Design And Verification Of Pneumatic Valve Controlled Droplet Injection Device For Cell Printing

Cell printing which is based on micro-droplet jetting is an important approach for patterning of cells.Its potential applications include 3D printing of organs or tissues,which might be used for researches of related diseases.Realizing a high viability of cells after a printing process is certainly crucial for this technology.To print cells and maintain high cell viability,a pneumatic droplet-on-demand(DOD)system is designed.The key components of the system include a chamber for liquid sample,a tiny orifice of 100 micron.The chamber is connected to a Nitrogen gas tank with a high speed solenoid valve,and to the ambiance with a venting tube.A photographic system is used to evaluate the uniformity and consistency of the DOD system.A pressure pulse is created within the chamber via controlling the solenoid valve.The liquid is pushed out through the nozzle,generating a droplet.The gas is then released through the venting tube,recovering the system back to equilibrium.As confirmed by the photographic system,the device is stable at not higher than 25 Hz injection frequency.The injection of human peripheral blood lymphocytes(diameter 10-15?m)and bronchial epithelial cells(diameter 50-70?m)was achieved.The results show that: when the diameter of the cell is far less than the orifice diameter,the effect of injection process on cell viability can be ignored;if the diameter of the cell is comparable to the diameter of the orifice,the survival rate of the cells decreases significantly.In order to further improve the injection efficiency,this paper makes improvements on the structure of the liquid storage chamber and optimization of the solenoid valve control.The results show that the injection frequency can be increased from 25 Hz to 70 Hz,and the improvement effect is obvious.Using the optimized injection device for cell injection experiments,we found that a significant increase in injection frequency has no significant effect on cell activity.Pneumatic valve-controlled micro droplet injection technology is expected to be used in cell 3D printing field,and provides basis for the realization of tissue organ printing.