Immediate drop on demand technology - a new technology for cell dispensing in a nanoliter range

The handling and dosing of cells is the most critical step in the microfabrication of cell-based assay systems for screening and toxicity testing applications. The use of robotic workstations for liquid handling has increased enormously over the last decades, in order to meet the requirements for high accuracy and high throughput of current bioanalytics. However, dispensing small volumes of cell suspensions up to the single cell level is still a great challenge.

The Fraunhofer IPA developed the immediate drop on demand technology (I-DOT) to overcome the challenge of dispensing cells in a small volume precisely and with low shear stress. It is a fast and flexible non-contact liquid handling system enabling dispensing liquids without the risk of cross-contamination down to a precise volume in the nanoliter range. 
Liquid is dispensed from a special source plate with a nozzle at the bottom. The small diameter keeps the liquid due to capillary forces inside the well and prevents leaking under normal pressure. To release a defined amount of liquid a short compressed air pulse is given through a quick release valve into the well, exceeding the capillary pressure in the nozzle. Droplets with a defined volume can be spotted directly onto plates or other cell culture devices.

We present a study on the performance and biological impact of this technology by applying viable mammalian cells. The cell line MCF-7, primary skin cells and human mesenchymal stem cells (hMSCs) were tested for viability, adherence capability, apoptosis induction and proliferative capacity after printing with the I-DOT. Since stem cells are more sensitive to stress compared to cell lines and primary cells, hMSCs were analyzed for their adipogenic and osteogenic differentiation capacity after printing. For all cell types tested, viability after dispensing was comparable to the control, all cells had a viability > 80 %. I-DOT application did not affect hMSCs in undergoing adipogenic and osteogenic differentiation.

I-DOT is an automated dispensing platform which can be easily integrated into automated work stations. It enables the user to apply accurate cells without detrimental fluorochrome tagging and shows promising potential for single cell and non-invasive stem cell application, 3D-bioprinting and biomarker screening.