RESUMO
In the present study, we investigated the dynamics of a femtosecond (fs) laser induced bio-printing with cell-free and cell-laden jets under the variation of laser pulse energy and focus depth, by using time-resolved imaging. By increasing the laser pulse energy or decreasing the focus depth thresholds for a first and second jet are exceeded and more laser pulse energy is converted to kinetic jet energy. With increasing jet velocity, the jet behavior changes from a well-defined laminar jet, to a curved jet and further to an undesired splashing jet. We quantified the observed jet forms with the dimensionless hydrodynamic Weber and Rayleigh numbers and identified the Rayleigh breakup regime as the preferred process window for single cell bioprinting. Herein, the best spatial printing resolution of 42 ± 3 µm and single cell positioning precision of 12.4 µm are reached, which is less than one single cell diameter about 15 µm.
RESUMO
Femtosecond laser pulses have been successfully used for film-free single-cell bioprinting, enabling precise and efficient selection and positioning of individual mammalian cells from a complex cell mixture (based on morphology or fluorescence) onto a 2D target substrate or a 3D pre-processed scaffold. In order to evaluate the effects of higher pulse durations on the bioprinting process, we investigated cavitation bubble and jet dynamics in the femto- and picosecond regime. By increasing the laser pulse duration from 600 fs to 14.1 ps, less energy is deposited in the hydrogel for the cavitation bubble expansion, resulting in less kinetic energy for the jet propagation with a slower jet velocity. Under appropriate conditions, single cells can be reliably transferred with a cell survival rate after transfer above 95% through the entire pulse duration range. More cost efficient and compact laser sources with pulse durations in the picosecond range could be used for film-free bioprinting and single-cell transfer.