Bioprinting techniques are emerging as potential instruments for the multidisciplinary field of tissue engineering and regenerative medicine. The possibility to arrange multiple cell types in a computer-controlled 3 D manner may substantially improve our understanding about complex cell-cell and cell-environment interaction. Among all bioprinting techniques [1-3], laser-assisted bioprinting (LaBP) approaches based on laser-induced forward transfer were demonstrated to possess additional benefits: (i) tiny amounts of different hydrogels with a wide range of rheological characteristics can be printed in a controlled and precise way [4-8], which is important for the realisation of 3 D cell-hydrogel constructs mimicking various stiffnesses of native tissues; (ii) any desired cell amount ranging from single [9] to dozens of cells [10] can be printed without observable damage to pheno- and genotype [7,9-12]; and (iii) the printing speed (number of droplets per second) depends mainly on the pulse repetition rate of the applied laser. Printing speed of 5000 droplets per second was recently demonstrated [4], which enables fast generation of large cell constructs.
Already demonstrated biological applications reflect the flexibility of this laser printing technique, for instance: (1) generation and differentiation of 3 D stem cell grafts [13], which can be used as in vitro tissue models for the screening of drug effects; (2) assembly of cellular micro arrays of single [11] and multiple [14] cell types for systematic studies of fundamental aspects of cell-cell and cell-environment interaction; (3) computer-controlled seeding of 3 D scaffolds with multiple cell types [15]; and (4) in vivo bioprinting of nano-hydroxyapatite [16]. The principal laser-assisted bioprinting setup (see Figure 1) consists of a pulsed laser source and two positioning systems on which a donor-slide coated with an energy-absorbing material layer carrying the cell-hydrogel compound, and a collector-slide receiving the printed biological material are located. In brief, laser pulses are focussed through the donor-slide onto the gold layer which is evaporated locally at the focal point. This rapid energy deposition leads to the generation of a jet dynamic [17] resulting in the deposition of a tiny hydrogel volume on the collector-slide. Control of the printed volume is a key issue and great efforts have been made to understand the relationship between the printed volume and the processing parameters [5,6,8,18]. Providing a deeper understanding of this relationship is crucial in order to make the printed volume with embedded cells more predictable, and to enable theoretical simulation of cell-cell interaction, cell-extracellular matrix interaction and signalling pathways [12]. However, the whole jet generation process is not completely understood. Moreover, recent studies mainly used glycerol-based fluids to investigate the effects of the laser fluence and fluid properties on the droplet volume [5,8,18] instead of fluids based on fibrin-precursors, which are widely used for bioprinting of different cell types
Already demonstrated biological applications reflect the flexibility of this laser printing technique, for instance: (1) generation and differentiation of 3 D stem cell grafts [13], which can be used as in vitro tissue models for the screening of drug effects; (2) assembly of cellular micro arrays of single [11] and multiple [14] cell types for systematic studies of fundamental aspects of cell-cell and cell-environment interaction; (3) computer-controlled seeding of 3 D scaffolds with multiple cell types [15]; and (4) in vivo bioprinting of nano-hydroxyapatite [16]. The principal laser-assisted bioprinting setup (see Figure 1) consists of a pulsed laser source and two positioning systems on which a donor-slide coated with an energy-absorbing material layer carrying the cell-hydrogel compound, and a collector-slide receiving the printed biological material are located. In brief, laser pulses are focussed through the donor-slide onto the gold layer which is evaporated locally at the focal point. This rapid energy deposition leads to the generation of a jet dynamic [17] resulting in the deposition of a tiny hydrogel volume on the collector-slide. Control of the printed volume is a key issue and great efforts have been made to understand the relationship between the printed volume and the processing parameters [5,6,8,18]. Providing a deeper understanding of this relationship is crucial in order to make the printed volume with embedded cells more predictable, and to enable theoretical simulation of cell-cell interaction, cell-extracellular matrix interaction and signalling pathways [12]. However, the whole jet generation process is not completely understood. Moreover, recent studies mainly used glycerol-based fluids to investigate the effects of the laser fluence and fluid properties on the droplet volume [5,8,18] instead of fluids based on fibrin-precursors, which are widely used for bioprinting of different cell types
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