Bone tissue regeneration is a rapidly evolving field aimed at the development of biocompatible materials and devices, such as scaffolds, to treat diseased and damaged osseous tissue. Functional scaffolds maintain structural integrity and provide mechanical support at the defect site during the healing process, while simultaneously enabling or improving regeneration through amplified cellular cues between the scaffold and native tissues. Ample research on functionalization has been conducted to improve scaffold–host tissue interaction, including fabrication techniques, biomaterial selection, scaffold surface modifications, integration of bioactive molecular additives, and post-processing modifications. Each of these methods plays a crucial role in enabling scaffolds to not only support but actively participate in the healing and regeneration process in bone and joint surgery. This review provides a state-of-the-art, comprehensive overview of the functionalization of scaffold-based strategies used in tissue engineering, specifically for bone regeneration. Critical issues and obstacles are highlighted, applications and advances are described, and future directions are identified.

Direct ink writing (DIW) enables patient-specific fabrication of multifunctional bone scaffolds, but formulating inks that combine ceramic osteoconductivity, magnetic hyperthermia capability, and controlled drug delivery while retaining printability remains challenging. This study investigates the composition-dependent rheology and printability of polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP)/magnetite (Fe₃O₄) colloidal gels (formulated inks) for DIW-based scaffold fabrication. Five formulations spanning 10–50 wt% PCL (with β-TCP adjusted accordingly and Fe₃O₄ fixed at 5 wt%) were synthesized via solvent-based gel casting, characterized, and evaluated rheologically (flow sweep, amplitude and frequency sweeps, three-interval thixotropy, gelation kinetics). All inks exhibited shear-thinning behavior. Intermediate PCL compositions showed higher storage moduli, broader linear viscoelastic regions, higher yield stress, and rapid post-shear recovery, indicative of well-percolated particle–polymer networks, while high-ceramic-loaded formulations displayed brittle behavior. Calculated yield pressures for intermediate compositions fell within practical DIW operating ranges. Printing tests confirmed that only intermediate solid loadings are reliably printed through both nozzle diameters, demonstrating that printability depends jointly on yield stress and solid fraction. These findings establish composition-based guidelines for optimizing multifunctional PCL/β-TCP/Fe₃O₄ inks toward printable, patient-specific bone scaffolds.