By combining a metamaterial cylinder with artificially grown heart tissue, researchers in the US have developed the miniPUMP – an on-chip device that closely mimics the function of a ventricular chamber. Using an advanced laser writing technique, a team led by Christos Michas at Boston University ensured that the miniPUMP could expand and contract in a cycle reminiscent of the beating human heart.
The latest advances in biomimetic tissue models are leading to increasingly sophisticated artificial organs, along with 3D-printed organ-on-chip models, which allow researchers to study the function of our organs in unprecedented detail. These models are based on induced pluripotent stem cell (iPSC) technology, in which a specific set of genes is introduced to a cell, which allow it to differentiate into a diverse array of stem cells.
For now, iPSC technology can’t be adapted to reproduce the nano- or micro-scale architectures that are widely found in human organs, and are often essential for producing their unique material properties. To address this challenge, Michas and colleagues turned to a technique named two-photon direct laser writing (TPDLW).
Here, the molecules in a photosensitive material are forced to absorb two photons simultaneously, which drastically enhances their responses to light compared with conventional laser writing. As a result, TPDLW allows researchers to carve out precise, nanoscale features within these materials, without the need for complex optical set-ups. TPDLW is particularly well-suited to fabricating metamaterials: whose nano- or micro-scale elements act collectively to produce advanced material properties in the macro-scale material.
In their case, Michas and colleagues applied the technique to recreate the human ventricle – one of two chambers at the bottom of the heart, which expands to draw in blood from one valve, then rapidly contracts to pump it at high speeds through another valve. Named miniPUMP, the device features a millimetre-sized, hollow cylindrical metamaterial, whose nanoscale features allow it to expand and contract perpendicular to its axis. This cylinder was then wrapped in a thick layer of iPSC-derived heart tissue, which expanded and contracted in a closed cycle.
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The researchers connected their artificial ventricle to a blood-filled passage, whose one-directional flow was controlled by a pair of 3D-printed valves. In experiments, miniPUMP’s cylinder demonstrated a perfect loop of varying volume and pressure – pumping blood out of the tube in carefully controlled cycles of varying flow rate.
Through further improvements, Michas’ team hopes that miniPUMP will allow researchers to closely study the heart’s function in the lab – potentially providing an ideal platform for testing new treatments for heart disease. Elsewhere, the technology may even be generalized to fabricating on-chip devices that mimic the function of other organs.
The team describes the miniPUMP in Science Advances.
