Constrained distribution of bacteria on biodegradable AZ31 Mg alloy. Protective effect of a polymerized phytocompound

BERTUOLA M.; MIÑÁN A.; GRILLO C.A.; CORTIZO, M.C.; FERNÁNDEZ LORENZO M.

Oxford

Simposio; 10th Biometal-Symposium on Biodegrable Metals for Biomedical Applications; 2018

Université Laval, University of Oxford, University of Canterbury, Universitátsmedizin Berlin, Peking University

INTRODUCTION: The prevention of microbial biofilm formation on the biomaterial surface is crucial in avoiding implants failures and the development of antibiotic resistant bacteria [1,2]. The objective of this work was to analyze bacterial distribution over corroding AZ31 surface and examine possible preferential sites for attachment according the surface composition. In order to achieve an effective constriction of bacterial attachment a polymer coating (polythymol) was developed to investigate possible antibiofilm and corrosion inhibition effects. METHODS: Cylindrical AZ31 alloy samples were mechanically polished, cleaned and dried with nitrogen. The polymerization of thymol (polyTOH) was performed by cyclic voltametry in an electrochemical cell using 0.1 M TOH water/ethanol (70:30) with 0.5 M sodium salicilate as electrolyte. The samples were exposed to S. aureus culture for 2h. Adherent bacteria were detached by sonication and then were enumerated after serial dilutions. The samples with bacteria attached were also observed by epifluorescence microscopy after acridine orange staining, by SEM microscopy and finally, EDS element mapping was performed. Corrosion test were additionally conducted in nutrient broth at 33ºC using anodic polarization and measurements of Mg ions released in the solution for 1, 2 and 3 days by colorimetric test were made. RESULTS: Epifluorescence microscopy image showed the non uniform distribution of bacteria on AZ31 surface (Fig. 1A). Bacteria were found preferentially on the corrosion products where, apart from Mg, Al, the presence of P, C, O, and Ca was detected by EDS. Corrosion active centre with hydrogen bubbles evolution, associated with localized changes of pH, were not selected as suitable places for bacterial attachment. The polyTOH layer increased the corrosion resistance of AZ31 (ions release was reduced to almost the half, and the corrosion current decreased from 96.90±7.65 mAcm-2 to 6.74±2.61 mAcm-2) and created an anti-biofilm surface (bacterial attachment was 50-fold lower on polyTOH-AZ31 than on non-coated Mg alloy). Corrosion of polyTOH-AZ31 was weaker than on bare AZ31 and was restricted to smaller regions. High P, Al and O percentages were found in the pit surroundings probably due to the change of pH in this region. P was absent on the rest of the metal surface (Fig. 2B). DISCUSSION & CONCLUSIONS: Results shown here demonstrated that bacterial adhesion on AZ31 shows some preferential sites (P- and C- containing precipitates) and others that are particularly avoided (active corrosion sites). Polythymol layer was able to constrain even more bacterial attachment by reducing the formation of corrosion products. REFERENCES: 1 P. Tian, D. Xu, X. Liu, (2016) Colloids Surfaces B Biointerfaces 141:327?337. 2 J. Sun, Y. Zhu, L. Meng, et al (2016) Acta Biomater 45:387?398. ACKNOWLEDGEMENTS: CONICET (PIP 2016-2018 GI 0601, P-UE 22920170100100CO), UNLP (11/I221), ANPCyT (PICT 2016-1424).