3D printing of strontium-enriched biphasic calcium phosphate scaffolds for bone regeneration

Calcium phosphate (CaP) scaffolds doping with therapeutic ions are one of the focuses of recent bone tissue engineering research. Among the therapeutic ions, strontium stands out for its role in bone remodeling. This work reports a simple method to produce Sr-doped 3D-printed CaP scaffolds, using Sr-doping to induce partial phase transformation from (3-tricalcium phosphate ((3-TCP) to hydroxyapatite (HA), resulting in a doped biphasic calcium phosphate (BCP) scaffold. Strontium carbonate (SrCO3) was incorporated in the formulation of the 3Dprinting ink, studying (3-TCP:SrO mass ratios of 100:0, 95:5, and 90:10 (named as (3-TCP, (3-TCP/5-Sr, and (3-TCP/ 10-Sr, respectively). Adding SrCO3 in the 3D-printing ink led to a slight increase in viscosity but did not affect its printability, resulting in scaffolds with a high printing fidelity compared to the computational design. Interestingly, Sr was incorporated into the lattice structure of the scaffolds, forming hydroxyapatite (HA). No residual SrO or SrCO3 were observed in the XRD patterns of any composition, and HA was the majority phase of the (3-TCP/10-Sr scaffolds. The addition of Sr increased the compression strength of the scaffolds, with both (3-TCP/5Sr and (3-TCP/10-Sr performing better than the (3-TCP. Overall, (3-TCP/5-Sr presented higher mineralized nodules and mechanical strength, while (3-TCP scaffolds presented superior cell viability. The incorporation of SrCO3 in the ink formulation is a viable method to obtain Sr-BCP scaffolds. Thus, this approach could be explored with other CaP scaffolds aiming to optimize their performance and the addition of alternative therapeutic ions.