Aptamer-functionalized stiff hydrogel for enhanced BMSC enrichment and osteogenesis

To address the need to both enrich stem cells and direct their osteogenic fate in bone tissue engineering and bone regeneration, we developed a stiffness-gradient hydrogel (~4.5-33 kPa) functionalized with a cell-enriching aptamer (Apt19s). This design forms a combined "enrich-and-differentiate" system: Apt19s actively enriches endogenous bone marrow-derived mesenchymal stem cells (BMSCs) at the scaffold site, while the osteoinductive high-stiffness niche (~33 kPa) directs their differentiation. Crucially, the combined cues produced an enhanced osteogenic outcome-evidenced by significantly greater alkaline phosphatase (ALP) activity (>2-fold increase), upregulated RUNX2/osteocalcin (OCN) gene expression (186.5% relative to control), and enhanced mineralization-that surpassed the additive effects of either cue presented independently. This integrated platform provides a practical strategy for developing cell-free osteogenic materials that actively tackle the dual challenges of endogenous cell sourcing and lineage-specific induction.