Working with a team of scientists from the Technical University of Munich (TU Munich), Brandeis University, and Leiden University in the Netherlands, Dr. M. Cristina Marchetti and Dr. Mark Bowick, professors in the Soft Matter Program in the College of Arts and Sciences at Syracuse University, have engineered and studied “active vesicles." These purely synthetic, molecularly thin sacs are capable of transforming energy, injected at the microscopic level, into organized, self-sustained motion. The team’s findings are the subject of a cover story in the September 5, 2014 issue of Science. The ability to generate spontaneous motion and stable oscillations is a hallmark of living systems. Cells crawl to heal wounds and the heart contracts periodically to pump blood through the entire body. Reproducing and understanding this behavior, both theoretically and experimentally, remains one of the great challenges of 21st-century science. By confining cell extracts of important biological ingredients (i.e., bundles of long filamentary proteins known as microtubules and kinesin motor proteins) to the surface of a lipid vesicle, the TU Munich and Brandeis experimental part of the team has created "active vesicles" that undergo spontaneous oscillations and striking changes in shape. These biomimetic sacs are fueled by energy-consuming kinesins–i.e., nanomachines capable of transforming chemical energy into mechanical work–and may be thought of as the first step toward fabricating artificial cells. Fueled by kinesins, these defects form spatial patterns that oscillate between distinct configurations, turning the active vesicle into a robust miniature clock with tunable frequency. When confined, the long microtubule bundles coat the surface of the vesicle, forming a liquid crystal, where the filaments are, on average, aligned in a common direction.
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