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Antibacterial zinc oxide nanoparticles in polymer biomaterial composites Justin T. Seil and Thomas J. Webster Laboratory for Nanomedicine Research, School of Engineering, Brown University, Providence, RI, USA ABSTRACT Particulate zinc oxide (ZnO) is a known antibacterial agent. Studies have shown that reducing the size of ZnO particles to nanoscale dimensions further enhances their antibacterial properties. Polymers, like all biomaterials, run the risk of harboring bacteria which may produce an antibiotic-resistant biofilm. The addition of ZnO nanoparticles, to form a composite material, may reduce undesirable bacteria activity. The purpose of the present in vitro study was to investigate the antibacterial properties of ZnO nanoparticles when incorporated into a polymer biomaterial. Staphylococcus aureus were seeded at a known cell density onto coverslips coated in a film of polyvinyl chloride (PVC) with varying concentrations of ZnO nanoparticles. Samples were cultured for 24 or 72 h. Methods of analysis, including optical density readings and crystal violet staining, indicated a reduced presence of biofilm on ZnO nanoparticle and polymer composites compared to polymer control. Live/dead assays provided images to confirm reduced presence of active bacteria on samples with zinc oxide nanoparticles. Development of this technology may improve biomaterial effectiveness for applications, such as endotracheal tubes and implanted biomaterials, which are prone to bacterial infection. INTRODUCTION Bacterial infection is one of the most common and universal complications associated with biomaterial implantation. The high rate of infection of biomaterials implanted into or in contact with the body is of perpetual concern to the medical device community. Orthopedic implant failure due to infection occurs in approximately 1.5-2.5% of implants (3,000 – 6,000 incidents/year) [1]. These infections increase hospital costs by $50,000 per episode, on average. Ventilator-associated pneumonia (VAP), a hospital-acquired respiratory infection that frequently develops in patients who receive mechanical ventilation for extended periods of time, develops at a rate of 8-28% in intubated patients [2]. The mortality rate of VAP is estimated to be 24-50% [3], and its positive diagnosis increases treatment costs by an average of $40,000 [4]. Orthopedic implants and endotracheal tube material surfaces can harbor bacterial infections in the form of biofilms that are resistant to antibiotic treatment. Infections associated with endotracheal tubes and orthopedic implants are often attributed to Staphylococcus aureus and Pseudomonas aeruginosa. An increase in infections attributed to multidrug-resistant Staphylococcus aureus (MRSA) has led to increased interest in identifying novel ways to reduce bacteria activity without the use of antibiotics. The Center for Disease Control and Prevention reported an increase in the incidence of MRSA infection from 127,000, with 11,000 associated deaths, in 1999 to 278,000 infections, with 17,000 associated deaths,