Growing Vascularized Heart Tissue From Stem Cells:

NOS3 regulates angiogenic potential of human induced pluripotent stem cell-derived endothelial cells

Incorporation of blood capillaries in engineered tissues and their functional connection to host blood vessels is essential for success in engineering vascularized tissues, a process which involves spatial patterning of endothelial cells (ECs) to form functional and integrated vascular networks. Different types of ECs have been employed for vascular network formation and each source offers advantages and disadvantages. While ECs derived from induced pluripotent stem cells (iPSC-ECs) offer advantages over primary ECs in that they can be generated in large quantities for autologous applications, their suitability for disease modelling and cell replacement therapies is not well-explored. The present study compares the angiogenic capacity of iPSC-ECs and primary ECs (cardiac microvascular ECs and lymphatic microvascular ECs) using an in vitro tubulogenesis assay, revealing comparable performance in forming a pseudo-capillary network on Matrigel. Analysis of genes encoding angiogenic factors (VEGFA, VEGFC, VEGFD and ANG), endothelial cell markers (PECAM1, PCDH12 and NOS3) and proliferation markers (AURKB and MKI67) indicates a significant positive correlation between NOS3 mRNA expression levels and various tubulogenic parameters. Further experimentation using a CRISPR activation system demonstrates a positive impact of NOS3 on tubulogenic activity of ECs, suggesting that iPSC-ECs can be enhanced with endogenous NOS3 activation. Collectively, these findings highlight the potential of iPSC-ECs in generating vascularized tissues and advancing therapeutic vascularization.

A Tissue Engineering Chamber for Continuous Pulsatile Electrical Stimulation of Vascularized Cardiac Tissues In Vivo

Background: Cardiomyocytes derived from pluripotent stem cells are immature. Maturation of cardiomyocytes is a multifactorial dynamic process that involves various factors in vivo that cannot be fully recapitulated in vitro. Here, we report a novel tissue engineering chamber with an integrated electrical stimulator and electrodes that will allow wireless electrical stimulation of cardiac tissue in vivo. Materials and Methods: Immunocompromised rats were implanted with tissue engineering chambers containing the stimulator and electrodes, and control chambers (chambers with electrical stimulator but without the electrodes) in the contralateral limb. Each chamber contained cardiomyocytes derived from human induced pluripotent stem cells (iPSCs). After 7 days of chamber implantation, the electrical stimulators were activated for 4 h per day, for 21 consecutive days. Results: At 4 weeks postimplantation, cardiomyocytes derived from human iPSCs survived, were assembled into compact cardiac tissue, and were perfused and vascularized by the host neovessels. Conclusion: This proof-of-principle study demonstrates the biocompatibility of the tissue engineering chamber with integrated electrical stimulator and electrodes. This could be utilized to study the influence of continuous electrical stimulation on vascularized cardiac or other tissues in vivo.

Vascularization Strategies for Porous Polyethylene Implants

Porous polyethylene (pPE) is a frequently implanted biomaterial in craniofacial reconstructive surgery. Its rapid vascularization and tissue incorporation are major prerequisites to prevent complications, such as material infection, migration, and extrusion. To achieve this, several sophisticated strategies have been introduced and evaluated during the last 20 years. These include (i) the angiogenic stimulation of the host tissue with epidermal growth factor, basic fibroblast growth factor or macrophage-activating lipopeptide-2, (ii) material modifications, such as increase of surface roughness and incorporation of bioactive glass particles, (iii) surface coatings with growth factors, glycoproteins, acrylic acid, arginine/glycine/aspartic acid peptide as well as components of the plasminogen activation system and autologous clotted blood or serum, and (iv) the seeding with fibroblasts, chondrocytes, stem cells, or adipose-tissue-derived microvascular fragments. The majority of these approaches showed promising results in experimental studies and, thus, may be capable of improving the success rates after pPE implantation in future clinical practice.

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and trade one defect for another. Tissue engineering holds the promise to address this increasing demand. However, most tissue engineering strategies fail to generate stable and functional tissue substitutes because of poor vascularization. This paper focuses on an in vivo tissue engineering chamber model of intrinsic vascularization where a perfused artery and a vein either as an arteriovenous loop or a flow-through pedicle configuration is directed inside a protected hollow chamber. In this chamber-based system angiogenic sprouting occurs from the arteriovenous vessels and this system attracts ischemic and inflammatory driven endogenous cell migration which gradually fills the chamber space with fibro-vascular tissue. Exogenous cell/matrix implantation at the time of chamber construction enhances cell survival and determines specificity of the engineered tissues which develop. Our studies have shown that this chamber model can successfully generate different tissues such as fat, cardiac muscle, liver and others. However, modifications and refinements are required to ensure target tissue formation is consistent and reproducible. This article describes a standardized protocol for the fabrication of two different vascularized tissue engineering chamber models in vivo.