Antibacterial Behaviour of Nanoengineered Conductive DLC Film

Introduction: Biofilm formation on the surface of orthopedic implants may cause serious casualties therefore, many scientists have been tried to design antibacterial surfaces [1]. Traditionally, bacteria colony formed on the surface of implants have been killed by using antibiotics or elements, such as Ag, Au, …, which were already available on the surface of implants [2]. Chemically repelling or killing bacteria has been raised some concerns about antimicrobial resistance problem [3]. To solve this problem, researchers have designed inherently antibacterial surfaces inspired from nature [4]. DLC coatings on the surface of medical devices enhance corrosion and wear properties and applying current can help to reduce bacteria attachment and killing them [5,6]. Improving antibacterial properties of conductive DLC coatings by using plasma etching to introduce some nanopatterns on its surface and applying electrical current may increase the usage of DLC-coated implants in future. 
Materials and Methods: Conductive DLC was deposited on the surface of silicon wafer by plasma ion immersion technique (Ar/C₂H₂ : 1/5). Arrays of 500nm polystyrene particles were placed on the surface of DLC-coated silicon wafer followed by plasma etching with equal ratio mixture of Argon and Oxygen. Prepared samples were examined by SEM, Raman spectroscopy, AFM and Water contact angle equipment. E. coli and S. aureus were cultured on the surface of DLC-coated silicon wafer to study its antibacterial behavior on and without presence of electrical current. Cell cytotoxicity on and without presence of electrical current was determined by culturing MC3T3 cells followed by MTT and cytoskeleton assay. 
Results and Discussion: The SEM and AFM results demonstrated that the nanopatterns were fabricated successfully on the surface of DLC-coated silicon wafer (Figures 1-a & b). It is obvious that because of nanopatterns bacteria attachment decreased significantly after 24 h culturing (Figures 2-a & b). Also, it can be seen that some bacteria which were attached to the surface, killed by nanocones (Figure 2-c). It is expected that by applying current, the antibacterial properties of nanopatterned samples will be enhanced while remained non-cytotoxic against MC3T3 cells. 
Conclusions: Nanopatterns improved the antibacterial properties of DLC-coated silicon wafers and some bacteria were killed because of penetrating of cones inside of their cell walls.