3D printing antimicrobial polymer materials
Non-leachable, antimicrobial, 3D-printable materials could be on the horizon thanks to a study completed at Stellenbosch University, South Africa.
The researchers claim to be adding to just a few studies on making antimicrobial polymer materials via 3D printing that are suitable for use in everyday clinical objects.
The material is manufactured by blending a polyamide 11 matrix (PA11) and a styrene-alt-maleimide copolymer with pendant quaternary amine moieties.
PA11 serves as the structural matrix and is reportedly well-suited for selective laser sintering (SLS).
The amorphous styrene-alt-maleimide copolymer, with pendant quaternary amine cation (QAC) moieties (SMI-Pq12) provides permanent, non-leaching, antimicrobial properties – conferred by the QAC functionalities.
The PA11 and SMI-Pq12 are mechanically blended by physically mixing them in a rotating drum. The final polymer-blend products – 3D printed via selective laser sintering – are composed of 95wt.% PA119 and 5% SMI-Pq12.
Dr Rueben Pfukwa at Stellenbosch University, (who was supported by postgraduate student Miché Daniels on the project) says the material displays 'good mechanical strength, comparable to those of neat PA11, indicating that blending is feasible for this type of material'.
However, the mechanical properties are directionally dependent – horizontally printed samples show greater strengths compared to vertically printed samples, and so this is a consideration when preparing the material for load-bearing applications.
The microstructure of the 3D-printed materials was further characterised via diffusion-ordered spectroscopy and nuclear magnetic resonance spectroscopy.
Although SLS polymers are common in engineering, these polymers are diffcult to functionalise with antimicrobial moieties, explain the researchers. Pfukwa adds, '3D printing did not alter the antimicrobial activity of the polymer blend, based on the PA11 95%/SMI-Pq12 5% blend, which was more effective against S. aureus RN 4220 than E. coli.'
Blend properties were studied prior to printing via differential scanning calorimetry, powder X-ray diffraction and fourier transform infrared (FTIR) spectroscopy.
Pfukwa explains, 'We studied the thermal properties of various PA11/SMI-Pq12 blends (5, 10, 15, 20, 25 and 30wt.% SMI-Pq12), specifically the melting and crystallisation temperatures, critical for defining the operating window for the SLS process.
'The blends exhibited a lower degree of crystallinity compared to pure PA11. This is a known behaviour for miscible polymer blends. They are known to display lower degrees of crystallinity than the pure semicrystalline components due to thermodynamically favourable interactions.
'We also investigated the molecular interactions of the blend components via FTIR spectroscopy, which showed possible hydrogen bonding between the blend components.'
The final material blend was chosen 'since it presented the least SMA-Pq12 sample volume demand'.
Pfukwa says, 'Instead of developing new functional polymers or modifying existing ones, two different polymers with the right properties can be blended to develop a material with the right properties.
'Polymer blending therefore offers an attractive, quick, effective and affordable method for preparing new polymer materials with tailored properties. 3D printing enables access to fully customised geometrically complex materials in an economic manner.'
They claim their approach is adaptable and has commercial potential as an alternative to combat hospital-acquired infections, especially from drug-resistant bacteria.
'Current sterilisation methods rely on disinfectants such as hypochlorite, small molecule QCAs and alcohols. However, these have a short duration of antibacterial activity and may cause environmental toxicity in the case of some disinfectants and leaching of transition metals, as observed with silver salt compounds,' shares Pfukwa.
