Antimicrobial effect of silver-doped phosphate-based glasses I. Ahmed, 1 D. Ready, 2 M. Wilson, 3 J.C. Knowles 1 1 Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray’s Inn Road, London, WC1X 8LD, United Kingdom 2 UCLH NHS Foundation Trust, Eastman Dental Hospital, 256 Gray’s Inn Road, London, WC1X 8LD, United Kingdom 3 Division of Microbial Diseases, UCL Eastman Dental Institute, 256 Gray’s Inn Road, London, WC1X 8LD, United Kingdom Received 17 January 2006; revised 18 February 2006; accepted 1 March 2006 Published online 6 July 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.30808 Abstract: In this study a range of phosphate-based glasses (PBG) doped with silver have been investigated for their antimicrobial activities. In disk diffusion assays, these com- positions demonstrated microbistatic effects against a range of organisms including Staphylococcus aureus, Escherichia coli, Bacillus cereus, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and Candida albicans. The data ob- tained from the above studies allowed for an additional range of PBG containing lower amounts of silver to be studied for their effects on the growth and viability of S. aureus, E. coli, and C. albicans. PBG containing 3 and 5 mol % Ag were bactericidal for S. aureus and E. coli and signifi- cantly decreased the growth rate of C. albicans. A decrease in the dissolution rates of the glasses was seen with increasing Ag content over the range of concentrations investigated. Overall, 3 mol % Ag incorporated into the PBG investigated was sufficient to mount a potent antibacterial effect against the test organisms, and these compositions also gave excellent long-term release of Ag ions into the medium. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res 79A: 618 – 626, 2006 Key words: phosphate glasses; silver; antimicrobial; con- trolled release INTRODUCTION The antibacterial effect of silver is well known, 1 and the use of silver in surgery has been exploited to inhibit the spread of infection. However, it was only since the nineteenth century that these beneficial ef- fects were attributed to trace amounts of silver in aqueous solution. 2 With the onset of multidrug resistance in many bacterial strains, new treatment methodologies are be- ing sought, and the powerful antibacterial properties of silver at low concentrations make it worthy of fur- ther study in this respect. 3 A large number of healthcare products now contain silver, because of its antimicrobial activity and low toxicity to human cells. These products include silver- coated catheters, municipal water systems, and wound dressings. Antimicrobial silver-containing films, textiles, composite coatings, and dendrimers have also been reported in the literature. 4 The underlying need to improve the properties of existing biomaterials centers on the incidence of bio- material-related infections, which often lead to revi- sion surgery. At present, prophylaxis in the form of systemically administered antibiotics serves as the main weapon against infection following implant sur- gery. 5 Antimicrobial ceramics are becoming increasingly important because of their wide range of applications, including cosmetics, electrical appliances, fabrics, and building materials. 6 Antibacterial silver-containing sil- ica glass has even been produced via the sol– gel route. 7 Bioactive glasses generally composed of SiO 2 , P 2 O 5 , CaO, and Na 2 O and prepared via the traditional melt quench method have also been investigated for antimicrobial properties. 8 These glasses have found extensive applications as orthopaedic and dental graft materials and, more recently, also as tissue engineer- ing scaffolds. A silver-doped bioactive glass powder has been used to coat resorbable Vicryl® and non- resorbable Mersilk® surgical sutures, thereby convey- Correspondence to: J.C. Knowles; e-mail: j.knowles@ eastman.ucl.ac.uk © 2006 Wiley Periodicals, Inc.