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Research Papers

Alternating Force Based Drop-on-Demand Microdroplet Formation and Three-Dimensional Deposition

[+] Author and Article Information
Long Zhao, Rui Yao, Feng Lin

Department of Mechanical Engineering,
Biomanufacturing Center,
Tsinghua University,
Beijing 100084, China
Biomanufacturing and Rapid Forming
Technology Key Laboratory of Beijing,
Beijing 100084, China
Key Laboratory for Advanced Materials
Processing Technology,
Ministry of Education,
Beijing 100084, China

Karen Chang Yan

Department of Mechanical Engineering,
The College of New Jersey,
Ewing, NJ 08628

Wei Sun

Department of Mechanical Engineering,
Biomanufacturing Center, Tsinghua University,
Beijing 100084, China
Biomanufacturing and Rapid Forming
Technology
Key Laboratory of Beijing,
Beijing 100084, China
Key Laboratory for Advanced Materials
Processing Technology,
Ministry of Education,
Beijing 100084, China
Department of Mechanical Engineering,
Drexel University,
Philadelphia, PA 19104
e-mails: weisun@tsinghua.edu.cn; sunwei@drexel.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received April 20, 2014; final manuscript received February 9, 2015; published online March 2, 2015. Assoc. Editor: Joseph Beaman.

J. Manuf. Sci. Eng 137(3), 031009 (Jun 01, 2015) (9 pages) Paper No: MANU-14-1237; doi: 10.1115/1.4029803 History: Received April 20, 2014; Revised February 09, 2015; Online March 02, 2015

Drop-on-demand (DOD) microdroplet formation and deposition play an important role in additive manufacturing, particularly in printing of three-dimensional (3D) in vitro biological models for pharmacological and pathological studies, for tissue engineering and regenerative medicine applications, and for building of cell-integrated microfluidic devices. In development of a DOD based microdroplet deposition process for 3D cell printing, the droplet formation, controlled on-demand deposition and at the single-cell level, and most importantly, maintaining the viability and functionality of the cells during and after the printing are all remaining to be challenged. This report presents our recent study on developing a novel DOD based microdroplet deposition process for 3D printing by utilization of an alternating viscous and inertial force jetting (AVIFJ) mechanism. The results include an analysis of droplet formation mechanism, the system configuration, and experimental study of the effects of process parameters on microdroplet formation. Sodium alginate solutions are used for microdroplet formation and deposition. Key process parameters include actuation signal waveforms, nozzle dimensional features, and solution viscosity. Sizes of formed microdroplets are examined by measuring the droplet diameter and velocity. Results show that by utilizing a nozzle at a 45 μm diameter, the size of the formed microdroplets is in the range of 52–72 μm in diameter and 0.4–2.0 m/s in jetting speed, respectively. Reproducibility of the system is also examined and the results show that the deviation of the formed microdroplet diameter and the droplet deposition accuracy is within 6% and 6.2 μm range, respectively. Experimental results demonstrate a high controllability and precision for the developed DOD microdroplet deposition system with a potential for precise cell printing.

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Figures

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Fig. 1

(a) Principle of microdroplet formation based on AVIFJ and (b) process of microdroplet formation based on AVIFJ

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Fig. 2

Microdroplet deposition system based on AVIFJ

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Fig. 3

Actuation waveforms: (a) quadratic wave, (b) sinusoidal wave, (c) triangular wave, (d) square wave, and (e) region of single droplet formation under various waveforms

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Fig. 4

Applied quadratic voltage waveform

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Fig. 5

Effect of the applied voltage on the microdroplet diameter (a) and the microdroplet velocity (b). (Printing condition: alginate concentration: 0.5% (w/v), nozzle diameter: 45 μm, frequency: 50 Hz, and height of liquid column H: 70 mm).

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Fig. 6

Effect of the signal frequency on the microdroplet diameter (a) and the microdroplet velocity (b). (Printing condition: alginate solution concentration: 0.5% (w/v), nozzle diameter: 45 μm, applied voltage U: 90 V, and height of liquid column H: 70 mm).

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Fig. 7

Effect of the duty ratio of nozzle elongation stage on the microdroplet diameter (a) and the microdroplet velocity (b). (Printing condition: alginate solution concentration: 0.5% (w/v), nozzle diameter: 45 μm, applied voltage U: 90 V, and height of liquid column H: 70 mm).

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Fig. 8

(a) Fine-tuning quadratic waveform can yield microdroplets with diameter very close to the nozzle diameter and (b) microsphere of 1% (w/v) alginate (CaCl2.cross-linking). (Printing condition: nozzle diameter: 95 μm, applied voltage U: 90 V, frequency: 50 Hz, and height of liquid column H: 70 mm).

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Fig. 9

Effect of the nozzle diameter on the diameter of microdroplet (a) and the velocity of microdroplet (b). (Printing condition: alginate solution concentration: 0.5% (w/v), nozzle diameter: 45 μm, applied voltage U: 90 V, frequency: 50 Hz, and height of liquid column H: 70 mm).

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Fig. 10

Effect of the liquid column height on the diameter of microdroplet (a) and the velocity of microdroplet (b). (Printing condition: alginate solution concentration: 0.5% (w/v), nozzle diameter: 45 μm, applied voltage U: 90 V, and frequency: 50 Hz).

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Fig. 11

Effect of the viscosity of alginate solution on the diameter of microdroplet (a) and the velocity of microdroplet (b). (Printing condition: nozzle diameter: 45 μm, applied voltage U: 90 V, frequency: 50 Hz, and height of liquid column H: 70 mm).

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Fig. 12

Comparison between the experimental data and the predictions from the fitted model: (a) the upper and lower limits of the applied voltage for forming single droplet versus the frequency of the actuation signal (viscosity = 4.3 mPa s and nozzle diameter = 45 μm); (b) the upper and lower limits of the applied voltage for forming single droplet versus the viscosity of the alginate solution (frequency = 50 Hz and nozzle diameter = 45 μm); (c) the upper and lower limits of the applied voltage for forming single droplet versus the diameter of the dispensing nozzle (frequency = 50 Hz and viscosity = 4.3 mPa s); (d) the 3D plot of the predictions of the upper and lower voltage limits rendered from the fitted model as a function the diameter of the dispensing nozzle and the viscosity of the alginate solution (frequency = 50 Hz); (e) the 3D plot of the predictions of the upper and lower voltage limits rendered from the fitted model as a function the diameter of the dispensing nozzle and the frequency of the actuation signal (viscosity = 4.3 mPa s); and (f) the 3D plot of the predictions of the upper and lower voltage limits rendered from the fitted model as a function the viscosity of the alginate solution and the frequency of the actuation signal (nozzle diameter = 45 μm)

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Fig. 13

(a) Micrograph of the printed microdroplet array and (b) distribution of the measured diameter of microdroplet

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