Khan, Madiha F.
The Antibacterial Activity of Silicone-Polyether Surfactants.
The increase in microbial resistance to antibiotics underscores the need for novel antibacterial surfaces, particularly for silicone-based implants, because the hydrophobicity of silicones has been linked to undesirable microbial adhesion and biofilm formation. Unfortunately, current strategies for mitigation, such as pretreatment of surfaces with antiseptics/antibiotics, are not consistently effective. In fact, they can facilitate the prevalence of resistant pathogens by exposing bacteria to sublethal concentrations of biocides. Therefore, scientific interest has shifted to preventing initial adhesion (prior to surface colonization) by using surfactants as surface modifiers.
Accordingly, Chapter 2 studied the bioactivity of ACR-008 UP (an acrylic-terminated superwetting silicone surfactant) after it was copolymerized in increasing weight percentages with butyl methacrylate (BMA) and/or methyl methacrylate (MMA). Interestingly, copolymers of 20 wt % ACR showed at least 3x less adhesion by Escherichia coli BL21 (E. coli) than any other formulation. This was not a consequence of wettability, which followed a parabolic function with ACR concentration: high contact angles (CA) with sessile water drops were observed at both low (< 20 wt %) and high (> 80 wt %) concentrations of ACR in materials. The CA at 20 wt % ACR was 66°. The lack of E. coli adhesion was ascribed to surfactant-membrane interactions; hence, the antibacterial potential of compounds related to ACR was further probed.
Chapter 3, therefore, examines the structure-activity relationships of nonionic silicone polyether surfactants in solution. Azide/alkyne click chemistry was used to prepare a series of eight compounds with consistent hydrophilic tails (8- 44 poly(ethylene glycol) units), but variable hydrophobic heads (branched silicones with 3-10 siloxane linkages, and in two cases phenyl substitutions). The compounds were tested for toxicity at 0.001 w/v %, 2.5 w/v % and their critical micelle concentrations (CMCs), against different concentrations of E. coli in a 3-step assay. Surfactants with smaller head groups had as much as 4x the bioactivity of larger analogues, with the smallest hydrophobe exhibiting potency equivalent to SDS. Smaller PEG chains were similarly associated with higher potency. This data suggests that lower micelle stability, and the theoretically enhanced permeability of smaller silicone head groups in membranes, is linked to antibacterial activity. The results further demonstrate that the simple manipulation of nonionic silicone polyether structures, leads to significant changes in antibacterial action.
To ensure similar results were achievable when such surfactants are immobilized on surfaces, 8 compounds with shorter, ethoxysilylpropyl-terminated PEG chains, and branched or linear hydrophobes, were incorporated into a homemade, room temperature vulcanization (RTV) silicone (Chapter 4). The materials, containing 0- 20 wt% surfactants) were then tested for contact killing and cytophobicity against the same E. coli strain.…
Advisors/Committee Members: Brook, Michael A., Biomedical Engineering.
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APA (6th Edition):
Khan, M. F. (2017). The Antibacterial Activity of Silicone-Polyether Surfactants. (Doctoral Dissertation). McMaster University. Retrieved from http://hdl.handle.net/11375/21971
Chicago Manual of Style (16th Edition):
Khan, Madiha F. “The Antibacterial Activity of Silicone-Polyether Surfactants.” 2017. Doctoral Dissertation, McMaster University. Accessed July 23, 2018.
MLA Handbook (7th Edition):
Khan, Madiha F. “The Antibacterial Activity of Silicone-Polyether Surfactants.” 2017. Web. 23 Jul 2018.
Khan MF. The Antibacterial Activity of Silicone-Polyether Surfactants. [Internet] [Doctoral dissertation]. McMaster University; 2017. [cited 2018 Jul 23].
Available from: http://hdl.handle.net/11375/21971.
Council of Science Editors:
Khan MF. The Antibacterial Activity of Silicone-Polyether Surfactants. [Doctoral Dissertation]. McMaster University; 2017. Available from: http://hdl.handle.net/11375/21971