Antimicrobial efficacy of laser sintered polyamide 12 / silver microcomposites

The spread of infectious disease is at the centre of global attention, with the demand for novel methods to control this spread higher than ever before. Antimicrobial materials, such as the ones presented here, can prove an effective tool for this, even against those with Antimicrobial Resistance. This research sought to exploit the nuances of the Laser Sintering process to introduce antimicrobial properties into Additively Manufactured parts.

Commercial and bespoke silver-containing additives, chosen to determine the effects of particle size and degradation rates, were successfully used to create intrinsically antimicrobial materials for use in Laser Sintering. These were mixed into a polyamide 12 powder feedstock, with the resulting printed microcomposite parts analysed for their engineering properties and antimicrobial functionality.

The composite powder feedstock was processed effectively and showed no significant effect on the mechanical properties, crystallinity, or microstructure of the printed parts. The additive was found to be well-dispersed throughout the printed parts, and antimicrobial silver ions were seen to be released in water as expected.

The microcomposite parts showed both bactericidal and antibiofouling effects (planktonic and biofilm) against both Gram-positive and Gram-negative bacteria (Staphylococcus aureus and Pseudomonas aeruginosa) in nutrient-poor conditions, even when the parts had no direct contact with the bacteria. No antimicrobial effect was measured in nutrient-rich conditions, with thiols present identified as preventing the silver from affecting the bacteria; and parts shown to have no cytotoxic effect against human cells. The custom-made additives were found to be more effective against Staphylococcus aureus than Pseudomonas aeruginosa, with the efficacy found to be more sensitive to the silver content of the additive than the degradation rate.

This research has demonstrated the potential for this approach to be adopted more broadly, and has provided crucial insights into significant factors influencing its effectiveness. Further work should focus on testing the efficacy against a wider range of microbes, the effect of additive loading, and the use of different base polymers.