A Novel Bioreactor for Stimulating Skeletal Muscle In Vitro

For over 300 years, scientists have understood that stimulation, in the form of an electrical impulse, is required for normal muscle function. More recently, the role of specific parameters of the electrical impulse (i.e., the pulse amplitude, pulse width, and work-to-rest ratio) has become better appreciated. However, most existing bioreactor systems do not permit sufficient control over these parameters. Therefore, the aim of the current study was to engineer an inexpensive muscle electrical stimulation bioreactor to apply physiologically relevant electrical stimulation patterns to tissue-engineered muscles and monolayers in culture. A low-powered microcontroller and a DC–DC converter were used to power a pulse circuit that converted a 4.5 V input to outputs of up to 50 V, with pulse widths from 0.05 to 4 ms, and frequencies up to 100 Hz (with certain operational limitations). When two-dimensional cultures were stimulated at high frequencies (100 Hz), this resulted in an increase in the rate of protein synthesis (at 12 h, control [CTL] = 5.0 ± 0.16; 10 Hz = 5.0 ± 0.07; and 100 Hz = 5.5 ± 0.13 fmol/min/mg) showing that this was an anabolic signal. When three-dimensional engineered muscles were stimulated at 0.1 ms and one or two times rheobase, stimulation improved force production (CTL = 0.07 ± 0.009; 1.25 V/mm = 0.10 ± 0.011; 2.5 V/mm = 0.14146 ± 0.012; and 5 V/mm = 0.03756 ± 0.008 kN/mm 2 ) and excitability (CTL = 0.53 ± 0.022; 1.25 V/mm = 0.44 ± 0.025; 2.5 V/mm = 0.41 ± 0.012; and 5 V/mm = 0.60 ± 0.021 V/mm), suggesting enhanced maturation. Together, these data show that the physiology and function of muscles can be improved in vitro using a bioreactor that allows the control of pulse amplitude, pulse width, pulse frequency, and work-to-rest ratio.