Mechanics helps design better living robotics

Engineering living systems is a rapidly emerging discipline where the functional biohybrid robotics (or ‘Bio-bots’) are built by integrating of living cells with engineered scaffolds. Inspired by embryonic heart, we presented earlier the first example of a biohybrid valveless pump-bot, an impedance pump, capable of transporting fluids powered by engineered living muscle tissues. The pump consists of a soft tube attached to rigid boundaries at the ends, and a muscle ring that squeezes the tube cyclically at an off-center location. Cyclic contraction results in a net flow through the tube. We observed that muscle force occasionally buckles the tube in a random fashion, i.e., similar muscles do not buckle the tube consistently. In order to explain this anomaly, here we develop an analytical model to predict the deformation and stability of circular elastic tubes subjected to a uniform squeezing force due to a muscle ring (like a taught rubber band). The prediction from the model is validated by comparing with experiments and finite element analysis. The non-linear model reveals that the circular elastic tube cannot buckle irrespective of muscle force. Buckling state can be reached and sustained by bending and folding the tube before applying the muscle ring. This imperfection may appear during assembly of the pump or from non-uniform thickness of the muscle ring. This insight from the model explains the apparent anomalous experimental observation of inconsistent buckling of hydrogel tubes of the pump. The analysis will guide the design of more complex, high-performance biohybrid pump-bots and other living machines by harnessing the structural buckling to achieve higher net flow.

This work was recently published in J. Appl. Mech. and here is the link: Zhengwei Li and M Taher A Saif, Mechanics of Biohybrid Valveless Pump-bot, J. Appl. Mech., 2021. 

The pump-bot work was previously published in PNAS, and the link is: Zhengwei Li et al., "Biohybrid valveless pump-bot powered by engineered skeletal muscle." PNAS 116.5 (2019): 1543-1548.