## 3 Results  
In order to show how to transfer a vascular pattern from an image of a rat mesenteric vascular bed, obtained after the in vivo perfusion of an optical contrast enhancer to a printed construct (Figure 1A) [27], we used the procedure employed in our recent publication [19]. After background color reversal and segmentation, the vascular segments were identified (Figure 1B) and split in two separate arterial and venous groups (Figure 1C,D) respectively. To these vascular fields, we then applied the branch analysis provided by the VESGEN 2D software, which identified three branch generations (in colors in Figure 1E,F). These files served for branch-specific.stl file generation (Figure 2A,B); then, we proceeded to direct-write printing with colored Nivea paste as a surrogate bioink (Figure 2C,D). We also printed these mesenteric vascular patterns with hydrogels (Figure S1), specifically with acidic (Figure S1A,B) and neutral (Figure S1C,D) collagen bioinks, with alginate-nanocellulose bioink (Figure S1E,F), and also with two-colors labeled EC in collagen bioink (1:1 with culture medium) (Figure S1G,H). Altogether, we found that acidic collagen best preserved the lines' morphology and resolution, as in our previous study [19]. Figure 1: **Preparation and analysis of rat vascular mesenteric images. ** (**A**) The background-inverted fluorescence image (from [27]). (**B**) This image was segmented and separated into the arterial (red) and venular (blue) components. (**C**) Separated arterial pattern. (**D**) Separated venous pattern. (**E**) VESGEN 2D assignment of branching in the arterial patterns to three generations. (**F**) Similar assignment of the venous pattern branches to three generations. Bar: 2 mm for all images. Similarly, to assess the usefulness of this workflow for generation of printable vascular patters with a different organization, we applied the same protocol to a segment of mouse colon. As shown in Figure 3, compared to that of the mesentery, the colon microvasculature has a criscrossed and a more uniform network-like (rather than branched) organization. In this case, we could not separate the arterial from venous components, as there was no identifiable branch-originating ('trunk') vessel visible in these images, taken from the luminal side of the colon (Figure 3A). However, by applying the standard VESGEN 2D image processing protocol in the 'network analysis' mode (Figure 3B-D), and after generation reduction (Figure S2A), the program still identified a gradient of vessel dimensions and connections, suggesting a progressive branching going from left to right in Figure S2B-D.  
Figure 3: **Image processing of a mouse colon vascular pattern**. (**A**) Original light microscopy image. (**B**) Image’s background color inversion. (**C**) Image segmentation. (**D**) Identification with VESGEN 2D of six generations of vascular branches (color code in the insert). Bar in **A**: 5 mm for all images. The original length of the segment in this image is 3.5 cm (from [22]). Figure 2: **Conversion of mesenteric vascular branches into printable objects**. The individual classes were separated and converted in printable arterial (**A**) and venous (**B**).stl files, and direct-write printed with the colored bioink surrogate ((**C**) and (**D**), respectively). Bars: 5 mm. For printing, we selected a central region of the image containing the overlap of these three 'pseudo-generations' (Figure 4A). The background was reverted again for clarity of the image (Figure 4B), and the three generations were separated and converted in individual stl files (Figure 4C). These files were then printed in contiguity with the correspondingly colored surrogate bioink (Figure 4D), as well as with two common bioinks, one based on collagen (Figure S3A) and one on nanocellulose-containing alginate (Figure S3B). The colonic vascular network was also projected on a cylinder, as described in Materials and Methods.