Use of silver-based additives for the development of antibacterial functionality in Laser Sintered polyamide 12 parts

Abstract

Infectious diseases (exacerbated by antimicrobial resistance) cause death, loss of quality of life and economic burden globally. Materials with inherent antimicrobial properties offer the potential to reduce the spread of infection through transfer via surfaces or solutions, or to directly reduce microbial numbers in a host if used as implants. Additive Manufacturing (AM) techniques offer shorter supply chains, faster delivery, mass customisation and reduced unit costs, as well as highly complicated part geometries which are potentially harder to clean and sterilise. Here, we present a new approach to introducing antibacterial properties into AM, using Laser Sintering, by combining antimicrobial and base polymer powders prior to processing. We demonstrate that the mechanical properties of the resultant composite parts are similar to standard polymer parts and reveal the mode of the antibacterial activity. We show that antibacterial activity is modulated by the presence of obstructing compounds in different experimental media, which will inform appropriate use cases. We show that the material is not toxic to mammalian cells. This material could be quickly used for commercial products, and our approach could be adopted more generally to add new functionality to Laser Sintered parts.

Figure 1

Engineering properties of parts (a) Photograph of a selection of parts made from PA2200 (left) alongside the 1% B65003 composite material (right). (b) Raw stress-strain curves from tensile testing. (c) A comparison of Young’s modulus (E), ultimate tensile strength (σ_uts) and elongation at break (ε_max) for both materials.

Figure 2

Images of parts – (a,b) SEM images of base material (sintered PA2200), (c,d) composite material. The lighter, more angular objects in d are likely silver phosphate glass. (e) X-Ray micro tomography section of base material (PA2200), showing pores. (f) X-Ray micro tomography section of the composite showing even distribution of silver phosphate glass particles.

Figure 3

SEM and EDX map of composite PA2200 + B65003 surface. (a) SEM micrograph of the surface scanned with EDX. (b–d) Elemental map from EDX analysis of the surface with colour indicating detection of the corresponding element.

Figure 4

Comparison of amount of S. aureus (CFU/ml) in PBS surrounding (a), or attached to (b) polyamide 12 or antibacterial polyamide 12 (containing 1.0% B65003); and comparison of amount of P. aeruginosa (CFU/ml) in PBS surrounding (c), or attached to (d) polyamide 12 or antibacterial polyamide 12 (containing 1.0% B65003). Comparison of amount of S. aureus (CFU/ml) in PBS previously incubated with polyamide 12 or antibacterial polyamide 12 (containing 1.0% B65003) (e).

Figure 5

(a) comparison of the amount of S. aureus (CFU/ml) in BHI surrounding, or attached to polyamide 12 or antibacterial polyamide 12 (containing 1.0% B65003), (b) comparison of amount of P. aeruginosa (CFU/ml) in BHI surrounding, or attached to polyamide 12 or antibacterial polyamide 12 (containing 1.0% B65003), (c) comparison of the amount of S. aureus (CFU/ml) in PBS containing 1 mM reduced glutathione surrounding, or attached to polyamide 12 or antibacterial polyamide 12 (containing 1.0% B65003).

Figure 6

Comparison of metabolic activity between fibroblast monolayers containing parts, a disc made of polyamide 12 or one made of antibacterial polyamide 12 (containing 1.0% B65003). A Kruskal-Wallis test indicates no difference between groups.

Figure 7

Dimensions of a type I tensile test specimen according to ASTM D638.