Bacterial Attachment on Large Area Two-Photon Polymerised Scaffolds with Different Nanostructured Surfaces

An ultrashort pulsed laser is used to directly write large area, electrically conductive tissue scaffolds by photo-polymerisation. The structures are used to optimise the mechanical and electrical stimulation of cardiomyocyte and other cells [1], [2]. Polymers used for manufacturing implants are at risk of microbial attachment and biofilm formation leading to infections, thus an understanding of the bacterial-surface interaction is essential for the design of biomaterial surfaces for tissue engineering applications. The aim of this study was to investigate the interaction of Staphylococcus aureus and Pseudomonas aeruginosa, bacteria important in device-associated infections, with laser-modified biomaterials in order to understand the capability of the functionalised biomaterials to promote or inhibit bacterial attachment. Precision structures were written over large area by two-photon polymerisation of a commercially available photoresin using ultrashort pulse femtosecond laser and scaffolds were coated with gold to make them conductive. Three types of hexagonal structures and a smooth surface were written on the polymerised scaffold (Fig. 1a). Sterile 1 cm
²
scaffolds were added into respective bacterial suspension (10
³
CFU ml
⁻¹
) in a 24-well plate and incubated for 24 hours at 37°C. S. aureus had significantly higher (
$\mathrm{P}=0.0351$
)) attachment to the scaffolds than P. aeruginosa. Although, the smooth scaffold had lower bacterial population attached to its surface (S. aureus -
$1.07\times 10^{8}\ \text{CFU ml}^{-1}$
; P. aeruginosa -
$4.08\ \times 10^{7}\ \text{CFU ml}^{-1})$
compared to the surfaces with hexagonal structures. Although Type 1 had the highest bacteria population attached to its surface (S. aureus -
$4.37\times 10^{8}\ \text{CFU ml}^{-1}$
; P. aeruginosa
$-2.37\times 10^{8}$
CFU ml
⁻¹
) among the nanostructured surfaces, there was no significant differences among them. Gold coating resulted in 85–98% reduction in attached bacteria, with a significantly lower attachment of P. aeruginosa to Type
$2(\mathrm{P}=0.011)$
and Type 3 (
$\mathrm{P}=0.014$
) nanostructures.