3D printing technology has unlocked various opportunities for patient-specific bone grafts manufacturing, which may revolutionise the orthopedic field. Direct ink writing (DIW), also known as robocasting, is a filament-based extrusion technology that has been highly explored in the bioceramics fabrication, namely, calcium phosphate (CaP)-based materials. The inks for this technology should present proper rheological behavior for injection and retain the shape afterwards to withstand the weight of the subsequent layers. CaP-based scaffolds obtained by DIW usually are submitted to a post-processing step at high temperature (sintering) to attain the required mechanical performance, hindering the addition of any kind of thermosensitive agents, as growth factors, before this step. Self-setting CaP inks that harden at environment temperatures could be a solution to overcome this drawback. Furthermore, platelet lysates (PL) have been employed as an autologous supply of growth factors to bone tissue engineering constructs to improve regeneration.
 
In this light, this work aimed to develop novel apatite self-setting inks enriched with different amounts of PL as a cell-free and protein-rich biological material. Rheological properties of the inks were fine-tuned by optimizing alpha-tricalcium phosphate (-TCP) powder particle size distribution, aqueous-based setting liquid composition, liquid-to-powder ratio and other rheological modifier additives. Inks in the presence and absence of different concentrations of PL were prepared and then used to produce scaffolds with different macropore sizes (300 and 500 µm) through robocasting. The scaffolds were characterised by mechanical performance, crystalline phases composition and structural features. Printable inks and 3D scaffolds were successfully obtained by the formulations developed, opening the way for the production of innovative bioactive components for bone regeneration purposes.

Acknowledgments: This study was funded by European Union’s Horizon 2020 research and innovation programme under the scope of InterLynk project with grant agreement No 953169. The project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MCTES (PIDDAC) is also acknowledged. P. M. C. Torres and S. M. Olhero acknowledge FCT for CEECIND/01891/2017 and CEECIND/03393/2017 contracts, respectively.