Abstract
In vitro 3D skeletal muscle models attached to flexible pillars are particularly interesting to mimic in vivo muscle anchorage to the bone as well as analysing contraction. However, most systems provide limited (e.g. only mechanical) or destructive (e.g. histology) characterization. There is a need for sensors allowing continuous measurements to investigate transient responses and dynamics of tissue properties. In this context, bioimpedance measurement appears as a promising tool for achieving a more comprehensive characterization of muscle function and structure. We present here a platform designed to conduct both mechanical and electrical characterizations of a 3D in vitro model.PDMS chips with two pillars were designed using CAD software, a 3D printer and several molding steps [1]. Muscle tissues were generated by mixing C2C12 cells with a hydrogel [2]. To induce muscle contraction, we designed an electrical stimulation system comprising carbon electrodes, a waveform generator and ad hoc electronics [3]. The contraction force was assessed by measuring the bending of the pillars, through video analysis. In order to develop the bioimpedance measurement system, we first carried out Finite Element Method simulations (FEM) to optimize the sensitivity and compute the electrodes form factor. Electrodes were then fabricated using flexible printed circuit board technology. A custom hardware interface was designed to enable 4-point bioimpedance measurements with a commercial impedance analyzer.We first validated the culture protocol and the electrical stimulation system. After differentiation, we obtained mature and contractile 3D muscle tissues. Low frequency stimuli (1 Hz) induced twitch contractions while above 10 Hz we observed tetanic contractions. The bioimpedance system was characterized with Phosphate Buffered Saline, and the results were in agreement with our FEM simulations. Experiments are ongoing to validate our platform's ability to assess the bioimpedance of 3D muscle tissue.