Synthesis, Characterization, and Bacterial Fouling-Resistance Properties of Polyethylene Glycol-Grafted Polyurethane Elastomers

Abstract

Despite advances in material sciences and clinical procedures for surgical hygiene, medical device implantation still exposes patients to the risk of developing local or systemic infections. The development of efficacious antimicrobial/antifouling materials may help with addressing such an issue. In this framework, polyethylene glycol (PEG)-grafted segmented polyurethanes were synthesized, physico-chemically characterized, and evaluated with respect to their bacterial fouling-resistance properties. PEG grafting significantly altered the polymer bulk and surface properties. Specifically, the PEG-grafted polyurethanes possessed a more pronounced hard/soft phase segregated microstructure, which contributed to improving the mechanical resistance of the polymers. The better flexibility of the soft phase in the PEG-functionalized polyurethanes compared to the pristine polyurethane (PU) was presumably also responsible for the higher ability of the polymer to uptake water. Additionally, dynamic contact angle measurements evidenced phenomena of surface reorganization of the PEG-functionalized polyurethanes, presumably involving the exposition of the polar PEG chains towards water. As a consequence, Staphylococcus epidermidis initial adhesion onto the surface of the PEG-functionalized PU was essentially inhibited. That was not true for the pristine PU. Biofilm formation was also strongly reduced.

Keywords: antifouling materials; medical device-related infections; microbial biofilm; polyethylene glycol; segmented polyurethanes; wound dressings.

Figure 1

Chemical structure of the repeat unit of PEUA (A) and PEUA-PEG (B).

Figure 2

Numeration of methylene bis-phenyl-diisocyanate (MDI) carbons in PEUA (A); ¹³C-NMR spectrum of PEUA (B) and PEUA-PEG obtained with a 5:1 PEG:PEUA molar ratio (C). In the inset of B, the magnification of the signal at 175 ppm, attributed to the PEUA carboxylic group, is reported.

Figure 2

Numeration of methylene bis-phenyl-diisocyanate (MDI) carbons in PEUA (A); ¹³C-NMR spectrum of PEUA (B) and PEUA-PEG obtained with a 5:1 PEG:PEUA molar ratio (C). In the inset of B, the magnification of the signal at 175 ppm, attributed to the PEUA carboxylic group, is reported.

Figure 3

¹H-NMR spectrum of PEUA (A) and PEUA-PEG obtained with a 5:1 PEG:PEUA molar ratio (B).

Figure 4

Thermograms of PEUA and PEUA-PEG₃₀ in the I cycle (A) and the II cycle (B) of heating.

Figure 5

Thermogravimetric curves of PEUA, PEUA-PEG_1:2, PEUA-PEG₂₀, and PEUA-PEG₃₀ (A); first derivative (Δ(weight)/ΔT) of the thermogravimetric curves (B). The subscript 1:2 on PEUA:PEG_1:2 indicates the molar ratio employed during functionalization.

Figure 6

Swelling curves of PEUA and PEUA-PEG₃₀ (A); Ratio between the swollen polymer mass at time t, and at the equilibrium (W_t/W_eq), as a function of the ratio of the square root of time (B). The diffusion coefficient was extrapolated by the slope of the linear fitting of the initial points.

Figure 7

DCA cycles of immersion for PEUA-PEG₃₀ by using the Wilhelmy plate method. In the figure, numbers 1 to 4 indicate the position of the plate with respect to the liquid, as shown in the image below the figure. 1—Out of the liquid; 2—point of touch of the sample with the liquid; 3—Immersion into the liquid (θ_adv); 4—Emersion from the liquid (θ_rec).

Figure 7

DCA cycles of immersion for PEUA-PEG₃₀ by using the Wilhelmy plate method. In the figure, numbers 1 to 4 indicate the position of the plate with respect to the liquid, as shown in the image below the figure. 1—Out of the liquid; 2—point of touch of the sample with the liquid; 3—Immersion into the liquid (θ_adv); 4—Emersion from the liquid (θ_rec).

Figure 8

Stress-strain curves of PEUA and PEUA-PEG₃₀.

Figure 9

Initial bacterial adhesion after 30 min incubation on PEUA (A) and PEUA-PEG₃₀ (B). Biofilm formation after 24 h incubation on PEUA (C) and PEUA-PEG₃₀ (D). Scale bar = 10 µm.