The Manufacture and Characterization of Silver Diammine Fluoride and Silver Salt Crosslinked Nanocrystalline Cellulose Films as Novel Antibacterial Materials

Abstract

There is an unmet need for biocompatible, anti-infective, and mechanically strong hydrogels. This study investigated the use of poly vinyl alcohol (PVA), polysaccharides, and nanocrystalline cellulose (CNC) to deliver silver in a controlled manner for possible use against oral or wound bacteria. Silver was included in solvent cast films as silver diammine fluoride (SDF) or as nitrate, sulphate, or acetate salts. Hydrogel formation was assessed by swelling determinations and silver release was measured using inductively coupled plasma methods. Antibacterial studies were performed using Gram-positive and negative bacteria turbidity assays. PVA formed homogenous, strong films with SDF and swelled gently (99% hydrolyzed) or vigorously with dissolution (88% hydrolyzed) and released silver slowly or quickly, respectively. CNC-SDF films swelled over a week and formed robust hydrogels whereas CNC alone (no silver) disintegrated after two days. SDF loaded CNC films released silver slowly over 9 days whereas films crosslinked with silver salts were less robust and swelled and released silver more quickly. All silver loaded films showed good antibacterial activity. CNC may be crosslinked with silver in the form of SDF (or any soluble silver salt) to form a robust hydrogel suitable for dental use such as for exposed periodontal debridement areas.

Keywords: antibacterial; hydrogels; nanocrystalline cellulose; poly vinyl alcohol; silver; silver diammine fluoride.

Figure 1

Appearance of CNC cast films including various silver salts. (1) SDF with CNC, (2) SDF with CNC and glycerol, (3) AgNO₃ with CNC, (4) AgNO₃ with CNC and glycerol, (5) Ag₂SO₄ with CNC, (6) Ag₂SO₄ with CNC and glycerol, (7) Ag Acetate with CNC, and (8) Ag Acetate with CNC and glycerol.

Figure 2

(a) Time course of swelling of SDF loaded CNC or PVA hydrogel films in water. (b) Time course of swelling of SDF loaded PVA (88% hydrolyzed) films in water.

Figure 3

(a) Time course of swelling of silver nitrate loaded CNC hydrogel films in water. (b) Time course of swelling of silver sulphate loaded CNC hydrogel films in water. (c) Time course of swelling of silver acetate loaded CNC hydrogel films in water.

Figure 4

Time course of swelling of SDF loaded CNC hydrogel films (1–10 mg) in water. Loadings describe weight of silver in 500 mg manufactured films, thus 10 mg is equivalent to 2% w/w silver loading in CNC.

Figure 5

Swollen appearance of SDF loaded CNC film. (A) day 1; (B) day 5.

Figure 6

Time course of swelling of silver nitrate loaded CNC hydrogel films in water using various loadings of silver nitrate. Loadings describe weight of silver in 500 mg manufactured films, thus 10 mg is equivalent to 2% silver loading.

Figure 7

Swollen appearance of various silver salt loaded CNC films. (1) silver nitrate with CNC, (2) silver nitrate with CNC and glycerol, (3) silver sulphate with CNC, (4) silver sulphate with CNC and glycerol, (5) silver acetate with CNC, (6) silver acetate with CNC and glycerol.

Figure 8

Time course of the release of silver from SDF loaded CNC hydrogels films in water.

Figure 9

Time course of the release of silver from various silver salt loaded CNC hydrogels with or without glycerol in water.

Figure 10

Inhibition of MRSA growth by (a) release media from incubation of SDF or silver salt crosslinked CNC at 4 h, 1, 2, 3, and 4 days; (b) MRSA growth as a function of silver concentration using SDF or silver nitrate in solution.

Figure 11

Inhibition of E. coli growth by (a) release media from incubation of SDF or silver salt crosslinked CNC at 4 h, 1, 2, 3, and 4 days; (b) E. coli growth as a function of silver concentration using SDF or silver nitrate in solution.