Supplementary Information

I. Transfer of solution from mixing to printing

The Cellulose Acetate (CA)-acetone mixer was first sealed and mixed by SpeedMixer (FlackTec Inc.) under 2000 rpm for 4 minutes. Then the flask remained sealed with its cover for another 5 hours for a complete dissolve of CA. Later, the flask’s cover was quickly replaced with a concentric-ring shape piston (FlackTec Inc.) connected to a 30-cc 3D printing cartridge. The piston was pushed towards the mixed solution, and enable it transferred into the cartridge easily.

Next, the cartridge was separated from the concentric shape piston and another red-color piston was pushed into the cartridge. The red-color piston was pushed further for around 0.5 mm to remove the solution exposed to air. The ink that flowed out of the cartridge tip was wiped out and followed with an immediate installation of the printing needle. The ink was completely sealed within the cartridge before and during the printing (Please see Figure 1).

We believe the above methods and operation can limit the solvent evaporation into a negligible extent.

(a) (b) (c)

Figure 1. Mixing flask, concentric ring shape piston, 3D printing cartridge, top to bottom (a), their assembly (b), and cartridge loaded with solution (c)

II. Tensile test fixture

The tensile fixture was purchased with the HR-2 Rheometer, TA Instruments and shown in Figure 2. The fixture can deform the tension rectangular sample with a constant velocity, typically 3-10 µm/s.

The bulk solid sample and printed scaffold samples were cut into a rectangular shape and width 4-5 mm. the length of test was the same as the loading gap.

Figure 2. Tensile test fixture from HR-2 Rheometer (TA Instruments)

III. 3-D printing equipment, deposition method/mechanism, and specification of printing head

The 3D-bioplotter (EnvisionTec) is an effective prototyping tool for processing a wide variety of materials and create scaffold structures. The instrument is managed by the VisualMachine software which imports 3D CAD models created by the user and form a complex inner structure with a user-designed interconnectivity porosity.

The main mechanism of printing is extrusion. The instrument is connected to compressed air, which not only power ups the movement of the printing robot head, but also creates pressure to extrude the ink for the printing process. There are two major parameters that controls the printing performance: pressure of compressed air, and the movement speed of the printing head (or the needle).

There are three printing heads: Low-Temperature-Viscous (LTV)-Dispense Head, High-Temperature-Viscous (HTV)-Dispense Head, and UV-Curing Head. The HTV-Dispense Head is used to melt thermoplastic polymers in a stainless-steel cartridge and extrude the melt. The head can be used from room temperature to 250 , and pressure up to 8 bar. The UV-Curing Head is designed to cure the UV-℃curable resin printed by the other two heads. LTV-Dispense Head is used in this study. It is designed to take 30cc Polyethylene (PE) cartridges with luer-lock needles, and print viscous material that flows at

lower temperature, such as hydrogel or polymer solution. The head runs in a temperature range 0-70 ℃ and up to 5 bar pressure.

Figure 3. LTV- Dispense Head (left) and its schematic [1] (Right)

A straight-line pattern was used to print the scaffold structure. The parameters for pattern control are shown in Figure 4. The angles are controlled as 0 and 90 degrees in alternating layers to create a scaffold with perpendicular strands.

Figure 4. Printing pattern and its parameter control [1]

IV. Steady shear rate ramp of all inks: The first derivative of log (viscosity)

Figure 5. Steady shear rate ramp of all inks: The first derivative of log (viscosity)

The contents in Figure 5 has been discussed in the manuscript, Secession 3.1.

Reference:

[1] Instruction Manual for the 3D-Bioplotter, EnvisionTec