One of the greatest challenges when engineering skeletal muscle is creating a construct that can withstand and produce physiologically relevant force levels. In an effort to improve force production, many tissue engineering approaches have started to apply mechanical or electrical stimulation to fully formed tissue constructs. However, our lab seeks to apply these stimuli to skeletal muscle constructs as they develop, to explore how such biophysical stimuli influence maturation and biomechanical function.

In this work, we developed a bioreactor that enables precise, controlled, reproducible, mechanical, and electrical stimulations to be applied, independently or in combination, to skeletal muscle constructs as they develop. Using our custom bioreactor and scaffold-free, tissue engineering approach, we studied the influence that mechanical loading, electrical stimulation, and their combination had on the passive and active (contractile) mechanical properties of engineered skeletal muscle fibers. Mechanical and electrical stimulation each increased the fibers’ passive and/or active mechanical properties when delivered independently, with electrical stimulation showing a much more significant influence on fiber contractile properties. However, when delivered concurrently, the benefits were greatly amplified, suggesting synergies between the different stimuli. Indeed, when the most promising electrical stimulation was augmented with mechanical loading, engineered fibers showed signs of accelerated maturation and greatly enhanced biomechanical function, including greater isometric force generation, a ~10-fold increase in strength, and a ~4-fold increase in work and power generated.

Taken together, this work provides a novel platform to investigate the role of biophysical stimuli on muscle fiber development, and how these stimuli can be leveraged to accelerate maturation and tune the biomechanical performance of future engineered skeletal muscle replacements.