P15 Surface engineering of novel polydimethylsiloxane composites to attract bacteria: potential to treat chronic infected wounds and reduce antimicrobial resistance
Authors: Norton Paul , Katsikogianni Maria , Ansell David , Chang Chien-Yi , Thornton Julie 
Published: July 2023

Abstract
Chronic nonhealing wounds, such as pressure sores, venous leg ulcers and diabetic foot ulcers are a silent pandemic, and represent a significant economic and health burden, with billions exhausted per annum in the UK and USA alone. Chronic wounds are at high risk of infection with biofilms that are difficult to treat with broad-spectrum antibiotics. Another option is to develop a nontoxic dressing that can physically remove the live bacteria, thus reducing the risk of antimicrobial resistance (AMR). Thousands of wound dressings are commercially available to combat various degrees of wounding. Polydimethylsiloxane (PDMS), a biocompatible and inexpensive polymer to fabricate, can undergo various modifications. The ability of fabricated, patterned polymers to attract the opportunist Staphylococcus aureus and Pseudomonas aeruginosa, either from the planktonic state or while sessile in biofilms, on ex vivo human skin was investigated. These are the most common species isolated from chronic wounds, contributing to prolific biofilm formation, and decreasing antimicrobial efficiency. Different combinations of PDMS polymers patterned (PT) or flat (FL) ± triclosan (1% or 10%) were assessed with regard to their ability for selective bacterial attachment. Patterned PDMS + 10% triclosan (PT 10%) attracted significantly more live S. aureus and P. aeruginosa, as determined via colony-forming units (CFU) mL–1 (P &lt; 0.01), scanning electron microscopy (P &lt; 0.01) and confocal scanning laser microscopy (P &lt; 0.01). The released triclosan was not cytotoxic against either type of bacteria (P &lt; 0.05) or primary cultures of human dermal fibroblasts (P &lt; 0.05). High performance liquid chromatography analysis of the culture medium confirmed a low level of phase release. Dermal fibroblast viability increased in the presence of PDMS, when subject to infection in co-culture via the Boyden chamber assay (P &lt; 0.05). Compared to all the other polymer combinations, PT 10% demonstrated superior removal of biofilms that had been established on human ex vivo epidermis (P &lt; 0.5). Histological examination of ex vivo full-thickness human skin confirmed the superior attraction qualities of PT 10% on the removal of the bacterial biofilm. In summary, the unique topography of PDMS combined with triclosan attracted a substantial number of live bacteria, in their planktonic state, and, significantly, when in an established biofilm. A coinfection model demonstrated the protective nature of the polymer on cultured dermal fibroblast viability by drawing the planktonic bacteria away from them in a co-culture model. Successful establishment of biofilms on epidermal sheets from full-thickness skin allowed the demonstration of the favourable polymer topography for biofilm removal from human skin. Defined patterned polymers also presented with higher attachment rates than nonpatterned polymers, highlighting the potential for engineering specific patterned polymers to transfer biofilms physically from wounds. Significantly, these polymers lack bactericidal properties, which is vital in the quest to combat antimicrobial resistance.