  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.
