Development of bioinks for 3D printing microporous, sintered calcium phosphate scaffolds

Beta-tricalcium phosphate (β-TCP)-based bioinks were developed to support direct-ink 3D printing-based manufacturing of macroporous scaffolds. Binding of the gelatin:β-TCP ink compositions was optimized by adding carboxymethylcellulose (CMC) to maximize the β-TCP content while maintaining printability. Post-sintering, the gelatin:β-TCP:CMC inks resulted in uniform grain size, uniform shrinkage of the printed structure, and included microporosity within the ceramic. The mechanical properties of the inks improved with increasing β-TCP content. The gelatin:β-TCP:CMC ink (25:75 gelatin:β-TCP and 3% CMC) optimized for mechanical strength was used to 3D print several architectures of macroporous scaffolds by varying the print nozzle tip diameter and pore spacing during the 3D printing process (compressive strength of 13.1 ± 2.51 MPa and elastic modulus of 696 ± 108 MPa was achieved). The sintered, macroporous β-TCP scaffolds demonstrated both high porosity and pore size but retained mechanical strength and stiffness compared to macroporous, calcium phosphate ceramic scaffolds manufactured using alternative methods. The high interconnected porosity (45-60%) and fluid conductance (between 1.04 ×10^-9 and 2.27 × 10^-9 m⁴s/kg) of the β-TCP scaffolds tested, and the ability to finely tune the architecture using 3D printing, resulted in the development of novel bioink formulations and made available a versatile manufacturing process with broad applicability in producing substrates suitable for biomedical applications.