Stable ejection of micro droplets containing microbeads by a piezoelectric inkjet head
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The droplet ejection technology commonly used in inkjet printers has become the focus of numerous biofabrication research field including recent research that examined the ejection of cells through the jets. However, no studies have addressed clogging causes, or the trajectory errors that occur when ejecting particles several tens of micrometers in diameter. Nor have any studies investigated the specific conditions that permit stable ejection of liquid suspensions containing particles that are over 10 μm in diameter. In this study, one of our objectives was to experimentally establish the optimal conditions that gave stable ejection of suspensions containing particles at least 10 μm in size without trajectory errors. An inkjet head was fabricated from transparent glass to permit its interior to be observed. The behaviors of microparticles in the head were recorded using a high-speed camera, and a survey of the optimal conditions was conducted to determine conditions necessary for reliable ejection of particles over 10 μm in diameter. Furthermore, we also investigated the optimal dimensions of the print head nozzle required for stable ejection, the optimal waveform of the voltage pulse applied to a piezoelectric actuator mounted in the head, and the relation between the particle concentration and stable ejection. For stable particle ejection, the nozzle diameter must be at least three times the particle diameter and the voltage waveform driving the piezoelectric actuator generates droplets using the push-pull method. The upper limit of particle volume concentration that permits stable ejection depends on the nozzle diameter, the particle diameter, and the ejection waveform.
KeywordsDroplet Inkjet printing Micro bead Particle Ejection Piezoelectric actuator
The present work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology in Japan Nos. 21676002, 21111503, 21225007 and 23111705, the MEXT project, “Creating Hybrid Organs of the future” at Osaka University, Microjet Corporation, and the Industrial Technology Research Grant Program from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.
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