Antifungal hydrogels

Abstract

Fungi are increasingly identified as major pathogens in bloodstream infections, often involving indwelling devices. Materials with antifungal properties may provide an important deterrent to these infections. Here we describe amphogel, a dextran-based hydrogel into which amphotericin B is adsorbed. Amphogel kills fungi within 2 h of contact and can be reused for at least 53 days without losing its effectiveness against Candida albicans. The antifungal material is biocompatible in vivo and does not cause hemolysis in human blood. Amphogel inoculated with C. albicans and implanted in mice prevents fungal infection. Amphogel also mitigates fungal biofilm formation. An antifungal matrix with these properties could be used to coat a variety of medical devices such as catheters as well as industrial surfaces.

Fig. 1.

Antifungal properties of dextran-based hydrogels with or without AmB. (a) Schematic representation of the preparation of amphogels. (b) C. albicans viability on the hydrogel surface as assessed by a colony growth assay after a 2-h exposure to dextran-based hydrogels with or without AmB. (c) SEM images of dextran-based gels without (c1) and with (c2) AmB incubated with C. albicans for 48 h.

Fig. 2.

Schematic of fungal survival experiments. (a) In one type of experiment that studied the effect of direct exposure to the disks, the disks were placed in medium containing fungi, and the extent of fungal survival in the medium (a-1) and on the disks' surfaces (a-2) was determined. (b) In a second type of experiment designed to determine the effect of AmB released from the disks, they were first incubated in medium without fungi. After that incubation, the medium was removed, fungi were added to that incubation medium, now without the disk, and survival was assessed (b-1). In both contexts, disks were used repeatedly in serial experiments describing the time course of fungicidal activity.

Fig. 3.

Yeast killing by amphogels. Survival was assessed by a colony growth assay. Data are means with standard deviations. (a) Time course of yeast cell killing in medium upon contact with amphogel. More than 99% of C. albicans cells exposed to amphogel were killed after 120 min. (b) Survival of fungi added to medium that had been exposed to amphogels over the course of 30 days (release medium; see Fig. 2b). The individual medium samples had been exposed to the gels for a time period equal to the interval between the predetermined time points. ∗∗ denotes statistical significance (P < 0.001, n ≥ 5) between the various samples and cells cultured without amphogels. (c) Effect of 2-h exposure to amphogels on survival of C. albicans in medium over the course of 53 days (see Fig. 2a). Dextran-based hydrogels without AmB (“Blank”) were used as controls. (d) Fungal survival in the medium after exposure for 2 h to PEG and inulin gels loaded with AmB. Hydrogels without AmB were used as controls.

Fig. 4.

In vivo biocompatibility studies and biological activity of amphogels. (a and b) Representative light micrographs of amphogel implanted s.c. and surrounding tissue after 3 days (a) or 3 weeks (b), stained with hematoxylin/eosin. Minimal to mild inflammation was observed at day 3 and only mild to moderate inflammation at 3 weeks. (Original magnification: ×50, a; ×200, b.) (c–f) SEM photographs from the surface of amphogel (c and d) or dextran gel without AmB (e and f) incubated with C. albicans that were implanted into mice and then removed after 5 days. Amphogels did not have any Candida biofilm (c) and had only a few host cells (mainly white blood cells) (d). Dextran gels without AmB were covered with fungal biofilm (e, arrow). Certain areas of the disks were covered with a large number of Candida cells (f, arrow) mixed with white blood cells (arrowhead).