These printers use something like a toothpaste tube of plastic or other material held vertically in an X-Y plotter that squirts out thin layers of tiny dots of material that build up, layer by layer, to produce a 3D replica of the computer-generated design.

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Backfill: material used to build up and consolidate the land behind a seawall or similar structure.

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The technology works by building up layer upon layer of material - typically plastic - to build complex solid objects.

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That gives the material strength, as there are fewer places for stress to build up and fractures to form than in hydroxyapatite made haphazardly of larger, more heterogeneous grains.

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Accordingly, Dr Lin and his colleagues tried to build up covalent bonds between the layers of a water-repellent, or hydrophobic, material called cellulose acetate butyrate, which is used to make water-resistant fabrics.

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