Page 65 - MSAM-3-4

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

A B C

Figure 5. (A) Polyamide (PA) 12 disk printed by high-speed sintering (HSS); diameter: 25 mm; thickness: 1.55 mm. (B) Two PA 12 disks made by HSS
after placing them inside the pods. The bacterial broth is poured into the pods, sealed with caps labeled L and R, and then placed in the agitator. One pod
would hold a control PA 12 disk, the other the PA 12 disk that had been immersed in the Mg(OH) suspension. The PA 12 disks made by injection molding
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were also tested in these pods for antibacterial activity. (C) The tensile bar is made by HSS (bottom bar), and the tensile bar after dip coating with Mg(OH) 2
(top bar). Length of the bars: 150 mm.
Table 2. Weight percentage of elements present at the
surface of the IM PA 12 disks was determined using
energy‑dispersive X‑ray spectroscopy
Sample Element Wt.% Comments
PA 12 IM disk with 5 C 79.3 Circular surface of the
wt.% Mg(OH) NPs O 11.6 disk (Figure 7A)
2
N 7.9
Mg 1.3
PA 12 IM disk with 5 C 41.9 Cross-section after
wt.% Mg(OH) NPs O 33.4 cutting the disk along the
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diameter (Figure 7B)
N 5.1
Mg 19.2
Figure 6. Anti-microbial activity of (1) metallic copper disks (positive PA 12 IM disk Mg 45.7 Circular surface of the
control); (2) neat PA 12 made by high-speed sintering (negative control); dip-coated with O 53.6 disk (Figure 8A); C and N
(3) dip-coated PA 12 disks with 1 wt.% Mg(OH) nanoplatelets (first run); Mg(OH) NPs peaks were not detected
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2
(4) dip-coated PA 12 disks with 1 wt.% Mg(OH) nanoplatelets (second PA 12 IM disk C 63.3 Circular surface of the
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run); (5) injection-molded PA 12 disks; and (6) injection-molded disk dip-coated with O 23.4 disk; washing removes
from melt compounded with 5% Mg(OH) with PA 12. A negative Mg(OH) NPs, after most of the Mg(OH) NPs
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2
2
log CFU/mL means a reduction of the bacterial count by a factor of 10 −x washing Mg 7.1 (Figure 8C)
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Abbreviations: T4: 4 h; T24: 24 h; PA: Polyamide; NPs: Nanoplatelet N 5.8
Note: The weight percentage was obtained from the mean of
nanocomposite with 5 wt.% Mg(OH) NPs made by a measurements at five positions.
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conventional fabrication technology, such as IM, most of Abbreviation: NP: Nanoplatelet, IM: injection-molded; PA: Polyamide.
the NPs will be ineffective.
To increase the anti-microbial activity in IM plastics, surface, leading to droplet formation after immersion in
the amount of NPs on the surface of the disk can be raised the NP suspension leading to the deposition of crystal
by augmenting the additive level in the plastic. However, islands; and (ii) poor adhesion of the NPs to the surface
from our experience of IM plastics with fillers, over 5 after drying. Figure 8A displays an SEM image of an IM
PA 12 disk after dip-coating, revealing a dense outlay of
vol.% Mg(OH) nanocrystals would be required to form Mg(OH) crystals; i.e., no islands were observed (the entire
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protrusions on the article surfaces, which is challenging surface was covered with crystals), suggesting that wetting
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with melt compounding.
had not been a problem for the combination of suspending
To get the crystals protruding on the surface of the IM fluid and polymer. The EDX (Table 2) detected mostly Mg
PA 12 disks, an alternative method was employed with the and O (45.7% and 53.6%, respectively) on the surface of
IM disks. They were dip-coated in an aqueous suspension the dip-coated IM PA 12 disks. Figure 8B displays a higher
of Mg(OH) and dried. Based on our experience with magnification SEM image of the dip-coated IM disk, where
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coating plastic sheets with aqueous Mg(OH) suspensions, NPs of various orientations, including edge-on, could be
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two problems can occur: (i) poor wetting of the polymer observed.
Volume 3 Issue 4 (2024) 8 doi: 10.36922/msam.4970