Attachment and detachment of bacteria on surfaces with tunable and switchable wettability

Biofouling
Vol. 26, No. 1, January 2010, P. 111-118

Attachment and detachment of bacteria on surfaces with tunable and switchable wettability

Linnea K. Istaa, b, Sergio Mendeza, c{ and Gabriel P. Lopeza, c*
ACenter for Biomedical Engineering, The University of New Mexico Albuquerque, NM 87131, USA; bDepartment of Biology, The
University of New Mexico Albuquerque, NM 87131, USA; cDepartment of Chemical and Nuclear Engineering, The University of
New Mexico Albuquerque, NM 87131, USA
(Received 8 June 2009; final version received 26 September 2009)

Controlling accumulations of unwanted biofilms requires an understanding of the mechanisms that organisms use to interact with submerged substrata. While the substratum properties influencing biofilm formation are well studied, those that may lead to cellular or biofilm detachment are not. Surface-grafted stimuli-responsive polymers, such as poly (N-isopropylacrylamide) (PNIPAAm) release attached cells upon induction of environmentally-triggered phase changes. Altering the physicochemical characteristics of such polymeric systems for systematically studying release, however, can alter the phase transition. The physico-chemical changes of thin films of PNIPAAm grafted from initiator-modified self-assembled monolayers (SAMs) of o-substituted alkanethiolates on gold can be altered by changing the composition of the underlying SAM, without affecting the overlying polymer. This work demonstrates that the ability to tune such changes in substratum physico-chemistry allows systematic study of attachment and release of bacteria over a large range of water contact angles. Such surfaces show great promise for studying a variety of interactions at the biointerface. Understanding of the source of this tunability will require further studies into the heterogeneity of such films and further investigation of interactions beyond those of water wettability.
Keywords: fouling release;

poly (N-isopropylacrylamide); Cobetia marina; Staphylococcus epidermidis; self-assembled monolayers

Introduction
Biofilms are ubiquitous and ancient, if sometimes unwanted, form of microbial life. The basic biological outline of biofilm development has been established and elaborated (O’Toole et al. 2000; Stoodley et al. 2002; Hall-Stoodley et al. 2004). The interfacial interactions between the cells and the supporting substrata are, beyond the points of primary and secondary attachment, less well understood. Removal of unwanted biofilms, or biofouling, requires interruption of the association between the cells and substrata and, therefore, also requires a better understanding of the substratum properties that are important in the maintenance of a biofilm.
Hydrophobicity appears to play a role in maintaining cellular attachment. Prior studies have shown that, although some cells may initially attach well to hydrophobic surface, they are easily removed upon application of low shear forces (Ista et al. 2004). Indeed, hydrophobic and superhydrophobic foulingrelease surfaces show great promise for control of biofouling (Yebra et al. 2004; Genzer and Efimenko 2006; Genzer and Marmur 2008). One limitation of low energy fouling-release surfaces is that they often require large shear stresses (Yebra et al. 2004).
A means by which fouling-release can be achieved at relatively low shear stress is by changing the wettability of the surface on which the biofilm is maintained.