Filamented Light (FLight) Bioprinting of Mini-Muscles with Self-Renewal Potential

The plasticity and regenerative capacity of skeletal muscle arise from quiescent stem cells activated upon overload, injury, or inflammation. Developing in vitro muscle models to study these properties could advance muscle disease modeling and pre-clinical evaluation. Here, we leverage Filamented Light (FLight) bioprinting as a high-throughput approach for producing mini-muscle tissues. Using Pax7-nGFP myoblasts, we bioprinted mini-muscles from pristine collagen-fibrinogen. The FLight hydrogel consisted of aligned microstructures which guided the formation of aligned myotubes. Mini-muscles demonstrated in vivo-like tissue organization, including highly aligned myotubes and a Pax7+ cell pool embedded in newly deposited laminin. Both spontaneous and electrically stimulated contractions were observed. Collagen-fibrinogen matrix was promising for maintenance of the Pax7+ cell pool. Damage from cardiotoxin-induced injury of the mini-muscles led to a massive proliferation of Pax7+ cells and restoration of the contractile properties. Notably, small molecules such as Repsox could enhance regeneration. FLight printed mini-muscles have potential for applications in muscle biology, exercise/atrophy, disease models, and drug screening.