Development of a novel high-throughput culture system for hypoxic 3D hydrogel cell culture.

Animal models lack physiologic relevance to the human system which results in low clinical translation of results derived from animal testing. Besides spheroids or organoids, hydrogel-based 3D in vitro models are used to mimic the in vivo situation increasing the relevance while reducing animal testing. However, to establish hydrogel-based 3D models in applications such as drug development or personalized medicine, high-throughput culture systems are required. Furthermore, the integration of oxygen-reduced (hypoxic) conditions has become increasingly important to establish more physiologic culture models. Therefore, we developed a platform technology for the high-throughput generation of miniaturized hydrogels for 3D cell culture. The Oli-Up system is based on the shape of a well-plate and allows for the parallel culture of 48 hydrogel samples, each with a volume of 15 µl. As a proof-of-concept, we established a 3D culture of gelatin-methacryloyl (GelMA)-encapsulated mesenchymal stem/stromal cells (MSCs). We used a hypoxia reporter cell line to establish a defined oxygen-reduced environment to precisely trigger cellular responses characteristic of hypoxia in MSCs. In detail, the expression of hypoxia response element (HRE) increased dependent on the oxygen concentration and cell density. Furthermore, MSCs displayed an altered glucose metabolism and increased VEGF secretion upon oxygen-reduction. In conclusion, the Oli-Up system is a platform technology for the high-throughput culture of hydrogel-based 3D models in a defined oxygen environment. As it is amenable for automation, it holds the potential for high-throughput screening applications such as drug development and testing in more physiologic 3D in vitro tissue models.

A novel concept for scaffold-free vessel tissue engineering: self-assembly of microtissue building blocks.

Current scientific attempts to generate in vitro tissue-engineered living blood vessels (TEBVs) show substantial limitations, thereby preventing routine clinical use. In the present report, we describe a novel biotechnology concept to create living small diameter TEBV based exclusively on microtissue self-assembly (living cellular re-aggregates). A novel bioreactor was designed to assemble microtissues in a vascular shape and apply pulsatile flow and circumferential mechanical stimulation. Microtissues composed of human artery-derived fibroblasts (HAFs) and endothelial cells (HUVECs) were accumulated and cultured for 7 and 14 days under pulsatile flow/mechanical stimulation or static culture conditions with a diameter of 3mm and a wall thickness of 1mm. The resulting vessels were analyzed by immunohistochemistry for extracellular matrix (ECM) and cell phenotype (von Willebrand factor, alpha-SMA, Ki67, VEGF). Self-assembled microtissues composed of fibroblasts displayed significantly accelerated ECM formation compared to monolayer cell sheets. Accumulation of vessel-like tissue occurred within 14 days under both, static and flow/mechanical stimulation conditions. A layered tissue formation was observed only in the dynamic group, as indicated by luminal aligned alpha-SMA positive fibroblasts. We could demonstrate that self-assembled cell-based microtissues can be used to generate small diameter TEBV. The significant enhancement of ECM expression and maturation, together with the pre-vascularization capacity makes this approach highly attractive in terms of generating functional small diameter TEBV devoid of any foreign material.