Page 63 - MSAM-3-4

Materials Science in Additive Manufacturing 3D printing of anti-microbial parts

known to kill microbes by leaching of ions. When testing
the disks melt compounded with Mg(OH) and injection
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molded, injection-molded pure PA 12 disk was used as the
reference; and when the coated HSS disks were tested, an
uncoated HSS disk was used as the reference.
The CFU number was plotted against time (4 h and
24 h) to see if the bacterial count had decreased for the PA
12 with Mg(OH) . For all the anti-microbial tests, five disk
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replicates were used, and the results are presented as the
mean ± standard deviation.
2.9. Tensile properties of coated and uncoated PA 12
bars
The HSS parts have a certain degree of porosity, which leads
to lower intrinsic tensile strength and elongation-to-break Figure 3. Mg(OH) nanoplatelets after casting from aqueous suspension
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than their IM counterparts . The incorporation of rigid and drying. Thickness = 10 nm; aspect ratio (width: thickness) = 10:1;
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particles in plastics often leads to a decrease in strength, scale bar = 100 nm.
elongation-at-break, and impact resistance. To determine
whether the surface absorption of NPs significantly broth and then plating it on agar, followed by counting
decreased strength and elongation-at-break, the tensile the bacterial colonies over time 18,19,37,38 . When Mg(OH) is
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properties of PA 12 bars manufactured with HSS and added, cell viability typically reduces in 4 – 24 h, depending
coated with Mg(OH) NPs were measured and compared on the bacterium, and the concentration of the NPs . In
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with uncoated PA 12 bars. The test specimens (five contrast, the plastic parts (with Mg(OH) NPs embedded
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replicates of PA 12 made by HSS) for tensile measurements or coated on them) were tested for anti-bacterial activity
were maintained at standard conditions (23°C, 50% relative in this study.
humidity) for a minimum period of 40 h before testing. The
tensile tests were conducted using an Instron tensile testing 3.2. Disks made by IM and HSS, and tensile bars
system (model 5565; Instron, USA). The tensile bars were made by HSS
held in pneumatic grips with an initial grip separation of Figure 4 features the IM PA 12 disks, with and without
15 mm. Extension was controlled at a constant speed of 5 wt.% of Mg(OH) . Normally the PA 12 would be white
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20.27 mm/min and 25 % strain rate. or off-white after extrusion or molding. However, the PA
12 powder used here for IM was the same as the one used
3. Results and discussion for HSS; it had 70% used powder and 30% virgin powder.
3.1. Properties of the Mg(OH) NPs The used PA 12 powder is the material left in the print bed
2 after the printed articles are removed; it has typically been
Figure 3 displays the Mg(OH) NPs, featuring a hexagonal exposed to a temperature of ~173°C for up to 10 h. When a
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habit with a lateral width of ~100 nm and a thickness of used PA 12 mix is employed at melt temperatures, it turns
~10 nm. These are low aspect-ratio NPs; hence, they lie at brown due to polymer degradation (Figure 4). However,
all angles, including edgewise.
this does not affect the result of its anti-microbial activity,
The anti-bacterial activity of Mg(OH) has been which is primarily regulated by the contact interaction of
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documented for E. coli and other Gram-negative the microbes with the Mg(OH) NPs.
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bacteria 18,19,37,38 . Pan et al. found that anti-microbial In the HSS manufacturing method, incorporating
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efficiency is related inversely to the size of the platelets and Mg(OH) poses challenges, as it necessitates adding
their aggregates; i.e., finer particle size is more effective. it during the PA 12 polymerization process, which is
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Figure 3 indicates that the NPs were of suitable size for difficult to achieve. However, there are examples where
effective anti-bacterial activity. The activity also depends nanocomposite articles have been printed with a dry mix
on the synthesis route and raw material; Mg(OH) NPs of of a polymer powder and a second non-polymer powder.
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different efficiencies can be made from MgCl , MgSO , and An example is the SLS of polyethylene terephthalate
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MgO .
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(PET) powder and aluminum powder . Dry mixing of
Generally, the anti-bacterial activity is tested by adding PA 12 powder with Mg(OH) powder would have been
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a suspension of the Mg(OH) NPs directly to a bacterial problematic, as the incorporation of the latter could
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Volume 3 Issue 4 (2024) 6 doi: 10.36922/msam.4970