Controlling the Bioprinting Efficiency of Alginate–Gelatin by Varying Hydroxyapatite Concentrations to Fabricate Bioinks for Bone Tissue Engineering

A major objective of this study is to investigate the incorporation of hydroxyapatite nanoparticles (nHA) in a biopolymeric matrix of alginate (Alg) and gelatin (Gel), with particular emphasis understanding how controlled variation in nHA concentration affects rheological, mechanical, printing, and biological performance. Although Alg–Gel blends and nHA-containing hydrogels have been previously explored, a systematic and quantitative correlation between nHA loading, viscoelastic recovery, yield behavior, filament fidelity, and cell viability under optimized bioprinting conditions has not been established. Here, we address this by preparing and evaluating six composite inks (0, 1, 2, 3, 4, and 5% w/v nHA). The parameters of interest included the printing accuracy, the rheological profile, including over 70% viscosity recovery after 10 s in almost all formulations, the elastic modulus, which was over 10 kPa, and the swelling degree. In addition, pre-osteoblastic cells were embedded in these formulations, subsequently bioprinted, and demonstrated viability over 70% after 7 days. The results advance our understanding on the effect of the chemical composition behind the modification of the properties of the composite materials and their applications for biofabrication. This work contributes quantitative insight into how compositional tuning influences the performance of alginate–gelatin–nHA bioinks for extrusion-based bioprinting applications.