Silver Ion Release from Antimicrobial Acrylate Photopolymer Layers

Abstract

Crosslinked silver-filled acrylate photopolymer layers on polyetheretherketone (PEEK) films were prepared by a heterogeneous photocatalytic polymerisation initiation using silver-coated titanium dioxide as a catalyst material. The silver ion release from 5 μm thick acrylate photopolymer layers was studied as a function of the chemical structure of the polymer matrix. The silver ion release increases with the number of ethoxy groups per monomer unit, although the filler content in all acrylate samples was the same (2.5 wt.% titanium dioxide coated with 1 mol.% elemental Ag). This finding can be explained on the basis of the water uptake of the polymer matrix: silver ions are generated from elemental silver particles only in the presence of water. The maximum water absorption of the photopolymers as well as the diffusion coefficient of water in the polymers increases with the number of hydrophilic ethoxy groups per monomer unit. The silver ion release from the acrylate photopolymer layers is governed by diffusion. The diffusion coefficient of silver ions, however, is at least two orders of magnitude smaller than that of water. This finding suggests that the interactions between silver ions and the polymers and/or the titanium dioxide must be stronger than the interactions between water molecules and the polymers and/or the titanium dioxide because the mobility of a diffusing species decreases if the interactions with the surrounding matrix become stronger. Acrylate photopolymer layers containing at least 6 ethoxy groups per monomer unit release an amount of silver ions of 3 μg*l-1*cm-2 or more per day. This amount is sufficient to eliminate Escherichia coli completely within 24 h.