Fig 1.
Schematic representation of the cell transfer setup.
The fs-laser beam is focused through the transparent acceptor petri dish into the reservoir containing the cell-laden hydrogel. The cells accumulate at the hydrogel surface due to the density of histopaque-1083 used for gel preparation. The focus depth is chosen to be between 50 and 65 μm and is therefore located directly beneath the cells. The highly confined optical breakdown generates a rapidly expanding cavitation bubble, which ejects a cell-laden hydrogel jet towards the acceptor slide.
Fig 2.
Representative microscope images of cell-laden hydrogel droplets.
(a) In the bright field image, the large droplets show a diameter of about 200 μm, while the small droplets size up to a diameter of only 80 μm. (b) The fluorescence image reveals a cell survival of up to 91 ± 2% in the larger droplets (red PI staining indicates dead cells, live cells are displayed in green), in small droplets only 62 ± 14% of cells survive the laser-induced transfer.
Fig 3.
(a) Phase contrast microscopy images of droplet arrays printed by femtosecond laser-induced transfer on an acceptor slide with varying laser pulse energies. Scale bar = 200 μm. (b) Plot of transferred droplet diameter versus the laser pulse energy. Pulse energies were determined behind the focusing objective, which has a transmittance of 65% at 1030 nm.
Fig 4.
Time-lapse microscopy of cell migration and proliferation.
Live cells are left to adhere to the Matrigel substrate for 15 min, whereas dead cells are washed away when adding 3 ml DMEM medium, which was gently pipetted into the dish (arrows at 0:00 and 1:00 h). The cells were monitored for a period of 40 h. After two hours of incubation, individual cells start migration and cluster formation, after 09:00 h a common cluster comprising of all cells was formed. Increase of cell number and cluster volume after 30 h indicates proliferation with a cell doubling time of 15 ± 2 hours. Scale bar corresponds to 100 μm.