Sustained TGF-β3 delivery and stem cell loading via injectable microspheres enhance cartilage defect repair

Microspheres can efficiently load and sustainably deliver growth factors and stem cells. • Microspheres provide a favorable microenvironment that supports chondrogenic differentiation of stem cells. • Injectable microspheres can be applied to irregular and complex cartilage defects in a minimally invasive manner. • Microspheres loaded with stem cells and growth factors offer a new strategy for cartilage defect repair. Cartilage defects severely compromise patients’ quality of life, as the unique structural characteristics of native cartilage endow it with extremely limited self-repair capacity. Mesenchymal stem cells (MSCs) possess tremendous therapeutic potential for cartilage tissue engineering due to their multilineage differentiation capability; however, technical bottlenecks associated with current cell delivery systems greatly restrict their clinical translation. Herein, we fabricated an injectable, multifunctional hydrogel microsphere system (PGCT-MS). Specifically, arginine-glycine-aspartate (RGD) sequences conjugated on gelatin molecules facilitate MSC adhesion, while chondroitin sulfate—an essential component of the chondrocyte extracellular matrix—constructs a favorable microenvironment for MSC spreading. Moreover, polydopamine modification on the microsphere surface enables efficient immobilization and sustained release of transforming growth factor-β3 (TGF-β3), which effectively induces the chondrogenic differentiation of bone marrow MSCs (BMSCs) at cartilage defect sites after in situ injection. In vitro experimental results demonstrated that PGCT-MS significantly enhances BMSC adhesion and chondrogenic differentiation, as verified by the upregulated expression of chondrogenic marker genes, and exhibits excellent adhesion affinity for native cartilage matrices. In vivo animal studies further validated that BMSC-loaded PGCT-MS markedly accelerates high-quality cartilage regeneration. Collectively, this multifunctional therapeutic delivery system provides a promising and feasible strategy for clinical cartilage defect repair.