Abstract
Denervated muscle atrophy is a common complication following nerve injury, which often leads to irreversible muscle fibrosis due to low treatment efficiency. Recently, bioactive substances such as extracellular vesicles (EVs) have been emerging as an effective therapeutic modality for muscle atrophy. However, the complicated microenvironments of denervated muscle atrophy could reduce the delivery efficiency and even result in the deactivation of EVs. To meet this challenge, an ultrasound and pH-responsive anti-inflammatory injectable hydrogel was developed, which can effectively load and deliver stem cells derived EVs with satisfactory treatment outcomes of denervated muscle atrophy. Carboxymethyl chitosan, oxidized chondrotin sulfate and cystamine dihydrochloride were crosslinked in situ by Schiff base reaction to form an injectable hydrogel, where the reversible covalent bond would break under ultrasound and acidic environments to promote hydrogel degradation and cargo release. Meanwhile, the hydrogel loaded with EVs isolated from human umbilial cord mesenchymal stem cells(HUC-MSCs) can release EVs in a controlled manner upon facile pH/ultrasound manipulation. The experimental results confirmed that the hydrogel loaded with EVs (EVs@UR-gel) was effective in preserving muscle function. After six weeks nerve reconstruction, the maximum muscle strength which is closely related to muscle function, the muscle circumference, the wet weight, can be restored to 89.53 ± 0.96%, 76.02 ± 7.49%, 88.0 ± 2.65% of the healthy state, and the sciatic nerve index (SFI) to -0.11 ± 0.09, respectively. Overall, this hydrogel provided a new platform to maintain the long-term in vivo bioactivity of EVs, achieve tunable EVs release at the site of denervated muscle atrophy based on the state of disease, and restore the morphology and function of muscle as a promising approach for treating denervated muscle atrophy.