Multifunctional Bilayer Scaffolds Integrating Melt Electrowriting Fibers and Drug-Loaded Microspheres Promote Osteochondral Regeneration through PI3K–AKT–Mediated Chondro-Osteogenic Signaling

Osteochondral defects (OCDs) remain challenging to repair due to the complex structural and biological heterogeneity of the cartilage–bone interface. Here, we developed a bilayer microsphere–scaffolds composite by integrating melt electrowriting (MEW) scaffolds with two types of functionalized hydrogel microspheres (HMPs). The upper layer consisted of disulfide-containing poly ethylene glycol diacrylate (HB-PBHE)/thiolated hyaluronic acid (SH-HA) microspheres encapsulating kartogenin (KGN) liposomes (HM@PHK) to promote chondrogenesis, while the lower layer was formed by GelMA/nano-hydroxyapatite (nHAP) microspheres loaded with curcumin (Cur) liposomes (HM@GMAC) to provide osteoinductive, antioxidative, and anti-inflammatory cues. This bilayer construct exhibited uniform architecture, favorable mechanics, and controlled drug release. In vitro, the system promoted bone marrow–derived mesenchymal stem cells (BMSCs) migration, chondrogenic and osteogenic differentiation, and attenuated oxidative stress–induced apoptosis while modulating macrophage polarization. Transcriptomic analysis revealed that both layers activated the PI3K-AKT pathway, with the upper phase regulating the PI3K-AKT-SOX9 axis for chondrogenesis and the lower phase promoting osteogenesis and cytoprotection via PI3K-AKT-RUNX2/BAX signaling. In vivo implantation in rat femoral condyle defects demonstrated superior cartilage–bone reconstruction. Collectively, this multifunctional bilayer microsphere–scaffolds system provides stratified regulation of osteochondral repair through coordinated structural support, bioactive delivery, and immunomodulation, offering a clinically translatable approach to osteochondral defect regeneration.