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Nano and Micro Technologies

Nano and Micro Technologies - Poster Session A

Poster Y20 - Design and microfabrication of a fast, muscle-powered biohybrid swimming robot through application of low Reynolds number elastohydrodynamic theory and supportive mechanical and chemical cues

Thursday, October 24, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction: Integration of biological actuators and sensors with soft, synthetic scaffolds has allowed for the development of a class of microscale, emergent, motile biohybrid robots capable of crawling and swimming. These robots also offer unique platforms to study the co-differentiation of, and interactions between multicellular systems, and between cells and scaffold. This study presents a novel biohybrid swimming robot which uses skeletal muscle, neurons, and a compliant mechanism (1) to convert the muscle actuation into flagella rotation, and (2) to provide a nonlinear stiffness cue to the muscle to support its maturation and performance (Fig. 1a). Motor neurons are introduced to the swimmer scaffold for improved maturity of the emergent muscle tissue (Fig. 1b).

Materials and

Methods: The swimmer scaffold is made of PDMS by filling a mold etched in a silicon wafer. It consists of two slender tails attached to two compliant supports with anchors for a muscle ring, and a head hosting neuron spheroids. Muscle ring formed with mouse myoblasts (C2C12) suspended in extracellular matrix (ECM) is mounted on the scaffold. Spheroids of mouse embryonic stem cell derived motor neurons are dispensed on the head. ECM is placed between the muscle and the neurons. Neurites from the spheres extend towards the muscle (Fig. 1c). Upon electrical actuation, muscle contracts in a periodic fashion, twisting the tails resulting in a flagellar motion propelling the swimmer. The swimmer is floated in a density gradient media, and electrically stimulated at multiple frequencies (Fig. 1d). The motions of the swimmer and the muscle are tracked with ImageJ template matching.

Results, Conclusions, and Discussions: The presence of motor neurons significantly enhances muscle performance. Muscle contraction due to a given applied electric field increases by 4 times in the presence of neurons compared to those without neurons. It is likely that muscle-neuron interaction enhances muscle maturation. This interaction is evidenced by extension of neurites towards the muscle. Alpha-actinin staining of the muscle showed mature sarcomeric structures in the center of the muscle rings, and under-developed nascent myotubes near the grips.
Muscle contractions results in twisting of the swimmer tails by up to 10º giving swimming speeds up to 86.8 µm/s (Fig. 1e), corresponding to a Reynolds number Re~O(10^(-1) ). This high speed is an order of magnitude higher than that predicted by low Re hydrodynamics theory (no inertial effects, i.e., swimming stops instantaneously when stimulation is stopped). The higher speed is possibly originating from inertial effects induced by multiple factors, including swimmer size and high muscle contraction rate.

Acknowledgements (Optional):