The First Natural Metamaterial<\/p>\n
Drosophila, the fruit fly, is one of the most powerful biological models in science. We share a large portion of our genes with it, as well as the way cells use these genes to form tissues and organs, which allows scientists to study complex processes such as morphogenesis: the process by which chemical and mechanical signals guide groups of cells to organize themselves and form an organ with a specific function and shape.<\/p>\n
By definition, metamaterials were supposed to be artificial\u2026 until now. This multidisciplinary team has shown that, during its development, the fly\u2019s eye possesses a network of interconnected cells forming triangles. What is striking is that the size of these cellular triangles is not uniform: in some areas, the triangles are larger than in others. This mesh functions exactly like a programmable metamaterial: the two-dimensional (2D) distribution of these triangles (the eye tissue during development) contains the precise instructions so that, when hydrostatic pressure is applied to the tissue (a process similar to inflating a water balloon), it assumes the exact three-dimensional (3D) curvature necessary for the adult fly to see properly.<\/p>\n
\u201cIt\u2019s fascinating to see how nature not only uses biology to shape organs, but also employs advanced engineering principles,\u201d explain the lead authors. \u201cOnce again, biology surprises us by using mechanisms that have been in place for millions of years\u2014mechanisms that, to us, represent cutting-edge technology,\u201d says Juan Garrido Garc\u00eda, the study\u2019s first author.<\/p>\n
“We have discovered that the fly’s eye has a 2D architectural ‘plan’ that predetermines its final 3D shape. This blueprint allows the fly\u2019s eye to have flatter areas with higher visual acuity (for example, to identify fruits where its favorite food, yeast, grows, or to find a mate), and other more curved areas with lower resolution but a more panoramic view, for detecting predators. Another surprising aspect is its size: a fly\u2019s eye has a diameter of approximately 0.5 millimeters. \u201cThe metamaterial nature of the developing eye allows for precise control of the eye\u2019s shape at this tiny scale,\u201d the researcher continues.<\/p>\n
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In the pupal stage, the cells that make up the Drosophila retina form a triangular lattice. In the image, triangles of different sizes are colored with varying shades of violet. The triangular lattice of the retina in the pupal stage functions as a metamaterial. Using a computational model, the team has demonstrated that inflating this (2D) lattice with the triangular pattern found in the pupal-stage tissue results in a 3D curvature similar to that of the adult eye.<\/p>\n
Toward the Medicine of the Future: Synthetic Morphogenesis<\/p>\n
Beyond its biological significance (it is possible that many other insects use this same metamaterial property to generate eyes of different shapes that serve different functions), this discovery lays the foundation for synthetic morphogenesis. By understanding how nature programs the shape of a tissue without the need for rigid external molds, scientists can begin to design \u201cprogrammable living tissues.\u201d<\/p>\n
In the future, this ability to control the 3D shape of cell cultures using substrates with geometric patterns could revolutionize bioengineering, enabling the creation of artificial organs or grafts that, when implanted, take on their designed shape with unprecedented precision, eliminating the reliance on non-biological synthetic materials.<\/p>\n
A global and multidisciplinary effort<\/p>\n
This milestone was made possible by the synergy among various institutions, research centers, and scientific disciplines, bringing together the group led by Luis M. Escudero at the University of Seville and the IBiS\u2014whose researchers include Juan Garrido Garc\u00eda, an expert in the mathematical analysis of the organization of biological tissues\u2014 with the group led by CSIC researcher Fernando Casares at the CABD, leaders in the study of the development and evolution of the eye; and with Franck Pichaud\u2019s team at the Laboratory for Molecular Cell Biology (UCL), specialists in the cell biology of epithelia and the visual system. By integrating cutting-edge cell biology and genetics with complex mathematical models and computational simulations\u2014developed in collaboration with the Higher Technical School of Engineering at the University of Seville\u2014 the project demonstrates that the intersection of biology, mathematics, and engineering is essential to unraveling the secrets of life.<\/p>\n
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