Abstract
Hydrophobicity is a very important surface property and there is a growing interest in the production and characterization of superhydrophobic surfaces. Accordingly, it was recently shown how to obtain a superhydrophobic surface using a simple and cost-effective method on a polymer named poly(L-lactic acid) (PLLA). To evaluate the ability of such material as a substrate for bacterial colonization, this work assessed the capability of different bacteria to colonize a biomimetic rough superhydrophobic (SH) PLLA surface and also a smooth hydrophobic (H) one. The interaction between these surfaces and bacteria with different morphologies and cell walls was studied using one strain of Staphylococcus aureus and one of Pseudomonas aeruginosa. Results showed that both bacterial strains colonized the surfaces tested, although significantly higher numbers of S. aureus cells were found on SH surfaces comparing to H ones. Moreover, scanning electron microscopy images showed an extracellular matrix produced by P. aeruginosa on SH PLLA surfaces, indicating that this bacterium is able to form a biofilm on such substratum. Bacterial removal through lotus leaf effect was also tested, being more efficient on H coupons than on SH PLLA ones. Overall, the results showed that SH PLLA surfaces can be used as a substrate for bacterial colonization and, thus, have an exceptional potential for biotechnology applications.
Highlights
Industrial bioconversion processes can be performed using different kinds of reactors, some of which are called “immobilized cell reactors”, (Tyagi and Ghose 1982) that imply high cell concentrations, normally achieved by fixing the cells on various substrates
Quantification of bacterial colonization and removal As can be seen in Figure 1, the enumeration of S. aureus and P. aeruginosa cells showed that both bacteria extensively colonized both poly(L-lactic acid) (PLLA) surfaces, achieving values of 4 Log colony forming units (CFU)/cm2
The removal was more effective on the H surface, since both bacteria suffered a significant reduction (1 Log reduction) on the number of cells adhered to this substratum comparing to the values found when no removal procedure was performed
Summary
Industrial bioconversion processes can be performed using different kinds of reactors, some of which are called “immobilized cell reactors”, (Tyagi and Ghose 1982) that imply high cell concentrations, normally achieved by fixing the cells on various substrates. A great deal of research has been devoted to the preparation and theoretical modelling of superhydrophobic surfaces (Nakajima et al 2001; Callies and Quéré 2005; Parkin and Palgrave 2005; Sun et al 2005), which result from the combination of a very large contact angle (≥ 150°) and a low contact-angle hysteresis. This kind of materials was originally inspired by the unique water-repellent properties of the lotus leaf (Barthlott and Neinhuis 1997) and the leaves of a number of other plants (Bhushan and Jung 2006). This minimizes the attractive forces between the water molecules and the atoms of the surface, and allows the water to “bead up” and rolls off (Frim 2008)
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