Piezoelectric Drop-on-Demand Inkjet Printing of Rat Fibroblast Cells: Survivability Study and Pattern Printing

A novel piezoelectric, drop-on-demand (DOD) inkjet system has been developed and used to print L929 rat fibroblast cells. We investigate the survivability of the cells subjected to the large stresses during the printing process. These stresses are varied by changing the diameter of the orifice (36 to 119 microns) through which the cells are dispensed, as well as changing the electrical pulse used to drive the piezoelectric element. It is shown that for the smallest 36 microns diameter orifice, cell survival rates fall from 95% to approximately 76% when the ejection velocity is increased from 2 to 16 m/s. This decrease in survival rates is less significant when the larger orifice diameters of 81 microns and 119 microns are used. Analysis shows that there is a clear inverse relationship between cell survival rates and the mean shear rates during drop formation. By using the same printing set-up, fibroblast cells are printed onto alginate and collagen into patterns. Printed cells are cultured over a period of days to verify their long-term viability. Fibroblasts printed onto the collagen are found to successfully adhere, spread and proliferate, subsequently forming a denser patterns after 5 days in culture. Cell agglomeration is found to affect the printing performance, especially for the printhead with the smallest orifice, leading to frequent clogging of the nozzle. We also study the number of cells in each droplet, when printed under optimal conditions. The probability density of this number follows a binomial distribution, which consistent with a uniform distribution of cells in the medium and within the printhead.