Controlled and sustained delivery of siRNA/NPs from hydrogels expedites bone fracture healing.

Despite great potential, delivery remains as the most significant barrier to the widespread use of siRNA therapeutics. siRNA has delivery limitations due to susceptibility to RNase degradation, low cellular uptake, and poor tissue-specific localization. Here, we report the development of a hybrid nanoparticle (NP)/hydrogel system that overcomes these challenges. Hydrogels provide localized and sustained delivery via controlled release of entrapped siRNA/NP complexes while NPs protect and enable efficient cytosolic accumulation of siRNA. To demonstrate therapeutic efficacy, regenerative siRNA against WW domain-containing E3 ubiquitin protein ligase 1 (Wwp1) complexed with NP were entrapped within poly(ethylene glycol) (PEG)-based hydrogels and implanted at sites of murine mid-diaphyseal femur fractures. Results showed localization of hydrogels and controlled release of siRNA/NPs at fractures for 28 days, a timeframe over which fracture healing occurs. siRNA/NP sustained delivery from hydrogels resulted in significant Wwp1 silencing at fracture callus compared to untreated controls. Fractures treated with siRNA/NP hydrogels exhibited accelerated bone formation and significantly increased biomechanical strength. This NP/hydrogel siRNA delivery system has outstanding therapeutic promise to augment fracture healing. Owing to the structural similarities of siRNA, the development of the hydrogel platform for in vivo siRNA delivery has myriad therapeutic possibilities in orthopaedics and beyond.