Living systems are capable of locomotion, reconfiguration and replication. To perform these tasks, cells spatiotemporally coordinate the interactions of force-generating, ‘active’ molecules that create and manipulate non-equilibrium structures and force fields of up to millimetre length scales1,2,3. Experimental active-matter systems of biological or synthetic molecules are capable of spontaneously organizing into structures4,5 and generating global flows6,7,8,9. However, these experimental systems lack the spatiotemporal control found in cells, limiting their utility for studying non-equilibrium phenomena and bioinspired engineering. Here we uncover non-equilibrium phenomena and principles of boundary-mediated control by optically modulating structures and fluid flow in an engineered system of active biomolecules. Our system consists of purified microtubules and light-activatable motor proteins that crosslink and organize the microtubules into distinct structures upon illumination. We develop basic operations—defined as sets of light patterns—to create, move and merge the microtubule structures. By combining these operations, we create microtubule networks that span several hundred micrometres in length and contract at speeds up to an order of magnitude higher than the speed of an individual motor protein. We manipulate these contractile networks to generate and sculpt persistent fluid flows. The principles of boundary-mediated control that we uncover may be used to study emergent cellular structures and forces and to develop programmable active-matter devices.
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The data that support the findings of this study are available from the Caltech Research Data Repository at https://data.caltech.edu/records/1160. All plasmids used in this study are available at https://www.addgene.org. All of the other reagents and the source code used for this study are available from the corresponding authors upon reasonable request.
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We thank M. Anjur-Dietrich, J. Brady, J. Bruck, V. Galstyan, S. Hirokawa, C. Hueschen, Y. Lazebnik, W. Lim, W. Marshall, D. Mullins, D. Needleman, P. Rothemund and E. Winfree for scientific discussions. We thank L. Bugaj, Z. Dogic, A. Frost, W. Huynh, R. Ismagilov, L. Metcalf, H. Nguyen and R. Vale for advice and assistance during the development of the experimental system; K. van den Dries for assistance with three-dimensional visualization of asters; P. Sternberg for use of a microscopy system for initial light-activation experiments. We are grateful to N. Orme for assistance with figures and illustrations. We acknowledge support from the NIH through grants 1R35 GM118043-01 (R.P.) and NIH DP5 OD012194 (M.T.); the NSF through NSF 1330864 (M.T.); the John Templeton Foundation as part of the Boundaries of Life Initiative through grants 51250 & 60973 (R.P.); the Foundational Questions Institute and Fetzer Franklin Fund through FQXi 1816 (R.P., M.T.); and the UCSF Center for Systems and Synthetic Biology NIGMS P50 GM081879 (M.T.). M.T. acknowledges support from the Heritage Medical Research Institute.
The authors declare no competing interests.
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Peer review information Nature thanks Andreas Bausch, François Nédélec and Suraj Shankar for their contribution to the peer review of this work.
This file contains supplementary materials and methods, data acquisition, analysis and a supplementary discussion, including Supplementary Figures 1–25 and supplementary references.
3D aster 100-µm excitation disk. 3D projection of aster formed with a 100-μm excitation disk. Scale bars are 30 μm. X, Y and Z axis are represented by the red, green, and blue bars, respectively.
3D aster 30-µm excitation disk. 3D projection of aster formed with a 300-μm excitation disk. Scale bars are 30 μm. X, Y and Z axis are represented by the red, green, and blue bars, respectively.
Aster formation and decay. Formation and decay of an aster with a 50-μm disk. Yellow disk indicates when and where light pattern is being projected. Time stamp is in min: sec.
Aster with moving disk. Aster following an excitation disk moving at 100 nm s−1. Time stamp is in min: sec.
Aster merger. Asters spaced 375 μm apart are linked together with light. Light pattern is indicated in yellow. Time stamp is in min: sec.
Patterned asters. Asters of different sizes and positions are simultaneously patterned.
Simultaneous movement of asters. Two asters simultaneously following disk patterns that are moving at 200 nm s−1. Time stamp is in min: sec.
Spiralling aster. Aster following a spiralling disk pattern moving at 200 nm s−1. Time stamp is in min: sec.
Active flow with labelled microtubules. Fluorescent microscopy time lapse of flow generated with a 750 × 20-μm bar. Time stamp is in min: sec.
Active flow with tracer beads. Brightfield microscopy of flow generated with a 700 × 20-μm bars. Sample contains 1-μm beads for measuring advective flow. Time stamp is in min: sec.
Plus-shape excitation and flow. Flow generated with a plus-shape pattern. The ‘+’ is composed of two 350 × 20-μm bars. Time stamp is in min: sec.
T-shape excitation and flow. Flow generated with a T-shape pattern. The ‘T’ is composed of two 350 × 20-μm bars. Time stamp is in min: sec.
L-shape excitation and flow. Flow generated with an L-shape pattern. The ‘L’ is composed of two 350 × 20-μm bars. Time stamp is in min: sec.
Active stir bar. Dynamic flow pattern made with a rotating 450 × 30-μm bar. The ends of the bar rotate at 200 nm s−1. Time stamp is in min: sec.
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Ross, T.D., Lee, H.J., Qu, Z. et al. Controlling organization and forces in active matter through optically defined boundaries. Nature 572, 224–229 (2019). https://doi.org/10.1038/s41586-019-1447-1
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