Biofabrication of zinc-reinforced PLA scaffolds by FDM for bone tissue engineering

The development of biodegradable scaffolds with improved mechanical and biological performance is a pressing challenge in bone tissue engineering. Poly(lactic acid) (PLA), widely used in fused deposition modelling (FDM) due to its processability and biocompatibility, lacks sufficient bioactivity and strength for demanding applications. In this study, we fabricated and evaluated zinc-reinforced PLA composite filaments (5-30 wt% Zn) via melt extrusion and FDM to define a practical printability window and establish process-structure-function relationships aimed at enhancing osteointegration and stability. Microstructure, density, and crystallinity were characterized by optical microscopy/scanning electron microscope, Archimedes' principle, X-ray diffraction, and differential scanning calorimetry. Mechanical performance was quantified by tensile testing of standardized samples and compression of gyroid lattices. In vitro performance was evaluated using human osteoblasts through viability assays, adhesion quantification, and Alizarin Red S staining. Composites incorporating ≤10 wt% Zn showed uniform particle dispersion without impairing printability. Zn10 (10 wt% Zn) recovered PLA-like tensile strength with the highest strain-at-fracture among groups and exhibited significantly higher compressive strength and modulus than PLA and Zn5 (5 wt% Zn). All groups were found to be non-cytotoxic (∼100% viability) and supported osteoblast adhesion. Notably, zinc-containing scaffolds promoted significantly higher calcium deposition after 28 days, demonstrating enhanced late-stage osteogenic differentiation. These findings demonstrate that low-level Zn reinforcement can improve both structural integrity and biological performance of PLA-based scaffolds, supporting Zn-reinforced PLA as a scalable, extrusion-ready platform for the biofabrication of patient-specific bone-regenerative implants.