in vitro vessel network systems frequently serve as models for investigating cellular and functional mechanisms underlying angiogenesis and vasculogenesis. Understanding the cues triggering the observed cell migration, organization, and differentiation, as well as the time frame of these processes, can improve the design of engineered microvasculature. Here, we present first evidence of the migration of endothelial cells into the depths of the scaffold, where they formed blood vessels surrounded by extracellular matrix and supporting cells. The supporting cells presented localization-dependent phenotypes, where cells adjacent to blood vessels displayed a more mature phenotype, with smooth muscle cell characteristics, whereas cells on the scaffold surface showed a pericyte-like phenotype. Yes-associated protein (YAP), a transcription activator of genes involved in cell proliferation and tissue growth, displayed spatially dependent expression, with cells on the surface showing more nuclear YAP than cells situated deeper within the scaffold

Enhanced Host Neovascularization of Prevascularized Engineered Muscle Following Transplantation into Immunocompetent versus Immunocompromised Mice

Engineering of functional tissue, by combining either autologous or allogeneic cells with biomaterials, holds promise for the treatment of various diseases and injuries. Prevascularization of the engineered tissue was shown to enhance and improve graft integration and neovascularization post-implantation in immunocompromised mice. However, the neovascularization and integration processes of transplanted engineered tissues have not been widely studied in immunocompetent models. Here, we fabricated a three-dimensional (3D) vascularized murine muscle construct that was transplanted into immunocompetent and immunocompromised mice. Intravital imaging demonstrated enhanced neovascularization in immunocompetent mice compared to immunocompromised mice, 18 days post-implantation, indicating the advantageous effect of an intact immune system on neovascularization. Moreover, construct prevascularization enhanced neovascularization, integration, and myogenesis in both animal models. These findings demonstrate the superiority of implantation into immunocompetent over immunocompromised mice and, therefore, suggest that using autologous cells might be beneficial compared to allogeneic cells and subsequent immunosuppression. Taken together, these observations have the potential to advance the field of regenerative medicine and tissue engineering, ultimately reducing the need for donor organs and tissues