3D bio-printed in vitro skeletal muscle with pennate fibers architecture to enhance contractile function

Skeletal muscle tissue engineering (SMTE) has important research value and broad applicational prospect in areas such as muscle repair, disease modelling, drug testing, and biohybrid robotics. With the deepening of research on engineered skeletal muscles, it is still challenging for improvement in functional performance especially with relatively large size. Inspired by pennate muscles with large force output capacity, a novel design of in-vitro skeletal muscle tissue mimicking the macro and micro structure of gastrocnemius muscle in frogs was put forward with design optimization by simulation. Then three-dimensional (3D) bioprinting with cell-laden hydrogel was applied to fabricate tissues with fusiform geometry and induced microchannels with a pennate angle of 15°. The morphology, cell status and contraction performance of 3D-bioprinted muscle tissues were evaluated after electrical stimulation which induced directional alignment of myotubes. The results indicated that our 3D bio-printed pennate skeletal muscle tissues have achieved high cell viability (79.89%) and alignment of muscle fibers (51.93%), also demonstrated maximum contraction force of 443.085 μN, which was almost twice the force of 3D printed parallel muscle tissues in our study. This work will support the exploration of design strategies and rapid manufacturing techniques for the next-generation SMTE with high functional performance.