Laser bioprinting of cell spheroids has been investigated, since this approach is generally considered promising for the fabrication of vasculature structures. For laser printing experiments, an automated detection of spheroids and spatial pulse shaping (to reach flat-top or donut-like intensity distributions) was developed. It has been observed that the printability of spheroids strongly depends on the type of applied cells and their bounding. If the cell bounding is too loose, spheroids disintegrate during the printing procedure. Others remain intact and all cells in the spheroid remain viable. However, a considerable amount of bio-ink is also transferred during printing. If two spheroids are printed directly next to each other, the spheroid printed first is sometimes washed away when the second one is printed. The positioning accuracy is also reduced compared to printing of dissociated cells. It has been observed that spheroids consisting only from endothelial cells (ECs) can fuse into continuous strands with the formation of a lumen inside.
As a basis for a tissue perfusion system, an Arduino-controlled microfluidic actuation platform with peristaltic pump and sensors was developed, together with different designs for microfluidic chips for applications with and without scaffolds. For the fabrication of large-scale vascular scaffolds with high structural resolution and at high throughput, a new 2PP machine prototype was designed; currently, customised machine parts are in production, commissioning, and testing. Furthermore, material selection and construction of experimental scaffold-like vascular structures suitable for perfusion has been performed with the existing 2PP system. Scaffolds were protein-coated, pre-colonized with ECs and smooth muscle cells (SMCs), and perfused, partially embedded in tissue. Moreover, vascular networks embedded in tissue, extra-cellular matrix (ECM) with fibroblasts (partially with overlying keratinocyte layers), were printed, cultivated for a few days, and a potential vessel formation was studied; printed tissue with integrated vascular structure was perfused for up to 7 days.
