The impact of fabrication parameters and substrate stiffness in direct writing of living constructs.

Biomolecules and living cells can be printed in high-resolution patterns to fabricate living constructs for tissue engineering. To evaluate the impact of processing cells with rapid prototyping (RP) methods we modelled the printing phase of two RP systems that employ biomaterial inks containing living cells: a high-resolution inkjet system (BioJet) and a lower resolution nozzle based contact printing system (PAM(2) ). In the first fabrication method, we reasoned that cell damage occurs principally during drop collision on the printing surface, in the second we hypothesise that shear stresses act on cells during extrusion (within the printing nozzle). The two cases were modelled changing the printing conditions: biomaterial substrate stiffness and volumetric flow rate, respectively in BioJet and PAM(2) . Results show that during inkjet printing impact energies of about 10(-8) J are transmitted to cells, while extrusion energies of the order of 10(-11) J are exerted in direct printing. Viability tests of printed cells can be related to those numerical simulations, suggesting a threshold energy of 10(-9) J to avoid permanent cell damage. To obtain well-defined living constructs, a combination of these methods is proposed for the fabrication of scaffolds with controlled 3D architecture and spatial distribution of biomolecules and cells