Editors' ChoiceBIOROBOTICS

Squeezing inspiration from embryonic hearts

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Science Translational Medicine  30 Jan 2019:
Vol. 11, Issue 477, eaaw5317
DOI: 10.1126/scitranslmed.aaw5317

Abstract

Bioinspired valveless impedance pumps are driven by contracting rings of tissue engineered muscle cells.

Our hearts are the first functional organs to develop, pumping a mere three weeks postfertilization. While the fully developed heart directs blood flow through the choreographed control of four valves, embryonic hearts are simple valveless tubes that are morphologically similar to blood vessels. Li et al. have developed a biorobotic pump that harnesses the energy of contracting muscle cells, inspired by the simplicity of our nascent hearts.

The authors engineered “muscle rings” by polymerizing skeletal muscle myoblasts loaded into Matrigel/collagen extracellular matrix within silicone molds. The rings were then slipped over soft hydrogel tubing coupled with silicone channels in closed loop configurations and immersed in differentiation medium. The asymmetrical placement of the muscle ring over the hydrogel tube coupled with the impedance mismatch between the loop materials led to net unidirectional flow. The mechanism responsible for this flow was the Liebau effect, a pumping phenomenon that generates fluid flow within tubular structures. Unlike peristaltic pumping that uses contractions propagating along the direction of transport, Liebau pumping requires contractions at only a single location and has been theorized as the operating principle behind embryonic hearts. Pumping was achieved either by the spontaneous contraction of muscle rings or by their direct electrical stimulation. The authors observed volumetric flow rates up to 22.5 μl/min, three orders of magnitude greater than previously reported in similar-sized myocyte-powered valve-based pumps.

Many challenges remain for this emergent technology in real-world applications, such as the logistics of incorporating fragile living cells into machines and potential concerns around the fatigue and longevity of skeletal muscle cells. However, without the need for valves or other moving mechanical parts, these simple pumps may serve as reliable components of lab-on-chip platforms, medical devices, or even implantables. As we continue to draw inspiration from nature, it would be wise to remember that the even the most juvenile organisms are the result of millions of years of life-or-death problem solving.

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