Granulate-to-Filament: An Extrusion-Mixed PLA–Human Bone Material System for 3D-Printed Bone Scaffolds

Fused filament fabrication (FFF) enables patient-specific scaffolds for critical-size bone defects, but most filaments are bioinert and difficult to functionalize at high particulate loadings due to segregation, agglomeration, clogging, and diameter instability. We developed a mechanism-guided extrusion toolkit to stabilize polylactic acid (PLA) filaments containing human demineralized bone matrix (DBM) or cortical granulate (CG) up to 70 wt%. PLA was ground, dried, silicone pre-coated, and compounded with DBM or CG (25/40/70 wt%) using starve-fed extrusion, sequential extrusion, and post-die mixing to maintain stable diameters. FFF produced disks and tubes. MSC adhesion was assessed by SEM. qPCR (control vs. osteogenic medium) quantified RUNX2, ALP, BGLAP, COL1A, VEGF, IL-6, MAPK8. Tubes underwent three-point bending. The toolkit yielded printable, dimensionally stable filaments at 25-70 wt% with uniform dispersion and surface-exposed filler. Both composites increased early mesenchymal stromal cells (MSC) adhesion versus PLA. RUNX2 was increased on DBM40 versus PLA. VEGF was elevated on CG25 (DBM40 trend). Under osteogenic medium, IL-6 and MAPK8 were generally reduced. Mechanics were loading-dependent: CG25 exceeded CG70 and DBM25, while DBM40/70 recovered stiffness versus DBM25. A mechanism-guided extrusion toolkit enables high-loading PLA-DBM/CG filaments with excellent printability and material-specific biological and mechanical advantages over PLA.