How the Sea Urchin Grows New Spines


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natural engineering



When the sea urchin’s tough yet brittle spines are broken off, they grow back within a few days. A team led by Profs. Lia Addadi and Steve Weiner of the Weizmann Institute’s Structural Biology Department discovered the key to this engineering wonder: The organism first forms a loosely structured material and then crystallizes it.
To begin construction of this single-crystal structure, from the broken base to a needle-sharp tip, the sea urchin produces a non-crystalline material, termed amorphous calcium carbonate (ACC), and delivers it to the stump. ACC first forms into microscopic needles that grow straight out from the stump then branch into a highly organized latticework that crystallizes into a calcite crystal. This precision process of aligning and crystallizing the ACC is controlled by the molecular structure of the crystalline stump and by specialized proteins.Each stage of construction, from ACC delivery to shaping and crystallization, takes just a few hours, and in this manner the new spine continues to grow until it is complete.
Study of this biological process - growing single crystals by first creating the material in an amorphous state - might prove useful to materials scientists and engineers wanting to produce sophisticated synthetic materials that have the properties of single crystals. 
Prof. Lia Addadi’s research is supported by the J & R Center for Scientific Research; the Ilse Katz Institute for Material Sciences and Magnetic Resonance Research; the Helen and Milton A. Kimmelman Center for Biomolecular Structure and Assembly; the Women’s Health Research Center; the Philip M. Klutznick Fund for Research; the Minerva Stiftung Gesellschaft fuer die Forschung m.b.H.; and the Ziegler Family Trust, Encino, CA. Prof. Addadi is the incumbent of the Dorothy and Patrick Gorman Professorial Chair.
Prof. Steve Weiner’s research is supported by the Helen and Martin Kimmel Center for Archaeological Science; the Women’s Health Research Center; the Philip M. Klutznick Fund for Research; the Alfried Krupp von Bohlen und Halbach Foundation; and George Schwartzman, Sarasota, FL. Prof. Weiner is the incumbent of the Dr. Walter and Dr. Trude Borchardt Professorial Chair in Structural Biology.