1904756 (1 of 11) © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com FULL PAPER Precontrolled Alignment of Graphite Nanoplatelets in Polymeric Composites Prevents Bacterial Attachment Santosh Pandit, Karolina Gaska, Venkata R. S. S. Mokkapati, Emanuele Celauro, Abderahmane Derouiche, Sven Forsberg, Magnus Svensson, Roland Kádár,* and Ivan Mijakovic* Dr. S. Pandit, Dr. V. R. S. S. Mokkapati, Dr. E. Celauro, Dr. A. Derouiche, Prof. I. Mijakovic Department of Biology and Biological Engineering Chalmers University of Technology Kemivägen 10, 41296 Göteborg, Sweden E-mail: ivan.mijakovic@chalmers.se Dr. K. Gaska, Prof. R. Kádár Industrial and Materials Science Chalmers University of Technology SE 412 96 Göteborg, Sweden E-mail: roland.kadar@chalmers.se S. Forsberg 2D fab AB Bultgatan 20, 853 50 Sundsvall, Sweden Dr. M. Svensson Wellspect HealthCare Aminogatan 1, SE 431 21 Mölndal, Sweden The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201904756. DOI: 10.1002/smll.201904756 1. Introduction Graphene and its derivatives have recently attracted attention as key components of antimicrobial materials and coatings, Graphene coatings composed of vertical spikes are shown to mitigate bacterial attachment. Such coatings present hydrophobic edges of graphene, which pen- etrate the lipid bilayers causing physical disruption of bacterial cells. However, manufacturing of such surfaces on a scale required for antibacterial applica- tions is currently not feasible. This study explores whether graphite can be used as a cheaper alternative to graphene coatings. To examine this, composites of graphite nanoplatelets (GNP) and low-density polyethylene (LDPE) are extruded in controlled conditions to obtain controlled orientation of GNP flakes within the polymer matrix. Flakes are exposed by etching the surface of GNP–LDPE nanocomposites and antibacterial activity is evaluated. GNP nanoflakes on the extruded samples interact with bacterial cell membranes, physically damaging the cells. Bactericidal activity is observed dependent on orientation and nano- flakes density. Composites with high density of GNP (≥15%) present two key advantages: i) they decrease bacterial viability by a factor of 99.9999%, which is 10 000-fold improvement on the current benchmark, and ii) prevent bacterial colonization, thus drastically reducing the numbers of dead cells on the surface. The latter is a key advantage for longer-term biomedical applications, since these surfaces will not have to be cleaned or replaced for longer periods. microbe-resistant biomedical devices and filtration devices. [1–4] Antimicrobial activity of pristine graphene, graphene oxide, and reduced graphene oxide has been clearly established. [5–8] Since the first demonstra- tion of graphene antimicrobial activity, several mechanisms such as physical damage, generation of oxidative stress, and wrapping of cells have been sug- gested. [9,10] Recent studies have suggested that physiochemical damage of bacterial cells can be greatly enhanced by a pre- cise sterical alignment of graphene flakes perpendicular to the coated surface. [11,12] These findings represent a promising venue for manufacturing antibacterial coating on surfaces of biomedical devices. However, chemical and physical routes for producing surfaces coated with such pure 2D-materials from bulk graphite are too time consuming, laborious, and costly. [13] Therefore, we asked whether GNP, which are considerably cheaper and readily avail- able in bulk quantities, could be processed in a way that would lead to similar antibacterial effects. [2] We hypothesized that controlled orientation of GNP could be achieved within a polymer nanocomposite. GNP are semimetallic graphite crystals that are 1 to 5 nm thick and exist in a form of nanoflakes (with a twisted shape similar to propeller shape). Their diameter is in the range of few micrometers and they exhibit interplanar distances similar to that of graphite. [14] GNP, when used in composites above densities of 3 wt%, significantly improve imperme- ability, can be aligned in an electric field, and impart elec- trical conductivity. Above 20 wt%, GNP are known to outper- form most of the known carbon forms in terms of thermal conductivity and mechanical properties in thermoplastic and elastomeric systems. [15] When integrating GNP with polymer systems, the main challenge lies in achieving uniform distri- bution and proper dispersion of particles within the polymer matrix. In addressing this challenge, matching polarity between GNP and the polymer, as well as the interfacial com- patibility of polymer and filler particles, are known to be quite important. [16,17] Nanocomposites based on thermoplastic polymers as a matrix have the advantage of being processable using mass pro- duction techniques such as extrusion and injection molding, Small 2020, 1904756