Robust Copper Metal-Organic Framework-Embedded Polysiloxanes for Biomedical Applications: Its Antibacterial Effects on MRSA and In Vitro Cytotoxicity

Abstract

Polysiloxanes (PSs) have been widely utilized in the industry as lubricants, varnishes, paints, release agents, adhesives, and insulators. In addition, their applications have been expanded to include the development of new biomedical materials. To modify PS for application in therapeutic purposes, a flexible antibacterial Cu-MOF (metal-organic framework) consisting of glutarate and 1,2-bis(4-pyridyl)ethane ligands was embedded in PS via a hydrosilylation reaction of vinyl-terminated and H-terminated PSs at 25 °C. The bactericidal activities of the resulting Cu-MOF-embedded PS (PS@Cu-MOF) and the control polymer (PS) were tested against Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus. PS@Cu-MOF exhibited more than 80% bactericidal activity toward the tested bacteria at a concentration of 100 μg⋅mL^-1 and exhibited a negligible cytotoxicity toward mouse embryonic fibroblasts at the same concentration. Release tests of the Cu(II) ion showed PS@Cu-MOF to be particularly stable in a phosphate-buffered saline solution. Furthermore, its physical and thermal properties, including the phase transition, rheological measurements, swelling ratio, and thermogravimetric profile loss, were similar to those of the control polymer. Moreover, the low cytotoxicity and bactericidal activities of PS@Cu-MOF render it a promising candidate for use in medicinal applications, such as in implants, skin-disease treatment, wound healing, and drug delivery.

Keywords: Cu-MOF; antibacterial agent; biomedical application; cytocompatibility; hydrosilylation; polysiloxane (PS).

Figure 1

(a) Schematic illustration of the synthesis of Cu-MOF. (b) Hydrosilylation of vinyl-terminated PS and hydrogen-terminated PS with Cu-MOF in the presence of a Pt catalyst. (c) Curing mechanism for the hydrosilylation of PS-vinyl and PS-H containing a Pt catalyst. (d) Photographic images of PS and the PS@Cu-MOF. Scale bar: 0.5 cm.

Figure 2

Characterization of PS and PS@Cu-MOF; (a) PXRD patterns, (b) DSC scans, and (c) TGA profiles.

Figure 3

SEM images of PS and PS@Cu-MOF with the accompanying EDS spectra and corresponding elemental maps. Scale bar: 50 μm.

Figure 4

Physical properties of PS and PS@Cu-MOF. (a) Storage modulus and (b) swelling ratio of PS and PS@Cu-MOF (n = 4).

Figure 5

(a) Representative images of bacteria grown on PS and PS@Cu-MOF after incubation for 24 h: Top (blank), middle (PS), and bottom (PS@Cu-MOF); left to right: E. coli, S. aureus, and MRSA. (b) The antibacterial efficiency of PS and PS@Cu-MOF towards E. coli, S. aureus, and MRSA (means ±standard deviation with n = 3; **: p < 0.01).

Figure 6

Concentration of Cu(II) ions released from PS@Cu-MOF (1 mg) in 0.9% PBS (1 mL).

Figure 7

(a) Staining images of the live/dead MEFs after contact with PS only or PS@Cu-MOF for 1 or 3 d. Cells cultured without any PS contact were used as a positive control. As a negative control, cells exposed to EtOH were used. (b) In vitro cytotoxicity of the extract solution of PS and PS@Cu-MOF to MEFs (n = 4); means ± standard deviation with n = 4; NS: not significant; *** p < 0.001. Scale bar: 200 μm.