Laser-induced-forward transfer - a tool for cell sorting and printing

Motivation Printing of living cells enables the development of new concepts in cell biology, tissue engineering and cell based in vitro assays. Today several technologies, which allow multi-cell printing are under investigation. Within this study, we developed a process, which allows single cell printing. Single-cell resolution printing may become a key technology towards understanding the fundamental interactions between different cell types and their stoichiometry. Methodology A highly automated single cell printing system, using Laser Induced Forward Transfer (LIFT) technology has been developed. Besides cell printing transferring of biomolecules and hydrogels over distances up to 2 mm is possible. The LIFTSYSTM cell printing system uses a transfer slide consisting of three layers. The first layer is a support layer (glass) which is transparent for laser irradiation, followed by an irradiation absorbing layer (e.g. 80 nm titanium) and a transfer layer laden with cells or proteins. By applying a laser pulse from a UV-laser source on the absorption layer, a vapor bubble is generated in the transfer layer. Its expansion and collapse propels the transfer layer with forward. Hence, the embedded cell is transferred onto a receiver slide within a fluid jet in a well-defined volume. The developed machine offers the capability to analyze the cells on the transfer slide before transferring. Optical methods are used for single cell selection. Parameters for cell sorting could be proliferation activity. Results With LIFTSYSTM we show a tool design, which enables us to localize single cells before the transfer process. By using an automated positioning system defined cell patterns can be generated. By using various hydrogels or proteins, we demonstrated that we could vary the surrounding ECM conditions. Single cell printing with an accuracy of less than 50 mm is possible. For higher cell viability we established a two-layered transfer layer and printed different cells like BHK, 3T3, K562 and HUVEC-Cells. With this approach the transfer volume is minimized and the cell survival rate of single cell transfer is more than 90%. Further investigations have been carried out to study the behavior of printed single pericytes in a colony of HUVECS and the subsequent behavior and proliferation of the cells. Discussion With our results we show that our technology allows for new insight in the optimization of cell-cell positioning. The technology allows us to investigate their interactions, the influence of cell stoichiometry as well as the selection of specific cells in large cell colonies. In future developments we will include analytical tools into our LIFTSYSTM machine for improving the automated cell selection.