3. Sacrificial Solid Scaffolds
• Time consuming process
• Low precision placement
of material
Laser Assisted
• Constrained to a layer
by layer approach
• Limited to one print
material
• 200-1600 mm/s
• High precision
Direct-Write
• Require the design of
self-supporting structures
Or
• Complex methods of
encapsulating and
supporting print materials
• 0.01 to 4 mm/s
3D bioprinting methods1,2,3,4
4. 3D printing in a liquid-like solid5
Granular microgels form a “jammed”
solid when dispersed in water
(Typ. 0.2% (w/v) concentration)
~ 5 μm
The granular microgel transitions from a solid
to a fluid state under shearing stresses. It is
termed a liquid-like solid (LLS).
5. How fast is necessary?4,6
0.1
1
10
100
1000
10000
100000
1 10 100 1000 10000
PrintTime(min)
Needle Tip Speed (mm/s)
𝜌 𝑐𝑒𝑙𝑙𝑠 ≈ 104
𝑐𝑒𝑙𝑙𝑠
𝜇𝐿
𝑃𝑟𝑖𝑛𝑡 𝐹𝑒𝑎𝑡𝑢𝑟𝑒 𝑆𝑖𝑧𝑒 ≈ 500 𝜇𝑚
Current published maximum speed = 2.5 mm/s
Proposed maximum print speed = 1000 mm/s
7. Methods and materials to test theory
(b) The granular microgel
demonstrated a yield stress of 20 Pa
and an elastic shear modulus of 120
Pa.
(c) Two different polyethylene glycol
(PEG) print materials were used,
a relatively high viscosity (0.6 Pa-s)
solution and a relatively low viscosity
(3.5 mPa-s) solution.
(a) A spinning dish was used to rotate
the body of LLS, generating high tip
velocities.
𝑉𝑡𝑖𝑝 = 𝜔𝑟 2 + 𝑉𝑟,𝑧
2
≈ 𝜔𝑟
8. Material preparation – granular microgel
Carbopol ETD 2020 (Lubrizol Corp.) was dispersed in ultrapure water
at concentrations of 0.2% (w/v). Acrylates/ C10-30 Alkyl Acrylate
Crosspolymer
1. Higher concentrations of the microgel (2.5%) were initially
speedmixed in 100 cc cups for approximately 5 minutes. These
were then added to the remaining water to bring the final
concentration to the desired 0.2%.
2. The mixture was vigorously shaken for approximately 5 minutes.
3. A measured amount of 10 N NaOH were added to the final
solution to increase the PH to a range between 6 and 7.
9. Material preparation – print material
Two different molecular weight polyethylene glycol (PEG) compounds
were used. A 35,000 MW PEG at concentration of 30% (w/v) in
ultrapure water served as a “high viscosity” material. A 700 MW PEG
at a concentration of 25% (w/v) in ultrapure water served as a “low
viscosity” material.
1. The PEG was dispersed into test tubes at the desired
concentrations and mixed on a vortex mixer for approximately 10
minutes.
2. Black spectra dye was added to the materials at a concentration of
0.35% (w/v) to increase visibility of the printed lines.
10. 3D printer and spinning dish
3D printer:
• XY&Z Newport ILS servo-driven stages (50 mm/s maximum
speed)
• Microstepping linear actuator syringe pump depresses a 10 mL
disposable syringe (1 mm/s maximum speed)
• 100 mm stainless steel needle, 2.1 mm outer diameter
Spinning dish:
• Final design uses an 8 inch diameter by 4 inch tall clear acrylic
cylinder
• Driven by a coaxially aligned hybrid stepper motor with a
microstepping drive to provide smooth rotation
12. Results
High viscosity print material Low viscosity print materialHigh viscosity print material
Test parameters:
Rotational speed = 2.01 rot/s
Needle tip velocity = 1.05 m/s
Needle OD = 2.01 mm
Flowrate = 160 μL/s
14. Air gap formation
Average observed height:
ℎ = 20 𝑚𝑚
Closing time:
𝑡 = 0.02 𝑠𝑒𝑐𝑜𝑛𝑑𝑠
𝜎𝑔 = 𝜌𝑔ℎ 𝜎𝜇 = 𝛾𝜇 𝐿𝐿𝑆Gravitational Stress: Viscous Stress:
𝜎𝑔 = 𝜎𝜇 → ℎ =
𝛾𝜇 𝐿𝐿𝑆
𝜌𝑔
Two methods proposed to calculate 𝛾:
𝑣 𝑓𝑖𝑙𝑙 =
ℎ
𝑡
𝛾 =
𝑣 𝑓𝑖𝑙𝑙
𝑑
𝛾 =
𝑣 𝑡𝑖𝑝
𝑑
𝜇 𝐿𝐿𝑆 = 0.4 𝑃𝑎 − 𝑠
Both methods predict similar depths of ℎ = 19 𝑚𝑚
15. Conclusion
Stable printing of soft materials at high tip velocities has been demonstrated.
The hypothesis that the maximum stable printing speed will occur at a
Reynold’s number of 5 has been shown to be plausible, but further testing is
required to isolate specific ranges of Reynold’s numbers at which printing in a
LLS becomes unstable.
Other characteristics of high speed printing: the formation of air gaps and the
distortion of the printed stream, have been witnessed but shown to not have
an adverse affect on print quality under the test conditions experienced.
16. References
[1] Trachtenberg, J. E.; Mountziaris, P. M.; Miller, J. S.; Wettergreen, M.; Kasper, F. K.; Mikos, A. G. Open-source
three-dimensional printing of biodegradable polymer scaffolds for tissue engineering. J. Biomed. Mater. Res. -
Part A 2014, 102 (12), 4326–4335 DOI: 10.1002/jbm.a.35108.
[2] Yan, J.; Huang, Y.; Chrisey, D. B. Laser-assisted printing of alginate long tubes and annular constructs.
Biofabrication 2013, 5, 015002 DOI: 10.1088/1758-5082/5/1/015002.
[3] Wu, W.; DeConinck, A.; Lewis, J. A.; Omnidirectional Printing of 3D Microvascular Networks. Adv. Mater.
2011, 23, M178-M183 DOI: 10.1002/adma.201004625.
[4] Murphy, S. V.; Atala, A.; 3D bioprinting of tissues and organs. Nature biotechnology 2014, 32 (8), 773-785
DOI: 10.1038/nbt.2958.
[5] Bhattacharjee, T.; Zehnder, S. M.; Rowe, K. G.; Jain, S.; Nixon, R. M.; Sawyer, W. G.; Angelini, T. E. Writing
in the granular gel medium. Sci. Adv. 2015, 1 (8) DOI: 10.1126/sciadv.1500655.
[6] Miller, J. S. The Billion Cell Construct: Will Three-Dimensional Printing Get Us There? PLoS Biol. 2014, 12
(6), 1–9 DOI: 10.1371/journal.pbio.1001882.
[7] Blevins, R. D. Flow-induced vibration, 2nd ed. Van Nostrand Reinhold: New York, 1990.
17. References continued
[8] Coutanceau, M.; Defaye, J.-R. Circular Cylinder Wake Configurations: A Flow Visualization Survey. Appl.
Mech. Rev. 1991, 44 (6), 255 DOI: 10.1115/1.3119504.
