Taking its cues from computer-aided-design software, an extruder stacks thin layers of gooey thermoplastic that cure into shape.

FORBES: Almost Out of the Woods

Some melted at such high temperatures that unmelted pebbles blocked the extruder nozzle.

FORBES: Almost Out of the Woods

Other times the nozzle plugged up, the wafer loader jammed or the platform on which the prototype was formed slammed into the extruder.

FORBES: Almost Out of the Woods

IBM's design involved feeding small plastic wafers into a heated pump that melted them and pushed the goo through an extruder.

FORBES: Almost Out of the Woods

It starts with BB-size pellets of polyethylene that are fed into a long, cylindrical extruder and heated to 400 degrees Fahrenheit.

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In 1991 a boss decreed that Gruber couldn't buy a machine called an extruder, which turns plastic pellets into clear film.

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Ms. REBECCA JENNINGS (Worker): We have compounds and you have the color chips that drop down, they're heated up, comes to the comes to the extruder, here...

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The research team uses a RepRap 3D printer and a custom extruder head to print a filament network composed of sucrose, glucose and dextran which is later encased in a bio-gel containing living cells.

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The extruder is designed specifically for use with MakerBot PLA, a new plastic material based on corn, that Bre Pettis claims wont expand when exposed to the heat -- which means it wont contract when it cools, leading to smoother printed objects and less cracking.

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