Thermodynamic Surface Analyses to Inform Biofilm Resistance

Abstract

Biofilms are the habitat of 95% of bacteria successfully protecting bacteria from many antibiotics. However, inhibiting biofilm formation is difficult in that it is a complex system involving the physical and chemical interaction of both substrate and bacteria. Focusing on the substrate surface and potential interactions with bacteria, we examined both physical and chemical properties of substrates coated with a series of phenyl acrylate monomer derivatives. Atomic force microscopy (AFM) showed smooth surfaces often approximating surgical grade steel. Induced biofilm growth of five separate bacteria on copolymer samples comprising varying concentrations of phenyl acrylate monomer derivatives evidenced differing degrees of biofilm resistance via optical microscopy. Using goniometric surface analyses, the van Oss-Chaudhury-Good equation was solved linear algebraically to determine the surface energy profile of each polymerized phenyl acrylate monomer derivative, two bacteria, and collagen. Based on the microscopy and surface energy profiles, a thermodynamic explanation for biofilm resistance is posited.

Keywords: Microbiology; Polymer Chemistry; Thermodynamics.

Graphical abstract

Figure 1

Normalized Quantitative Evaluation of Multiple Species Biofilm Resistance Species evaluated include E. coli, P. aeruginosa, S. aureus, S. pneumoniae, and S. typhimurium. Normalized relative to biofilm growth on control coating. Reduced biofilm resistance relative to the control is negative. Increased biofilm resistance relative to the control is positive. See also Figures S2–S7.

Figure 2

Overall Surface Energy Comparison (${\mathit{\gamma }}_{\mathit{s}}$) of Phenyl Acrylic Coatings, Collagens, and Bacteria All units are mJ/m² ± SEM where number of samples (N) is 36 (3a), 24 (3b), 18 (3c), 18 (3d), 24 (3e), 36 (3f), 18 (3g), 18 (collagen, insoluble), 36 (collagen, soluble), 21 (S. aureus), and 18 (P. aeruginosa). See Transparent Methods. ^aCalculations based on contact angles from bromonaphthalene, formamide, and water for insoluble collagen (100 μg/mL). ^bCalculations based on contact angles from bromonaphthalene, formamide, and water for soluble collagen (100 μg/mL) in phosphate buffer solution (1x, pH = 7.4). ^cCalculations based on contact angles from bromonaphthalene, dimethylsulfoxide, and water. ^dObtaining a smooth coating without smearing or orange peeling was difficult and may have contributed to an anomalous/inaccurate surface energy profile; however, for completeness, the surface energy profile for 3b was included in the dataset.

Figure 3

Surface Energy Polar Component (${\mathit{\gamma }}_{\mathit{s}}^{\mathit{AB}}$) Comparison of Phenyl Acrylic Coatings, Collagens, and Bacteria All units are mJ/m² ± SEM where number of samples (N) is 36 (3a), 24 (3b), 18 (3c), 18 (3d), 24 (3e), 36 (3f), 18 (3g), 18 (collagen, insoluble), 36 (collagen, soluble), 21 (S. aureus), and 18 (P. aeruginosa). See Transparent Methods. ^aCalculations based on contact angles from bromonaphthalene, formamide, and water for insoluble collagen (100 μg/mL). ^bCalculations based on contact angles from bromonaphthalene, formamide, and water for soluble collagen (100 μg/mL) in phosphate buffer solution (1x, pH = 7.4). ^cCalculations based on contact angles from bromonaphthalene, dimethylsulfoxide, and water. ^dObtaining a smooth coating without smearing or orange peeling was difficult and may have contributed to an anomalous/inaccurate surface energy profile; however, for completeness, the surface energy profile for 3b was included in the dataset.

Figure 4

Surface Energy Base Component (${\mathit{\gamma }}_{\mathit{s}}^{-}$) Comparison of Phenyl Acrylic Coatings, Collagens, and Bacteria All units are mJ/m² ± SEM where number of samples (N) is 36 (3a), 24 (3b), 18 (3c), 18 (3d), 24 (3e), 36 (3f), 18 (3g), 18 (collagen, insoluble), 36 (collagen, soluble), 21 (S. aureus), and 18 (P. aeruginosa). See Transparent Methods. ^aCalculations based on contact angles from bromonaphthalene, formamide, and water for insoluble collagen (100 μg/mL). ^bCalculations based on contact angles from bromonaphthalene, formamide, and water for soluble collagen (100 μg/mL) in phosphate buffer solution (1x, pH = 7.4). ^cCalculations based on contact angles from bromonaphthalene, dimethylsulfoxide, and water. ^dObtaining a smooth coating without smearing or orange peeling was difficult and may have contributed to an anomalous/inaccurate surface energy profile; however, for completeness, the surface energy profile for 3b was included in the dataset.