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Caption : figure s1. (a) photograph of 10% agarose/gelma hydrogel (1:1 ratio). (b) elastic modulus of 10% gelma and 10% agarose/gelma hydrogels. a stable construct with no apparent phase separation or visible disintegration was obtained from mixing agarose and gelma precursors.

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Caption : figure s2. diameter of the bioprinted templates versus time after bioprinting. template diameter was assessed by dispensing 6% (w/v) agarose fibers from 250 µm, 500 µm and 1000 µm capillaries on a glass slide (n=3), recorded immediately after printing and followed for a period of 7 minutes at room temperature with an optical microscope (nikon te 2000-u). results showed that bioprinted templates with a wide range of diameters could be obtained, ranging from 1124.6 ± 11.0 µm to 99.4 ± 27.4 µm, varying according to time after printing.

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Caption : figure s3. microchannels fabricated in fluorescent microbead-laden (red and green) 10% pegdma, pegda and spela hydrogels. all hydrogels had a preserved circular lumen upon removal of agarose template fibers (100 μm scale bars).

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Caption : figure s4. integrated bifurcating microchannel network fabricated in gelma hydrogels. (a) phase contrast microscopy image of microchannels from a top view (500 μm scale bar). (b) photograph of gelma hydrogel construct with fabricated bifurcating microchannels after perfusion with a green dye (2 mm scale bar).

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Caption : figure s5. mc3t3 cell proliferation and spreading upon encapsulation (5x106 cells/ml) in 5, 7 and 10% gelma hydrogels. cells were stained with f-actin and dapi and the cell number was quantified by counting cellular nuclei of 5 individual regions within each sample (n=3) at each time point (**p<0.01, ***p<0.001 compared to gelma 10%). (50 μm scale bar)

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Caption : figure s6. gelma hydrogel concentrations for huvec proliferation and spreading upon seeding. (a-c) 5, (d-f) 7 and (g-i) 10% gelma hydrogels were seeded with 2x105 cells/sample. cells were stained with f-actin and dapi and the cell number was quantified by counting cellular nuclei of 5 individual regions within each sample (n=3) at each time point (***p<0.001 compared to gelma 10%). (100 μm scale bar)

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Caption : figure s7. photographs of microchannels before and after the formation of an endothelial monolayer. (a) gelma hydrogel with fabricated 1 mm diameter microchannels before endothelial monolayer formation. (b) gelma hydrogel with 500 μm diameter microchannels after endothelial monolayer formation (14 d). (c) gelma hydrogel with fabricated 1 mm diameter microchannels under uv light. (d) after endothelial monolayer formation, gfp-expressing huvecs fluoresced under uv light and showed the complete lining of the channels with endothelial cells (10 cent us coin is shown for size comparison).