|Think the zombie apocalypse shown in numerous movies and TV's The Walking Dead are just fiction? Not so fast. Researchers have now created "zombie" mammalian cells that may function better after they die at Sandia National Laboratories and the University of New Mexico.|
The technique coats a cell with a silica solution to form a near-perfect replica of its structure. The process may simplify a wide variety of commercial fabrication processes from the nano- to macroscale.
The work, reported in the Proceedings of the National Academy of Sciences (PNAS), uses the nanoscopic organelles and other tiny components of mammalian cells as fragile templates on which to deposit silica. The researchers then heat the cell to burn off its protein. The resultant hardened silica structures are faithful to the exterior and interior features of the formerly living cell, can survive greater pressures and temperatures than flesh ever could, and can perform some functions better than when they were alive, said lead researcher Bryan Kaehr, a Sandia materials scientist.
Kaehr offers what may be the first distinction in scientific literature between a mummy cell and a zombie cell: “King Tut was mummified,” he said, “to approximately resemble his living self, but the process took place without mineralization [a process of fossilization]. Our zombie cells bridge chemistry and biology to create forms that not only near-perfectly resemble their past selves but can do future work.”
“It’s very challenging for researchers to build structures at the nanometer scale,” said Kaehr. “We can make particles and wires, but 3D arbitrary structures haven’t been achieved yet. With this technique, we don’t need to build those structures — nature does it for us. We only need to find cells that possess the machinery we want and copy it using our technique. And, using chemistry or surface patterning, we can program a group of cells to form whatever shape seems desirable.”
UNM professor and Sandia Fellow Jeff Brinker added, “The process faithfully replicates features from the nanoscale to macroscale in a robust, three-dimensionally stable form that resists shrinkage even upon heating to over 500 degrees Centigrade [932 degrees Fahrenheit]. The refractoriness of these delicate structures is amazing.”
The unusual but simple procedure may serve as a model for creating hardier classes of nanoscopic products.
Because a cell is populated by a vast range of proteins, lipids and scaffolding, its interior is ready-made to model catalysts, funnels, absorbents and other useful nanomachinery, said Kaehr, a former Sandia Truman Fellow.
UNM post-doctoral student Jason Townson said the most immediate use for silicification may be as a simple way to preserve the structure of organic materials for imaging.
“Formerly, for internal preservation and subsequent imaging, a cell would be fixed in formaldehyde or some other preservative. But many of these methods are labor-intensive,” Townson said. “This method is simple. The preserved cells will never get sloppy in decay. And when we cracked open the resulting structure, we were blown away by how well the cell was preserved, down to the minor groove of the cell’s DNA.”
Heating the cell to still higher temperatures (greater than 400 degrees C) evaporates the organic material of the cell — its protein — and leaves the silica in a kind of three-dimensional Madame Tussauds wax replica of a formerly living being. The difference is that instead of modeling the face, say, of a famous criminal, the hardened silica-based cells display internal mineralized structures with intricate features ranging from nano- to millimeter-length scales.
The construction process is relatively simple: Take some free-floating mammalian cells, put them in a petri dish and add silicic acid.
Through the action of methanol, a byproduct of the acid, the cell’s lipid layers — the protective casings that keep the cell intact — are softened and made porous enough for the silica to flow in at about the temperature of the human body.
The silicic acid, for reasons still partially obscure, enters without clogging and in effect embalms every organelle in the cell from the micro- to the nanometer scale.
If the cell isn’t heated, the silica forms a kind of permeable armor around the protein of the living cell. This may support it enough to act as a catalyst at temperatures and pressures undreamed of by nature.
“Once we’ve used silica to stabilize the cellular structure, it can still carry out reactions and, more importantly, that reaction is stable enough to work at high temperatures,” Kaehr said. “The method is also a means to take a soft, potentially valuable biological material and convert it to a fossil that will stay on our shelves indefinitely.”
SOURCE Sandia National Labs
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