A bone-like structure of alginate-hydroxyapatite 3D printed by laser-induced forward transfer

Laser-Induced Forward Transfer (LIFT) is a widely used laser-based technique intended to print materials without modifying their properties. One of the main advantages of this transfer technique is that, properly setting the laser parameters and the structure of the donor substrate, materials with different rheology and even physical state can be printed, ranging from low viscosity newtonian fluids to solid state materials. On the other hand, Blister-Assisted Laser-Induced Forward Transfer (BA-LIFT) is a variant of the standard LIFT, wherein a polyimide layer is interposed between the donor substrate and the material to be printed. This configuration eliminates direct laser-material interaction, thereby mitigating photothermal degradation and, in particular in the case of bioinks containing living cells, preserving cell viability. In addition, as nozzle free technologies both avoid clogging problems when ceramic particles are added in the formulation. In this study, we optimized key parameters for the fabrication of three-dimensional scaffolds composed of alginate and tri-calcium phosphate (ALG–TCP) composites using BA-LIFT. The aim was to engineer bone-mimetic constructs capable of acting as extracellular matrices that support cell adhesion and proliferation. The formulation and curing process were tailored and studied to enhance crosslinking efficiency, improving overall biocompatibility while preserving the mechanical stability in the final structure, and minimizing aggressive conditions during the curing process, allowing good cell viability in case of use the formulation to design an ink within embedded living cells. This study demonstrates that a 0.1 M CaCl₂ solution is sufficient to induced effective gelation. Furthermore, the inclusion of TCP particles (20% wt) enhanced the gelation efficiency (75–95%) via surface-mediated release of Ca 2+ ions.