Paper Title
Superhydrophobic Modification of Aluminum Surface: The Role of Surface Chemistry and Structure on the Biological Interactions

One of the main challenges in biomedical engineering is creating biomaterials with antimicrobial activity. The interaction of protein molecules with the surface of medical devices or prosthesis may result in the attachment of bacterial cells, which eventually triggers the colonization of cells to the biomaterial surfaces and leads to the formation of biofilm and infection. One way to prevent or postpone the biofilm formation and infection is altering the surface architecture and chemistry such that the surface becomes less prone to biofouling. Here, the surface chemistry and structure of aluminum based surfaces were modified through a cost-effective two step superhydrophobic modification method. In this method, a controlled etching process were applied to create a dual micron- and nano-scale hierarchical structures followed by a fluoro-silanization step to reduce the surface free energy. The surfaces were characterized by SEM, EDAX, AFM, FTIR, contact angel goniometry, surface free energy measurement, flow cytometry and Bradford protein assay. The effect of modification on the biofilm formation was analyzed by using microtiter plate assay using three different bacteria. The results showed that the water contact angle and surface free energy changed from 68o to 163o and 43.7 to 0.1mN/m, respectively. A good thermomechanical and chemical stability was observed for modified samples. They also possessed a long-term superhydrophobicity over a 4 month study period. It was also found that the BSA protein absorption capacity reduced from 3772 to 378µ after modification. An excellent antibiofilm formation was observed for the modified samples such that, the percent inhibition of biofilm growth was found 71 percent. It was also observed that when Aluminum surface becomes superhydrophobic its bacterial adhesion becomes independent of bacterium type. This could be attributed to the fact that the nano-roughness could limit the level of contact that occurs between the substratum and the bacterium, which results in a reduction of anchor points and aggregate force of adhesion. Index Terms— Aluminum Alloys, Biofilm formation inhibition, Hierarchical structure, Micro-nano roughness, Superhydrophobicity. The authors acknowledge the financial support provided by University of Isfahan Research Council.