Page 67 - MSAM-3-4

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

A B Table 3. Weight percentage of elements in the PA 12 disks
made through HSS determined using energy‑dispersive
X‑ray spectroscopy

Sample Element Wt.% Comments
PA 12 disk by HSS C 97.2 Circular surface of
O 2.1 the disk (Figure 9A)
C PA 12 disk by HSS, Mg 39.3 Circular surface of
after dip-coating with O 51.6 the disk (Figure 9B)
Mg(OH) NPs
2
C 5.2
Cl 2.5
PA 12 disk by HSS, Mg 40.2 Circular surface of
after dip-coating with O 56.6 the disk (Figure 9C)
Mg(OH) NPs, drying,
2
and washing C 3.2
Figure 9. Scanning electron microscopy images of various PA 12 disks Note: The weight percentage was obtained from the mean of
made by HSS. (A) Neat PA 12 HSS disk without coating and washing. measurements at five positions.
(B) PA 12 HSS disk, dip-coated with Mg(OH) suspension, and without Abbreviation: NP: Nanoplatelet; HSS: High-speed sintering;
2
washing. (C) PA 12 HSS disk, dip-coated with Mg(OH) suspension and PA: Polyamide
2
dried, and then washed in a running water stream. Scale bars: 100 µm
Abbreviation: HSS: High-speed sintering; PA: Polyamide
bursting of cell walls would have occurred due to the
A B embedded Mg(OH) NPs on the surface of dip-coated HSS
2
PA 12 disks.
The spontaneous fixing of Mg(OH) nanocrystals on
2
the HSS PA 12 disk was unexpected. The Mg(OH) NPs
2
did not adhere to the dip-coated IM disks (Figure 8).
Hence, for the PA 12 disk made by HSS, it was initially
assumed that a thermal fixing process would be required
to adhere the Mg(OH) crystals on the surface, as disclosed
Figure 10. Scanning electron microscopy images at higher magnification. 20 2 20
(A) PA 12 disk made by HSS, dip-coated with Mg(OH) suspension, by Alkarri et al. for PP sheet coated with Mg(OH) . Heat
2
2
without washing. (B) PA 12 HSS disk, dip-coated with Mg(OH) 2 pressing can be applied to a flat specimen like a sheet but
suspension, dried, and then washed in a running stream of water. Scale not easily to a non-flat 3D shape produced by HSS. Thus,
bars: 1 µm an attempt was made to thermo-fix the NPs on the HSS
Abbreviation: HSS: High-speed sintering; PA: Polyamide
disks after dip coating using microwave heating. Heating
the residual water left after dip coating softened the PA 12
The second-use experiment with the coated HSS disk, grains, and presumably, the Mg(OH) crystals were more
besides indicating the efficacy of sustained article use for embedded. This was effective, but it was later found that
2
anti-microbial protection, also confirms that the positive the microwaving step was unnecessary. The rough surface
kill recorded in the first test is legitimate and is not due to of sintered PA 12 leads to adsorption of the nanocrystals
the Mg(OH) crystals flaking off and entering the broth in in the pores. It appears that the first layer of Mg(OH)
2
2
the pod leading to the reduced cell count. crystals would be attached this way, and further layers of
Due to laboratory restrictions on handling pathogens, crystals may attach to the lower layers of Mg(OH) crystals
2
an SEM image could not be recorded for the dip-coated by hydrogen bonding. Better nanocrystal adhesion on the
HSS PA 12 disks taken from the immersion pods to surface of polymer articles produced by HSS compared
demonstrate directly that the bacteria were disintegrated. with IM articles may be due to the relatively rough surfaces.
However, Halbus et al. directly mixed the E. coli broth The arithmetic mean surface roughness (R ) of IM parts is
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a
with Mg(OH) suspensions and examined the bacterial ~1 µm and that of HSS parts is ~40 µm.
2
morphology; the E. coli bacteria appeared sausage-shaped The anti-microbial mechanism of Mg(OH)
2
at ~2 µm long, but after treatment with the Mg(OH) nanocrystals was not investigated in this work, but
2
suspension, the SEM and transmission electron microscope some comments are necessary. Figure 11 summarizes
(TEM) images revealed the cell walls disintegrated without several modes of microbe destruction by anti-microbial
the NPs entering the cell . We presume that a similar agents. Some anti-microbials, such as silver and copper
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Volume 3 Issue 4 (2024) 10 doi: 10.36922/msam.4970