Polyurethane-Based Composites: Effects of Antibacterial Fillers on the Physical-Mechanical Behavior of Thermoplastic Polyurethanes

Abstract

The challenge to manufacture medical devices with specific antibacterial functions, and the growing demand for systems able to limit bacterial resistance growth, necessitates the development of new technologies which can be easily produced at an industrial level. The object of this work was the study and the development of silver, titanium dioxide, and chitosan composites for the realization and/or implementation of biomedical devices. Thermoplastic elastomeric polyurethane was selected and used as matrix for the various antibacterial functions introduced during the processing phase (melt compounding). This strategy was employed to directly incorporate antimicrobial agents into the main constituent material of the devices themselves. With the exception of the composite filled with titanium dioxide, all of the other tested composites were shown to possess satisfactory mechanical properties. The best antibacterial effects were obtained with all the composites against Staphylococcus aureus: viability was efficiently inhibited by the prepared materials in four different bacterial culture concentrations.

Keywords: antibacterial; chitosan; physical-mechanical properties; polymer matrix composites; silver; thermoplastic polyurethane (TPU); titanium dioxide.

Figure A1

Storage modulus and loss modulus at 10 rad/s as a function of the temperature range T = 160–200 °C, on cooling (filled symbols) and on heating (open symbols) for TPU (a), and TPU-Ag (b), TPU-Chit (c), and TPU-TiO₂ (d).

Figure 1

Compression molded films (dimensions 80 × 115 mm, thickness 0.25 mm) of TPU (a), TPU-Ag (b), TPU-Chit (c) and TPU-TiO₂ (d).

Figure 2

Bidimensional heteronuclear ¹H-¹³C spectra of TPU.

Figure 3

WAXD (a) and SAXS (b) profiles of TPU and TPU-based composites.

Figure 4

TGA (a) and DTG (b) curves for TPU and TPU-based composites.

Figure 5

DSC traces (first heating, cooling and second heating) of TPU (a), TPU-TiO₂ (b), TPU-Chit (c), and TPU-Ag (d); T_gs of TPU and TPU-based composites from first heating run (e). Three endotherm regions (I, II, III) are visible and related to different morphologies of the crystallizable segments.

Figure 6

Average contact angle values in water, Luria-Bertani broth (LB) and brain heart infusion (BHI) for TPU and TPU composites.

Figure 7

SEM image of TPU-Ag (a), map showing the relative position of Ag on the surface (b), and EDS spectrum for TPU-Ag film (c).

Figure 8

SEM image of TPU-TiO₂ (a), map showing the relative position of TiO₂ on the surface (b), and EDS spectrum for TPU-TiO₂ (c).

Figure 9

Stress–strain curves for TPU and TPU-based composites. The inset picture highlights the initial part of the stress-strain curves.

Figure 10

Storage modulus (G’) and loss modulus (G’’) as function of the frequency range ω = 628.3–0.04 rad/s at 190 °C for TPU (a), TPU-Chit (b), TPU-TiO₂ (c), and TPU-Ag (d).

Figure 11

Complex viscosity as function of the frequency range ω = 628.3–0.04 rad/s at 190 °C for TPU and TPU-based composites.

Figure 12

G’ at 10 rad/s as a function of the temperature range T = 160–200 °C, on cooling (filled symbols) and on heating (open symbols) for TPU and TPU composites.

Figure 13

Antibacterial activity of TPU composites. Viability of E. coli (A) and S. aureus (B) was evaluated at different bacterial culture densities after 24 h culture period. Data are presented as viability percentage to TPU set equal to 100%.

Figure 14

SEM micrographs of S. aureus ATCC25923 cultured on TPU (a), TPU-Ag (b), TPU-Chit (c), and TPU-TiO₂ (d). Main micrograph: magnification 5000×, scale bar 10 μm, inset: magnification 10,000×, scale bar 2 μm.