Injectable Hydrogel-Based Delivery of Soluble Cripto Protein Enhances Repair After Skeletal Muscle Injury

: Injectable protein therapies offer a minimally invasive approach for enhancing skeletal muscle regeneration, yet their clinical translation has been limited by poor in vivo stability, rapid diffusion, and insufficient temporal bioavailability at the injury site. Here, we report a thermoresponsive, fully injectable Pluronic F127-fibrinogen (FF) hydrogel that enables temporally synchronized delivery of a soluble form of Cripto, a GPI-anchored co-receptor that promotes myogenic regeneration by counteracting myostatin signaling. Cripto is physically entrapped within the FF precursor and undergoes in situ gelation at physiological temperature, allowing localized delivery without chemical modification or pre-fabrication. The FF hydrogel sustains Cripto release for up to 28 days while preserving receptor-binding activity. In a cardiotoxin-induced skeletal muscle injury model, bolus Cripto delivery failed to enhance regeneration, whereas FF-mediated delivery significantly improved muscle repair, as evidenced by increased centrally nucleated myofibers, enlarged fiber cross-sectional area, and elevated desmin expression. Importantly, FF biodegradation overlapped with the biologically permissive regeneration window, synchronizing protein bioavailability with muscle repair. Together, these findings identify injectable FF hydrogels as a practical and generalizable platform for temporally controlled protein delivery in skeletal muscle regeneration.