Contents lists available at ScienceDirect Materials Science & Engineering C journal homepage: www.elsevier.com/locate/msec Antibacterial efficiency assessment of polymer-nanoparticle composites using a high-throughput microfluidic platform Sina Kheiri a,b , Mohamed G.A. Mohamed a , Meitham Amereh a , Deborah Roberts a , Keekyoung Kim a,c, ⁎ a School of Engineering, University of British Columbia, Kelowna, BC V1V1V7, Canada b Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S 3G8, Canada c Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada ARTICLE INFO Keywords: Microfluidic device Antibacterial assessment Nanocomposites Nanoparticles Liquid silicone rubber ABSTRACT Over the past decades, inorganic nanoparticles (NPs), particularly metal oxide NPs, have attracted great at- tention due to their strong bactericidal effects. Researchers have used NPs to fabricate nanocomposite materials which have innate antibacterial capability. Herein, we present a straightforward method to fabricate anti- bacterial nanocomposites. Ag, TiO 2 , and ZnO NPs were dispersed within liquid silicone rubber (LSR) structure in four concentrations. Three different methods were used to evaluate the antibacterial efficiency of the NPs forming the nanocomposite materials: (I) the diffusion method, (II) agar counting plate, and (III) a live/dead assay of E. coli. The mechanical properties and hydrophobicity of the nanocomposites were characterized and correlated to the antibacterial efficiency of the NPs. In order to test the antibacterial efficiency in a high- throughput, cost-effective and efficient manner, a microfluidic device fabricated by 3D printing and soft-litho- graphy methods was used. The LSR-15 wt% TiO 2 nanocomposites showed the best antibacterial efficiency. In addition, TiO 2 NPs formed the stiffest nanocomposites with very fine, even surface which increased the hy- drophobicity of the surface where bacteria attach to grow, preventing bacteria from further growth. 1. Introduction The antibacterial performance of implantable devices plays an im- portant role in the prevention of device failure. Over millions of years of their existence, bacteria have evolved versatile mechanisms to colonize different material surfaces [1,2]. Bacteria can adhere to surfaces and reproduce to form dense structures or biofilms with thicknesses varying from micrometers to half a meter [3]. In 1935, Zobell and Allen pub- lished a study focusing on bacterial adherence on a solid substrate [4]. Since then, many studies of bacterial adherence on various natural and artificial substrates have been broadly conducted [5–8]. Bacteria can generate biofilm on various surfaces such as soil, surfaces under marine and aquatic conditions, and the tissue of organisms. Various conditions can affect biofilm generation, including nu- trients, pH, surrounding temperature, and the existence of dissimilar bacteria on the attachment substrate. The lifecycle of a biofilm starts with the bacteria first adhering to a surface by forces, such as thermal forces, van der Waals forces, electrostatic and hydrophobic interactions, steric hindrances and hydrodynamic forces [9]. The second layer is then induced by interactions between the hydrophobic part of the outer cell wall and surface [10]. The adhesion facilitates the development of an irreversible matrix and biofilm on the surface which is called the ex- tracellular polymeric substance (EPS) [11,12]. Biofilms normally form mushroom-like structures with three major development stages: (I) at- tachment, (II) growth and (III) detachment [13–15]. Antibiotics are less effective on bacterial cells in biofilms and thus biofilm formation is a major concern in implantable biomedical devices [16,17]. High chemical and mechanical resistance among the cells in the biofilm makes the bacterial cells extremely difficult to destroy or eliminate. In addition, the biofilm is considered as the main source of bacterial infection and ~ 80% of bacterial contamination in medical devices is caused by biofilms [18]. Therefore, developing materials resistant to biofilm formation is one of the challenging topics in bio- materials research and health management [19,20]. One of the most common techniques to fabricate an antibacterial material is to combine the antibacterial agent into a base material structure. Adopting nanoparticles (NPs) as antibacterial agents is a promising approach to develop antibacterial materials. NPs are classi- fied as particles that have a diameter of < 100 nm. Various classes of NPs have been used for antibiotic delivery, and have shown the https://doi.org/10.1016/j.msec.2020.110754 Received 1 October 2019; Received in revised form 28 January 2020; Accepted 15 February 2020 ⁎ Corresponding author at: Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB T2N1N4, Canada. E-mail address: keekyoung.kim@ucalgary.ca (K. Kim). Materials Science & Engineering C 111 (2020) 110754 Available online 19 February 2020 0928-4931/ © 2020 Published by Elsevier B.V. T