3D-printed titanium scaffolds negatively affect the interplay between macrophages and skeletal progenitors in vitro

Orthopedic implants can guide endogenous tissue regeneration, with outcomes shaped by early interactions between immune cells and tissue specific progenitors. While interest in the osteoimmunomodulatory function of 3D printed bone scaffolds is increasing, most studies focus on the effects of immune cells on bone forming cells, often overlooking the immunomodulatory role of skeletal progenitors. This study examines how 3D printed titanium scaffolds influence macrophage polarization mediated by skeletal progenitors and how the resulting macrophage response affects osteogenic differentiation of these progenitors. An indirect co culture system was used, with primary human macrophages seeded on titanium scaffolds and human periosteum derived cells cultured separately. After five days, conditioned media were exchanged. Titanium scaffolds promoted an inflammatory macrophage profile and limited the modulatory effect of skeletal progenitors under specific readouts. In turn, macrophage conditioned media from scaffold cultures selectively altered osteogenic gene expression in skeletal progenitors, with effects on SPP1 and COL1A1. These findings indicate that 3D printed titanium scaffolds influence macrophage-progenitor crosstalk that may affect regenerative signaling.