Abstract
In this work, we introduce a one-step strategy that is suitable for continuous flow manufacturing of antimicrobial PDMS materials. The process is based on the intrinsic capacity of PDMS to react to certain organic solvents, which enables the incorporation of antimicrobial actives such as salicylic acid (SA), which has been approved for use in humans within pharmaceutical products. By combining different spectroscopic and imaging techniques, we show that the surface properties of PDMS remain unaffected while high doses of the SA are loaded inside the PDMS matrix. The SA can be subsequently released under physiological conditions, delivering a strong antibacterial activity. Furthermore, encapsulation of SA inside the PDMS matrix ensured a diffusion-controlled release that was tracked by spatially resolved Raman spectroscopy, Attenuated Total Reflectance IR (ATR-IR), and UV-Vis spectroscopy. The biological activity of the new material was evaluated directly at the surface and in the planktonic state against model pathogenic bacteria, combining confocal laser scanning microscopy, electron microscopy, and cell viability assays. The results showed complete planktonic inhibition for clinically relevant strains of Staphylococcus aureus and Escherichia coli, and a reduction of up to 4 orders of magnitude for viable sessile cells, demonstrating the efficacy of these surfaces in preventing the initial stages of biofilm formation. Our approach adds a new option to existing strategies for the antimicrobial functionalisation of a wide range of products such as catheters, wound dressings and in-dwelling medical devices based on PDMS.
Highlights
Polydimethylsiloxane (PDMS) is a silicon-based polymer commonly used in biomedical and industrial applications[1,2,3], including the fabrication and prototyping of medical devices[4,5,6,7], and the formulation of pharmaceutical, cosmetic and food products (European Union Regulation (EC) No 1333/2008 of the European Parliament and of the Council of 16 December 2008 on food additives in force 02/07/2020, (2020) Document 02008R1333-20200702, data.europa.eu/eli/reg/2008/ 1333/2020-07-02)
Fabrication and characterisation of PDMS-salicylic acid (SA) materials PDMS is widely used in several applications because it is chemically inert, but this characteristic imposes big challenges for the chemical functionalisation of PDMS devices
Antimicrobial activity in the planktonic state After demonstrating the release of sub-surface SA within PDMS-SA materials, we subsequently investigated the antimicrobial activity of these materials against two model microorganisms, Escherichia coli and Staphylococcus aureus (i.e. E. coli strain J96 and S. aureus strain SH1000), which are relevant clinical pathogens[19,20,21]
Summary
Polydimethylsiloxane (PDMS) is a silicon-based polymer commonly used in biomedical and industrial applications[1,2,3], including the fabrication and prototyping of medical devices[4,5,6,7], and the formulation of pharmaceutical, cosmetic and food products (regulated food additive E900) (European Union Regulation (EC) No 1333/2008 of the European Parliament and of the Council of 16 December 2008 on food additives in force 02/07/2020, (2020) Document 02008R1333-20200702, data.europa.eu/eli/reg/2008/ 1333/2020-07-02). Covalent functionalisation of PDMS devices with antimicrobial components can be challenging, often requiring complex and invasive approaches that cannot be translated from labscale into industrial production lines within strict regulatory environments. The use of antimicrobial coatings on PDMS devices has been explored before[10,11,12]; in-depth characterisation of surface and sub-surface distributions of active molecules is scarce, limiting the development of knowledge-based design strategies for industrial scale processes. Our detailed characterisation of the chemical properties and the performance of the new material demonstrates reliability and robustness of the manufacturing protocol. We envision that this alternative approach will allow the functionalisation of PDMS-based medical devices with different active components, opening opportunities for novel technological applications
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