Search

In tissue engineering applications, vascularization can be accomplished by coimplantation of tissue forming cells and endothelial cells (ECs), whereby the latter are able to form functional blood vessels. The use of three-dimensional (3D) bioprinting technologies has the potential to improve the classical tissue engineering approach because these will allow the generation of scaffolds with high spatial control of endothelial cell allocation. This study focuses on a side by side comparison of popular commercially available bioprinting hydrogels (Matrigel, fibrin, collagen, gelatin, agarose, Pluronic F-127, alginate, and alginate/gelatin) in the context of their physicochemical parameters, their swelling/degradation characteristics, their biological effects on vasculogenesis-related EC parameters and their printability. The aim of this study was to identify the most suitable hydrogel or hydrogel combination for inkjet printing of ECs to build prevascularized tissue constructs. Most tested hydrogels displayed physicochemical characteristics suitable for inkjet printing. However, Pluronic F-127 and the alginate/gelatin blend were rapidly degraded when incubated in cell culture medium. Agarose, Pluronic F- 127, alginate and alginate/gelatin hydrogels turned out to be unsuitable for bioprinting of ECs because of their nonadherent properties and/or their incapability to support EC proliferation. Gelatin was able to support EC proliferation and viability but was unable to support endothelial cell sprouting. Our experiments revealed fibrin and collagen to be most suitable for bioprinting of ECs, because these hydrogels showed acceptable swelling/degradation characteristics, supported vasculogenesis-related EC parameters and showed good printability. Moreover, ECs in constructs of preformed spheroids survived the printing process and formed capillary-like cords. [ABSTRACT FROM AUTHOR]

Mesenchymal stem cells (MSCs) represent a very attractive cell source for tissue engineering applications aiming at the generation of artificial bone substitutes. The use of three-dimensional bioprinting technologies has the potential to improve the classical tissue engineering approach because bioprinting will allow the generation of hydrogel scaffolds with high spatial control of MSC allocation within the bioprinted construct. In this study, we have performed direct comparisons between commercially available hydrogels in the context of their cytocompatibility toward MSCs and their physicochemical parameters with the aim to identify the most suitable hydrogel for drop-on-demand (DoD) printing of MSCs. In this context, we examined matrigel, fibrin, collagen, gelatin, and gelatin/alginate at various hydrogel concentrations. Matrigel, fibrin, collagen, and gelatin were able to support cell viability, but the latter showed a limited potential to promote MSC proliferation. We concentrated our study on fibrin and collagen hydrogels and investigated the effect of hydroxyapatite (HA) inclusion. The inclusion of HA enhanced proliferation and osteogenic differentiation of MSCs and prevented degradation of fibrin in vitro. According to viscosity and storage moduli measurements, HA-blends displayed physicochemical characteristics suitable for DoD printing. In bioprinting experiments, we confirmed that fibrin and collagen and their respective HA-blends represent excellent hydrogels for DoD-based printing as evidenced by high survival rates of printed MSCs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3231-3241, 2017. [ABSTRACT FROM AUTHOR]

Angiogenesis is a fundamental process in bone formation, remodeling, and regeneration. Moreover, for the regeneration of bone in tissue engineering applications, it is essential to support neovascularization. This can be achieved by cell-based therapies using primary endothelial cells, which are able to form functional blood vessels upon implantation. In bone composite grafts, coimplanted endothelial cells do not only support neovascularization but also support osteogenic differentiation of osteoblasts and osteoprogenitor cells. In this study, we investigated the effect of endothelial cells on proliferation and cell survival of human primary osteoblasts (hOBs) and human mesenchymal stem cells (MSCs). Human umbilical vein endothelial cells (HUVECs) stimulated hOB and MSC proliferation, whereas proliferation of HUVECs was unaffected by cocultured hOBs or MSCs. The effect of HUVEC cocultivation on hOB and MSC proliferation was more pronounced in direct cocultures than in indirect cocultures, indicating that this effect is at least partially dependent on the formation of heterotypic cell contacts between HUVECs and hOBs or MSCs. Furthermore, HUVEC cocultivation reduced low-serum induced apotosis of hOBs and MSCs by a mechanism involving increased phosphorylation and inactivation of the proapoptotic protein Bad. In summary, our experiments have shown that cocultured HUVECs increase the proliferation and reduce low-serum induced apoptosis of hOBs and MSCs. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1682-1689, 2012 [ABSTRACT FROM AUTHOR]

The neovascularization of three-dimensional voluminous tissues, such as bone, represents an important challenge in tissue engineering applications. The formation of a preformed vascular plexus could maintain cell viability and promote vascularization after transplantation. We have developed a three-dimensional spheroidal coculture system consisting of human primary endothelial cells and human primary osteoblasts (hOBs) to improve angiogenesis in bone tissue engineering applications. In this study, we investigated the survival and vascularization of the engineered implants in vivo. Endothelial cell spheroids were cocultured with hOBs in fibrin and seeded into scaffolds consisting of processed bovine cancellous bone (PBCB). The cell-seeded scaffolds were evaluated for their angiogenic potential in two different in vivo assays: the chick embryo chorioallantoic membrane (CAM) model and the severe combined immunodeficiency disorder (SCID) mouse model. In both assays, the development of a complex three-dimensional network of perfused human neovessels could be detected. After subcutaneous implantation into immunodeficient mice, the newly formed human vasculature was stabilized by the recruitment of murine smooth muscle α-actin-positive mural cells and anastomoses with the mouse vasculature. We conclude that this endothelial cell spheroid system can be used to create a network of functional perfused blood vessels in vivo. The finding that this process takes place with high efficacy in the presence of co-implanted primary osteoblasts and in an osteoconductive environment provided by the PBCB scaffold, suggests that this system may be suitable for improving vascularization in bone tissue engineering. [ABSTRACT FROM AUTHOR]