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Introduction

The rapidly expanding field of 3D printing has recently boomed with the development of low-cost, compact, and user-friendly printing devices designed for personal use in the office, classroom, and at home. These devices can be used to manufacture simple objects on a small scale, and do so by utilizing a technique known as molten polymer deposition (MPD). During this process, a thermoplastic filament is forced through a heated extrusion nozzle, which melts the feedstock and deposits the extruded plastic onto a baseplate in thin layers, eventually forming a three dimensional solid shape (Bumgarner 2013).

There are various types of thermoplastic feedstock in use today, including acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyvinyl alcohol (PVA), polycarbonate (PC), and high density polyethylene (HDPE), with ABS and PLA being the most commonly used(Stephens, Azimi et al. 2013). The primary variances between printers of different feedstock types are nozzle and baseplate operating temperatures. For example, PLA, a bio-degradable, corn-based plastic, requires a nozzle temperature of around 180°C and a baseplate temperature near room temperature. ABS, however, requires a higher nozzle temperature (~220°C) and a baseplate temperature of around 80°C (Weinhoffer 2012).

High temperature processing of thermoplastics has been shown to emit both gases and particles (Contos, Holdren et al. 1995, Unwin, Coldwell et al. 2013). The effect of toxic gases (such as carbon monoxide and hydrogen cyanide) on the human body are well understood, but the effect of inhaled particulates, specifically ultrafine particles (UFPs: particles with a diameter less than 100nm), are of great concern, and are continually being studied. UFPs have unique aerodynamic and biochemical properties that, when inhaled, allow them to reach the deepest part of the lungs (Oberdorster, Oberdorster et al. 2005), where they can then enter tissues and cells, interact on a molecular level, and directly (and indirectly) modify the immune response mechanisms (Chang 2010). This can lead to serious adverse cardiovascular and pulmonary effects in humans (Warheit, Sayes et al. 2008).

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