Antibacterial nanosized silver substituted hydroxyapatite: Synthesis and characterization N. Rameshbabu, 1 T.S. Sampath Kumar, 1 T.G. Prabhakar, 2 V.S. Sastry, 3 K.V.G.K. Murty, 4 K. Prasad Rao 1 1 Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India 2 Department of Veterinary Microbiology, Madras Veterinary College, Tamilnadu Veterinary and Animal Sciences University, Chennai 600007, India 3 Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India 4 AU-KBC Research Centre, M.I.T. Campus of Anna University, Chennai 600044, India Received 25 February 2005; revised 22 May 2006; accepted 5 June 2006 Published online 9 October 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.30958 Abstract: The silver (0.5–3 at %) substituted nanosize hydroxyapatites (AgHAs) were synthesized by microwave processing. The X-ray diffraction (XRD) peaks are very broad, indicating that the AgHAs were of nanosize (30 nm). Transmission electron microscopy analysis shows needle- like morphology of AgHA, having length 60–70 nm and width 15–20 nm. The AgHA phase was stable up to 7008C without any secondary phases. The antibacterial effect of AgHA against Escherichia coli and Staphylococcus aureus was observed by spread plate method, even for low concentration of silver ions (0.5%) with 1  10 5 cells/ mL of respective bacterial culture, after a 48 h incubation period. However, some colonies of E. coli were seen with a high dose of 1  10 8 cells/mL after 24 h. The zone of inhibition by disc diffusion test method was found to vary with the amount of silver in the sintered AgHA pel- lets, for both the bacteria, after 24 h of inoculation. Osteo- blast cell attachment in varying density was noticed on AgHA samples with 0.5, 1.0, and 1.5% silver substitution. However, osteoblast spreading was significantly greater on 0.5% AgHA compared to 1.0 or 1.5% substituted AgHA samples. Thus, the low amount of AgHA has a potential of minimizing the risk of bacterial contamina- tion, without compromising the bioactivity, and is ex- pected to display greater biological efficacy in terms of osseointegration. Ó 2006 Wiley Periodicals, Inc. J Biomed Mater Res 80A: 581–591, 2007 Key words: hydroxyapatite; nanoparticle; microwave pro- cessing; antibacterial; osteoblast INTRODUCTION The biomaterial-centered infection is one of the main causes of revision surgery. 1 The presence of implant materials inside the body will interfere with the host defense mechanism and influence the clini- cal dose of antibiotics that is needed to protect against infection. The concentration of antibiotic loaded in implant materials should be high enough to prevent bacterial infections at the biomaterial tis- sue interface. 2 However, the antibiotic released from the implant materials in the serum levels should be below the threshold required for systemic toxicity, so that no side effects are expected. The use of silver has recently become one of the preferred methods to confer microbial resiliency on biomaterials and med- ical devices. 3 Silver and silver-based compounds are highly antimicrobial by virtue of their antiseptic properties to as many as 16 kinds of bacteria, includ- ing Escherichia coli and Staphylococcus aureus. 4 An antimicrobial agent is an agent that has antiviral, antibacterial, and/or antifungal properties. Antivi- rals and antifungals are capable of killing or sup- pressing the replication of viruses and fungi, res- pectively. Antibacterials may be bacteriostatic or bactericidal. Bacteriostat inhibits the growth of mi- croorganisms, while bactericide kills the microor- ganisms. Silver-based antimicrobials capture much attention, because of the low toxicity of the active Ag ion to human cells, 5,6 as well as being a long last- ing biocide with high thermal stability and low vola- tility. Bioactive glass doped with 3 wt % Ag 2 O con- ferred antimicrobial properties of the glass, without compromising the glass bioactivity. 3 Hydroxyapatite [HA, Ca 10 (PO 4 ) 6 (OH) 2 ] has been extensively used as an implant material, because of Correspondence to: T.S.S. Kumar; e-mail: tssk@iitm.ac.in ' 2006 Wiley Periodicals, Inc.