Small but mighty: nanoemulsion particle size dictates bone regeneration potential of FTY720

The burgeoning field of nano-bone regeneration is yet to establish a definitive optimal particle size for nanocarriers. This study investigated the impacts of nanocarrier's particle size on the bone regeneration efficacy of fingolimod (FTY720)-loaded nanoemulsions. Two distinct particle sizes (60 and 190 nm, designated as NF60 and NF190, respectively) were produced using low-energy and high-energy emulsion techniques, maintaining a consistent surfactant, co-surfactant, and oil. <i>In vitro</i> studies using rat mesenchymal stem cells revealed that both NF60 and NF190 exhibited cell viability and reduced lactate dehydrogenase. Interestingly, NF60 demonstrated superior antioxidant properties, significantly reducing nitric oxide and intracellular reactive oxygen species (ROS) levels compared to NF190. Furthermore, NF60 significantly enhanced ALP activity and calcium deposition during osteogenic differentiation, indicating its potential to promote the early stages of bone formation. <i>In vivo</i> studies using a rat calvarial bone defect model demonstrated that both NF60 and NF190 significantly upregulated the expression of key osteogenic genes, including Runx2, Col, ALP, OCN, and BMP2. Notably, NF60 induced significantly higher expression of Runx2 and BMP2. X-ray and histological investigations revealed significantly improved bone regeneration in the NF60 group, highlighting the superior bone healing potential of smaller FTY720 nanoemulsions, without infiltration of inflammatory cells. The smaller particle size demonstrated superior antioxidant properties, enhanced osteogenic differentiation, and improved bone regeneration, suggesting smaller nanoparticles, with their larger surface area, accelerated drug release rate, and lower viscosity, interact more effectively with cells, leading to increased and effective drug delivery and cellular uptake. Findings highlight the importance of nanocarrier size in optimizing drug delivery for bone tissue engineering applications.