Diatom Frustules Serve as Scaffolds for 3D Polymeric Structures with Nanoscale Features
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Diatom Frustules Serve as Scaffolds for 3D Polymeric Structures with Nanoscale Features Shape-tailored microscale polymeric structures with feature sizes down to the nanoscale are becoming increasingly important for various applications, such as in microelectromechanical systems. Current techniques, such as lithographic-based layer-by-layer fabrication, are not well suited for the production of three-dimensional polymeric structures with complex shapes. In addition, large numbers of polymeric structures with a specific shape need to be created. C. Gaddis and K. Sandhage of the Georgia Institute of Technology have now demonstrated a technique that uses diatoms—single-celled algae—as scaffolds to form free-standing microscale polymeric structures. Diatoms have amorphous silica nanoparticle-based rigid cell walls (frustules). In this study, a thin (submicron) polymeric coating was applied to diatom frustules. The underlying silica frustules were then dissolved, leaving behind the polymer with the shape and features of the diatoms. Diatom frustules come in a wide range of shapes with nanoscale features. They can be precisely replicated in a massively parallel manner with ease. The frustules used in this study, as reported in the Journal of Materials Research (Web release date of accepted preprint, July 1) had hollow cylindrical shapes with diameters of 8–12 µm and mesoscale pores with diameters of several hundred nanometers in rows along the cylinder length. After being cleaned, the diatom frustules were dipped in a coating solution containing a two-part, 5-min-curing epoxy mixture dissolved in acetone. After evaporation of the acetone, the epoxy was allowed to cure. The concentration of the epoxy in the solution was adjusted to obtain a coating that a preserved the pores and fine features of the diatom frustules. The coated frustules were then dipped in hydrofluoric acid to dissolve the silica diatom shells, leaving behind the polymer coatings in the shape of the diatoms (see Figure 1). Gaddis and Sandhage found the polymer structures to be very similar in morphology to the starting diatom frustules. In addition to diatom species, other self-replicating biomineralized microand nanostructures (such as microshells 5 µm and sponges) can be used to yield various 3D polymeric shapes with desired morphologies. The technique is not limited to naturally available diatoms or biominerb alizing organisms. According to the researchers, genetic engineering could be used in the future to produce replicable bioscaffolds with non-natural shapes. The polymeric coatings are not confined to epoxy-based compositions. Other polymer structures can be produced, so long as a dilute coatable solution can be formed and the underlying scaffold can be removed, leaving the polymer structure intact without be
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