Targeted Dual Microdroplets for Modulating Osteoclast Differentiation and Function: A Novel Therapeutic Approach to Combat Osteoporosis

Osteoporosis, a condition marked by reduced bone mass and structural deterioration, continues to be a major public health concern, especially as global populations age. Excessive osteoclast formation is a hallmark of osteoporosis. The transcription factor nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) is indispensable for the early differentiation of osteoclasts, orchestrating the expression of essential genes, while at the later stages, cathepsin K (CTSK) is essential for bone resorption activities of mature osteoclasts. Here, we fabricated ultrasound-responsive microdroplets (MDs) by modulating both the early stages of osteoclast differentiation and the functions of mature osteoclasts via targeting the NFATc1 and CTSK. The internalization of these dual MDs was evaluated in human bone marrow-derived mesenchymal stromal cells (hBMSCs) and murine RAW 264.7 macrophages, alongside the biocompatibility assay. Their effects on osteogenesis and osteoclastogenesis were further investigated <i>in vitro</i>, followed by <i>in vivo</i> analysis in osteoporotic rat models. The dual MDs exhibited a well-defined core-shell structure and demonstrated efficient cellular uptake with minimal cytotoxicity. Furthermore, dual MDs showed a minimal effect on the osteogenic differentiation of the hBMSCs. In <i>in vitro</i> osteoclastogenesis assays, dual MDs effectively suppressed both osteoclast differentiation and formation through a synergistic inhibitory effect. <i>In vivo</i> studies demonstrated that osteoporotic rats receiving dual MDs showed significant protection against bone loss induced by ovariectomy. These results highlight the potential of dual MDs as a sophisticated, targeted therapeutic approach to osteoporosis treatment.