Ultrasound-triggered bio-scaffold integrating engineered stem cells for cartilage regeneration

Articular cartilage repair remains a major clinical challenge due to the limited regenerative capacity of the tissue and the poor therapeutic efficacy of current treatments. Although stem cell-based therapies hold promise, their clinical outcomes are often compromised by insufficient chondrogenic differentiation, phenotypic instability, and rapid cell loss in the dynamic joint environment. Herein, we report an ultrasound-responsive, bio-scaffold system (e-BMSCs/Gel) designed to enhance cartilage regeneration through coordinated biochemical and genetic regulation. In this system, bone marrow mesenchymal stem cells (BMSCs) are engineered by internalizing nanobubbles (NBs) loaded with TGF-β3 protein and CRISPR/Cas9 plasmids targeting the YAP (pCas9-YAP), termed T@NBs^pDNA. Additionally, to enhance cell retention and survival, engineered BMSCs (e-BMSCs) are encapsulated within a thermosensitive thiolated-chitosan/hydroxyapatite hydrogel that rapidly forms in situ. Under US stimulation, the synchronized activation of TGF-β3 release and YAP gene silencing significantly promoted the chondrogenic differentiation of e-BMSCs. Furthermore, in vivo evaluation in a rat articular cartilage defect model demonstrates that US-activated e-BMSCs/Gel effectively promotes hyaline-like cartilage regeneration and improves structural restoration of the defect site. Overall, this work presents a controllable bio-scaffold platform, offering a novel strategy for effective cartilage regeneration.